Shelf Life of an Extruded Corn Snack

SHELF LIFE DETERMINATION OF AN EXTRUDED CORN SNACK FOOD

A Thesis (Research Paper)

Submitted in Partial Fulfilment of the Requirements for the

Degree of Master Science in Food Science and Technology

of

The University of the West Indies

Tamayo Hutton

2007

Department of Chemical Engineering Food Science and Technology Unit St. Augustine Campus

Acknowledgements i

ACKNOWLEDGEMENTS

Thank you very much Dr. G.H. Baccus-Taylor and Prof. J. Akingbala for

guidance and tremendous support in finally completing this research paper.

Thanks to Dr. G. Legall for last minute help and advice on Statistical Analysis

methods. Many thanks to Ms. Giselle Ramtahal and Ms. Karen Camejo,

laboratory technicians for support through the many difficulties experienced in the

lab.

Many regards to Ms. Patricia Bhairo-Beekhoo, Mr. Allan Dass and Mr.

Ian Currie for facilitating key aspects of this project. Finally, a very special thank

you to Ms. Colleen Norville, Ms. Lucy Brown and Mr. Clinton Hutton for

emotional support through extremely challenging times.

Table of Contents ii

TABLE OF CONTENTS

Page

Acknowledgements i

List of Figures vii

List of Tables ix

Abstract x

1.0 Introduction 1

1.1 Definition of Shelf Life 1

1.2 Definition of an Extruded Corn Snack Food 2

1.3 Project Outline 2

1.4 Problem Definition 3

1.5 Scope of Work 4

2.0 Literature Survey 5

2.1 Extruded Corn Snack 5

2.1.1 Brief Process Description 5

2.1.2 Cornmeal 6

2.1.3 Flavour 6

2.1.4 Palm Olein Oil 7

2.1.5 Nutritional Composition 7

2.1.6 Packaging Material 8

2.1.7 The Extrusion Process 9

2.2 Food Quality 10

2.3 Intrinsic Factors 12

Table of Contents iii

Page

2.3.1 Taste 13

2.3.2 Smell 14

2.3.3 Vision 15

2.3.4 Hearing 15

2.3.5 Kinesthesis & Somethesis 16

2.4 Extrinisic Factors 17

2.5 Shelf Life 18

2.6 Legislation 20

2.6.1 The Republic of Trinidad & Tobago 22

2.6.2 Other Caribbean Territories 23

2.6.3 North America 25

2.6.4 The European Union 25

2.7 Shelf Life Importance 27

2.8 Factors Affecting Shelf Life 28

2.8.1 Biological Decay – Pre-harvesting 29

2.8.2 Senescence 29

2.8.3 Water Activity & Moisture Migration 30

2.8.4 Transfer of Substances other than Moisture and/or

Water Vapour 31

2.8.5 Microbial Factors 32

2.8.6 Rancidity Development 34

2.9 Review of Research on Similar Corn Based Snack Foods 38

2.9.1 Shelf Life Determination of Lightly Salted Potato Chips 38

2.9.2 Mathematical Models for Estimating the Shelf Life of

Corn Flakes 39

2.9.3 Flavour Properties and Stability of a Corn-Based Snack 43

2.10 Shelf Life Determination 46

Table of Contents iv

Page

2.11 Determination of the End of the Product’s Shelf Life 47

2.12 Determination of Suitable Shelf Life Tests & Procedures 49

2.12.1 Lipid Oxidation & Off-Flavour Development 50

2.12.2 Extraction of Lipids 52

2.12.3 Moisture Migration and its effect on Texture 56

2.12.4 Sensory Evaluation 57

2.13 Accelerated Shelf Life 59

3.0 Methodology 61

3.1 Storage of Samples 61

3.2 Sensory Evaluation of a Locally Manufactured

Cheese-Flavoured Extruded Corn Snack by Trained Panellists 62

3.3 Determination of the Moisture Uptake in Stored Samples 65

3.4 Texture Analysis of Samples using the Penetrometer 65

3.5 Lipid Extraction from the Extruded Corn Snack Food 66

3.6 Peroxide Value Evaluation of Extracted Oil 69

3.7 Treatment of Results 69

4.0 Results & Discussion 71

4.1 Results of Sensory Evaluation of the Extruded Corn

Snack Food 71

4.1.1 Sensory Evaluation of the Texture Attribute 71

4.1.1.1 Evaluation of the Texture Attribute of Sample ‘A’ 72

4.1.1.2 Evaluation of the Texture Attribute of Sample ‘R’ 72

4.1.2 Sensory Evaluation of the Flavour Attribute 73

4.1.2.1 Evaluation of the Flavour Attribute of Sample ‘A’ 74

4.1.2.2 Evaluation of the Flavour Attribute of Sample ‘R’ 74

4.1.3 Sensory Evaluation of the “Overall Attribute” 74

Table of Contents v

Page

4.1.3.1 Evaluation of the “Overall Attribute” of

Sample ‘A’ 75

4.1.3.2 Evaluation of the “Overall Attribute” of

Sample ‘R’ 76

4.2 Statistical Analysis of the Sensory Evaluation Results of the

Extruded Corn Snack Food 76

4.2.1 Statistical Analysis of the Texture Attribute Sensory

Results 76

4.2.2 Statistical Analysis of the Flavour Attribute Sensory

Results 79

4.2.3 Statistical Analysis of the “Overall Attribute” Sensory

Results 82

4.3 Results of Moisture Uptake in an Extruded Corn Snack Food 85

4.4 Results of Texture Analysis of an Extruded Corn Snack

Food using the Penetrometer 86

4.5 Comparison of Results of Sensory Evaluation of the

Texture with Penetrometer & Moisture Uptake of the

Extruded Corn Snack Food 87

4.5.1 Graphical Comparison of the Texture Attribute Sensory

Results with Moisture Uptake of an Extruded Corn

Snack Food 87

4.5.2 Statistical Comparison of the Texture Attribute Sensory

Results with Moisture Uptake of an Extruded Corn

Snack Food 88

4.5.3 Graphical Comparison of the Texture Attribute Sensory

Results with Penetrometer Readings of an Extruded Corn

Snack Food 90

Table of Contents vi

Page

4.5.4 Statistical Comparison of the Texture Attribute Sensory

Results with Penetrometer Readings of an Extruded Corn

Snack Food 90

4.6 Results of the Peroxide Value of the Oil Extracted

from an Extruded Corn Snack Food 92

4.7 Comparison of the Flavour Attribute Sensory Results with

the Peroxide Value of Oil Extracted from an Extruded Corn

Snack Food 93

4.7.1 Graphical Comparison of the Flavour Attribute Sensory

Results with the Peroxide Value of Oil Extracted from

an Extruded Corn Snack Food 93

4.7.2 Statistical Comparison of the Flavour Attribute Sensory

Results with the Peroxide Value of Oil Extracted from

an Extruded Corn Snack Food 94

4.8 Evaluation of the Control of the Snack Food 96

5.0 Conclusion 97

6.0 Recommendations 98

References 99

Appendix: Raw Data 112

Appendix: Minitab Logic Regression Data 122

Appendix: Sensory Evaluation Score Sheet 125

List of Figures vii

LIST OF FIGURES

Page

2.1 Development of rancidity in foods, storage times given in

arbitrary values, PV – peroxide value; IP – induction period 36

2.2 Food stability as a function of water activity 37

2.3 Aqualab 3TE moisture analyser 41

2.4 Texture technologies TA.XT2i texture analyser 42

2.5 Osme equipment and Osmegram 44

2.6 Osmegram showing panel member’s scorecard 45

2.7 Glassware used in Soxhlet extraction 54

2.8 Arrhenius’ equation 59

3.1 Sensory evaluation test booth set up 63

3.2 Rotary evaporator 68

4.1 Percentage of panellist that failed the Texture Attributes of the

snack food during 9 weeks of storage under retail and ambient

conditions 78

4.2 Percentage of panellist that failed the Flavour Attributes of the


conditions 81

4.3 Percentage of panellist that failed the Overall Attributes of the


conditions 83

List of Figures viii

Page

4.4 Comparison of the texture attribute results of sensory evaluation

with the results of mean moisture increase in an extruded corn

snack food stored for 9 weeks in ambient and retail conditions 89

4.5 Comparison of the texture attribute results of sensory evaluation

with the results of penetrometer in an extruded corn snack food

stored for 9 weeks in ambient and retail conditions 91

4.6 Comparison of the flavour attribute results of sensory evaluation

with the results of peroxide value of oil extracted from an extruded

corn snack food stored for 9 weeks in ambient and retail

conditions 95

List of Tables ix

LIST OF TABLES

Page

2.1 The nutritional facts of the snack 7

2.2 Water activity (aw) values of some foods 33

2.3 Water activity (aw) limits for microbial growth 34

2.4 Guidelines that can be followed to set shelf life end-point 47

2.5 Ranking of lipid oxidation methods 51

4.1 Sensory evaluation of the texture of an extruded corn snack food 71

4.2 Sensory evaluation of the flavour of an extruded corn snack food 73

4.3 Sensory evaluation results of a snack food showing

“overall attribute” 75

4.4 Moisture increase in an extruded corn snack food for a 9

week storage period 85

4.5 Penetrometer distance (in mm) of a snack food for 5 seconds 87

4.6 Peroxide values of oil extracted from an extruded corn snack

food during storage for control, ambient and retail conditions 92

Abstract x

ABSTRACT

This study was an attempt to determine the shelf life of a locally

manufactured cheese-flavoured extruded corn snack, packaged in metallised

oriented polypropylene film, using sensory evaluation techniques. Twenty (20)

trained panel members were instructed to evaluate samples, stored under two

conditions against a ‘control’. The samples were stored under ambient conditions

(33oC, relative humidity 100%), and retail conditions (18oC, relative humidity

75oC). The control was frozen at a temperature of -18oC. Panellists evaluated

samples for texture, flavour and overall attributes (appearance, texture, sound,

flavour) using an 11-point scale. Objective testing of physicochemical properties

of the snack food were performed to correlate with the subjective sensory

evaluation. Regression was used to fit sensory data and to determine an

established manufacturer’s cut-off point (the point at which the quality of the

snack became unacceptable). Logistic regression was used to correlate moisture

uptake in the snack food, and penetrometer readings, with sensory evaluation of

the texture attribute and, peroxide value of oil extracted from the snack food, with

sensory evaluation of the flavour attribute. The shelf of the packaged snack food

was found to be 50 days under ambient conditions (33oC, 100% RH), and 58 days

under retail conditions (18oC, 75% RH). Penetrometer results correlated best with

sensory analysis, producing a Pearson p-value of 0.000 (95% confidence).

Chapter 1: Introduction 1

CHAPTER 1

INTRODUCTION

1.1 DEFINITION OF SHELF LIFE

Shelf life can be defined generally as the period of time following

manufacture, over which a food maintains the specified quality (Eskin and

Robinson, 2001). Guidelines of the Institute of Food Science and Technology

(1993) define shelf life as the time during which the product will remain safe; will

be certain to retain the desired sensory, chemical, physical and microbiological

characteristics; and finally will comply with any label declaration of nutritional

data when stored under the recommended conditions. At the end of the shelf life,

the food is deemed unacceptable for sale and hence consumption. Characteristics

of the food that determine the shelf life are the sensory, nutritional,

microbiological properties (Eskin and Robinson, 2001).


1.2 DEFINITION OF AN EXTRUDED CORN SNACK FOOD

Snack food may be defined as a type of food not meant to be eaten as a

main meal of the day such as breakfast, lunch or dinner (WFI 2006c). It is a food

intended to be consumed between meals, providing a brief supply of energy

(Farlex Incorporated, 2007). Processed snack foods are designed to be less

perishable and more durable than prepared foods. These foods generally have

little or no nutritional value and are consumed purely for the enjoyment of its taste

(WFI 2006c). An extruded corn snack food is a processed snack food, consisting

of a corn base made from cornmeal or corn grits, that is cooked and expanded via

the extrusion process and then flavoured (Lusas and Rooney, 2001).

1.3 PROJECT OUTLINE

With the rapid increase of convenience stores, packaged snack foods are

significant business. The snack food industry in market-driven societies generates

billions of dollars in revenue annually. The market for processed snack foods is

enormous, and many large corporations compete rigorously to capture larger

shares of the snack food market (WFI 2006c).


Two (2) of the leading snack food companies in the Republic of Trinidad

and Tobago produce different types of snacks such as, tortilla chips, potato chips,

assorted nuts, pop corn, biscuits and cookies. However, the type of snack food

that is sold in the largest volume for both companies is extruded corn snack foods

(Anonymous 2007b; Anonymous 2007c, personal correspondence). Extruded

corn snack foods are easily shaped (which is critical in attracting children), its

texture attribute is easily adjusted, and many variations of products may be

created from a single process line (Anonymous 2007a, personal correspondence).

1.4 PROBLEM DEFINITION

Both snack companies determine the shelf life of their snack foods under

uncontrolled environmental conditions using sensory evaluation techniques only.

This is not reproducible and is not reliable in ensuring the quality of the product

(Man 2000). The snack companies rely on the measurement of physical

parameters such as salt percentage, moisture content, and lipid content, to control

quality of the snack foods during production, but do not incorporate this in the

determination of the foods’ shelf lives (Anonymous 2007a; Anonymous 2007c,

personal correspondence). Correlating sensory evaluation results with

physicochemical properties is an established practice in shelf life determination

(Man 2000). As the competition among local and international companies

Chapter 1: Introduction 4 increase, for larger shares of the market, quality assurance, and hence more

reliable shelf life determination methods, becomes more critical.

1.5 SCOPE OF WORK

This study intends to analyze the shelf life of a popular locally

manufactured extruded corn snack food flavoured with powdered cheese.

Confidentiality agreements demand that names of employees and details of the

formulation and process are not disclosed, thus Anonymous is liberally cited

throughout this study. The objectives of this project were:

1. To use sensory evaluation tests and statistical analysis to determine the

length of time within which a locally manufactured cheese flavoured

extruded corn snack became unacceptable for consumption under the

following conditions.

a. At the most extreme storage conditions in ambient, tropical

conditions at 33oC and 100% relative humidity.

b. Under typical retail outlet storage conditions at 18oC and 75%

relative humidity.

2. To evaluate physical and chemical properties of the snack food to

determine any correlation between physicochemical properties and

sensory tests, in determining the product’s shelf life.

Chapter 2: Literature Survey: Extruded Corn Snack Food 5

CHAPTER 2

LITERATURE SURVEY

2.1 EXTRUDED CORN SNACK FOOD

2.1.1 Brief Process Description

Anonymous (2007a, personal correspondence) gave a brief description of

the process used for the locally manufactured extruded corn snack. Water is added

to dry corn meal with a dry moisture content of approximately 11% in order to

increase the moisture content to approximately 15%. The mixture is then extruded

through dies at high pressure and temperature which expand the base, forms the

snack’s shape and gives it the required density. The expanded product is baked to

the required specification, ensuring the right texture and mouth feel. It is also the

only ‘kill’ step in the process. A cheese powder-based flavour is then mixed with

palm olein oil. The resulting slurry is pumped and sprayed on the extruded corn

base. The product is finally packaged in film consisting of metallized coextruded

biaxially oriented polypropylene (metallized OPP). The finished product is a dry

cheese-flavoured extruded corn snack, with a moisture content of approximately

1.5%.


2.1.2 Cornmeal

Corn is the key component for the extruded base of the snack food

(Anonymous 2007a, personal correspondence). Corn is dry milled to corn meal

that has a granulation of 0.59 mm – 0.193 mm. Meal has less than 1% oil, low ash

and fibre content, a long shelf life and a bright colour without black specks (Lusas

and Rooney, 2001). Suppliers consistently provide high quality corn meal. As the

cornmeal does not vary significantly in quality within a shipment, or from

shipment to shipment, the cornmeal does not change the product’s shelf life

(Anonymous 2007a, personal correspondence).

2.1.3 Flavour

Historically, the most popular flavours for salty snack seasonings have

been cheese, barbeque, sour cream and onion, and ranch (Lusas and Rooney,

2001). The seasoning typically has a salt content of 10 – 15% (Lusas and Rooney,

2001). The extruded corn snack is flavoured with a powdered cheese seasoning

which is typical of cheese seasonings currently used on the market. The cheese

supplier, similarly to the corn meal supplier, consistently supplies a raw material

that conforms to the major food standards worldwide. Therefore, its percentage

moisture content and microbial load are consistent and do not fluctuate

significantly (Anonymous 2007a, personal correspondence).


2.1.4 Palm Olein Oil

Palm olein oil is used in the manufacture of the extruded corn snack. This

oil is used to aid in extrusion, but its primary purpose is in flavouring the extruded

corn base (Anonymous 2007a, personal correspondence). Palm olein is the liquid

fraction obtained by fractionation of palm oil after crystallization at controlled

temperatures. It is fully liquid in warm climate and has a narrow range of

glycerides (APOC 2007). Palm oil resists oxidation and rancidity, therefore

products made using palm oil have an extended shelf life. Palm oil contains a

balance of polyunsaturated, monounsaturated and saturated fatty acids (Wright).

The oil is consistently supplied at a typical acceptable industry standard range of

peroxide values and free fatty acid percentages (Anonymous 2007a, personal

correspondence).

2.1.5 Nutritional Composition

Table 2.1 shows the nutritional composition of the extruded corn snack

food. The percentage composition of the snack by mass is as follows:

Total fat = 7/19 x 100 = 36.8%*

Total carbohydrates = 10/19 x 100 = 52.6%*

Total Sodium = 0.11/19 x 100 = 0.6%*

Moisture = 1.5% (maintained by process)


TABLE 2.1 The Nutritional Facts of the Snack (Anonymous 2007c, personal correspondence).

Serving Size 19 g

Amount per serving

Calories 110 Calories from fat 60

% Daily Value based on 2,000 calorie diet

Total Fat 7g 11%

Saturated Fat 4g 20%

Sodium 110mg 5%

Total Carbohydrates 10g 3%

Dietary Fibre 0g 0%

Sugar 0g

Protein 1g

Vitamin A 0% · Vitamin C 0%

Calcium 0% · Iron 0%

2.1.6 Packaging Material of the Extruded Corn Snack Food

The material that is used to package the extruded corn snack food is

typical metallised oriented polypropylene (OPP) that is used worldwide

(Anonymous 2007a, personal correspondence). Most snack food packaging use

OPP film in one of several forms. The resulting functional performance of OPP

meets the protection requirements of many snack foods (Lusas and Rooney,

2001).

The purpose of the packaging is to provide barriers to environmental

influences. The snack food requires barriers from moisture, oxygen and light from

entering the package, as well as flavour from leaving the package (Coles, et al.

2003). The shelf life of the snack food is to be determined within its packaging.

Chapter 2: Literature Survey: Extruded Corn Snack Food 9 The packaging will serve the purpose of extending the life of the food, but will

not affect the types of degradation typical of snack foods (Lusas and Rooney,

2001).

2.1.7 The Extrusion Process

Many forms of extruders exist, but they all function similarly (Lusas and

Rooney, 2001). A barrel, in which a close-fitting screw is continually rotating,

moves product towards the discharge end. Product moves to a restricted opening,

and as more product is conveyed, less becomes available and compression of the

product occurs (Charalambous 1993). The compression produces heat energy,

which converts raw granular, starch material, into a smooth viscous dough. This

heat converts moisture in the dough to steam, which upon discharge, causes

product expansion due to the reduction in pressure (Charalambous 1993).

This extrusion process is continuous. The high temperatures that are

formed are able to inactivate most micro-organisms and enzymatic systems, but

are applied for a short enough time (typically less than 15 seconds), that minimal

nutrient losses and functional changes occur (Lusas and Rooney, 2001). The

process is highly versatile. Modifications in ingredients, moisture content, screw

speed and discharge size opening, may produce a wide variety of products that

may be partially cooked, fully cooked or totally expanded from the same unit

(Lusas and Rooney, 2001).

Chapter 2: Literature Survey: Food Quality 10

2.2 FOOD QUALITY

Food quality has different meanings for different food industry

professionals (Taub and Singh, 1998). Food quality is dependent on three main

characteristics. Nutritionists consider the nutritional value, microbiologists

consider the food’s safety, while chemists consider the food’s stability as

measures of its quality (Singhal, et al. 1997). Despite these valid interpretations of

food quality, ultimately it is the consumer, through the purchase of the product,

who determines foods’ quality (Taub and Singh, 1998).

Food quality is defined in the United States Department of Agriculture

(USDA) Marketing Workshop Report (1951) as “the combination of attributes or

characteristics of a product that have significance in determining the degree of

acceptability of a product to a user”. Quality is often measured in industry by

different physical, chemical and microbial properties of the food, and any other

distinctive attribute or characteristic of the product (Gould 1977). Alli (2004)

defines food quality as “the extent to which all the established requirements

relating to the characteristics of a food are met”. It is important to define and

assign values to attributes of the food which coincide with the consumer’s

requirements and expectations, or to set the food’s standards. The term quality,

without being defined in terms of some standard, means very little (Gould 1977).

Chapter 2: Literature Survey: Food Quality 11

Cardello (1995) defines food quality as “the acceptance of the perceived

characteristics of a product by consumers who are the regular users of the product

category or those who comprise the market segment”. This definition of quality

takes into consideration all characteristics of the food, not only the sensory

attributes, but also factors that include convenience, cost and value (Taub and

Singh, 1998).

The quality of processed food deteriorates from the point of manufacture

over time. When the quality of the food is no longer fit for consumption the

product’s shelf life has ended (Man 2000).

Chapter 2: Literature Survey: Intrinsic Factors 12

2.3 INTRINSIC FACTORS

The factors that affect a consumer’s perception of food and food quality

are numerous. Many of these factors are intrinsic to the food, and are related to its

physicochemical characteristics (Singhal, et al. 1997). These include such factors

as ingredient, processing and storage variables. These factors are some of the

most salient and important variables, determining both the acceptability and

perceived quality of the item to the consumer (Man and Jones, 2000). Consumer

enjoyment of snack foods for example results from several factors, primarily

taste, texture and size (Lusas and Rooney, 2001). It is usually through these

sensory characteristics and the internal changes that occur over time, that

consumers develop opinions about other aspects of food quality, such as, safety,

stability, and even the nutritional value (Man and Jones, 2000).

Food’s quality is perceived by the interaction between the

physicochemical properties of the food and human sensory receptor organs (Taub

and Singh, 1998). The food becomes a stimulus which triggers sensory

experiences of the consumer that create complex perceptions of quality (Man and

Jones, 2000). Taste, smell, texture and appearance of food contribute greatly to

the consumer’s perception of the quality of that food (Singhal, et al. 1997).

Understanding the relationships between, physicochemical characteristics of food,

Chapter 2: Literature Survey: Intrinsic Factors 13 the sensory and physiological mechanisms that convert these characteristics into

human perceptions of food attributes, and the effects of these perceived attributes

on acceptance and/or consumption of the item, is critical to an understanding of

what constitutes food quality (Taub and Singh, 1998).

2.3.1 Taste

Taste is a sensory experience that results from stimulation of

chemoreceptors located on the tongue, palate, pharynx, larynx and other areas of

the oral cavity. There are five distinct taste categories, salty, sour, sweet, bitter,

and umami (Jackson and Linskens, 2002).

Saltiness is stimulated by the sodium ion (Na+) and cations of other low

molecular weight salts. Sourness is stimulated by the presences of hydrogen ions,

although the anion and undisassociated acid can modify its taste (Bessière and

Thomas, 1990). The sweet sensation may occur as a reaction to a variety of

organic and inorganic compounds (Taub and Singh, 1998). Bitter taste is more

complicated. It is triggered by alkaloids, heavy halide salts, as well as some amino

acids. It is believed that there may be three or more different bitter receptor

mechanisms (Bessière and Thomas, 1990).

Umami, the fifth recognised taste category is described as delicious or

savoury, and is associated with monosodium glutamate and the taste of meat

Chapter 2: Literature Survey: Intrinsic Factors 14 (UIC). Pungency and astringency are also associated with sensations of taste

(Taub and Singh, 1998). Pungency is the sensation associated with pepper or

spiciness. Taste receptors, especially the mucus membranes, react to the chemical

capsaicin (WFI 2006a). Astringency is a dry sensation that occurs when tannins

denature the salivary proteins, causing a rough ‘sandpapery’ feel in the mouth

(WFI 2006b). The sensations pungency and astringency are part of the ‘common

chemical sense’ (Green, et al. 1990).

2.3.2 Smell

Smell is the sensory experience which occurs when receptors in the

olfactory epithelium of the nose are stimulated by airborne compounds. The odour

of a food and its ‘taste’ are often confused, as during chewing of the food air from

the mouth is passed into the nasal cavity through the nasopharynx (Jacob).

There has been great difficulty over the years to classify the multitude of

smells into categories. Equally difficult has been the identification of the

attributes of the stimulus that elicit odour qualities (Taub and Singh, 1998).

It is now believed that there may be upwards of 300 to 1000 different

olfactory genes, a number so large that it could easily account for the over 10,000

perceptible odours. This large number of receptor types is unique in human

sensory systems, and accounts for the complexities involved in determining the

Chapter 2: Literature Survey: Intrinsic Factors 15 quality of smell in foods. It is also responsible for the vast differences among

persons in their perception of smells (Taub and Singh, 1998).

2.3.3 Vision

Visual perception occurs as a result of stimulation of receptors in the

retina of the eye by electromagnetic radiation (Taub and Singh, 1998). Colour is

critical in the appearance of food and the perception of its quality. However, other

visual attributes also play a critical role. All foods and beverages absorb some

light, and the rest is reflected or transmitted. The clarity and lustre of food and

beverages are thus also used as a means to determine food quality. Size, shape,

surface texture and wholeness (such as in nuts, potato chips and extruded snacks),

are also other visual attributes of food that determine the perception of quality

(Steele 2004).

2.3.4 Hearing

Hearing is the sensation that results from the stimulation of receptors in

the cochlea of the ear by sound waves (Vickers 1979). The sounds produced

during biting and mastication of food have significant effects on quality

perception in certain foods, such as cereals, potato chips and fresh fruits (OTA

1979). Recently, food has been analysed for their texture by the physical or

perceptual sounds emitted during mastication (Vickers 1979).

Chapter 2: Literature Survey: Intrinsic Factors 16

2.3.5 Kinesthesis & Somethesis

Food texture and quality may be perceived by kinesthesis, which is the

perception of limb position and limb movement (EBI 2007), as well as

somesthesis, which is the perception of pressure, pain and temperature. Since

foods provide resistance to active jaw movements (chewing), both kinesthetic

joint and muscle receptors are involved in the perception of food texture and

quality (Taub and Singh, 1998).

There are receptors that give rise to painful sensations as a result of

intense tactile, thermal, or chemical stimuli (Taub and Singh, 1998). The intensity

of the sensations may result in perceptions of stinging, chemical cool and

chemical warmth, even the perception of carbonation in soft drinks. These

sensations mediated by the trigeminal nerve, belong to what is called the

“common chemical sense” (Taub and Singh, 1998).

Chapter 2: Literature Survey: Extrinsic Factors 17

2.4 EXTRINSIC FACTORS

Although intrinsic factors are significant determinants of food quality,

there are several extrinisic factors that also play a role in consumers’ perception.

Attitudes, expectations, environmental conditions, biological factors (hunger,

thirst, health) and social or cultural influences may affect a consumer’s perception

of quality (Taub and Singh, 1998; Steele 2004).

These extrinisic factors must be considered and systematically eliminated

or regularised, so that the perception of the intrinsic factors of the food being

studied may be accurately determined. A well-trained panel will dramatically

reduce the likelihood of extrinisic factors affecting the quality of the sensory

results (Meilgaard, et al. 1999; Freitas, et al. 2003).

Chapter 2: Literature Survey: Shelf Life 18

2.5 SHELF LIFE

Except in the situations where microbiological deterioration has occurred

to the extent to which the product becomes unsafe, the definition of the shelf life

will be determined by the customer and the manufacturer (Kilcast and

Subramaniam, 2000; Man 2002). A lower quality, economy product may have a

longer shelf life than a high quality, premium product, even though the quality

index of the expired premium product may be higher than that of the economy

product at the start of its shelf life. The difference in the shelf life given to

different quality products, typically occur due to the expectations of the

consumer. The consumer of a premium product will have a higher expectation of

the product than the consumer of the economy product (Kilcast and

Subramaniam, 2000). However, a large degree of change is evidently tolerable to

many customers (Singhal, et al. 1997), and so acceptable sensory characteristics

are often defined by company policy (Kilcast and Subramaniam, 2000).

Shelf life is greatly affected by the storage conditions under which the

product is kept (Man 2002). IFST (1993) explicitly states that shelf life must be

defined under specific recommended conditions. Storage characteristics are

measured under carefully controlled environmental conditions, that are generally

not experienced for the period between product manufacture and consumption by

Chapter 2: Literature Survey: Shelf Life 19 the consumer. It is therefore important that the storage characteristics of the

product under different types of storage conditions are understood (Kilcast and

Subramaniam, 2000).

Shelf life is a complex concept that is dependent on the nature of the food

product under consideration, the preservation technologies applied, and the

environmental conditions to which the food product is exposed (Eskin and

Robinson, 2001). The packaging of the product also has a great influence in the

maintenance of the quality and the shelf life of the food, and is a major part of the

preservation system of the food (Eskin and Robinson, 2001).

Chapter 2: Literature Survey: Legislation 20

2.6 LEGISLATION

Food legislation in most countries requires most pre-packaged foods to

carry an “open date” or date of “minimum durability” (Man and Jones, 2000).

These dates help the consumer to decide how long the product may be stored prior

to consumption, and also help with stock rotation in grocery stores (Steele 2004).

According to Cadwallader and Weenen (2003), and LaBuza and Szybist

(2001), there are several methods in which the shelf life or open dating may be

employed.

.

The “best before” or “best if used by” date is the date up to, and including

which, the food “can reasonably be expected to retain its specific

properties”, providing it has been stored under specified conditions. Food

may still be safe for consumption after this date, but its appearance and

quality may deteriorate beyond product specifications (Man and Jones,

2000).

“Production date” or “pack date” is the actual date the product was

processed or harvested and packaged. This form of dating makes the

consumer aware of the age of the product in order to make a selection


judgement. This form of dating is used primarily for pre-packaged fresh

fruits and vegetables (Cadwallader and Weenen, 2003).

The “sell by” or “pull” date (Freitas, et al. 2003) is used for perishable

processed foods. This helps the retailer in stock rotation to sell the product

at a point where the consumer may purchase product, and will still be able

to have adequate storage time at home, before the end of the shelf life

(Cadwallader and Weenen, 2003).

The “used by” date may be a “sell by” date, with a warning to consume

within days of that date. It may also simply be a date determined by the

manufacturers as the end of the useful quality life of the product

(Cadwallader and Weenen, 2003).

“Closed” or “Coded Date” is a date that is used by the industry that

indicates production lots. It may also represent a packing date, and is

useful to the manufacturer in the case of a recall, but is not intended to be

used by the consumer (Cadwallader and Weenen, 2003).

Therefore, it is critical that procedures are established for shelf life to be

evaluated, accurately in order to satisfy legislation, ensure customer satisfaction,

while maximising the sale life of the product (Cadwallader and Weenen, 2003).


Modern society demands foods that are safe, nutritious, aesthetically

appealing, readily available, convenient to use and reasonably priced

(Charalambous 1993). Evaluation of local, regional and international food

legislative requirements, revealed that most countries require some form of dating

of product, so that the customer may be able to determine the age, and hence

quality and safety of the food.

2.6.1 The Republic of Trinidad & Tobago

The Food and Drugs Act of Trinidad & Tobago states in Item 16(1)(b)(vi)

that “any expiry date or date mark required by these Regulations” should be

placed “on any panel except the bottom of the package” (The Government of

Trinidad and Tobago, 1980). This regulation was then amended in 2001, by

changing the subparagraph to “the expiry date or date mark” (The Government of

Trinidad and Tobago, 2001).

The regulations as they exist leave much room for interpretation of the

law. However the Draft Revised Food Labelling Regulations has far more specific

and detailed regulations regarding how dating of food should be done (Food

Advisory Committee of Trinidad and Tobago). Only food with a durable life of

less than 90 days is required to possess a date. The date the food was packaged, as

well as the durable life (shelf life), and instructions for proper storage, if different

Chapter 2: Literature Survey: Legislation 23 from normal conditions, are required. The draft goes as far as to state how the

durable life dates should be written (Food Advisory Committee of Trinidad and

Tobago).

2.6.2 Other Caribbean Territories

Item 6.1 of Jamaica’s Standards Act, states that all processed food

packages must bear a code showing the date the food was packaged as a batch

number (Government of Jamaica, 1974). However, this was purely done with the

intent of traceability, and is clearly stated in Item 6.3 which reads, “manufacturer,

processor, importer or distributor of any processed food in relation to which the

code referred to in paragraph (1) is used shall, at the request of the Bureau, supply

to the Bureau the key to such code” (Government of Jamaica, 1974).

In 1988, The Jamaica Bureau of Standards amended the requirements for

the labelling of pre-packaged foods. The Bureau declared new requirements as a

standard specification pursuant to Section 7 of the Standards Act, 1968. Section 7

of the Standards Act refers to information that is required to be given on packages

of containers (Government of Jamaica, 1974). Item 3.2e of the Bureau’s standard

requires that a “datemark or date of minimum durability, where an indication of

the age of the goods is likely to be useful to the consumer of purchaser” (Jamaica

Bureau of Standards, 1988).


Guyana’s regulation, under The Food and Drugs Act, with respect to

dating, is identical to that of Jamaica. According to Item 18(2)(b)(vi), “the label

applied to a food shall carry on any panel the expiry date or date mark required by

these Regulations” (The Ministry of Health, Housing and Labour of Guyana,

1977). The same regulation is also required of importers of food products to the

country (Collins and Alves, 1993).

According to Item 4.7 of the Barbados National Standards Institution (2004)

Labelling Requirements of Prepackaged Foods, it is a requirement unless

otherwise specified in an individual Barbados National Standard, for the

following date markings to be applied as appropriate, along with any special

storage instructions.

a. the “date of minimum durability”;

b. the “date of manufacture” for all manufactured foods;

c. the “date of packaging” for all prepackaged foods not from a

manufacturing process.

These requirements are very similar to that have been proposed in Trinidad

and Tobago (Food Advisory Committee of Trinidad and Tobago).


2.6.3 North America

Canadian legislation requires the display of the “durable life” date (CFIA).

This country defines this period as “the period starting on the day a food is

packaged for retail sale, that the food will retain its normal wholesomeness,

palatability and nutritional value, when it is stored under conditions appropriate

for that product” (CFIA). The “durable life” date is required for prepackaged

foods with a durable life of 90 days or less, with a few exceptions. Storage

instructions are required to be displayed, if they differ from normal room storage

conditions on the package, if the food is packaged at a non-retail establishment.

Retail establishments may choose to place date and storage instructions on the

label, or on a poster beside the food (CFIA).

2.6.4 The European Union

The labelling requirements of the European Union are particularly detailed

(European Council). The European Union’s food labelling law was developed in

1979, and has been amended several times to inform and protect consumers of

changing threats through the years (European Council).

With respect to shelf life, Article 9 of the Directive 2000/13/EC defines

the date of minimum durability of a foodstuff, as the date until which the

foodstuff retains its specific properties when properly stored (European Council).

Chapter 2: Literature Survey: Legislation 26 This date is required to be indicated as ‘Best before …’ when the date includes an

indication of the day, or ‘best before end …’ in other cases. If required, the date

must incorporate storage conditions required to keep the product for the specified

period (European Council).

These requirements are typical of most labelling requirements throughout

the world. However, the European Union has included additional requirements for

highly perishable foods in Article 10. The Article states, “in the case of foodstuffs

which, from the microbiological point of view, are highly perishable and are

therefore likely after a short period to constitute an immediate danger to human

health, the date of minimum durability shall be replaced by the use by date”

(European Council).

Chapter 2: Literature Survey: Shelf Life Importance 27

2.7 SHELF LIFE IMPORTANCE

Legislations clearly indicate that it is a requirement to communicate with

potential consumers, the date by which food is acceptable and safe for

consumption. It is essential firstly, to have an expiry date that is accurate, so that

customers will be able to accurately determine the quality of the food (Man 2002).

If the customers gain confidence in the quality of the product, this influences

satisfaction (LaBuza 1982). Customer satisfaction generally equates to repeat

customers and ultimately profits (Man and Jones, 2000).

It is necessary to also have the maximum possible shelf life in order to

increase the product’s availability for sale, as well as to increase the product’s

distribution (LaBuza and Szybist, 2001). Therefore, it is critical to develop an

optimal date which ensures satisfactory quality, yet allows the greatest window of

time for consumption (Man and Jones, 2000).

Chapter 2: Literature Survey: Factors Affecting Shelf Life 28

2.8 FACTORS AFFECTING SHELF LIFE

With few exceptions, food quality decreases with time of storage,

irrespective of the preservation methods used and the control of storage

conditions, even for foods held in a frozen state (Steele 2004). Storage may affect

texture, flavour, colour, appearance and the nutritive value and safety of the food

(Eskin and Robinson, 2001).

There are intrinsic and extrinsic factors that may affect shelf life of the

snack. The intrinsic factors are as follows: raw materials, product formulation and

composition, product make-up, water activity value, pH value, availability of

oxygen and redox potential (Eskin and Robinson, 2001). The rate of deterioration

is affected by extrinsic deteriorative factors, such as, moisture, oxygen, light,

temperature and aroma transfer. Other factors that will affect shelf life are the

processing method, hygiene, packaging materials and system, storage, distribution

and retail display (Man and Jones, 2000).

Food systems are very complex. Their deterioration can be

multidirectional and have multistage characteristics (Man and Jones, 2000).

Although theoretically possible, it is not realistic to describe all geometrical

attributes of appearance; to determine all chemical components; as well as all

Chapter 2: Literature Survey: Factors Affecting Shelf Life 29 physicochemical and biological processes of real food systems. Analysis of the

maximum number of identified compounds may not provide the most valuable

information with respect to perception of spoilage and shelf life determination

(Man 2002). The selection of properties which may encompass the sensory

experience of the food is most important. The mechanisms of these substances’

retention and release and their proportions, may significantly influence the quality

attributes of the food, and provide more accurate meaningful shelf life

determination (Man and Jones, 2000).

2.8.1 Biological Decay – Pre-harvesting

Prior to harvesting and slaughter, foods from animals or plants are subject

to many diseases, including viruses, parasites, yeasts, molds and bacteria (OTA

1979). Pre-harvest deterioration will certainly determine the initial quality which

the food will possess. The shelf-life of snack foods obtained from untainted corn

kernels would be longer than kernels that suffered disease, or any other form of

pre-harvest deterioration (OTA 1979).

2.8.2 Senescence

Upon harvest or slaughter, the plant or animal is separated from its source

of nutrients and water. However, enzymes continue to operate and utilise nutrients

stored (Karel and Lund, 2003). This enzymatic activity may be beneficial or

Chapter 2: Literature Survey: Factors Affecting Shelf Life 30 detrimental to the manufacturer and the shelf-life determination process (OTA

1979).

All foods are affected by enzymatic processes during postharvest and

result in the degradation of sensory quality, including loss of colour, flavour,

nutrients and texture. The breakdown products themselves also damage the tissues

such that the decaying process becomes more rapid (OTA 1979).

2.8.3 Water Activity & Moisture Migration

Water activity influences the storage stability of foods (Steele 2004). Most

physical changes or instabilities involve moisture or mass transfer of components

in the food. A frequent cause of degradation of food products is a change in their

water content (Man 2002). Moisture transfer occurs in foods due to gradients in

chemical potential, which is directly a function of the food’s water activity (aw).

Water activity is defined as the equilibrium relative humidity for a product

divided by 100 (Steele 2004).

The change in moisture can lead to the food becoming unacceptable,

particularly affecting the texture of the food (Steele 2004). Low moisture foods

such as extruded corn salty snacks are particularly susceptible to absorption of

moisture from the environment (Bourne 2002). It is also possible for moisture to

migrate from the powdered cheese flavour to the corn base, as the water activity

Chapter 2: Literature Survey: Factors Affecting Shelf Life 31 of the flavour is higher than that of the base (Ray 2001). Dry food products are

expected to be crisp, however, if they absorb water, they may undergo glass

transition to become tough and soggy. Moisture content and texture analysis are

critical in the determination of food quality (Bourne 2002), and hence the

determination of shelf life. An increase in moisture absorption in snack foods can

lead to other problems such as microbial or chemical degradation (Steele 2004).

2.8.4 Transfer of Substances Other Than Moisture and/or Water Vapour

The transfer either into or out of food, of substances other than moisture

which affects its safety and/or quality, is likely also to have an impact on its shelf

life (Man 2002).

Volatile flavour components in snack foods may diffuse through the

packaging material, and can affect the shelf life of the food. Diffusion occurs at a

slower rate than moisture migration or oxidation. The slower rate is as a result of

the barrier properties of the packaging material, as well as the larger molecule size

of the flavour components, in comparison with water and oxygen molecules

(Lusas and Rooney, 2001).

Taint and off-flavours may develop as the food absorbs foreign and

objectionable flavours, depending on the packaging used and the prevailing

environment. Foods that have a large surface area to volume ratio such as leaf tea,

Chapter 2: Literature Survey: Factors Affecting Shelf Life 32 or with high a fat content such as snack foods, are particularly susceptible (Man

2002).

2.8.5 Microbial Factors

Micro-organisms are responsible for quality loss of many foods,

particularly fresh foods. Microbes are ubiquitous and they grow rapidly, under the

correct conditions (OTA 1979). Potential food spoilage micro-organisms include

bacteria, fungi (molds and yeasts), viruses and parasites (Steele 2004).

Ramstad and Watson (1987) state, that the final moisture level of the

processed extruded corn snack food for optimum keeping quality characteristics

should be less than 2%. Savoury snack foods have a water activity of less than

0.60 as seen in Table 2.2 (Man 2000). According to Man (2000) this water

activity is below that required for the growth of osmophilic yeasts, which are the

hardiest micro-organisms as seen in Table 2.3. These yeasts can survive in a water

activity no lower than 0.6 (Steele 2004). The Office of Technology Assessment

(OTA) (1979) states, that no microbiological hazards are presented by low

moisture snack foods, as they would lose crispiness before microbes would grow,

and thus become unacceptable before they would become a microbiological

threat.


TABLE 2.2 Water activity (aw) values of some foods.

Source: (Man 2000).


TABLE 2.3 Water activity (aw) limits for microbial growth.

Source: (Man 2000).

2.8.6 Rancidity Development

During the processing of foods, tissue damage occurs that causes the

release of various food chemical constituents into the cellular fluid environment

(OTA 1979). These chemicals can then react with each other or with external

factors, leading to deterioration of the food and resulting in quality deterioration

(OTA 1979).

Many foods contain unsaturated fats that are important in the nutrition of

humans. These fats are subject to three types of rancidity – hydrolytic rancidity,

Chapter 2: Literature Survey: Factors Affecting Shelf Life 35 ketonic rancidity and oxidative rancidity or lipid oxidation (Allen and Hamilton,

1999).

Hydrolytic rancidity is caused by hydrolysis of the triglycerides in the

presence of moisture, which gives rise to the liberation of free fatty acids (FFA).

These free fatty acids are particularly troublesome in the lauric oils, as the fatty

acids have strong soapy off-flavours (Allen and Hamilton, 1999; Man 2002).

Ketonic rancidity occurs when there is a fungal attack on foods, in the

presence of limited amounts of oxygen and water. Methyl ketones and aliphatic

alcohols are ultimately formed and possess a strong off-flavour (Allen and

Hamilton, 1999).

In lipid oxidation, fats are subject to direct attack by oxygen, through an

autocatalytic-free radical mechanism that results in rancid off-flavours, making

the food undesirable to consumers (Man 2002). Very little fat has to oxidize for

the consumer to detect rancidity and reject the food, even though it may still be

edible and nutritious (OTA 1979).

Lipid oxidation in food products develops slowly initially, and then

accelerates at later stages during storage seen in Figure 2.1 (Frankel 1998). The

rate of reaction depends on temperature to some degree; the rate increases two to

Chapter 2: Literature Survey: Factors Affecting Shelf Life 36 three times for every 10oC increase in storage temperature for dry foods (Frankel

1998). Lipid oxidation is also dependent on water activity (Man 2002). Foods if

too dry or not dried enough are more subject to rancidity as seen in Figure 2.2.

The extruded corn snack is particularly susceptible to lipid oxidation due to its

particularly low water activity. Knowledge of the rate of reactions of lipid

oxidation can be used to predict shelf life, along with the knowledge of how fast

oxygen permeates the food package (OTA 1979).

FIGURE 2.1 Development of rancidity in foods, storage times given in arbitrary values, PV – peroxide value; IP – induction period (Frankel 1998).


FIGURE 2.2 Food stability as a function of water activity (Frankel 1998).

Chapter 2: Literature Survey: Review of Research on Similar Corn Based Snack Foods 38

2.9 REVIEW OF RESEARCH ON SIMILAR CORN-BASED SNACK FOODS

2.9.1 Shelf Life Determination of Lightly Salted Potato Chips (British

Cellophane Limited, 1985)

The British Cellophane Limited (BCL) (1985) performed a shelf-life study

on potato chips. BCL examined lipid oxidation, moisture uptake percentage, as

well as sensory evaluation over time of the food. Man (2000) suggested that the

method used was acceptable for determining deep fat fried, quick fried, extruded,

roasted and baked savoury snack foods, made from cereals or potato.

Packs of salted potato chips were collected and stored at controlled

environmental conditions of a temperature of 25oC and a relative humidity of

75%, for a period of 12 weeks. The packs were stored flat and subjected to a 12-

hour cycling exposure to fluorescent lights. Similar packs were stored in a deep

freeze to be used as controls in subsequent sensory analysis (Man 2000). A

trained sensory panel conducted quantitative sensory evaluation every week,

comparing the deteriorating samples with the control. At the same time, the

peroxide value and free fatty acid value of oil extracted from the chips were

conducted to determine the state of lipid oxidation. The percentage moisture

uptake was determined by weighing packs before submitting them to the panel

Chapter 2: Literature Survey: Review of Research on Similar Corn Based Snack Foods 39 each week and recording the difference from that of the weight of the packs when

they were obtained on the manufacture date (BCL 1985).

It was found that moisture uptake percentage showed a closer correlation

to sensory evaluation results, more so than the peroxide values of the extracted

oil. This occurred as peroxide values are a measure of the primary lipid oxidation

products, but these compounds normally decompose quickly to secondary and

tertiary oxidation products (Man 2000).

2.9.2 Mathematical Models for Estimating the Shelf Life of Corn Flakes

(Azanha and Faria, 2005)

These researchers performed shelf life studies on cornflakes. Four

deterioration factors were identified in storing dried cereals: (a) moisture gain,

resulting in loss of crispiness; (b) lipid oxidation, resulting in rancidity and off-

flavours; (c) loss of vitamins, resulting in the nutritional labelling being incorrect;

(d) breakage, resulting in an aesthetically undesirable product. Therefore, even

though the extruded corn snack food and the cornflakes were not identical, they

were both manufactured from the same raw materials and had similar

deteriorative factors.

After identifying the major deteriorative forces of cornflakes, Azanha and

Faria (2005) focussed on texture analysis of the cornflakes. The objective of the

Chapter 2: Literature Survey: Review of Research on Similar Corn Based Snack Foods 40 study was to determine the critical moisture content of cornflakes and to evaluate

the adequacy of three mathematical models (linear, middle point and logarithm

interval), to estimate the shelf-life of cornflakes packaged in three different

flexible packages under simulated storage conditions.

Sensory evaluation with 32 trained panellists following the procedure of

Meilgaard, et al. (1999), differentiated between the control product at the initial

moisture content, and the ageing samples which were stored at 100% relative

humidity and 23oC. Panellists evaluated the texture of the control and the

experimental samples using a 9-point scale, with a difference of 1 indicating

difference not detectable and 9 indicating extremely intense level of difference. At

the same time, the moisture content was measured by means of the Aqualab 3TE

as seen in Figure 2.3.


FIGURE 2.3 Aqualab 3TE moisture analyser (DDI 2007).

The texture was also analysed mechanically, with hardness determined as

a peak force, in gram force (gf), required to compress the product by 50%, and

overall crispness evaluated as the total number of positive peaks, using the

Texture Analyzer (TA.XT2i) as seen in Figure 2.4. The experimental moisture

points determined were then compared with points predicted by the three different

mathematical models, and the best fit determined (Azanha and Faria, 2005).


FIGURE 2.4 Texture technologies TA.XT2i texture analyser (TT 2007).

A similar predictive approach via mathematical modelling was also

explored, but for the growth of micro-organisms (McMeekin and Ross, 1996).

Steele (2004) also explored the use of several other deteriorative properties as a

basis for predictive analysis by mathematical modelling. This procedure may be

widely used for various applications in shelf life determination.


2.9.3 Flavour Properties and Stability of a Corn-Based Snack (Charalambous

1993)

A corn-based extruded snack was subjected to five separate types of tests,

all of which dealt with flavour analysis. Five separate batches of the snack were

stored at a controlled temperature for 0, 3, 6, 9 and 12 month periods, after which

they were frozen to prevent further ageing effects.

The first test was a descriptive sensory analysis by a trained panel of 27.

The panellists evaluated aroma and flavour of the snack food, for the different

batches. In a separate test, the volatile compounds in the sample were extracted

using methanol, which were then isolated in dichloromethane. The extract was

concentrated and its aroma also analysed by a sensory panel for the different

batches.

The extracts from 3 of the batches were separated by gas chromatography

and assessed by the Osme technique, as seen in Figures 2.5 and 2.6. Four panel

members documented the time and intensity of the aroma as it left the gas

chromatograph. The difference over time was analysed.


FIGURE 2.5 Osme equipment and Osmegram (Charalambous 1993).


FIGURE 2.6 Osmegram showing panel member’s scorecard (Charalambous 1993).

The peaks found in the gas chromatograph were tentatively identified by

matching published mass spectra. Pure chemicals were then purchased, and

chemical identities were confirmed by a match of retention indices and mass

spectra (Charalambous 1993).

Lastly, the hexanal content in all 5 samples was measured by static

headspace gas chromatograph analysis. The oxygen in the canisters headspace

was measured in the samples also by a Systeck instrument. The changes in

hexanal and oxygen content over time were analysed, and it was found that

hexanal content increased over time and was a reliable off-flavour predictor

(Charalambous 1993).

Chapter 2: Literature Survey: Shelf Life Determination 46

2.10 SHELF LIFE DETERMINATION

A shelf life study is done to determine as accurately as possible, under

specified storage conditions, the point in time at which the product has become

either unsafe, or in the case of the extruded corn snack food, unacceptable to the

target consumers (Man 2002). Different types of foods have different quality

expectations. Consumer enjoyment of snack foods results from several factors,

but the overwhelming key factors are taste, texture and size (Lusas and Rooney,

2001).

Chapter 2: Literature Survey: Determination of the end of the Product’s Shelf Life 47

2.11 DETERMINATION OF THE END OF THE PRODUCT’S SHELF LIFE

The period of time from manufacture or processing to the end point of the

food’s life, or the point which food is unacceptable, is found by different methods

depending on the type of food (Man 2002). Examples of established guidelines

for determining the end point of the shelf life of some foods may be seen in Table

2.4 (Man 2002).

Established guidelines for dry, salty snack foods, such as the one under

study, were not obtained from the reviewed literature, as was found for perishable

foods. However, Man (2002) states that where guidelines are not available,

manufacturers and processors have to establish their own end-points, using

microbiological examination, chemical analysis, physical testing and properly

designed and conducted sensory evaluation, to define product-specific sensory

criteria.

Chapter 2: Literature Survey: Determination of the end of the Product’s Shelf Life 48

TABLE 2.4 Guidelines that can be followed to set shelf life end-point.

Source: (Man 2002).

Chapter 2: Literature Survey: Determination of Suitable Shelf Life Tests & Procedures 49

2.12 DETERMINATION OF SUITABLE SHELF LIFE TESTS & PROCEDURES

As Lusas and Rooney (2002) stated, consumers choose snack foods,

because of taste, texture and size. Market research also showed that for the

particular target market of the product being tested, the taste of the snack, along

with the perception of value for money and quantity for price, were the key

characteristics that drove sales numbers (Anonymous 2007b, personal

correspondence). However, it was also found that the key complaints with respect

to the quality of the product, as a result of fluctuations during production and/or

changes that may have occurred during storage, were almost all texture related

(Anonymous 2007a, personal correspondence).

Changes in texture due to moisture migration, and off-flavour

development due to lipid oxidation, were found to be the two critical properties

responsible for consumer acceptability and hence shelf life determination. The use

of a trained sensory panel to complement the chemical and/or physical analysis is

always required (Man 2002).


2.12.1 Lipid Oxidation & Off-Flavour Development

The major contributor to rancidity and off-flavour development in

extruded corn snacks is lipid oxidation (Allen and Hamilton, 1999). Table 2.5

shows ten different methods used to determine the extent of lipid oxidation,

ranked in decreasing order of usefulness (Frankel 1998).

Gas chromatography’s results vary with different unsaturated oils, as well

as with different additives such as antioxidants and metal inactivators (Frankel

1998). Gas chromatography provides useful data on the origin of volatiles and

flavour precursors (Ranken, et al. 1997). However, their significance and impact

on flavour stability are not clearly established and are difficult to evaluate

(Frankel 1998).

Possibly the best non-human chemical method of determining lipid

oxidation is ultraviolet absorption, as it is sensitive, precise and simple to evaluate

(Frankel 1998). Ultraviolet absorption measurements involve the determination of

conjugated dienes by ultraviolet spectrophotometry, related to the contents of

polyunsaturated hydroperoxides that act as flavour precursors (Min and Smouse,

1985). These measurements are sensitive and reproducible, but the information is

only useful to determine precursors of volatiles formed from polyunsaturated oils

(Frankel 1998).


TABLE 2.5 Ranking of lipid oxidation methods.

Source: (Frankel 1998).

British Cellophane Limited’s (1985) study clearly stated that due to further

decomposition of the primary products of lipid oxidation, peroxide values (PV) of

the extracted oil from the snack food did not correlate as closely as moisture

absorption, with product deterioration. More recent studies state that the peroxide

value (PV) is accepted as an indication of the extent of oxidative rancidity (Man

2002; Cadwallader and Rouseff, 2001). Peroxide value is also widely used in the

food industry as an indication of oil stability (Anonymous 2007a, personal

correspondence).


Peroxide value methodology is precise, however the method is empirical

and the results may be misleading in samples that have been thermally abused or

subjected to light oxidation (Frankel 1998). Since the snack is packaged in opaque

metallised OPP, elevated oxidation due to light is not a factor. However, it is

important that samples are stored at a constant temperature (throughout

experimentation) (Man 2002).

2.12.2 Extraction of Lipids

In order to determine the extent of rancidity of the lipids, the lipid must be

extracted from the food samples (McDonald and Mossoba, 1997). There are three

basic types of procedures that are used to extract lipids from foods: reflux

extraction, acid or alkaline digestion prior to solvent extraction, and non-heating

methods (McDonald and Mossoba, 1997). There are numerous standard methods

of extraction that use a variety of solvents ranging from non-polar hydrocarbons,

to mixtures containing alcohols and water. The methods involve simple shaking,

refluxing or prolonged extraction in a Soxhlet apparatus, preliminary grinding,

homogenisation of a suspension in solvent and/or partitioning of the sample

between an organic and aqueous phase (King 1980).

The aim of all extraction procedures is to separate cellular or fluid lipids

from the other constituents, proteins, polysaccharides, small molecules, but also to

preserve these lipids for further analyses (King 1980). Removing the non-lipids

Chapter 2: Literature Survey: Determination of Suitable Shelf Life Tests & Procedures 53 without losing some lipids is a complex challenge, while extracting some specific

lipids is not always reliable for other kinds of lipids. Therefore, knowledge of the

type of lipids being extracted is also critical in the determination of a suitable

method (Leray 2007).

The extraction of lipids from foodstuff and its subsequent storage before

analysis, must take into account that most lipids consist of hydrolysable esters

containing unsaturated centres vulnerable to further oxidation by air (King 1980).

The method chosen should depend on the nature of the foodstuff; whether its

lipids are free, physically entrapped or molecularly bound by non-lipid

components; whether the lipids are abnormally liable or volatile and the time

available for extraction (King 1980).

The Soxhlet method is the most common method used for lipid extraction

from foods (Leray 2007), and is recognised by the Association of Official

Analytical Chemists (AOAC) as the standard method (AOAC method 960.39) for

crude fat analysis (Food Science Australia). The oil and fat from solid material is

extracted by percolation with an organic solvent, usually hexane or petroleum

ether, under reflux in special glassware as seen in Figure 2.7. The solvent is held

in (1), the extraction chamber houses the sample in (2), some devices contain a

funnel to recover solvent as in (3), and (4) is the condenser which condenses

solvent vapours (Leray 2007).


FIGURE 2.7 Glassware used in Soxhlet extraction (Leray 2007).

Despite its popularity, there are several disadvantages in using this method

of extraction: poor extraction of polar lipids; long times involved; large volumes

of solvents; tendency for the lipids to oxidise; and the hazard of boiling solvents

(Leray 2007; Christie 2007). However, automated extraction instruments have

been developed that have improved on the original method. They are able to boil,

rinse and recover solvent automatically in a significantly shorter time period

(Leray 2007). An example of this equipment is the Lab Synergy: Fast Extraction

(Viscal 2006).


Accelerated Solvent Extraction (ASE) is a technique that was made to

replace Soxhlet and other extraction techniques required for numerous samples.

The automation and rapid extraction time of ASE overcome the shortcomings of

Soxhlet extraction. Common liquid solvents are used at an increased temperature

and pressure to accelerate the extraction process (Dionex Corporation, 2004).

Another method of extraction is the Folch method (Folch, et al. 1957).

This procedure remains one of the best described and most widely used by

lipidologists (Leray 2007). Folch et al. (1957) suggest the use of a chloroform-

methanol (2:1 by volume) solvent combination, as well as saline solution. This

method is a useful, multipurpose extraction technique for biological specimens,

mixed diets and all types of animal tissues, and recovers greater than 96% of

lipids (Spiller 1996). With this method, the proportions of chloroform, methanol

and water are critical in order to reduce lipid losses (Christie 2007). This method

is best suited for the extraction of lipids for peroxide value evaluation, as it avoids

over exposure to solvents and the possibility of oxidation of the extracted lipids

(Spiller 1996).

An alternative to the traditional Folch method was described by Marmer

and Maxwell (1981) using a dry-column method. This method was found to

produce similar results as Folch’s chloroform/methanol method in analysing

muscle and adipose tissues. However, this technique has been generally used in

Chapter 2: Literature Survey: Determination of Suitable Shelf Life Tests & Procedures 56 the isolation of drugs, herbicides, pesticides and other pollutants from animal

tissues, fruits and vegetables (Leray 2007).

Other more complex solvent extraction methodologies, including

supercritical fluid extraction and microwave irradiation or ultrasonification to

improve yields, are widely researched (Leray 2007). These methods require

specialised equipment, and are also more specific, requiring testing on a wider

range of sample matrices (Christie 2007). Leray (2007) also suggested variations

of extraction methods, as suggested by Christie (2007) However, these methods

are specific for extraction of particular types of lipids.

2.12.3 Moisture Migration and its effect on Texture

There are three primary methods of measuring food texture – instrumental,

acoustic emission and sensory attributes (Rosenthal 1999). There are force,

distance, time, work energy and power, measuring instruments that are effective

in measuring texture of foods (Bourne 2002). Cumming, et al. (1971) stated that

the most widely used instruments for texture evaluation in quality control were

rotational viscometers (for liquids) and penetrometers (for solids).

Some food technologists use a compressive or tensile force and relate the

magnitude of the force to the deformation done in millimetres of the sample

(Rosenthal 1999). Katz and Labuz (1981) used the initial slope of the force-

Chapter 2: Literature Survey: Determination of Suitable Shelf Life Tests & Procedures 57 deformation curve. The value of the initial slope was found to be a good indicator

of crispness for saltines (cracker) and potato chips. However, for extruded corn

snacks, the initial slope was nonlinear and unsatisfactory. The work done to

compress the corn snack by 75% was an acceptable indicator of crispness (Katz

and Labuz, 1981). The work done to compress the snack by 50% was used by

Azanha and Faria (2005).

Moisture absorption is determined by the difference between the weight of

the sample initially at the point of manufacture, and the weight after some time of

storage (Man and Jones, 2000). The weight gained is taken to be the moisture

uptake of the product (Man 2002). This is not accurate as the many chemical

reactions, including those of rancidity, may also be responsible for changes in

weight. Despite this limitation, this method is acceptable in determining moisture

absorption (Steele 2004).

2.12.4 Sensory Evaluation

Sensory evaluation is critical in the accurate determination of a product’s

shelf life (Man 2002; Steele 2004). However, dependable sensory analysis is

based on the skill of the sensory analyst (Meilgaard, et al. 1999). All humans are

afflicted by factors, physiological and psychological, which can influence sensory

perception such as adaptation, expectation, stimulus, logical and the halo effect

(Meilgaard, et al. 1999).


In addition to these factors, which can be minimised by proper procedure

of testing, humans by nature are quite variable over time; and very variable

among themselves (Meilgaard, et al. 1999). Meilgaard, et al. (1999) suggests that

measurements are repeated; enough subjects are used (≥ 20) so that verdicts are

representative. Literature reviewed revealed that panels with as few as 6 subjects

may be used effectively (Ucherek 2004; Freitas, et al. 2003). The sensory analysts

must either all be untrained, or all be properly trained and respect the many rules

and pitfalls that govern panel attitudes (Meilgaard, et al. 1999).

The type of sensory evaluation test that is used for the determination of the

shelf life of all products, is the difference from control test (Man 2000). An

example of an applicable scorecard can be seen in Appendix. The test evaluates

the key components of the extruded corn snack food, which are flavour and

texture, as well as the overall acceptability of the product (Man 2000).

Panellists who are experienced with this the extruded corn snack food,

determined when the sample is no longer acceptable. The development of a scale

used to measure panellists’ responses must be done with several reference points

(Meilgaard, et al. 1999). Statistical analysis is critical to accurately determine the

end of the product’s life (Meilgaard, et al. 1999; Freitas, et al. 2003).

Chapter 2: Literature Survey: Accelerated Shelf Life 59

2.13 ACCELERATED SHELF LIFE

Accelerated shelf life determination is used to shorten the time required to

estimate a shelf life which otherwise can take an unrealistically long time to

determine (from a number of months to a few years) (Kilcast and Subramaniam,

2000). Shelf life is accelerated by elevating a condition under which the product is

being stored (Man 2000). The effect of elevating the temperature on many

chemical reactions, as well as adverse changes in food during storage, have been

explored. The assumption is that by storing food at a higher temperature, any

adverse effect on its storage behaviour, and hence the end of the shelf, becomes

apparent in a shorter time (Kilcast and Subramaniam, 2000). Accelerated tests are

based on Arrhenius’ model see Fig 2.8, but this is only appropriate for simple

chemical systems and often fails for foods that are, in reality, more complex (Man

2000).

FIGURE 2.8 Arrhenius’ equation (Man 2000).

TR

Ea

eAk

k = rate constant, A = constant, Ea = Activation Energy, R = Universal Gas Constant, T = Temperature in Kelvin

Chapter 2: Literature Survey: Accelerated Shelf Life 60

Accelerated determinations are useful when the patterns of changes are

practically identical during normal and accelerated storage, so that shelf life under

normal storage can be predicted with a high degree of certainty, such as the

quality of orange juice made from frozen concentrate. Changes found after 6

months at 20oC corresponded to the changes after 13 days at 40oC, and after 5

days at 50oC (Man 2000).

Accelerated determinations have 2 limitations – (i) temperature rises can cause a

change of physical state, which may in turn affect the rates of certain reactions

and (ii) storage at a constant elevated temperature, without a corresponding

elevated relative humidity, that may lead to unexpected results (Man 2000). The

second limitation has particular relevance, as moisture migration and texture

degradation have been found to be critical in consumer acceptability of the

extruded corn snack food (Anonymous 2007a, personal correspondence).

Chapter 3: Methodology 61

CHAPTER 3

METHODOLOGY

3.1 STORAGE OF SAMPLES

Two hundred and eighty eight (288), twenty-gram (20g) packets of the

snack food, from a production, run were randomly assigned to the following three

storage conditions:

Frozen: Samples ‘C’ were kept frozen, in a deep freezer at approximately

-18oC as recommended by Man (2000), and were used as the Control for

the duration of the evaluations.

Ambient: Samples ‘A’ were stored in a cage at ambient temperature of

33oC, and relative humidity 100%. This storage condition was chosen to

simulate the worst case scenario as recommended by Bryce, LCCP and

WFI (2007a).

Retail: Samples ‘R’ were stored in an air-conditioned room of 18oC with a

relative humidity 75%. This storage condition was chosen to simulate

the environment typical of a retail outlet.


3.2 SENSORY EVALUATION OF A LOCALLY MANUFACTURED CHEESE-

FLAVOURED EXTRUDED CORN SNACK BY TRAINED PANELLISTS

The aim of the experiment was to determine the shelf life of a popular

locally manufactured cheese-flavoured extruded corn snack food, stored under

two separate conditions.

Twenty (20) employees of the product’s company’s trained sensory panel,

who were therefore familiar with the product, formed the sensory panel. They

attended panel sessions weekly, every Tuesday, between the hours of 1:30pm –

2:30pm. The “difference from control” test was issued to the panellists to

compare Samples ‘C’, ‘R’ and ‘W’ as recommended by Meilgaard et al. (1999)

see Appendix. Panel members were all given a copy of the score sheet, a bottle of

still water, and a pencil.

Ten (10) packs of samples from each of the storage conditions were placed

in the panel room fifteen (15) minutes before panel sessions, so that they all

attained room temperature (20oC). The panel room contained six (6) booths, and

was designed to facilitate the reduction of errors as recommended by Meilgaard et

al. (1999). Four (4) small Styrofoam containers were labelled, one (1) was

labelled control, while the other three were labelled with a random three-digit

Chapter 3: Methodology 63 number as recommended by Meilgaard et. al (1999). Each three-digit number for

that week was assigned to one of each of the three different sample conditions,

“blind control”, “retail” and “ambient”. The control sample was placed into the

container labelled, “control” and the three-digit number assigned to the “blind

control” for that week as seen in Figure 3.1.

FIGURE 3.1 Sensory evaluation test booth set up


Panellists were instructed to compare the coded samples with the control,

and to assign a score on an eleven-point scale (0 to 10) to each attribute of texture

and flavour. Panellists were also instructed to assign a score to the “overall

attribute” of the sample. The overall attribute was the total sensory experience of

the snack food experienced by the panellists. This included the appearance,

flavour, sound and texture experienced during consumption of the snack food.

Each attribute was scored separately, such that it would be possible to have a

sample fail in one attribute, but acceptable regarding another.

A score of “0” was equated with “no difference” between sample and

control, while a score of “10” signified “extreme” difference. A score of six “6”

was defined as unacceptable. Samples were evaluated weekly until sixty-five

percent (65%) of the panel rejected the “overall attribute” of the samples, as

recommended by Anonymous (2007a, personal correspondence).


3.3 DETERMINATION OF THE MOISTURE UPTAKE IN STORED SAMPLES

The aim of the experiment was to determine, over time, the mean increase

(in g) in weight per pack of snack food. This increase in weight was equivalent to

the moisture absorbed by the snack food (Man 2002).

All samples (packs) were numbered and weighed at week 0, prior to

randomly placing them into the three storage conditions. Each week, five (5)

samples from each storage condition, were removed and then weighed before

sensory evaluations. The difference from the initial weight of the pack was

recorded as recommended by Man (2002).

3.4 TEXTURE ANALYSIS OF SAMPLES USING THE PENETROMETER

The aim of the experiment was to evaluate the change in the texture of the

extruded corn snack food over time, with the aid of a digital penetrometer.

One (1) snack piece was taken from each of five separate packets from

Samples ‘A’, stored under ambient conditions. The five pieces were tested at the

identical position at the top and centre of each piece. An automatic penetrometer

was used with a 47.5g base and a 2.5g needle (50g total weight). The tip of the

Chapter 3: Methodology 66 needle was placed on the very edge of the snack piece, and then allowed to plunge

into the piece under its own weight for 5 seconds. The distance (in mm) which the

needle travelled into the snack piece was determined automatically by the

penetrometer. The mean of the five distance readings was calculated weekly for

each of the three storage conditions.

3.5 LIPID EXTRACTION FROM THE EXTRUDED CORN SNACK FOOD

The aim of the experiment was to extract the maximum quantity of lipid

(oil) possible from the extruded corn snack, in order to determine the peroxide

value of the oil.

Folch’s lipid extraction method (Folch, et al. 1957) was modified due to

the increase in sample size from 2g to 10g. The modified method was used

weekly in order to extract available lipids from the snack foods stored under the

different conditions. One (1) extraction was done initially (Week 0), as all

samples were the same. Subsequently, lipids were extracted weekly from samples

stored under the different conditions.

One (1) pack of the snack food (approximately 20g) was opened and the

contents emptied into a mortar. The packaging material was discarded. A pestle

was used to crush the sample. The crushed sample was divided into 2 – 10g

Chapter 3: Methodology 67 samples and added to a 250ml conical flask. Two hundred millilitres (200 ml) of a

homogenised mixture of two parts chloroform – one part methanol was added to

each of the 10g samples. The whole mixture was agitated at a speed of 600 rpm,

for 20 minutes, using a magnetic stirrer.

“Whatman #4” fast filtering speed, filter paper was used for filtration. The

filter paper was 11.0cm in diameter, and had a retention (in microns) of 20 – 25.

The filter paper was folded in half, and then into quarters. The folded filter paper

was then opened to form a cone. The homogenate was filtered with a glass funnel

and the folded filter paper. The filtrate was recovered in a 250 ml conical flask.

The residue and filter paper were discarded.

The filtrate was washed with 40ml of a 0.9% sodium chloride (NaCl)

solution. The mixture was manually swirled for a few seconds. The mixture was

placed into four (4) 50ml test tubes and sealed with fitting covers. The closed test

tubes were then each placed into four (4) centrifuge canisters which were also

sealed with a fitting cover. The canisters were placed into a centrifuge, where they

were centrifuged at 2000 rpm for 10 minutes. The mixture was centrifuged in

order to separate the two phases. The upper phase was siphoned, using a Mohr

pipette, and discarded.


The lower phase from both 10g samples were combined and added to a

pear-shaped glass flask. The solvent was evaporated using a rotary evaporator

under vacuum as seen in Fig 3.2. The oil that remained after evaporation was

weighed and then evaluated for peroxide value.

FIGURE 3.2 Rotary evaporator (Sigma-Aldrich, 2007).


3.6 PEROXIDE VALUE EVALUATION OF EXTRACTED OIL

The aim of the experiment was to determine the peroxide value of the

extracted oil. The peroxide value can be equated to off-flavour production (a

function of the flavour attribute) in the snack food as suggested by Man (2002)

and Cadwallader and Rouseff (2001).

After the oil was extracted from the samples, the oil was analysed for

peroxide value using the Association of Analytical Chemists (AOAC) procedure

for peroxide evaluation of oils and fats as recommended by Cunniff (1997) with

no modifications.

3.7 TREATMENT OF RESULTS

The blind control was used to evaluate the validity of the panellists’

results. In analysing the sensory data from the panel sessions, only panellists who

gave the “blind control” a score of “0-2” were accepted as recommended by

Freitas et al. (2003). The scores of all the panellists may be seen in the Appendix.

Several methods of regression (linear, exponential and polynomial) were

used to evaluate the sensory data, with the aid of Microsoft Excel. Microsoft

Chapter 3: Methodology 70 Excel is one type of software that is designed to accurately fit data to a variety of

different regression models. The regression model that was used for each test

condition was chosen to fit as many of the data points as possible as

recommended by Triola (2004).

Minitab® 15.1.1.0 is a statistical software that was used to perform

logistic regression. Logistic regression was used to compare objective testing

results (penetrometer, moisture increase and peroxide value) with sensory

evaluation results (texture and flavour attributes), in order to determine if any

correlation existed. The number of panellists with acceptable texture attribute

sensory scores (blind control ≤ 2), for each week for both ambient and retail

conditions, were placed together in one column. The corresponding number of

failures per sensory evaluation that occurred were placed in the second column,

and the objective moisture uptake value was placed in the third column. The same

was done for penetrometer values, however peroxide value results were paired

with flavour attribute sensory scores.

Minitab’s logistic regression was able to determine Pearson’s p-value,

which is and indication of statistical correlation. The p-value is the probability of

obtaining a result at least as extreme as a given data point, under the null

hypothesis. A p-value that is less than 0.05, suggests that one variable has a

statistical impact on another (Freund 2004; WFI 2007b).

Chapter 4: Results & Discussion 71

CHAPTER 4

RESULTS & DISCUSSION

4.1 RESULTS OF SENSORY EVALUATION OF THE EXTRUDED CORN SNACK FOOD

4.1.1 Sensory Evaluation of the Texture Attribute

Table 4.1 shows the results of the sensory evaluation of the texture of the

extruded corn snack food, stored under ambient (33oC, 100% RH) and under retail

(18oC, 75% RH) conditions.

TABLE 4.1 Sensory evaluation of the texture of an extruded corn snack food.

Sample Storage Period in Weeks

1 2 3 4 5 6 7 8 9

A

(33o C

| 10

0% R

H) 1. average

score 1.8±1.6

2.5±1.9

2.6±1.9

3.3±1.3

3.6± 2.0

5.1±1.4

5.7±1.3

8.8±1.2

9.0±1.2

2. %fail 6 8 7 7 18 27 44 94 100

R

(18o C

|

75%

RH

) 1. average score

1.8±1.5

2.3±1.7

1.7±1.3

2.4±1.7

3.1± 1.5

4.2±1.4

4.7±1.3

5.8±1.1

7.1±1.8

2. %fail 0 0 0 7 12 13 33 59 83

The average score of the panel members is the mean score of the members

that gave the “blind control” a score less than 3 (acceptable score). While percent

Chapter 4: Results & Discussion 72 (%) fail is the percentage of panellists, with acceptable scores, that gave Samples

‘A’ or ‘R’, where applicable, a failing grade (score greater than 5).

4.1.1.1 Evaluation of the Texture Attribute of Sample ‘A’

Between Weeks 1 – 5, the sensory panel detected a very gradual change in

the difference between the textures of the Control and Sample ‘A’. Texture scores

increased from 1.8 to 3.6 from Week 1 – 5. From Week 5 the difference in texture

between the Control and Sample ‘A’ increased more rapidly weekly; from 3.6 to

9.0 from Week 5 – 9. Thus shelf life of Sample ‘A’ as determined by subjective

texture evaluation ended within the seventh week of storage. At the start of Week

7, 44% of the panellists had failed Sample ‘A’, but by Week 8, 94% of the

panellists failed Sample ‘A’.

4.1.1.2 Evaluation of the Texture Attribute of Sample ‘R’

Average scores over time from the sensory evaluation of texture of

Sample ‘R’, were very similar to results obtained from Sample ‘A’. At Week 1,

the average score of Sample ‘R’ was the same as that for Sample ‘A’ (1.8).

However, from Week 2 onwards, Sample ‘R’ was consistently given a lower

average score than Sample ‘A’ by the sensory panel. Thus shelf life of Sample ‘R’

as determined by subjective texture evaluation ended a week later than with

Sample ‘A’. The shelf life of Sample ‘R’ ended within the eighth week of storage.

Chapter 4: Results & Discussion 73 At the start of Week 8, 59% of the panellists had failed Sample ‘R’, and by Week

9, 83% of the panellists failed Sample ‘R’, again as determined by its texture.

According to Man (2002) and Kilcast and Subramaniam (2000), foods

stored at higher temperatures generally have a shorter shelf life than those stored

at lower temperatures. This could explain why at the higher ambient temperature

the shelf life of the extruded corn snack based on the deteriorations in texture,

ended a week earlier than at the lower retail temperature.

4.1.2 Sensory Evaluation of the Flavour Attribute

Table 4.2 shows the results for sensory evaluation of the flavour attribute

stored under ambient (33oC, 100% RH) and under retail (18oC, 75% RH)

conditions.

TABLE 4.2 Sensory evaluation of the flavour of an extruded corn snack food.


1 2 3 4 5 6 7 8 9

A

(33o C

| 10

0% R

H) 1. average

score 2.2±1.7

3.0±2.1

2.2±1.6

3.0±1.2

3.4± 2.1

4.7±1.8

5.8±1.4

8.9±1.5

8.9±0.9

2. %fail 6 8 7 7 12 27 67 94 100

R

(18o C

|

75%

RH

) 1. average score

2.3±1.5

1.9±1.5

1.7±1.4

2.8±1.5

3.5± 1.2

4.1±1.5

5.1±1.5

5.8±1.1

7.4±1.9

2. %fail 0 0 0 7 6 27 39 59 83


4.1.2.1 Evaluation of the Flavour Attribute of Sample ‘A’

The flavour attribute of Sample ‘A’ was given, by the panel, a consistent

average score between 2.2 and 3.0, within the first 4 weeks of storage, when

compared to the Control. Similar to the texture attribute, there was a sharp

increase in the average score after Week 4. The end of the shelf life of the snack

food as determined by the deterioration of the flavour, occurred near the end of

Week 6, as at the beginning of Week 6, 27% of panellists failed Sample ‘A’, but

by the beginning of Week 7, 67% of panellists failed Sample ‘A’.

4.1.2.2 Evaluation of the Flavour Attribute of Sample ‘R’

The average score of Sample ‘R’ at Week 1 was 2.3. The average score

given by the panel in the subsequent 2 weeks was lower, however from Week 3,

the panellists’ average score consistently increased. Samples ‘A’ and ‘R’

possessed very similar flavour attributes up until Week 6. As with Sample ‘A’ the

average score increased rapidly after Week 4. The end of the shelf life of the

snack food as determined by the deterioration of the flavour, occurred within the

eighth week of storage


4.1.3 Sensory Evaluation of the “Overall Attribute” (sound, texture, flavour,

appearance)

Table 4.3 shows the results of the sensory evaluation, of the “overall

attribute”, of the extruded corn snack food, stored under ambient (33o, 100% RH)

and under retail (18oC, 75% RH) conditions.

TABLE 4.3 Sensory evaluation results of a snack food showing “overall attribute”.


1 2 3 4 5 6 7 8 9

A

(33o C

| 10

0% R

H) 1. average

score 2.1±1.5

2.8±1.9

2.9±1.7

3.6±1.4

3.8± 1.9

4.7±1.5

5.8±1.1

9.5±0.6

9.2±0.9

2. %fail 6 8 7 7 24 33 50 100 100

R

(18o C

| 75

% R

H) 1. average

score 2.1±1.3

2.2±1.5

2.1±1.5

2.9±1.5

3.7± 1.3

4.4±1.2

5.2±1.1

5.9±1.2

7.6±1.9

2. %fail 0 0 0 7 12 13 39 53 83

4.1.3.1 Evaluation of the “Overall Attribute” of Sample ‘A’

The average score of the overall attribute of Sample ‘A’ increased steadily

from Week 1 – 5, similar to previous attributes, a sharp rise in the average score

occurred from Week 5 – 9. The end of the shelf life of the snack food as based on

the sensory evaluation of the “overall attribute” was found to be within the

seventh week of storage.


4.1.3.2 Evaluation of the “Overall Attribute” of Sample ‘R’

The “overall attribute” average score of Sample ‘R’ remained constant at

approximately 2.1 from Week 1 – 3. Then a steady increase in average score from

2.1 to 7.6 from Week 3 – 9. The shelf life of the overall attribute for Sample ‘R’

ended within Week 8.

Sensory results of the “overall attribute” of the snack food were very

similar to sensory results of texture and flavour attributes.

4.2 STATISTICAL ANALYSIS OF THE SENSORY EVALUATION RESULTS OF THE

EXTRUDED CORN SNACK FOOD

4.2.1 Statistical Analysis of the Texture Attribute Sensory Results

Fig 4.1 shows the percentage of panellists that failed the texture attribute

of the snack food, stored under retail and ambient conditions. Third order

polynomial regression was the least complex fit that best fit both sets of data

(ambient and retail conditions) using Microsoft Excel. Equations 4.1 and 4.2 are

the equations of best fit for the texture attribute of the snack food, stored under

ambient conditions, and retail conditions respectively, where y represents the

probability of failure and x represents storage time in weeks (Triola 2004). This

Chapter 4: Results & Discussion 77 was determined by trial and error using different regression models in Microsoft

Excel.

The end of the product’s shelf life was set to 65% of panel rejection of the

sample. The cubic equations relating failure probability and storage time may be

solved, for y = 0.65, in order to determine storage time in weeks x.

y = 0.002x3 - 0.005x2 + 0.005x + 0.033 Equation 4.1

y = 0.002x3 - 0.009x2 + 0.016x - 0.004 Equation 4.2

Using Equation 4.1, for the evaluation of the texture attribute of the snack

food stored under ambient conditions,

when y = 0.65, x = 7.7 weeks ≡ 53 days

Using Equation 4.2, for the evaluation of the texture attribute of the snack

food stored under retail conditions,


Therefore, panellists determined that under ambient conditions (33oC,

100% RH) the time in days that the texture attributes of the extruded corn snack

food remained acceptable was 53 days. While the texture attributes of the

extruded corn snack food, stored under retail conditions (18oC, 75% RH)

remained acceptable for 58 days.



Texture attribute results from both storage conditions obtained from

Weeks 1 – 4, could be fit using linear regression, while and an exponential fit

could be fit from Weeks 4 – 9. This does not correlate with Charalambous (2003)

and Man (2000). In those studies, a linear regression was the best fit for the

sensory evaluation of the texture attribute for the entire life of the snack food.

Panellists made increasingly negative comments about the texture of the snack

food as it aged over the weeks. Panellists found that Samples ‘A’ and ‘R’ became

harder and rubbery as they aged (Taub and Singh 1998). In addition to the

samples becoming harder and rubbery overall, the panellists commented on an

increase in the presence of small areas within the snack food of significant

roughness (tough spots). It is possible that the combination of the increase in

overall hardness and the increase in these ‘tough spots’, created the exponential

increase in the average score of the texture attribute from Weeks 4 – 9.

4.2.2 Statistical Analysis of the Flavour Attribute Sensory Results

Fig 4.2 shows the percentage of panellists that failed the flavour attribute

of the snack food, stored under retail and ambient conditions. For the flavour of

the snack food stored under ambient conditions the equation of best fit was a

quadratic expression (Equation 4.3). While, for the snack food stored under retail

conditions the equation of best fit was a third order polynomial expression

(Equation 4.4).


y = 0.020x2 - 0.073x + 0.066 Equation 4.3

y = 0.001x3 + 0.003x2 - 0.020x + 0.007 Equation 4.4

Using Equation 4.3, for the evaluation of flavour attribute of the snack



Using Equation 4.4, for the evaluation of flavour attribute of the snack




100% RH) the time in days that the flavour attributes of the extruded corn snack

food remained acceptable was 51 days. While the flavour attributes of the





Some panel members were able to detect slight off-flavours from as early

as Week 3. Those panellists detected a slight “plastic/chemical” odour and a

slightly sour aftertaste (Lusaas and Rooney 2001). Similarly to the sensory

evaluation of the texture attribute, the flavour attribute of the snack food stored

under both conditions, showed a linear best fit up to Week 4, and then an

exponential fit from Week 4 – 9. Charalambous (2003) found that there was a

linear change in the flavour attribute of the snack food within the first quarter of

storage. However, the rate of degradation declined for the final three-quarters of

the snack food’s shelf life. However, Charalambous (2003) studied a snack food

stored with a different packaging system. The snack food was stored in nitrogen-

flushed canisters. Modified atmosphere packaging systems generally reduce the

rate of degradation in foods (Man and Jones 2000).

4.2.3 Statistical Analysis of the “Overall Attribute” Sensory Results

Fig 4.3 shows the percentage of panellists that failed the “overall attribute”

of the snack food, stored under retail and ambient conditions. The equations of

best fit for sensory evaluation of the “overall attribute” of the snack food stored,

under ambient and retail conditions, were both third order polynomial expressions

see Equation 4.5 and 4.6.

y = 0.005x3 - 0.038x2 + 0.098x - 0.003 Equation 4.5

y = 0.001x3 - 0.007x2 + 0.011x - 0.003 Equation 4.6



Using Equation 4.5, for the evaluation of the overall attribute of the snack



Using Equation 4.6, for the evaluation of the overall attribute of the snack




100% RH) the time in days that the “overall” attributes of the extruded corn snack

food remained acceptable was 50 days. While the “overall” attributes of the



Sensory results showed a very similar pattern for the six sensory trials.

Results obtained from Weeks 1 – 4, may be fit using linear regression, while an

exponential fit was seen from Weeks 4 – 9. Sensory evaluation of the “overall

attribute” of the snack food stored under ambient conditions resulted in the

shortest shelf life of the snack food, approximately 50 days. This suggests that the

combination of the flavour and texture attributes, particularly during the period of

exponential degradation (Weeks 4 – 9), gave the panellists a poorer, overall

sensory experience (overall attribute).


In analysing the shelf life, the attribute that when evaluated, contributes to

the snack food obtaining the shortest shelf life, should be used to determine the

“open date” (Man 2000). Therefore, with respect to this research, the shelf life

under ambient conditions was 50 days, using the flavour attribute, and 58 days

under retail conditions, using any attribute (they all yielded the same time).

4.3 RESULTS OF MOISTURE UPTAKE IN AN EXTRUDED CORN SNACK FOOD

Table 4.4 shows the moisture gained by the extruded snack food over 9

weeks of storage.

TABLE 4.4 Moisture increase in an extruded corn snack food for a 9 week storage period.

Weeks Stored Moisture Increase (g)

Control (-18oC) Ambient Storage

(33oC | 100% RH) Retail Storage

(18oC | 75% RH) 1 0 ± 0.01 0.04 ± 0.01 0 ± 0.01 2 0.02 ± 0.01 0.08 ± 0.01 0.04 ± 0.01 3 0.02 ± 0.01 0.10 ± 0.01 0.06 ± 0.01 4 0.02 ± 0.01 0.10 ± 0.01 0.06 ± 0.01 5 0.02 ± 0.01 0.12 ± 0.01 0.08 ± 0.01 6 0.04 ± 0.01 0.16 ± 0.01 0.10 ± 0.01 7 0.02 ± 0.01 0.22 ± 0.01 0.12 ± 0.01 8 0.04 ± 0.01 0.26 ± 0.01 0.18 ± 0.01 9 0.04 ± 0.01 0.28 ± 0.01 0.22 ± 0.01

Sample ‘A’ gained moisture more rapidly than sample ‘R’. This could be

due to the greater relative humidity found in the ambient storage conditions

(100%), than in the retail storage conditions (75%) (Eskin and Robinson 2001;

Man 2002).


Moisture uptake affected the texture of the snack food by plasticizing and

softening the starch/protein matrix, which altered the mechanical strength of the

product (Robertson 1993). Sample ‘C’ also showed an increase in its moisture

absorbed over the storage period, which suggests that there was significant

degradation in the texture of the Control over the 9 week storage period as well.

4.4 RESULTS OF TEXTURE ANALYSIS OF AN EXTRUDED CORN SNACK FOOD

USING THE PENETROMETER

The penetration depth of the snack food by the needle (in mm) decreased

over time (Table 4.5). Sample ‘A’ had a more rapid decrease in the depth of

penetration than Sample ‘R’. Similar to results from the moisture uptake in the

snack food, the difference in the two storage conditions’ relative humidity created

the difference in the rate of deterioration. As the snack food aged, the structure

became harder and this decreased penetration.


TABLE 4.5 Penetrometer distance (in mm) of a snack food for 5 seconds.

Weeks Stored PENETROMETER READINGS / mm



(18oC | 75% RH) 0 20.1 ± 3.7 1 18.3 ± 4.2 17.7 ± 4.4 17.9 ± 3.9 2 17.5 ± 4.6 16.1 ± 6.1 17.2 ± 3.9 3 16.5 ± 2.3 15.8 ± 4.4 15.3 ± 3.0 4 15.4 ± 3.9 10.9 ± 6.5 11.5 ± 5.4 5 14.6 ± 4.1 12.9 ± 2.4 13.5 ± 3.7 6 14.7 ± 1.4 11.0 ± 2.4 13.1 ± 5.4 7 15.1 ± 3.8 9.0 ± 4.2 12.0 ± 3.9 8 14.2 ± 3.5 9.2 ± 1.7 11.1 ± 3.0 9 13.9 ± 2.4 7.9 ± 3.0 9.3 ± 2.3

4.5 COMPARISON OF RESULTS OF SENSORY EVALUATION OF THE TEXTURE

WITH PENETROMETER & MOISTURE UPTAKE OF THE EXTRUDED CORN

SNACK FOOD

4.5.1 Graphical Comparison of the Texture Attribute Sensory Results with

Moisture Uptake of an Extruded Corn Snack Food.

Figure 4.4 compares sensory evaluation results of the texture attribute,

with the mean moisture increase of the extruded corn snack food, stored under

both ambient and retail conditions.

There was a linear increase in the moisture absorbed by the snack food

over the 9 week storage period, stored under both ambient and retail conditions.

Sensory evaluation results for the texture attribute of the snack food, stored under

Chapter 4: Results & Discussion 88 both ambient and retail conditions, exhibited an exponential relationship over

time. Therefore, sensory evaluation results and moisture absorbed by the snack

food over time, were not directly related. Man (2002) obtained a direct

relationship between sensory evaluation and moisture absorbed by the snack food.

4.5.2 Statistical Comparison of the Texture Attribute Sensory Results with

Moisture Uptake of an Extruded Corn Snack Food.

Pearson’s p-value determined by Minitab® 15.1.1.0 for the relationship

between moisture uptake in the snack food and sensory evaluation of the texture

attribute was 0.605. The p-value suggested that moisture uptake was not a good

predictor of the shelf life by sensory evaluation (Freund 2004; WFI 2007b). Full

analysis may be seen in the Appendix.



4.5.3 Graphical Comparison of the Texture Attribute Sensory Results with

Penetrometer Readings of an Extruded Corn Snack Food.

Figure 4.5 compares sensory evaluation results of the texture attribute,

with the penetrometer resultsof the extruded corn snack food, stored under both

ambient and retail conditions.

Penetrometer readings decreased linearly over time. However, sensory

evaluation of the texture attribute of the snack food exhibited an exponential

relationship. There was an inverse relationship between penetrometer readings

and sensory evaluation results, and they were not directly related.

4.5.4 Statistical Comparison of the Sensory Evaluation of the Texture Attribute

Results with Penetrometer Readings of an Extruded Corn Snack Food.

Logistic regression of the penetrometer results and the sensory evaluation

of the texture attribute resulted in Pearson’s p-value of 0.000. This suggests that

with a 95% confidence interval, penetrometer readings statistically correlated with

sensory results of the texture of the snack food. Penetrometer readings correlated

with the quality of the texture of the snack food (Freund 2004; WFI 2007b).



4.6 RESULTS OF THE PEROXIDE VALUE OF THE OIL EXTRACTED FROM AN

EXTRUDED CORN SNACK FOOD

Table 4.6 shows the peroxide value results of oil extracted from the

extruded snack food. There was a very slight increase (0.3 – 0.5) from Weeks 0 –

4, of the oil extracted from the snack food stored under ambient conditions. After

Week 4, the peroxide value of the oil increased rapidly. However, for retail

conditions, there was a slight increase (0.3 – 0.6) from Weeks 0 – 6, after Week 6

there was also a greater increase (0.6 – 1.7) in peroxide value of the oil. This

period of very slight increase in peroxide value was the ‘Induction Period’

(Frankel 1998).

TABLE 4.6 Peroxide values of oil extracted from an extruded corn snack food during

storage for control, ambient and retail conditions.

Weeks Stored

PEROXIDE VALUES / kg milliequivalents of peroxide oxygen per kg of product



(18oC | 75% RH) 0 0.3 ± 0.1 1 0.3 ± 0.1 0.4 ± 0.1 0.4 ± 0.0 2 0.4 ± 0.1 0.4 ± 0.1 0.4 ± 0.1 3 0.4 ± 0.1 0.4 ± 0.1 0.5 ± 0.1 4 0.4 ± 0.1 0.5 ± 0.1 0.6 ± 0.1 5 0.5 ± 0.1 0.9 ± 0.1 0.5 ± 0.1 6 0.6 ± 0.1 1.2 ± 0.1 0.6 ± 0.1 7 0.5 ± 0.1 1.6 ± 0.1 0.9 ± 0.1 8 0.6 ± 0.1 2.0 ± 0.2 1.2 ± 0.1 9 0.8 ± 0.1 2.5 ± 0.1 1.7 ± 0.1


The peroxide value at which food is not consumable due to rancidity is

10 milliequivalents (Min and Smousse 1998; Frankel 1998; Anonymous 2007a,

personal correspondence). The greatest peroxide value of the extracted oil from

the snack foods was 7.5 less than this value. However, foods may become

unacceptable due to rancidity, even before a peroxide value of 10 milliequivalents

has developed.

4.7 COMPARISON OF THE FLAVOUR ATTRIBUTE SENSORY RESULTS WITH THE

PEROXIDE VALUE OF OIL EXTRACTED FROM AN EXTRUDED CORN SNACK

FOOD

4.7.1 Graphical Comparison of the Flavour Attribute Sensory Results with the

Peroxide Value of Oil Extracted from an Extruded Corn Snack Food.

Figure 4.6 compares sensory evaluation results of the flavour attribute,

with the peroxide value of extracted oil from the extruded corn snack food stored

under both ambient and retail conditions.

Both sets of values (sensory and peroxide value) appear to have a linear,

slowly increasing beginning followed by an exponentially increasing end to the

snack food’s shelf life. Peroxide value and sensory evaluation of the flavour

attribute appear to have a direct relationship.


4.7.2 Statistical Comparison of the Flavour Attribute Sensory Results with the

Peroxide Value of Oil Extracted from an Extruded Corn Snack Food.

Pearson’s p-value for the relationship between peroxide value of the

extracted oil and sensory evaluation of the flavour attribute was 0.342. The p-

value suggests that peroxide value was not a good predictor of the shelf life by

sensory evaluation (Freund 2004; WFI 2007b).



4.8 EVALUATION OF THE CONTROL OF THE SNACK FOOD

The three objective tests performed (peroxide value, penetrometer,

moisture increase) showed degradation in all samples including the control

samples. The degradation of the control samples in all instances were appreciably

slower than samples stored under retail and ambient conditions (Table 4.4; Table

4.5; Table 4.6). The peroxide value of the oil extracted from the Control in

particular, increased to 0.8 milliequivalents at Week 9, which is the value that

would have been obtained from the oil extracted from Sample ‘R’ between Weeks

6 and 7.

This degradation in the control sample may have been significant enough

to alter the sensory evaluation results. As time elapsed, the panel members were

comparing the samples (ambient and retail conditions), to a “control” that was

closer in quality to the samples than it should have been. This may have had an

effect of extending the shelf life, as the panel members may have perceived a

smaller difference than they should due to the degrading Control.

Chapter 5: Conclusion 97

CHAPTER 5

CONCLUSION

The objectives of the research paper were met. The shelf life of the

extruded corn snack food, stored under ambient (33oC and 100% RH) and under

retail conditions (18oC and 75%RH) was 50 and 58 days respectively. In the first

4 – 5 weeks of storage, sensory evaluation results of all the attributes of the

extruded corn snack food, stored under both conditions, were closely linear.

However, from Week 5, there was an exponential increase in sensory data, and

regression of the data became less reliable.

For a 95% confidence interval, the p-value of the logistic regression

between penetrometer scores and texture attribute sensory scores was 0.000.

Therefore, penetrometer readings correlated to the texture attribute sensory

results. Moisture uptake had a p-value of 0.605 when compared to texture

attribute sensory results, and peroxide value had a p-value of 0.342 when

compared to flavour attribute sensory results. Therefore, moisture uptake and

peroxide value did not statistically correlate with sensory evaluation.

Chapter 6: Recommendations 98

CHAPTER 6

RECOMMENDATIONS

The regression method provides a simple method of shelf life

determination. However, shelf life is generally determined by inverse regression

and thus is very difficult to set an “open date” and incorporate confidence

intervals. Shelf life determination must be repeated several times in order to

determine a suitable confidence interval. In order to obtain a more accurate

estimation of shelf life, more frequent testing of samples should be done, during

the period of exponential growth. In this study this occurred after week 4.

The degradation of the Control provided a significant error for sensory

evaluation. A possible solution to this problem may be the use of freshly-

produced samples as controls for sensory evaluations. However, this may create

another source of error, if there are slight differences in raw materials or

manufacturing conditions.

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APPENDIX










Appendix: Minitab Logistic Regression Data 122 Welcome to Minitab, press F1 for help. Binary Logistic Regression: Failed, Panellists versus Moisture Link Function: Logit Response Information Variable Value Count Failed Event 89 Non-event 197 Panellists Total 286 Logistic Regression Table 95% CI Predictor Coef SE Coef Z P Odds Ratio Lower Constant -4.54058 0.474717 -9.56 0.000 Moisture 25.4051 2.80054 9.07 0.000 1.07965E+11 4.46084E+08 Predictor Upper Constant Moisture 2.61304E+13 Log-Likelihood = -103.534 Test that all slopes are zero: G = 147.600, DF = 1, P-Value = 0.000 Goodness-of-Fit Tests Method Chi-Square DF P Pearson 7.30910 9 0.605 Deviance 8.66043 9 0.469 Hosmer-Lemeshow 5.60035 6 0.469 Table of Observed and Expected Frequencies: (See Hosmer-Lemeshow Test for the Pearson Chi-Square Statistic) Group Value 1 2 3 4 5 6 7 8 Total Event Obs 1 1 3 4 9 14 23 34 89 Exp 1.0 1.4 2.2 5.1 6.4 14.4 26.7 31.8 Non-event Obs 45 29 26 39 26 18 13 1 197 Exp 45.0 28.6 26.8 37.9 28.6 17.6 9.3 3.2 Total 46 30 29 43 35 32 36 35 286 Measures of Association: (Between the Response Variable and Predicted Probabilities) Pairs Number Percent Summary Measures Concordant 15246 87.0 Somers' D 0.79 Discordant 1333 7.6 Goodman-Kruskal Gamma 0.84 Ties 954 5.4 Kendall's Tau-a 0.34 Total 17533 100.0

Appendix: Minitab Logistic Regression Data 123 ————— 1/23/2008 10:13:47 PM —————————————————— Binary Logistic Regression: Failed, Panellists versus Penetrometer Link Function: Logit Response Information Variable Value Count Failed Event 89 Non-event 197 Panellists Total 286 Logistic Regression Table Odds 95% CI Predictor Coef SE Coef Z P Ratio Lower Upper Constant 7.15950 0.980775 7.30 0.000 Penetrometer -0.684266 0.0883371 -7.75 0.000 0.50 0.42 0.60 Log-Likelihood = -116.556 Test that all slopes are zero: G = 121.556, DF = 1, P-Value = 0.000 Goodness-of-Fit Tests Method Chi-Square DF P Pearson 43.7997 16 0.000 Deviance 45.1632 16 0.000 Hosmer-Lemeshow 10.1885 7 0.178 Table of Observed and Expected Frequencies: (See Hosmer-Lemeshow Test for the Pearson Chi-Square Statistic) Group Value 1 2 3 4 5 6 7 8 9 Total Event Obs 1 2 2 5 7 14 16 24 18 89 Exp 0.2 0.7 2.5 4.9 9.2 12.7 18.3 25.2 15.3 Non-event Obs 33 36 31 27 25 18 16 11 0 197 Exp 33.8 37.3 30.5 27.1 22.8 19.3 13.7 9.8 2.7 Total 34 38 33 32 32 32 32 35 18 286 Measures of Association: (Between the Response Variable and Predicted Probabilities) Pairs Number Percent Summary Measures Concordant 14800 84.4 Somers' D 0.72 Discordant 2225 12.7 Goodman-Kruskal Gamma 0.74 Ties 508 2.9 Kendall's Tau-a 0.31 Total 17533 100.0

Appendix: Minitab Logistic Regression Data 124 Binary Logistic Regression: Failed Fl, Panellists Fl versus Peroxide Link Function: Logit Response Information Variable Value Count Failed Fl Event 99 Non-event 185 Panellists Fl Total 284 Logistic Regression Table Odds 95% CI Predictor Coef SE Coef Z P Ratio Lower Upper Constant -3.98499 0.411999 -9.67 0.000 Peroxide 3.27073 0.367137 8.91 0.000 26.33 12.82 54.07 Log-Likelihood = -106.810 Test that all slopes are zero: G = 153.631, DF = 1, P-Value = 0.000 Goodness-of-Fit Tests Method Chi-Square DF P Pearson 7.89731 7 0.342 Deviance 7.94099 7 0.338 Hosmer-Lemeshow 7.11620 5 0.212 Table of Observed and Expected Frequencies: (See Hosmer-Lemeshow Test for the Pearson Chi-Square Statistic) Group Value 1 2 3 4 5 6 7 Total Event Obs 3 2 5 14 14 27 34 99 Exp 4.6 3.9 3.4 9.1 15.5 28.9 33.5 Non-event Obs 69 43 24 21 18 9 1 185 Exp 67.4 41.1 25.6 25.9 16.5 7.1 1.5 Total 72 45 29 35 32 36 35 284 Measures of Association: (Between the Response Variable and Predicted Probabilities) Pairs Number Percent Summary Measures Concordant 15889 86.8 Somers' D 0.79 Discordant 1334 7.3 Goodman-Kruskal Gamma 0.85 Ties 1092 6.0 Kendall's Tau-a 0.36 Total 18315 100.0

Appendix: Sensory Evaluation Score Sheet 125

Documents

Shelf Life of an Extruded Corn Snack