Comparison Study of Conventional Hot-water and Microwave Blanching at Different Timetemperaturepower Combinations on the Quality of Potatoes

Bsc Hons Degree in Food Science and Nutrition

Letterkenny Institute of Technology

2013-2014

Project Report

Comparison study of conventional hot-water and microwave

blanching at different time/temperature/power combinations on

the quality of potatoes.

Submitted by: David Smith

Supervisor: Aisling Coyle

i

Abstract

In the 1930s the technology Blanching arose as a way extending fresh produces shelf-life. It

deactivates enzymes in particular those which are associated with quality deterioration such as

those involved in browning, lipid oxidation and textural damages. The heat treatment generally

comprises of fresh produce being exposed to steam or hot water (75-100oC) for various lengths

of times. (Owusu-Apenten, 2005). Microwave blanching of vegetables has been established as

a trustworthy substitute technique to the typical heating method.

In this study conventional hot-water and microwave blanching were compared at different

time/temperature/power combinations on the quality of potatoes. The samples were blanched

using both methods and a number of quality tests were carried out before and after heat

treatment and compared. This analysis involved testing for;

Internal quality factors:

Peroxidase Tests on blanched samples to give indication of deactivation of

peroxidise enzyme and indication of effective blanching end point.

Ascorbic acid analysis on end blanched samples using end point times shown

by peroxidase test using DCPIP method, to determine Vitamin C loss after each

blanching type/combination.

External quality factors:

Weight loss to samples throughout heat treatment.

Texture/Hardness changes to samples throughout blanching.

Colour changes to samples throughout blanching.

The findings showed that; conventional blanching is the most straightforward. It has the least

damaging effects with regards to hardness/texture decrease. However conventional blanching

was also shown to lead to decreased quality including loss of ascorbic acid. It is considerable

slower when using temperatures lower than 100oC and has high energy costs.

Microwave blanching was shown to have more effective enzyme inactivation, less processing

time, and has the best retention of quality (ascorbic acid and other vitamin, minerals and other

properties). Its energy cost of production is almost of half compared with conventional.

However the equipment needed for microwave blanching is expensive and not commonly used

in food industry. This study has shown that microwave blanching could potentially be used in

the future if further research highlights and promotes the benefits of using microwave over

conventional blanching.

ii

Acknowledgments

I would like to take this opportunity to thank my project supervisor Ms Aisling Coyle for all

her help and excellent advice and guidance throughout the course of my project.

I would also like to acknowledge Dr. Brian Carney as well as Ken MacIntyre for their

assistance and for being so generous with their time throughout the duration of my project.

Lastly I would like to show my thanks and appreciation to everyone who helped in any way

this year and especially to my classmates for all their input, advice and continued

encouragement throughout the year and for making it enjoyable and cherished.

iii

Table of Contents

Chapter 1 - Literature Review Page

1.0 Introduction 2

1.1 Why we cook? 3

1.2 Methods of cooking vegetables 5

1.3 Blanching and its uses 7

1.4 Vegetables & Potatoes

1.4.1 Vegetables 9

1.4.2 Potatoes 10

1.5 Types of Blanching. (Boiling Water vs Microwave) 13

1.6 Quality of foods 14

1.7 Enzymatic activity effects on food and determination of peroxidase enzyme. 16

1.8 Vitamin C 17

1.9 Relationship between Time/Temperature/Power combinations on quality 20

1.10 Economic Statistics of Industrial blanching & benefits of new technologies.

20

Chapter 2 Methodology

2.0 Methodology 24

2.1 Sampling 25

2.2 Conventional Blanching Analysis at Various Time/Temp. Combinations

2.2.1 Pre Conventional Blanching Physical Characterization of Samples 25

2.2.2 Conventional Blanching of Samples 27

2.2.3 Post Conventional Blanching Physical Characterization of Samples 28

2.2.4 Peroxidase Tests on Conventional blanched samples 29

2.3 Microwave Blanching Analysis at Various Time/Temp. Combinations

2.3.1 Pre Microwave Blanching Physical Characterization of Samples 30

2.3.2 Microwave Blanching of Samples 30

2.3.3 Post Microwave Blanching Physical Characterization of Samples 32

2.3.4 Peroxidase Tests on Microwave blanched samples. 32

2.4 Ascorbic acid analysis blanched samples

33

Chapter 3 - Results

3.0 Results 36

3.1 Peroxidase Tests 36

3.2 Pre and Post Blanching Physical Characterization of Samples

3.2.1 Weight loss 39

3.2.2 Texture/Hardness 40

3.2.3 Colour 44

3.3 Ascorbic acid analysis on blanched samples

45

Chapter 4 - Discussion

4.0 Discussion

48

Chapter 5 - Conclusion

5.0 Conclusion

54

Bibliography 56

iv

List of tables

Table number Description Page

1.01 Comparison of segments of plants with vegetables that

grow on each respectively.

9

1.02 Nutritional Values for raw Potatoes

11

1.03 Enzymes responsible for quality deterioration

16

1.04 Advantages and disadvantages of both the Peroxidase

and Lipoxygenase enzyme indicators

17

1.05 Vitamin C content of Some Common Foods.

19

2.01 Conventional & Microwave blanching, parameters of

investigation

24

2.02 Conventional blanching, parameters of investigation

27

2.03 Peroxidase Activity Index Scale

29

2.04 Microwave blanching, parameters of investigation

30

3.01 Peroxidase Activity Index Scale

36

3.02 Peroxidase activity across Conventional blanching 80oC

and 100oC, with blanching endpoints shown in yellow

37

3.03 Peroxidase activity across Microwave blanching 600W

and 800W, with blanching endpoints shown in yellow

38

3.04 Hardness across conventional blanching at 80oC, blanch

endpoint shown in yellow

40

3.05 Hardness across conventional blanching @ 100oC,

blanch endpoint shown in yellow

41

3.06 Hardness across microwave blanching at 600W, blanch


42

3.07 Hardness across microwave blanching at 800W, blanch


43

3.08 Luminance scale measurements 44

3.09 Ascorbic acid in Control, Conventional 80oC & 100oC

and Microwave 600W & 800W

45

v

List of Figures

Figure number Description Page

1.01 Calcium, iron, zinc percentage uptakes in digestion of

raw, and traditional cooked and ready-to-eat legumes

4

1.02 Aerobic oxidation of phenol by polyphenoloxidase to

quinones (melanin) in chemical browning of potatoes

12

1.03 Boling water vs microwave blanching of turnip greens,

retention of water-soluble vitamins

14

1.04 Chemical Structure of L-ascorbic acid.

18

1.05 Cost comparison of hot water and steam use in

blanching

21

1.06 Effluent discharge comparison chart for hot water and

steam use in blanching

22

2.01 Sample sizes

25

2.02 Brookfield Texture Analyser

26

2.03 CR-400 Chrom-Meter

26

2.04 ELTAC EKA 179 Waterbath

28

2.05 Samples after heat treatment and cut in half prior

peroxidase testing

29

2.06 Microwave blanching

31

3.01 Top samples peroxidase level: 100%, Bottom samples

peroxidase level: 0%

36

3.02 Peroxidase activity across Conventional blanching 80oC

and 100oC, showing blanching endpoints at 0%

37

3.03 Peroxidase activity across Microwave blanching 600W

and 800W, showing blanching endpoints at 0%

38

3.04 Average sample size weight loss after Conventional

blanching @ 80oC and 100oC

39

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Figure number Description Page

3.05 Average sample size weight loss after Microwave

blanching @ 600W and 800W

39

3.06 Hardness decrease in Conventional blanching at 80oC,

in 1cm3, 2 cm3, 3cm3 samples

40

3.07 Hardness decrease in Conventional blanching at 100oC,

in 1cm3, 2 cm3, 3cm3 samples

41

3.08 Hardness decrease in Microwave blanching at 600W, in

1cm3, 2 cm3, 3cm3 samples

42

3.09 Hardness decrease in Microwave blanching at 800W, in

1cm3, 2 cm3, 3cm3 samples

43

3.10 Average L*a*b (Colour) measurements as conventional

& microwave blanching times increase.

44

3.11 Vitamin C measurements in Control and Conventional

blanched samples at 80oC & 100oC to endpoint

46

3.12 Vitamin C measurements in Control & Microwave

blanched samples at 600W and 800W to endpoint

46

4.01 Sample shape pre-blanching vs. misshaped samples

after blanching with considerable weight loss

50

1

Chapter 1

Literature Review

2

1.0 Introduction

The consumption of food is essential to all living things for nutritional support, energy and

body survival. Generally food is obtained through plants and animals which are comprised of

vital nutrients. These include; carbohydrates, fats, proteins, vitamins, and minerals. Living

things consume food in order to obtain these in an attempt to sustain life, yield energy and

promote growth. In the past food people have gained food by hunting & gathering, and through

farming. Now however most of the first world countries acquire food through the food industry.

The food industry is a global market of the sale and distribution of food & drink items in a vast

network across the world. It accompanies the majority of the worlds population as we are all

consumers purchasing nearly all of our daily food derived from the industry. Today as earlier

skills of manual food salvaging have died out in the general population, most of the world is

reliant on the food industry as a source of food. The system itself is made up of Agriculture,

Manufacturing, Food processing, Regulation, Wholesale and distribution, Marketing, Research

and development, Education and Financial services.

Cooking techniques have improved as centuries has passed and have become more advanced

in the present day. Now that we live in a world driven by the food industry these advancements

have grown exponentially as food is the largest global market for business. Today most of the

decisions taken in the production of current and new food products are taken for capital gain.

For this reason there is a large strive for new, innovative, improved and most importantly more

profitable techniques to how food is processed.

Cooking is one of many processes carried out to food for many desired purposes. Cooking

methods differ largely around the world, due to contrasting environments, economies, and

cultures. As new cooking technologies have progressed so has the approach to cooking. It is

now more intuitive, radical, scientific and cutting-edge. This new scientific approach to food

has become known as Food science. A sub-discipline of Food science exists as Molecular

gastronomy which aims to study, illustrate and make functional use of the physical and

chemical changes of ingredients that happen during cooking, and also the social, creative and

practical features of culinary and gastronomic phenomena as a whole (This, 2006).

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Some modern methods and inventions such as the oven, microwave, refrigerator, atmosphere

packing, canning, pasteurization and sterilisation, have revolutionised the food industry and

household consumption of food.

Methods of cooking vary from a wide range of alternatives and combinations. Most of these

include; baking, frying, roasting, barbecuing, smoking, grilling, microwaving and boiling.

Boiling uses water as a heating medium. Types of boiling can be steaming, poaching, steeping,

simmering, braising, and blanching. Many types of cooking techniques use various amounts of

heat and moisture and can differ in cooking times also. The amount of heat, moisture and

lengths of time used will considerably influence the final product. For this reason cooking

differences are often experimented with to investigate different end results. The aim of doing

this is usually to improve quality, find a quicker cooking method, or to identify a cheaper or

more economic technique among other agendas.

1.1 Why we cook?

Cooking is the preparation of food using heat. It is generally carried out to destroy or deactivate

organisms which can cause damaging effects if consumed, for example bacteria, moulds,

viruses and parasites. The act of ingesting harmful microorganism can cause food poison to

those subjected to the agents. Susceptible or contaminated foods which have not been properly

cooked can lead to food poisoning by presence of infectious agents. Examples includes

Salmonella in foods containing bacteria, Peronopora hyoscyami in moulds, Norovirus in

viruses and Toxoplasma gondii which is a parasite. Generally parasites are established in foods

like salads, incorrectly cooked meats and contaminated water.

Cooking inhibits most sicknesses caused by food pathogens, which would subsequently cause

illness if the food was consumed fresh and uncooked. The use of cooking increases the number

of potential foods which can be eaten as it allows otherwise harmful produce to be safely

digested.

Generally the types of food which are consumed are from animal origins such as meat, fish,

eggs, and dairy products or from plant origins such as fruit, vegetables, grains, nuts, herbs and

spices. The mostly consumed plant derived foods are fruit and vegetables.

4

Cooking some foods can improve their nutritional quality for example cooked beans when

compared to raw beans. This usually involves increasing the efficiency of absorption of

nutrients by the body in food which has undergone a cooking process in comparison to which

has not been cooked. This is to say that cooking increases the bioavailability of nutrients. For

example traditional cooking significantly increases the intake of zinc, calcium & iron from

white beans, and of calcium in lentils. When mineral uptakes from raw, traditionally cooked,

and ready-to-eat lentils (they already been steamed, therefore they keep their shape and texture

when cooked) are compared, the highest uptake values correspond to the ready-to-eat product,

which is attributed to cooking under pressure (Viadel, Barber, & Farr, 2006).

Figure 1.1: Calcium, iron, zinc % uptakes in digestion of raw, cooked & ready-to-eat legumes

In addition, cooking is also carried out in some fruit and vegetables to deactivate enzymes. In

particular enzymes which are associated with food safety and quality deterioration such as

those involved in browning, lipid oxidation and textural damages. Sensory, nutritional quality

and shelf life of fresh vegetables are affected by the action of endogenous enzymes. In the

5

1930s the technology called Blanching arose as a way extending fresh produces shelf-life by

the application of a mild heat which inactivates enzymes and halts adverse changes in fresh

fruit and vegetables quality. Blanching generally comprises of fresh produce being exposed to

steam or hot water (75-100oC) for various lengths of times (Owusu-Apenten, 2005).

The method of cooking application depends on what the end result intends to be. Different

techniques and methods use varying amounts of heat, power and cooking times. The type of

cooking process used will considerably effect the final product. They will effect foods quality

(taste, weight loss, shrinkage, texture, colour, enzyme inactivation, & nutrient retention) shelf-

life, and level of safety from a present of pathogens point of view.

1.2 Methods of cooking vegetables

Baking/Roasting involves sustained dry heat by convection, instead of thermal radiation. It is

usually carried out in an oven. In roasting, the vegetables are placed onto a roasting tray, usually

fat or oil is added to give the final product and adds flavour. The addition of butter, lard or oil

also aims to reduce moisture loss by evaporation.

Roasting and baking are both cooking in hot air. They are very similar in process but the term

baking is generally referred to dough foods whereas the phrase roasting describes to the

treatment of dry heat to all other products (Berk, 2013).

Smoking is a another method of flavouring, cooking, or preserving food by subjecting it to the

smoke from burning or smouldering plant materials, generally charcoal or wood. Meats and

fish are the most smoked foods. However vegetables and other foods are often smoked also.

Commonly smoked vegetables are peppers, onions, corn, potatoes, asparagus, mushrooms and

paprika. Smoking food can be done either through a cold smoke or a hot smoke. Cold smoking

is carried out for increased flavour and retain moisture. Cold smoking will not cook foods. Hot

smoking subjects foods to smoke and heat. They are fully cooked, moist, and flavourful.

However smoking at high temperatures decreases yield due moisture and fat being lost (Berk,

2013).

Frying is the cooking process when fat/oil is used as the heat transfer agent in direct contact

with the product (Varela, Bender, & Morton, 1988). There are a number of types;

6

Pan frying. This type of frying is used on flat, wide and moderately thin cuts of food,

like bacon, egg and fillets. The food is cooked by contact without agitation with a small

amount of fat usually oil.

Stir frying. This applies to small to medium-size food pieces which are quickly cooked

with constant agitation in a small quantity of fat generally oil.

Deep frying. Here food pieces are submerged in hot fat or oil, and heat transfer occurs

evenly over the complete surface of the food.

Today deep-fat frying has grown to a big sized industrial process. Fried chips are undoubtedly

the most important industrial foods produced by immersion frying (Berk, 2013).

Microwaving is carried out in a microwave where the food is placed and cooked. It uses high

frequency radio waves, which penetrates the food molecules causing them to vibrate. The

vibrating of these molecules leads to friction, which causes heat formed, thus cooking the food.

The phrase microwaves refers to electromagnetic radiation in the wavelength range of 0.1-1 m

in air, corresponding to a frequency range of 0.3-3 GHz.

The technology is generally used in household and food service (for example; restaurants,

planes) ovens, to defrost frozen products, to heat food, to cook, to bake and to boil water. They

were originally launched in the 1950s, and now they have grown to be the foremost food

heating device in modern houses and in range of classes of food service institutions (Datta,

2001).

Subsequently, the food manufacturing industry devotes extensive resources to developing

products and packages compatible with the capacities and restrictions of the household

microwave unit. In industrial uses, the practice of microwave heating continues to be limited

to small numbers of instances where the technology gives defined technological and economic

advantages over traditional heating methods (Berk, 2013).

Boiling involves cooking through use of moisture, mainly water. Heat is transferred via

convection through the liquid and/or steam. It comprises of the heating of water which contains

the food to be cooked to its boiling point of 100oC. Food can either be completely covered by

the water and then heated, however this can result in high losses of vitamins and mineral

through a leaching activity. Moderate boiling helps to break down tough fibrous structures of

some foods which would be less tender if cooked using other techniques. When boiling is

7

carried out for the least amount of time possible, then the maximum colour and nutritive value

can be retained.

A particular study was undertaken on the effects of water while boiling (Sikora, Cielik,

Leszczyska, Filipiak-Florkiewicz, & Pisulewski, 2008). It showed that the smallest amount

of water capable of being used to cook is the amount that should be used to keep leaching of

vitamins and minerals to a minimum (Foskett, Campbell, Ceserani, & Paskins, 2009).

Potatoes can be blanched by boiling or steam to help to peel the skin, to maintain their quality

and colour, decrease microorganisms and preserves the potatoes for freezing. This is done to

retain fresher looking potatoes with improved taste (Buckner, 2013).

1.3 Blanching and its uses.

Blanching deactivates enzymes in particular those which are associated with quality

deterioration such as those involved in browning, lipid oxidation and textural damages. It

shrinks the product giving it a better fill. As well as this, blanching expels air/gas from a product

being canned which produces a vacuum in the closed can.

The process can also be carried out just to soften many fruit & vegetables or to partially or

completely cook them, or to eliminate sharp tastes e.g. in onions, bacon, and cabbage (Child,

Bertholle, & Beck, 2001).

Concerning potatoes chips, blanching frequently applies to the pre-cooking of potato chips in

oil at a low temperature before completing them at a high temperature. The benefit is that the

blanching stage cooks the potato. The following stage at a high temperature leaves the outside

of the chips crispy (Blumenthal, 2012).

Vegetables such as green beans are sometimes blanched to increase their natural green colour.

Studies have shown that the reduction or removal of peroxidase activity to be the best indicator

of blanching completion in relation to the retaining of quality after process has been carried out

(Joslyn & Berkeley, 2006). Lipoxygenase has also been shown to be an indicator of blanching

end point. Peroxidase is responsible for off-flavour development, lipoxygenase is responsible

for colour changes, and ascorbic acid has been shown to be linked with nutritional changes.

These can be used as indicators of blanching efficiency (Barrett & Theerakulkait, 1995).

8

After undergoing blanching, food quality can vary considerably depending on the

time/temperatures combination use as well as the size of the food blanched. Under-blanching

will increase the activity of enzymes and is more adverse than if no blanching was carried out.

Over-blanching results in loss of texture, colour, phytochemicals and minerals (Jaiswal, Gupta,

& Abu-Ghannam, 2012). Industrial blanching is generally carried out at combinations of 70 to

95 C for not longer than 10 minutes while for household purposes vegetables are usually

blanched at combinations of 98100 C for of 1012 min (Morales-Blancas, Chandia, &

Cisneros-Zevallos, 2002).

Blanching is mostly commonly carried out in a water bath where the food is exposed to; hot

water, hot air, or steam at the above range of time/temperature combinations. The food is the

cooled very quickly to remove any retained heat which may cause the fruit or vegetables to

continue cooking.

Blanching is often carried out as a precursor to canning. The objective of blanching as a pre-

treatment of vegetables for canning is the removal of tissue gases; the shrinking of the material

so that adequate fills can be contained in the can; and the heating of the material prior to filling

so that a vacuum will be obtained after heat processing and boiling (Lee, 1958).

Studies by (Afoakwa & Yenyi, 2006) have shown that blanching has considerable influences

on the moisture content, ash content, leached solids, phytates, tannins and the hardness of the

canned vegetables. In this study, blanching lead to increased moisture content and leached

solids while significant decreases were shown for the phytates, tannins and hardness of the

canned vegetables. The research also showed that the optimal pre-processing blanching

conditions required to achieve the optimum quality canned product from the vegetables was 5

minutes. These conditions were proven to give the best quality canned product with improved

nutritional quality and acceptable product quality characteristics, according to (Afoakwa &

Yenyi, 2006)

Blanching is also necessary as a part of the preparation for freezing preservation to inactivate

the enzymes in the tissues and to shrink the material so as to conserve space in packing. The

inactivation of the enzymes is very important in this process. This is because no final cook or

sterilization is used previous to freezing, therefore their inactivation is the only step taken to

prevent undesirable deterioration in flavour, odour, and colour on the part of the enzymes in

the tissues (Lee, 1958).

9

Microwave blanching of vegetables has been established as a trustworthy substitute technique

to the typical heating method used in the vegetable canning industry. The microwave treatment

of vegetables leads to an efficient enzyme inactivation, faster, and improved retention of

vitamin C (Ruiz-Ojeda & Peas, 2013).

1.4 Vegetables & Potatoes

1.4.1 Vegetables

In regards to cooking, a vegetable plant or part of one which can be eaten, used for cooking or

consumed raw. In relation to biology, a vegetable refers to members of the plant kingdom.

Vegetables are segments of plants which can be eaten and in nature occur in an array of forms.

Table 1.1: Comparison of segments of plants with vegetables that grow on each respectively.

Segment of Plants Vegetable

Flower bud Broccoli, Cauliflower, Globe artichokes,

Leaves Kale, Collard Greens, Spinach, Beet Greens, Turnip Greens,

Lettuce, Mustard Greens, Watercress, Garlic Chives,

Leaf sheaths Leeks

Buds Brussels sprouts

Stem Kohlrabi, Galangal, and Ginger

Stems of leaves Celery, Rhubarb, Cardoon, Chinese celery

Stem shoots Asparagus, Bamboo Shoots

Tubers Potatoes, Jerusalem Artichokes, Sweet Potatoes, and yams

Whole-plant sprouts Soybean, Mung Beans, Urad, and Alfalfa

Roots Carrots, Parsnips, Beets, Radishes, and Turnips

Bulbs Onions, Shallots, Garlic

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Vegetables for consumption are prepared in a number of methods. Vegetables nutritional value

differs from food to food with a range of vitamins (e.g. A, B, C, & K), provitamins, dietary

minerals and carbohydrates. Generally they contain very little fat and protein. Vegetables are

also composed of additional phytochemicals, several of which have been declared to have

antioxidant, antibacterial, antifungal, antiviral and anticarcinogenic properties (Steinmetz &

Potter, 1996). Certain vegetables have fibre, which plays a vital role in gastrointestinal

function.

The Food Safety Authority of Ireland recommends 3 to 5 servings of vegetables per day

(Ireland, 2011). The risk of cardiovascular disease and diabetes has been shown to be lowered

in people who diets consume the recommended amounts of fruits and vegetables (Sangita, Vik,

Pakseresht, & Kolonel, 2013). These diets have been shown to defend from certain cancers and

reduce loss of bone (Mirmiran, Hosseini-Esfahani, & Azizi, 2013) (Chen & Ho, 2010). The

potassium derived from fruits & vegetables could aid in the prevention of the development of

kidney stones (Grieff & Bushinsky, 2013).

Vegetables post-harvest should be properly storaged to extend their shelf life and quality.

Whilst being stored, leafy vegetables have moisture loss, and ascorbic acid content also

decreases quickly. Vegetables should be stored for short times, in cold conditions and in an air

controlled environment.

1.4.2 Potatoes

The potato is full of starch, it is a tuberous plant from the perennial nightshade Solanum

tuberosum. They are high in carbohydrates, contain a lot of starch and dietary fibre consisting

of insoluble cellulose, lignin in the skin and soluble pectins in the flesh. Table 1.2 shows this.

The proteins in potatoes are restricted to the essential amino acids methionine and cysteine.

They are a great source of the vitamin B and ascorbic acid. Fresh potatoes have more ascorbic

acid than potatoes which have been in storage.

One 170 g baked potato with its skin has 4 g dietary fibre, 4 g protein, 0.2 g total fat, 48 mcg

folate (12 percent of the RDA), and 16 mg vitamin C (21 percent of the RDA for a woman, 13

percent of the RDA for a man) (Ireland, 2011).

11

Table 1.2: Nutritional Values for raw Potatoes

Nutrient Value

Calories 278

Fat

12

the brown pigment melanin (Mathew & Parpia, 1971). This process is otherwise seen as the

involved in chemical browning of potatoes

Figure 1.2: Aerobic oxidation of phenol by polyphenoloxidase to quinones (melanin)

The reaction can be slowed by immersing the peeled sliced fresh potatoes in water containing

ice, however several vitamins in the potatoes will leach out into the water. Alternatively the

sliced potatoes can be submerged in an acid solution (lemon juice & water, or vinegar & water),

they have a low pH, and will denature the polyphenol oxidase but will also alter the taste.

Studies have shown that heat application from blanching will denature the enzymes

polyphenoloxidase and peroxidase involved in this reaction (Ndiaye, Xu, & Wang, 2009).

The starch in potatoes comprises of granules loaded with the molecules of amylose and

amylopectin. When potatoes are cooked, the starch particles absorb water molecules that

adhere to the amylose and amylopectin molecules, this results in swelling of the granules. If

the granules soak ample water, they can burst and the nutrients inside will escape. If the

potatoes are cooked in a soup or stew, the amylose & amylopectin compounds that are released

from the broken starch granule will bind water molecules in the liquid, this thickens the

product. Potatoes which have undergone a cooking stage have more nutrients available than

raw potatoes do. Cooked potatoes can additionally be a different colour to raw potatoes.

Potatoes also possess pale anthoxanthin pigments which react with metal ions to produce green,

brown or blue compounds (Rinzler, 2009).

Due to its characteristic taste and texture, french fries (chips) remain to be the most popular

processed potato product. In general, the preliminary steps in regular cut French fry production

include washing of raw potatoes, peeling, sorting, and cutting into strips. After this point, potato

strips are blanched, partially dehydrated, deep-fat par-fried, frozen, deep-fat finish-fried and

served (Bingol, Wang, Zhang, Pan, & McHugh, 2014).

In industrial production, the potato strips are generally blanched with water (6085 C) for

more than 10 min mainly to inactivate enzymes (lipoxygenase, polyphenoloxidase, peroxidase

ect.) and to obtain a uniform colour, and then pre-dried with warm air to improve texture. The

13

blanched potato strips are par-fried in hot oil (170190 C), cooled at room temperature, frozen,

packaged and distributed. (Nonaka, Sayre, & Weaver, 1977), (Tajner-Czopek, Figiel, &

Carbonell-Barrachina, 2008).The process of finish-frying is usually accomplished in

restaurants or at home and each of these steps is important for the final product quality and its

oil content.

Conventional blanching and pre-drying are two separate processes and have the drawbacks of

having low energy efficiency, long processing time (Tajner-Czopek et al., 2008). In a typical

water blanching operation, firstly the water needs to be procured and heated and secondly after

a certain amount of blanching operations this water needs to be replaced since it becomes

saturated with sugars leaching from the potato strips. This results in not only excessive energy

consumption due to re-heating of the water to the blanching temperatures but also consumption

of high amounts of water (Bingol et al., 2014).

1.5 Types of Blanching. (Boiling Water vs Microwave)

Blanching is an efficient method of preserving fruits & vegetables. Hot steam/ boiling water is

the most common method of blanching, although microwave blanching is increasingly in use

today (Bingol et al., 2014). Its recognised that conventional blanching of vegetables leads to

leaching of water-soluble B and C vitamins. Traditional blanching is carried out using boiling

water or steam. Conversely microwave blanching could be a practical alternative method which

may result in better overall quality and retention of essential vitamins & minerals. Still the

equipment needed for microwave blanching is expensive which results in the method not

commonly used in food industry. Conventional water blanching is generally used home

cooking. It is straightforward and cost-effective, but has greatest possibility of leaching water-

soluble B and C vitamins and minerals compared to microwave balancing. Traditional steam

blanching is presently the most frequently used technique in the food industry today. It is

reasonably cheap and retains minerals and water-soluble vitamins over boiling water and

microwave blanching.

Studies on the results of microwave blanching versus. boiling water blanching on retention of

selected water-soluble vitamins ion vegetables have shown microwave blanching in certain

circumstances to be more effective in the retaining the selected water-soluble B and C vitamins

and nutrients in vegetables (Osinboyejo, Walker, Ogutu, & Verghese, 2003).

14

In another study comparing traditional hot-water and microwave blanching on quality of green

beans, microwave blanching of green bean pods has been shown to be a reliable alternative to

the conventional heating process used in the vegetable canning industry. The microwave

treatment of pods, in addition to an effective enzyme inactivation in less processing time, led

to a better retention of ascorbic acid (Ruiz-Ojeda & Peas, 2013).

Research in the assessment of microwave methods in blanching of broccoli as an alternative

for traditional blanching has also proven that microwave blanching uses less energy on an

industrial scale to conventional blanching. Microwave blanching consumption and energy cost

of production is almost of the half in compare with the conventional (Patricia, Bibiana, & Jos,

2011).

The investigation of the results of microwave pre-treatment on the kinetics of vitamin c loss

and peroxidase deactivation in various parts of green asparagus during water blanching proved

that microwaves could be an reliable pre-treatment method for use before water blanching to

reduce the loss of vitamin c and to speed up the deactivation of peroxidase and therefore

preserve quality (Zheng & Lu, 2011).

(Osinboyejo et al., 2003)

Figure 1.3: Traditional versus microwave blanch, retention of turnip green water-soluble

vitamins

1.6 Quality of foods

Quality of foods is the quality features of food that is satisfactory to buyers. This incorporate

external factors such as appearance (size, shape, weight loss, shrinkage, colour, gloss, and

15

consistency), texture, & flavour; and internal (chemical, physical, microbial, enzyme

inactivation, and ascorbic acid retention.

Quality of food also involves all the attributes of excellence that create acceptable food for

consumers. Food buyers put a high priority on eye appeal of fresh foods in the market. Well

coloured fruits and vegetables, uniform sizes and products that are free of any kind of damage

will get a good rating from most food buyers. Exterior colour often has little to do with whats

inside and uniform sizes do not indicate how good or bad a food is from a nutritional point of

view, but is important factor for the quality and therefore saleability of the fruits or vegetables

(Ferree, 1973).

The nutritional value of fruits & vegetables is dependent on its components, which contains a

broad array of variation depending on the species, cultivar, and maturity stage. Overall,

vegetables contain more minerals than fruits, but both fruit and vegetables are recognised as

nutrient-dense foods because they release considerable quantities of micronutrients, such as

minerals and vitamins, but moderately little calories. Minerals have both direct and indirect

effects on human health. From a direct nutrition view, potassium and ascorbic acid has the

biggest presence in both fruits and vegetables (Vicente, Manganaris, Sozzi, & Crisosto, 2009).

Quality of foods can be drastically adversely affected by food decay. This is a process which

is vital to remove or decrease in food production. Decay is the method where food deteriorates

to the stage where it is not acceptable to be eaten by humans or is unsafe to be eaten. There are

three type of food decay also known as food spoilage; putrefaction, fermentation and rancidity.

The spoilage that happens in food is down to a reaction/breakdown of the chemical composition

of the product, involving its lipids, carbohydrates and proteins. The degree at which the

chemical reactions are undertaken is dependent on a number of elements, for example;

temperature, exposure to light, water activity, pH or oxygen.

A number of techniques to prevent food decay may be employed that may either completely

prevent, delay, or else decrease food spoilage. These include; use of preservatives or

refrigeration, freezing can preserve food even longer, canning, lactic acid fermentation, drying

and blanching.

In blanching the application of a mild head inactivates enzymes and halts adverse changes in

fresh fruit and vegetables quality. Blanching also deactivates enzymes in particular those which

are associated with quality deterioration such as those involved in browning, lipid oxidation

16

and textural damages. After undergoing blanching, food quality can considerably depend on

the time/temperatures/power combination use as well as the size of the food blanched.

1.7 Enzymatic activity effects on food and determination of peroxidase enzyme.

Many of the quality changes that vegetables undergo are catalysed by enzymes, therefore it is

reasonable to choose an enzyme as the indicator of the efficiency of the blanching method.

From about 1949 to 1975, catalase was used as the indicator enzyme for English green beans

and a number of other vegetables, while peroxidase served as the indicator enzyme for all other

vegetables. In 1975 the U.S. Dept. of Agriculture suggested that peroxidase inactivation was

necessary to reduce deterioration of quality during storage of vegetables and that catalase

inactivation was not an adequate indicator.

A number of enzymes can be used as an indicator of quality in vegetables. There is no sole

essential enzyme which is accountable for all the vegetable quality changes possible during

storage. However most studies agree that the two widely used and most effective enzyme

indicators of blanching are peroxidase and lipoxygenase (Gkmen, Sava Baheci, Serpen, &

Acar, 2005) (Garrote, Silva, Bertone, & Roa, 2004) (Gne & Bayindirli, 1993).

Table 1.3: Enzymes responsible for quality deterioration

Quality defect Responsible enzymes

Off-flavour

development

Lipoxgenase

Lipase

Protease

Textural

Changes

Pectic enzymes

Cellulose

Colour

changes

Polyphenol oxidase

Phlorophyllase

peroxidase

lipoxygenase

Nutritional

changes

Ascorbic acid

Oxidase

Thiaminase

(Williams, Lim, Chen, Pangborn, & Whitaker, 1986)

17

Research has shown that the biggest problem with using lipoxgenase as an indicator is that a

quick test is generally unavailable or not readily utilized by the food industry. Lipoxygenase

analysis may be carried out in a laboratory using either a spectrophotometric or a polarographic

method, however both can pose difficulties and neither would be feasible in a processing

facility environment (Barrett & Theerakulkait, 1995).

According to the research presented in table 1.4, peroxidase appears to be a more practical,

quicker, less expensive, simpler alternative to lipoxygenase. Other studies support this and have

shown that the reduction or removal of peroxidase activity to be the best indicator of blanching

completion in relation to the retaining of quality after process has been carried out (Joslyn &

Berkeley, 2006).

Table 1.4: Advantages and disadvantages of both the Peroxidase and Lipoxygenase indicators

Enzyme

Indicator

Advantages Disadvantages

Peroxidase

Wide distribution in vegetable

tissues.

Correlation to quality un clear

Resistant to destruction by heat Inactivation may require overheating

Simple and rapid test quantitative

test possible

Regeneration is possible

Lipoxygenase

Wide distribution in plants

Rapid assay either unavailable or not

utilisd

Good evidence to support

involvement in off-flavour

development and colour loss

Interference common in the

spectrophotometric assay

Polarographic method may not be

sensitive

Non-enzymatically catalysed lipid

oxidation may occur

(Barrett & Theerakulkait, 1995)

1.8 Vitamin C

Vitamin C or L-ascorbic acid, is an essential dietary nutrient for humans. Ascorbic acid is a

water-soluble vitamin which is vital for growth and repair of teeth, gums, bones, tendons

ligaments and skin, as it is required for the production of collagen. Vitamin C helps wounds

heal also and is required for normal immune system function. It works as an antioxidant which

defends the cells of the human body from free-radical damage.

18

L-ascorbic acid deficiency may lead to scurvy, a severe disease identified by anaemia, skin

hemorrhages (blood spots) and gingivitis (gum disease). Generally it is uncommon, however it

may take place in the extremely malnourished or alcoholics (Jegtvig, 2013).

(Sigma-Aldrich, 2013)

Figure 1.4: Chemical Structure of L-ascorbic acid.

Vitamin C is readily used in the food industry for two main uses, the first being as an additive

to increase a food products nutritious quality and the second is to act as a preservative. As an

additive it may be added in order to replace vitamin loss during processing. Examples of such

products would be in fruit juices, canned fruit and vegetables, etc. Vitamin C acts as a

preservative by preventing oxidation, increasing the acidity of the product and acts as a

stabiliser. It is widely used in bread making, where it is present as a flour improver, by

improving bread texture and size of resulting bread along with an increased elasticity of the

dough and increased gas retention. All of these factors make it a very useful additive in the

food industry (Davies, Partridge, & Austin, 1991).

Vitamin C cannot be manufactured in the body and must be acquired through our diet. Our

bodies benefit more from L-ascorbic acid than that of L-dehydroascorbic acid, which is of no

use to the bodies system and is removed during excretion. It is a very heat unstable vitamin and

is extremely soluble in water (Whitney & Rolfes, 2002).

Therefore the vitamin must be sourced through food. FSAI recommends a daily vitamin C

intake of 60 mg/day. Vegetables and fruit are a great source of ascorbic acid. The below table

shows you which foods are sources of vitamin C.

19

Table 1.5: Vitamin C content of Some Common Foods.

Vegetables Serving size Vitamin C (mg)

Cabbage, red, raw 250 mL (1 cup) 54

Brussels sprouts, cooked 125 mL (4 sprouts) 38-52

Broccoli, raw 125 mL ( cup) 42

Cabbage, cooked 125 mL ( cup) 30

Caulifower, cooked 125 mL ( cup) 29

Cauliflower, raw 125 mL ( cup) 26

Potato, with skin, cooked 1 medium 17-24

Sweet potato, with skin, cooked 1 medium 22

Asparagus, frozen, cooked 6 spears 22

Turnip greens, cooked 125 mL ( cup) 21

Tomato, raw 1 medium 16

(Dietitians.ca, 2012)

Potatoes are a commonly eaten vegetable in Ireland. They contain considerable amounts of

vitamin C, however the majority of it is lost because of the high heat temperatures for long

times in cooking. To avoid this, blanching a precursor to cooking can be used to help retain

Vitamin C before the actual cooking for longer times is undertaken. For this reason blanching

is a carried out on potatoes. Its quick processing time, and quick cooking step leads better

retention of ascorbic acid. Studies have proven that well-controlled blanching techniques can

add to the overall retention of vitamins in vegetable foods (Selman, 1994).

Methods of detecting Vitamin C in foods have evolved in recent years. Biological techniques

have been commonly used in vitamin C analysis, but have gradually been replaced with

chemical methods which were more sensitive and selective. However, the titrimetric method

(DCPIP) is commonly used due to its simplicity and for its rapid technique (Davies et al., 1991).

The official method used for the analysis of vitamin C is the 2, 6-dichloroindophenol titrimetric

methods, which is an Association of Official Analytical Chemistry method. This technique is

commonly used as it is a quick test for a variety of products such as vegetables (Helrich, 1990).

The determination of vitamin C content using the 2,6 -dichloroindophenol method works on

the principle that vitamin c reduces the indicator dye to a faint pink colour for 10 seconds and

then to a colourless solution. The titre of the dye can then be established using a standard

ascorbic acid solution. Food samples can then be titrated with the dye and the volume for the

titration used to calculate the vitamin C content of the sample (Nielsen, 2010). The type of

blanching (microwave or water) can have varying effects on Vitamin C retention.

20

1.9 Relationship between Time/Temperature/Power combinations on Quality

After undergoing blanching, food quality can vary considerably depend on the

time/temperatures combination used as well as the size of the food blanched. Under-blanching

will increase the activity of enzymes and is more adverse than if no blanching was carried out.

Over-blanching results in loss of texture, colour, phytochemicals and minerals (Jaiswal et al.,

2012). Industrial blanching is generally carried out at combinations of 70 to 95 C for not

longer than 10 minutes while for household purposes vegetables are usually blanched at

combinations of 98100 C for of 1012 min (Morales-Blancas et al., 2002).

Numerous investigations (Klein, Rastogi, Perry, & Brewer, 1994) on microwave blanching of

vegetables and fruits have been published. investigated the effect of different blanching

methods on the ascorbic acid content and the peroxidase activity in 225 g-batches of green

beans, and they concluded that a 3-min microwave treatment at 700 W resulted in a product

similar to that obtained by steam blanching. Muftugil, (1986) showed that the time to complete

the peroxidase inactivation in green beans was less with microwave blanching than with water

and steam treatment, whereas a higher greenness remained with the two latter methods.

(Brewer & Begum, 2003) investigated the effects of power and irradiation time on ascorbic

acid, colour, and peroxidase activity in microwave blanching of various vegetables. Compared

to raw unblanched samples, they found that the optimum conditions (2 min at 490 W, or 1 min

at 700 W) led to a peroxidase activity reduction up to 88%, and an ascorbic acid retention of

about 70%. Although, in spite all of this research, there are not many comparison studies of

microwave blanching with conventional industrial blanching.

The most efficient blanching time/temperature/power combinations, depends greatly on the

type of food blanched, why blanching is being carried out, the desired end result, and the type

of heating medium used.

1.10 Economic Statistics of Industrial blanching & benefits of improved technologies.

Both water and steam blanching have one thing in common, product is exposed directly to

food-grade water that typically ranges in temperature from 70oC to 100oC. With microwaving

blanching, the process is carried out in a microwave where the food is placed and cooked. It

uses high frequency radio waves, which penetrates the food molecules causing them to vibrate.

21

The vibrating of these molecules leads to friction, which causes heat formed, thus cooking the

food. The phrase microwaves refers to electromagnetic radiation in the wavelength range of

0.1-1 m in air, corresponding to a frequency range of 0.3-3 GHz (Berk, 2013).

With steam blanching, product is exposed directly to food-grade steam that is typically 100oC

as it is conveyed within a chamber. Some steam blanchers use convection technology that

forces the steam through the bed of product to increase the heat transfer efficiency, other steam

blanchers present the product in a single layer to achieve Individual Quick Blanching (IQB).

To minimize the product's exposure to heat, some steam blanchers follow the heat penetration

stage with a holding stage that allows the core temperature of the product to rise without the

addition of more steam.

Most water blanchers and steam blanchers require the steam to be produced by a boiler. With

water blanching, the steam heats the water and the product. With steam blanching, the steam

is applied directly to the product. Because the boiler is one of the most expensive pieces of

equipment pieces to operate in a food processing plant, given the high cost of energy, steam

consumption as a direct and significant effect on energy costs (Johnson, 2011).

Figure 1.5: Cost comparison of hot water and steam use in blanching of carrots or peas

Like energy costs, water use and wastewater effluent are directly correlated to the volume of

steam used. Steam blanchers require half the steam of water blanchers, therefore needing half

the volume of water.

22

Figure 1.6: Effluent discharge comparison chart for hot water and steam use in blanching

Overall, the use of microwave ovens in the food industry is limited. Currently, the most

expensive blanched foods are using microwave balancing. Although it has shown to be energy

saving in the case of potato fries (Bingol et al., 2014). The hugely high frequencies used in

microwave heating permits for quick energy transfers and thus high rates of heating. This is an

important feature of this method.

Research (Patricia et al., 2011) in the assessment of microwave methods in blanching of

broccoli as an alternative for traditional blanching has also shown that microwave blanching

uses less energy on an industrial scale to conventional blanching. Microwave blanching

consumption and energy cost of production is almost of the half in compared with the

traditional. (Patricia et al., 2011).

However microwave blanching is not as widespread as the conventional types, as soon as it has

exhibited its worth, it may be drawn to the freezing and canning industry. Replacements of

existing water or steam blanchers is not likely to happen. The vegetable industry would be

hesitant to substitute examples of equipment before full depreciation and particularly if their

market niche is stable. Lastly, it continues to appear that the shorter processing times of

microwave ovens will lead to reduced operating costs and higher value products, thus

compensating for equipment cost (Reyes De Corcuera, Cavalieri, & Powers, 2004).

23

Chapter 2

Methodology

24

2.0 Methodology

Samples of potatoes are blanched using both methods and a number of quality tests are carried

out before and after heat treatment and compared. This analysis involves testing for;

Internal quality factors as Conventional and Microwave blanching is carried out across

different time/temperature/power combinations.

Peroxidase Tests on blanched samples to give indication of deactivation of


Ascorbic acid analysis on end blanched samples using end point times shown

by peroxidase test using DCPIP method, to determine Vitamin C loss after each

blanching type/combination.

External quality factors as Conventional and Microwave blanching is carried out across

different time/temperature/power combinations.

Weight loss to samples throughout heat treatment.

Texture/Hardness changes to samples throughout blanching.

Colour changes to samples throughout blanching.

This below table is the time and temperature/power parameters for conventional and

microwave blanching that is used in this investigation.

Table 2.1: Conventional & Microwave blanching, parameters of investigation

Sample Size

Time

Conventional Blanching Microwave Blanching

x 3 Temperature (oC) Power (Watt)

1cm3, 2 cm3, 3cm3 30 secs 80oC, 100oC 600W, 800W

1cm3, 2 cm3, 3cm3 1 mins 80oC, 100oC 600W, 800W










25

2.1 Sampling

Rooster Potatoes were purchased fresh on the morning of each day of testing from a local

Tescos. All potatoes were non-organic and were checked prior to purchasing to make sure that

they were all free from any damage or bruising. Just samples which were free from

irregularities or any defects which could affect the result were chosen for use.

2.2.1 Pre Conventional Blanching Physical Characterization of Samples

Conventional Blanching Sample Preparation;

Method:

1. Potatoes selected, peeled, washed, sliced & diced into around:

(1cm x 1cm x 1cm), (2cm x 1cm x 1cm), (3cm x 1cm x 1cm),

(1cm3) (2cm3) (3cm3)

Figure 2.1: Sample sizes

2. Each sample size is done in triplicates, ie for each test

x (1cm3), 3 x (2cm3), 3 x (3cm3)

3. Soak samples in iced water and covered with cloth to prevent air exposure

The following determined:

Weight (to determine weight loss)

Texture/Hardness

Colour

Methods:


1. Samples weight measured using a mass balance and recorded in grams.

2. Length of samples measured using a stainless steel ruler, which was cleaned using sterilized

wipe before and after use.

26

Texture/Hardness

CT3 Texture Analyser used along with TA-MTP Magness-Taylor Probes (puncture

test) to measure hardness.

Figure 2.2: Brookfield Texture Analyser

Instrument calibrated and samples tested as per Brookfield Texture Analyser Operating

Instructions, Manual No: M08-372-C0113 (Brookfield, 2012)

Settings:

Probe: 4 mm diameter cylinder probe

Test type: Compression

Test Speed: 1.0 mm/s

Target Type: Distance: 5mm

Target value: 110.0 mm

Trigger Load: 10 g

The procedure produces a plot of force (N) vs. time (s) which is used to establish the value of

hardness in Newton (N).

Colour

CR-400 Series Colorimeter used to measure Luminance (colour). Tests as per Konica

Minolta CR-400 Chrom-Meter Catalogue No: 9242-4889-11 (Minolta, 2013)

Figure 2.3: CR-400 Chrom-Meter

After blanching samples of cubes are cut in half prior to peroxide tests and their colour

is measured internally using the Luminance CR-400 Series Colorimeter.

27

*** Following Pre Conventional Blanching Physical Characterisation of Potatoes, the

samples were placed back into iced water and covered with cloth to prevent air exposure

2.2.2 Conventional Blanching of Samples using Hot-water method using different

blanching Times/Temperature combinations and post blanching cooling step.

Table 2.2: Conventional blanching, parameters of investigation

Samples x 3 Time Temperature

1cm3, 2 cm3, 3cm3 30 secs 80oC, 100oC

1cm3, 2 cm3, 3cm3 1 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 2 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 3 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 4 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 5 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 6 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 7 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 8 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 9 mins 80oC, 100oC

1cm3, 2 cm3, 3cm3 10 mins 80oC, 100oC

Materials & Equipment:

ELTAC EKA 179 Waterbath

Vegetable baskets

Thermometer

Ice

Basins

Timer

Method:

1. ELTAC EKA 179 Waterbath is filled from bottom (enough to submerge the samples

which will be placed in and allowed to heat to specific temperature.

28

Figure 2.4: ELTAC EKA 179 Waterbath

2. Samples 3 x (1cm2), 3 x (2cm2), 3 x (3cm2) are removed from iced water and placed into

baskets, before being placed into the waterbath for scheduled times. Ensure lid is only

removed on entering of samples and quickly replaced on during blanching. Accurately

record the blanching time for accurate results.

ie first blanch is carried out at 800C for 30 seconds.

last blanch is carried out at 1000C for 10 minutes.

The sample sizes and quantities remain the same on each blanch.

3. On blanching completion remove lid and retrieve samples. Quickly place into fresh iced

water once again prior to enzyme testing.

2.2.3 Post Conventional Blanching Physical Characterization of Samples

Method:

In the same manner as the pre characterization of samples, the following determined:


Texture/Hardness

Colour

These tests should be carried out as quickly as possible to reduce air exposure to samples

Again place back samples back into iced water on completion.

29

2.2.4 Peroxidase Tests on Conventional blanched samples to give indication of

deactivation of peroxidise enzyme and indication of effective blanching end point.


Pipette filers.

3% Hydrogen Peroxide

1% Guaiacol Solutions

Method:

1. Remove samples from iced water and place on three different sheets of white paper

designated by the sample size & time/temperature combination used.

Figure 2.5: Samples after heat treatment and cut in half prior peroxidase testing

2. Cut the cubes from each treatment in half and saturate the cut surface with equal volumes

of 3% H2O2 and 1% guaiacol solutions.

3. After three minutes at room temperature note the extent of any colour change in terms of

percentage area of the cut surface.

4. The degree of surface colouring gives an indication of the peroxidase activity in the

sample.

Table 2.3: Peroxidase Activity Index Scale

Coloured Score

80 100% 5

60-80% 4

40-60% 3

20-40% 2

0-20% 1

0% 0

30

2.3 Microwave Blanching Analysis at Various Time/Temp. Combinations

2.3.1 Pre Microwave Blanching Physical Characterization of Samples

Methods:

Conventional Blanching Sample Preparation:

Potatoes selected, peeled, washed, sliced & diced into around:

(1cm 3), (2cm3), (3cm3)

Each sample size is done in triplicates, ie for each test

3 x (1cm3) 3 x (2cm 3) 3 x (3cm3)

Soak samples in iced water & covered with cloth to prevent air exposure

The following determined:


Texture/Hardness

Colour

*** Following Pre Microwave Blanching Physical Characterization of Potatoes, the

samples were placed back into iced water and covered with cloth to prevent air exposure

2.3.2 Microwave Blanching of Samples using different blanching Times/Power

combinations and post blanching cooling step.

Table 2.4: Microwave blanching, parameters of investigation

Samples x 3 Time Power (Watt)

1cm3, 2 cm3, 3cm3 30 secs 600W, 800W

1cm3, 2 cm3, 3cm3 1 mins 600W, 800W

1cm3, 2 cm3, 3cm3 2 mins 600W, 800W

1cm3, 2 cm3, 3cm3 3 mins 600W, 800W

1cm3, 2 cm3, 3cm3 4 mins 600W, 800W

1cm3, 2 cm3, 3cm3 5 mins 600W, 800W

1cm3, 2 cm3, 3cm3 6 mins 600W, 800W

1cm3, 2 cm3, 3cm3 7 mins 600W, 800W

1cm3, 2 cm3, 3cm3 8 mins 600W, 800W

1cm3, 2 cm3, 3cm3 9 mins 600W, 800W

1cm3, 2 cm3, 3cm3 10 mins 600W, 800W

31


Bosch Gourmet HFT879 HME9751GB Combination Oven & Microwave

Plastic microwavable container & lid.

Thermometer

Ice

Basins

Timer

Method:

1. Microwavable plastic container is filled way is (enough to submerge the samples)

with room temperature water

2. Samples 3 x (1cm2), 3 x (2cm2), 3 x (3cm2) are removed from iced water and placed

into plastic container, before being placed into the Bosch Gourmet HFT879

HME9751GB for scheduled times. Ensure lid is only placed on container before heat

treatment starts.

3. Accurately record the blanching time using the timer on microwave for accurate results.

ie. first blanch is carried out at 600W for 30 seconds.

last blanch is carried out at 800W for 10 minutes.

4. The sample sizes and quantities remain the same on each blanch.

Figure 2.6: Microwave blanching

5. On blanching completion remove lid and retrieve samples. Quickly place into fresh iced

water one again prior to enzyme testing.

32

2.3.3 Post Microwave Blanching Physical Characterization of Samples

Method:

In the same manner as the pre characterization of samples, the following determined:

Weight (weight loss),

Texture/Hardness (quality),

Colour (quality)

These tests should be carried out as quickly as possible to reduce air exposure to samples

Place back samples back into iced water on completion.

2.3.4 Peroxidase Tests on Microwave blanched samples to give indication of

deactivation of peroxidise enzyme and indication of effective blanching end point.


Pipette filers.

3% Hydrogen Peroxide

1% Guaiacol Solutions

Method:

1. Remove samples from iced water and place on three different sheets of white paper

designated by the sample size and time/temperature combination used.

2. Cut the cubes from each treatment in half and saturate the cut surface with equal volumes

of 3% H2O2 and 1% guaiacol solutions.

3. After three minutes at room temperature note the extent of any colour change in terms of

percentage area of the cut surface.

4. The degree of surface colouring gives an indication of the peroxidase activity in the

sample.

33

2.4 Ascorbic acid analysis blanched samples using end point times shown by peroxidase

test using DCPIP method, to determine Vitamin C loss after each blanching

type/combination (to be carried out in triplicates).

After the peroxidase test has been completed, the most suitable blanching time/temperature

combinations based on quality of the vegetable will be determined. Using these, new samples

can be balanced at each temperature/power for the lengths of time determined by the end points

needed to remove enzyme activity. These new samples are tested for Ascorbic acid, using the

2, 6-dichloroindophenol titrimetric method, which is an Association of Official Analytical

Chemistry method (AOAC Method 967.21, 45.1.14).

The results of the peroxidase test will yield the optimum time/temperature combination in the

case of conventional blanching and the optimum time/power combination in the case of

microwave blanching. These are the samples that will be tested for ascorbic acid along with

control samples which have not undergone any blanching.

For this the two optimum time/temperature and time/power combinations are redone with fresh

potatoes samples.

Materials & Equipment

Test samples & control samples 30g each

250 ml solution of 0.1g of 2,6-Dichlorophenol indophenol

1000ml solution of 0.1g of ascorbic acid dissolved in 3% metaphoric acid solution

(Concentration of standard vitamin C solution- 0.1mg/ml)

Beakers 250ml

Burette 50 ml

Erlenmeyer flasks 125ml

Funnel

Glass rods

Measuring cylinders 100ml,1000ml

Pipettes

Volumetric flasks 250ml, 200ml,50 ml

Analytical balance

34

Method:

Sample Preparation

Weigh and extract by homogenizing test sample in metaphoshoric acid-acetic acid solution

(i.e., 15 g HPO3 and 40 ml of HOAc in 500ml of deionized H20). Filter (and/or centrifuge)

sample extract, and dilute appropriately to a final concentration of 10-100 mg of ascorbic

acid/100 ml.

Standard Preparation

Weigh 50 mg of USP L-ascorbic acid reference standard and dilute to 50 ml with HPO3-HOAc

extracting solution.

Titration

Titrate standard, test samples, and blank with indophenol reagent (prepared by dissolving 50

mg of 2,6-dichlorindophenol sodium salt and 42 mg of NaHCO3 to 200 ml with deionized H20)

to a light but distinctive rose pink endpoint lasting > 5 seconds.

Calculations

Calculations can be carried out to determine the amount of ascorbic acid per 10 g of potato

sample.

Mg of ascorbic acid / g or ml of sample = (XB) x (F/E) x (V/Y)

Where:

X = average ml for the test solution titration

B = average ml for test blank titration

F = mg ascorbic acid equivalents to 1.0ml indophenol standard solution

E = sample weight (g) or volume (ml)

V = volume of initial test solution

Y = volume of test solution titration

Note: The (V/Y) term represents the dilution factor employed. (Nielsen, 2010)

35

Chapter 3

Results

36

3.0 Results

3.1 Peroxidase Tests on blanched samples to give indication of deactivation of


Figure 3.1: Top samples peroxidase level: 100%, Bottom samples peroxidase level: 0%

Table 3.1: Activity Index Scale

Coloured Score

80 100% 5

60-80% 4

40-60% 3

20-40% 2

0-20% 1

0% 0

37

Table 3.2: Peroxidase activity across Conventional blanching 80oC/100oC, endpoints in yellow

Time/Temp.

Combo.

Peroxidase Level Time/Temp.

Combo.

Peroxidase Level

1cm3 2cm3 1cm3 1cm3 2cm3 3cm3

Raw: 0 min 5 5 5 Raw: 0 min 5 5 5

30 secs @ 80oC 5 5 5 30secs @ 100oC 4 4 4

1 min @ 80oC 5 5 5 1 min @ 100oC 3 3 3

2 min @ 80oC 4 4 4 2 min @ 100oC 2 2 2

3 min @ 80oC 4 4 4 3 min @ 100oC 1 1 1

4 min @ 80oC 3 3 3 4 min @ 100oC 0 0 0

5 min @ 80oC 3 3 3 5 min @ 100oC 0 0 0

6 min @ 80oC 2 2 2 6 min @ 100oC 0 0 0

7 min @ 80oC 2 2 2 7 min @ 100oC 0 0 0

8 min @ 80oC 1 1 1 8 min @ 100oC 0 0 0

9 min @ 80oC 1 1 1 9 min @ 100oC 0 0 0

10 min @ 80oC 0 0 0 10 min @ 100oC 0 0 0

Figure 3.2: Peroxidase activity across Conventional blanching 80oC/100oC, endpoints at 0%

5

4

3

2

1

0 0 0 0 0 0 0

5 5 5

4 4

3 3

2 2

1 1

00

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5 6 7 8 9 10

PER

OX

IDA

SE L

EVEL

(5

-0, 1

00

%-0

%)

TIME (MINTUES)

CONVENTIONAL BLANCHING: PEROXIDASE LEVEL IN SAMPLES @ 80 OC & 100 OC

100*C 80*C Blanching end point.

38

Table 3.3: Peroxidase activity across Microwave blanching 600W/800W, endpoints in yellow

Time/Temp.

Combo.

Peroxidase Level Time/Temp.

Combo.

Peroxidase Level

1cm3 2cm3 1cm3 1cm3 2cm3 1cm3

Raw: 0 min 5 5 5 Raw: 0 min 5 5 5

30secs @ 600W 5 5 5 30secs @ 800W 5 5 5

1 min @ 600W 4 4 4 1 min @ 800W 4 4 4

2 min @ 600W 3 3 3 2 min @ 800W 3 3 3

3 min @ 600W 3 3 3 3 min @ 800W 2 2 2

4 min @ 600W 2 2 2 4 min @ 800W 1 1 1

5 min @ 600W 1 1 1 5 min @ 800W 0 0 0

6 min @ 600W 1 1 1 6 min @ 800W 0 0 0

7 min @ 600W 0 0 0 7 min @ 800W 0 0 0

8 min @ 600W 0 0 0 8 min @ 800W 0 0 0

9 min @ 600W 0 0 0 9 min @ 800W 0 0 0

10 min @ 600W 0 0 0 10 min @ 800W 0 0 0

Figure 3.3: Peroxidase activity across Microwave blanching 600W/800W, endpoints at 0%

0

1

2

3

4

5

0 2 4 6 8 10 12

PER

OX

IDA

SE L

EVEL

(5

-0, 1

00

%-0

%)

TIME (MINUTES)

MICROWAVE BLANCHING: PEROXIDASE LEVEL IN SAMPLES @ 600W & 800W

600W 800W Blanching end point.

39

3.2 Pre and Post Blanching Physical Characterization of Samples

3.2.1 Weight Loss

Refer to Appendix 1 for weight loss data tables.

Figure 3.4: Average sample size weight loss after Conventional blanching @ 80oC and 100oC

Figure 3.5: Average sample size weight loss after Microwave blanching @ 600W and 800W

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 1 2 3 4 5 6 7 8 9 10

We

igh

t lo

ss (

gram

s)

Time (minutes)

Average sample size weight loss after Conventional blanching @ 80oC and 100oC

80*C

100*C

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 1 2 3 4 5 6 7 8 9 10

We

igh

t lo

ss (

gram

s)

Time (minutes)

Average sample size weight loss after Microwave blanching @ 600 and 800 W

800W

600W

40

3.2.2 Texture/Hardness

Table 3.4: Hardness across conventional blanching at 80oC, blanch endpoint shown in yellow

Time/ Temp Combo.

Sample Size: 1cm3 Sample Size: 2cm3 Sample Size: 3cm3

Force (Newtons) Force (Newtons) Force (Newtons)

Raw: 0 min @ 100oC 4,304 N 4,299 N 4,303 N

30 secs @ 80oC 4,300 N 4,294 N 4,296 N

1 min @ 80oC 4,292 N 4,283 N 4,284 N

2 mins @ 80oC 4,279 N 4,271 N 4,274 N

3 mins @ 80oC 4,263 N 4,259 N 4,263 N

4 mins @ 80oC 4,248 N 4,233 N 4,236 N

5 mins @ 80oC 4,219 N 4,209 N 4,214 N

6 mins @ 80oC 4,188 N 4,186 N 4,186 N

7 mins @ 80oC 4,159 N 4,152 N 4,152 N

8 mins @ 80oC 4,128 N 4,129 N 4,129 N

9 mins @ 80oC 4,093 N 4,101 N 4,097 N

10 mins @ 80oC 4,057 N 4,065 N 4,062 N

Figure 3.6: Hardness across conventional blanching at 80oC, 1cm3, 2 cm3, 3cm3 samples

3,900

4,000

4,100

4,200

4,300

4,400

0 0.5 1 2 3 4 5 6 7 8 9 10

Har

dn

ess

(N

ew

ton

s)

Time (minutes)

Sample Texture/Hardness measurement as Conventional blanching is carried out @ 80oC

1cm3 2cm3 3cm

Blanching end point indicated by peroxidase test.

41

Table 3.5: Hardness across conventional blanching @ 100oC, blanch endpoint shown in yellow

Time/ Temp Combo.



Raw: 0 min @ 100oC 4,302 N 4,294 N 4,306 N

30 secs @ 100oC 4,291 N 4,287 N 4,301 N

1 min @ 100oC 4,266 N 4,278 N 4,284 N

2 mins @ 100oC 4,247 N 4,251 N 4,257 N

3 mins @ 100oC 4,117 N 4,122 N 4,125 N

4 mins @ 100oC 4,075 N 4,079 N 4,089 N

5 mins @ 100oC 4,032 N 4,028 N 4,054 N

6 mins @ 100oC 4,002 N 3,996 N 4,012 N

7 mins @ 100oC 3,975 N 3,968 N 3,984 N

8 mins @ 100oC 3,941 N 3,929 N 3,956 N

9 mins @ 100oC 3,898 N 3,888 N 3,928 N

10 mins @ 100oC 3,857 N 3,849 N 3,894 N

Figure 3.7: Hardness across conventional blanching at 100oC, 1cm3, 2 cm3, 3cm3 samples

3,600

3,700

3,800

3,900

4,000

4,100

4,200

4,300

4,400

0 0.5 1 2 3 4 5 6 7 8 9 10

Har

dn

ess

(N

ew

ton

s)

Time (minutes)

Sample Texture/Hardness measurment as conventional blanching iis carried out @ 100oC

1cm3 2cm3 3cm3


42

Table 3.6: Hardness across microwave blanching at 600W, blanch endpoint shown in yellow

Time/ Power Combo.



Raw: 0 min @ 100oC 4,302 N 4,304 N 4,297 N

30 secs @ 600W 4,286 N 4,289 N 4,288 N

1 min @ 600W 4,251 N 4,263 N 4,266 N

2 mins @ 600W 4,232 N 4,238 N 4,248 N

3 mins @ 600W 3,995 N 4,004 N 4,023 N

4 mins @ 600W 3,947 N 3,962 N 3,992 N

5 mins @ 600W 3,893 N 3,933 N 3,951 N

6 mins @ 600W 3,861 N 3,887 N 3,928 N

7 mins @ 600W 3,824 N 3,848 N 3,892 N

8 mins @ 600W 3,785 N 3,799 N 3,855 N

9 mins @ 600W 3,748 N 3,752 N 3,817 N

10 mins @ 600W 3,703 N 3,719 N 3,779 N

Figure 3.8: Hardness across microwave blanching at 600W, 1cm3, 2 cm3, 3cm3 samples

3,400

3,600

3,800

4,000

4,200

4,400

0 0.5 1 2 3 4 5 6 7 8 9 10

Har

dn

ess

(N

ew

ton

s)

Time (minutes)

Sample Texture/Hardness measurment as microwave blanching is carried out @ 600W

1cm3 2cm3 3cm


43

Table 3.7: Hardness across microwave blanching at 800W, blanch endpoint shown in yellow

Time/ Power Combo.



Raw: 0 min @ 100oC 4,298 N 4,295 N 4,300 N

30 secs @ 800W 4,244 N 4,249 N 4,238 N

1 min @ 800W 4,202 N 4,207 N 4,205 N

2 mins @ 800W 4,138 N 4,134 N 4,142 N

3 mins @ 800W 4,076 N 4,072 N 4,088 N

4 mins @ 800W 3,943 N 3,964 N 3,999 N

5 mins @ 800W 3,896 N 3,932 N 3,958 N

6 mins @ 800W 3,865 N 3,889 N 3,924 N

7 mins @ 800W 3,829 N 3,843 N 3,895 N

8 mins @ 800W 3,781 N 3,797 N 3,850 N

9 mins @ 800W 3,746 N 3,751 N 3,819 N

10 mins @ 800W 3,700 N 3,716 N 3,776 N

Figure 3.9: Hardness across microwave blanching at 800W, 1cm3, 2 cm3, 3cm3 samples

3,400

3,600

3,800

4,000

4,200

4,400

0 0.5 1 2 3 4 5 6 7 8 9 10

Har

dn

ess

(N

ew

ton

s)

Time (minutes)

Sample Texture/Hardness decrease as microwave blanching times increase @ 800W

1cm3 2cm3 3cm3


44

3.2.3 Colour

Table 3.8: Luminance scale measurements

L Brightness scale (from 0 - dark to 100 = white)

a Red-Green scale (+a for red; -a for green; the higher the numerical value, the more

intensive the colour impression)

b Yellow-Blue scale (+b for yellow: -b for blue; the higher the numerical value, the more

intensive the colour impression).

Refer to Appendix 2 for colour data tables.

Figure 3.10: Average L*a*b (Colour) measurements as conventional & microwave blanching

times increase.

45

3.3 Ascorbic acid analysis on blanched samples using end point times shown by

peroxidase test using DCPIP method, to determine Vitamin C loss after each

blanching type/combination. (To be carried out in triplicates).

Table 3.9: Ascorbic acid in Control, Conventional 80oC/100oC & Microwave 600W/800W

No. Samples 10 g each Vitamin C/10g Avg. Vit. C/100g

1.

Control Raw

Raw 2.18 mg

22.90 mg 1. Raw 2.32 mg

1. Raw 2.37 mg

2.

Conventional 800C

800C for 10 mins 1.12 mg

10.83 mg 2. 800C for 10 mins 1.05 mg

2. 800C for 10 mins 1.08 mg

3.

Conventional

1000C

1000C for 4 mins 0.83mg

8.33 mg 3. 1000C for 4 mins 0.89mg

3. 1000C for 4 mins 0.78 mg

4.

Microwave 600w

600w for 7 mins 1.92 mg

18.97 mg 4. 600w for 7 mins 1.81 mg

4. 600w for 7 mins 1.96 mg

5.

Microwave 800w

800w for 5 mins 1.43 mg

15.17 mg 5. 800w for 5 mins 1.58 mg

5. 800w for 5 mins 1.54 mg

46

Figure 3.11: Vitamin C in control & conventional 80oC & 100oC samples blanched to endpoint

Figure 3.12: Vitamin C in control & microwave 600W & 800W samples blanched to endpoint

22.9

10.83 8.33

0

5

10

15

20

25

0 20 40 60 80 100

Vit

amin

C c

on

ten

t/1

00

g (m

g)

Temperature (oC)

Vitamin C measurment across conventional blanching at: (0oC for 0 mins), (80oC for 10 mins) & (100oC for 4 mins)

22.9

18.97

15.17

10

12

14

16

18

20

22

24

0 100 200 300 400 500 600 700 800

Vit

amin

C c

on

ten

t/1

00

g (m

g)

Power (Watt)

Vitamin C measurement across microwave blanching at: (0W for 0 mins), (600W for 7 mins) & (800W for 5 mins)

47

Chapter 4

Discussion

48

4.0 Discussion

Quality refers to the characteristics of food that is acceptable to consumers. The

characteristics are made up of external and internal factors. External factors include;

Appearance (size, shape, weight loss, shrinkage, colour, gloss, & consistency), texture and

flavour. Internal factors include; chemical, physical, microbial, enzyme inactivation, and

ascorbic acid retention. Quality is adversely effected by food decay. Blanching deactivates

enzymes (polyphenoloxidase and peroxidase) which are associated with quality deterioration

such as those involved in browning, lipid oxidation and textural damages. In doing this

blanching delays decay (Mathew & Parpia, 1971).

After undergoing blanching, food quality can considerably depend on the

time/temperature/power combination used as well as the size of the food blanched. Under-

blanching will increase the activity of enzymes and is more adverse than if no blanching was

carried out. Over-blanching results in loss of texture, colour, phytochemicals and minerals

(Jaiswal et al., 2012).

This study was carried out to compare conventional hot-water and microwave blanching at

different Time/Temperature/Power combinations on the quality of potatoes. The parameters of

the investigation was 0 10 mins at 80oC & 100oC for conventional and 0 10 mins at 600W

& 800W for microwave blanching. The objects of this study was to answer the following:

Can a quicker, more economic processing time/temperature/power combination be

established between conventional and microwave blanching while maintaining

acceptable quality?

Which method is less damaging to product texture?

To test the efficiency of peroxidase activity testing as an indicator of blanching

completion.

Identify the relationship between blanching effectiveness and the size of the food which

undergoes the process.

Which method of blanching convention or microwave, best retains ascorbic acid?

On completion of each blanching sample, they were tested using the peroxidase test for an

indication of peroxidase level. The level of enzyme activity was measured from 100% to 0%

and scored 5 1 respectively. A result of 0% showed no peroxidase activity and thus the

endpoint of the blanching. The first blanch time/temperature combination at 80oC yielded an

49

endpoint of 10 minutes. The second time/temperature combination at 100oC yielded an

endpoint of 4 minutes. The third time/power combination 600W showed an endpoint of 7

minutes and the final fourth time/power combination showed an endpoint of 5 minutes. Sample

size did not appear to influence the rate of decrease in peroxidase activity. The sample sizes

used were 1cm3, 2cm3, 3cm3. They all decreased in peroxidase activity at the same rate from

100% to 0% at each time/temperature/power combination, i.e. for 4 minutes at 80oC, each

sample size was reduced to 40-60% peroxidase activity. If however larger intervals of size

were used, the relationship between size and decreased rate of enzyme activity in potatoes

during blanching could be investigated.

From this initial data, it could be noted; the most economic option would be microwave

blanching at 600W for 7 minutes as the energy cost of production is almost of half with

microwave compared with conventional (Patricia et al., 2011). For this reason the faster,

slightly less economic microwave alternative (800W for 5 minutes) of the two could be used if

time was a factor and still be a better method over the conventional styles cost wise. However

the quickest method is conventional blanching at 1000C for 4 minutes but the high costs

associated with heating water and the consumption of large volumes of water needed make this

method less economical. Research from the literature review indicated that microwave

blanching is faster than conventional blanching (Ruiz-Ojeda & Peas, 2013). This was not the

case of conventional blanching at 100oC (4 minutes) as it was the fastest, but was the case with

the other time/temperature/power combinations as microwave blanching was faster (600W for

7 minutes, 800W for 5 mins) than conventional blanching at 80oC (10 mins). This analysis

showed a visual change in samples by the peroxidase indicator that was used in alignment with

the scale shown in Table 3.2 to determine peroxidase activity after blanching. This use of the

peroxidase test was successful in showing peroxidase activity and therefore efficiently

indicates peroxidase activity as an indicator of blanching completion.

Further data was collected focusing more on quality of the potatoes after being subjected to the

different times and type of heat treatments. The first of these was a measure of weight loss/

shrinkage. Weight of vegetables is an important factor to both food producers and customers.

Most fresh produce contains from 65 to 95 percent water and potatoes contain around 79

percent water (Vicente et al., 2009). Cooking removes water content of vegetables. It is in the

interest of food producers to use a method of blanching which retains the most weight to

maintain as much value to the vegetables as possible. In this investigation sample size (1cm3,

2cm3, 3cm3) did appear to influence weight loss with relation to blanching times/methods. For

50

example conventional blanching at 80oC for 4 minutes was reduced by 227 N, 215 N, 217 N

for 1cm3, 2cm3, 3cm3 respectively. Blanching time and method of heating also had different

effects on weight loss of the samples. The conventional method at 100oC produced the least

weight loss with respect to blanching end point (quick at 4 minutes). The combination which

produced the second least amount of weight loss

Documents

Comparison Study of Conventional Hot-water and Microwave Blanching at Different Timetemperaturepower Combinations on the Quality of Potatoes