The Effect of Malay Herbs on the Storage Stability of Chilled Keropok Lekor

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THE EFFECTS OF MALAY HERBS ON THE STORAGESTABILITY OF CHILLED KEROPOK LEKOR

AZNI A.AZIZ

BACHELOR OF SCIENCE (HONS.)FOOD SCIENCE AND TECHNOLOGY

FACULTY OF APPLIED SCIENCESUNIVERSITI TEKNOLOGI MARA

NOVEMBER 2008


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THE EFFECTS OF MALAY HERBS ON THE STORAGESTABILITY OF CHILLED KEROPOK LEKOR

AZNI A.AZIZ

Final Year Project Report Submitted inPartial Fulfillment of the Requirement for the

Degree of Bachelor of Science (Hons.) Food Science and Technologyin the Faculty of Applied Sciences

Universiti Teknologi MARA

NOVEMBER 2008


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The Final year Project Report entitled The Effects of Malay Herbs onthe Storage Stability of Chilled Keropok Lekor was submitted by AzniA.Aziz, in partial fulfillment of the requirements for the Degree of Bachelor of Science (Hons.) Science and Food Technology, in the Facultyof Applied Science, and was approved by

Assoc. Prof. Dr. Noriham Abdullah

SupervisorB. Sc. (Hons.) Food Science and Technology

Faculty of Applied ScienceUniversiti Teknologi MARA

40450 Shah AlamSelangor

Pn. Azizah Othman Assoc. Prof. Dr. Norizzah Abd. RashidProject Coordinator Head of Programme

B. Sc. (Hons.) Food Science and Technology B. Sc. (Hons.) Food Science and TechnologyFaculty of Applied Science Faculty of Applied Science

Universiti Teknologi MARA Universiti Teknologi MARA40450 Shah Alam 40450 Shah Alam

Selangor Selangor

Date:


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ACKNOWLEDGEMENTS

In the name of Allah, The Most Gracious and The Most Merciful.

As the Author of this project, I would like to take this opportunity to convey mygreatest gratitude and appreciation to all the people who have assisted me during thepreparation of this project.

First of all, I would like to express my deepest thanks and appreciation to mysupervisor, Assoc. Prof. Dr. Noriham Abdullah for her understanding, patience,invaluable guidance, suggestion, and constant encouragement throughout theplanning of the execution of this project.

Special thanks and appreciation also goes to the Program Head of BSc. (Hons) FoodScience and Technology, Assoc. Prof. Dr. Norizzah Abd. Rashid and ProjectCoordinator Pn. Azizah Othman as well as all the lecturers for their guidance andinvaluable advices throughout all the years of my study in Universiti TeknologiMara, Shah Alam. The insightful information and help is duly acknowledged.

Sincere thanks are also extended to the Food Technology laboratory staffs for theirinformative guidance and support especially to Pn. Siti Mahani, Pn. Nora and Cik Shuhada. I am grateful to Izreen, Nor Azlin Tokiman and her colleagues for theirhelp in part of the experiment and preliminary discussion. Without all of you, thisproject might not be a success.

Not forgetting, my warmest and heartiest appreciation to all my classmates andfriends especially Mazuin Che Mahmood, Nurul Akma Muni, Faridah Ahamad,Norjuwariah Mukhtar, Farahana Basri, Wan Norshela Meor Zainol for theirkindness and helpfulness in completing the course.

Last but not least, my deepest thank to my beloved family, Abah, Mama, Angah,Kak lang, Kak Chik and adik for for their understanding, love, encouragement,financial support and motivation throughout my study.

Azni A.Aziz


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TABLE OF CONTENTS

Page

AKNOWLEDGEMENTS iiiTABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES viiLIST OF ABBREVIATIONS viii ABSTRACT ix ABSTRAK x

CHAPTER 1 INTRODUCTION 1 1.1 Background and Problem statement 11.2 Significance of study 21.3 Objectives of study 3

CHAPTER 2 LITERATURE REVIEW 42.1 Fish 4

2.1.1 Fish Muscle 62.1.2 Shortfin Scad Fish 7

2.1.2.1 Keropok Lekor 82.1.3 Chilled Fish 9

2.2 Spoilage in Fish 112.2.1 Microbiological Spoilage 132.2.2 Chemical Spoilage (oxidation) 152.2.3 Autolytic Spoilage 18

2.3 Antioxidant 192.3.1 Antioxidant as antimicrobial 222.3.2 Synthetic Antioxidant 24

2.3.2.1 BHA and BHT 262.3.3 Natural Antioxidant 27

2.3.3.1 Naturally occurring Phenolic compounds 282.4 Herbs 30

2.4.1 Malay herbs 322.4.1.1 Polygonum hydropiper (kesum) 342.4.1.2 Centella asiatica (pegaga) 36

CHAPTER 3 METHODOLOGY 39 3.1 Materials 39

3.1.1 Raw Material 393.1.2 Chemicals 393.1.3 Instrument/Apparatus 39

3.2 Sample preparation 403.2.1 Herbs preparation 40


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3.2.2 Keropok Lekor preparation 403.3 Chemical Analysis 41

3.3.1 Peroxide Value (PV) 413.3.1.1 Lipid Extraction 413.3.1.2 Peroxide Value 42

3.3.1 Thiobarbituric acid (TBA) 43

3.4 Microbiological Analysis 433.4.1 Total Plate Count 433.4.2 Mould and Yeast Count 44

3.5 Sensory Analysis 443.6 Statistical Analysis 44

CHAPTER 4 RESULTS AND DISCUSSSION 454.1 Chemical Analysis 45

4.1.1 Peroxide Value of chilled Keropok Lekor 454.1.2 Thiobarbituric acid Value of chilled Keropok Lekor 48

4.2 Microbiological Analysis 504.2.1 Total plate Count of chilled Keropok Lekor 504.2.2 Mould and yeast Count of chilled Keropok Lekor 53

4.3 Sensory Analysis 55

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 57

CITED REFERENCES 59APPENDICES 64CURICULUM VITAE 79


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LIST OF TABLES

Tables Page

2.1 The nutrient composition of oily and white fish 5

2.2 Predicted shelf life of fish products stored at different 5temperatures

2.3 Nutrient composition of Shortfin scad fish. 7

2.4 The causes of the various types of spoilage in fish 13

2.5 The recommended limit for bacteria present in a product 15

2.6 Solubility of the BHA and BHT in various solvents 23

2.7 Amount of total phenolic of various Malay herbs 34

3.1 Formulation of Keropok Lekor 41

4.1 Mean sensory attributes scores of chilled Keropok Lekor 57


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LIST OF FIGURES

Figure Page

2.1 Mechanism of Autoxidation 16

2.2 Oxidation process of polyunsaturated fatty acids found in fish 18tissue

2.3 Mechanism of antioxidant 21

2.4 Chemical structure of BHA & BHT 27

2.5 Structure of Phenolic compounds 29

4.1 Peroxide value of chilled Keropok Lekor 46

4.2 Thiobarbituric acid value of chilled Keropok Lekor 49

4.3 Total plate count of chilled Keropok Lekor 51

4.4 Mould and Yeast count of chilled Keropok Lekor 55


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LIST OF ABBREVIATIONS

BB : BHA/BHT

BHA : Butylated hydroxyl anisole

BHT : Butylated hydroxytoluene

CFU/g : Colony forming unit per gram

CFU/ml : Colony forming unit per milliliter

DH : Dry Herbs

FTC : Ferric thiocyanate

PG : Propyl gallate

PV : Peroxide value

SSO : Specific spoilage organisms

TBA : Thiobarbituric acid

TBHQ : Tertiary butyl hydroxyquinone

TMA : Trimethylamine

TMAO : Trimethyl amino oxide

TNTC : Too numerous to count

WH : Wet Herbs


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ABSTRACT

THE EFFECTS OF MALAY HERBS ON THE STORAGE STABILITY OFCHILLED KEROPOK LEKOR

Keropok Lekor is a famous traditional cuisine especially in the East Coast of Malaysia. The primary ingredients are fish, flour, sugar and salt. This study wasconducted on Keropok Lekor to observe the storage stability for 12 days at chilledtemperature (4C) after adding mixed local herbs. The formulation without anyincorporation was used as control. The other formulations were incorporation withdry mix Malay herbs, incorporation with wet mix Malay herbs and another one isincorporation with BHA/BHT as a comparison between synthetic and natural plantantioxidant. Analysis that was carried out is chemical analysis which evaluatedthrough measurement of primary (Peroxide Value) and secondary (ThiobarbituricAcid Value) oxidation products. Microbiological determinations included the TotalPlate Count and Mould and Yeast Count. Sensory evaluation tests were also carriedout. Dry and wet mix herbs of P. hydropiper and C. asiatica resulted in significant(P< 0.05) inhibition of lipid peroxidation as compared to control sample. At initial,the Thiobarbituric Acid Value obtained was not significantly different than toKeropok Lekor that was added with BHA/BHT. Total plate count showed a highcount for all the samples. But, the treated samples were significantly lower (P


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ABSTRAK

KESAN HERBA MELAYU KE ATAS KESTABILAN PENYIMPANAN

KEROPOK LEKOR DALAM KEADAAN DINGIN

Keropok lekor adalah makanan tradisi terkenal di Malaysia terutamanya di pantaitimur. Ramuan utama terdiri daripada ikan selayang, tepung sagu, gula dan garam.Kajian ini telah dijalankan ke atas Keropok Lekor untuk melihat kesan kestabilanpenyimpanan selama 12 hari dalam keadaan dingin (4C) selepas penambahantumbuhan tempatan. Formulasi tanpa sebarang penambahan antipengoksidadigunakan sebagai sampel kawalan. Formulasi yang lain adalah penambahancampuran herba kering, penambahan herba basah dan juga formulasi denganpenambahan BHA/BHT yang digunakan sebagai perbandingan antipengoksidasintetik dangan antipengoksida tumbuhan semulajadi. Analisis yang telah dijalankanialah analisis kimia yang dinilai melaui pengiraan hasil pengoksidaan primer (NilaiPeroksida) dan sekunder (Nilai Asid Tiobarbiturik). Penentuan mikrobiologitermasuk analisa Jumlah Kiraan Plat dan analisa Jumlah Kiraan Yis dan Kulat. Ujianpenilaian sensori juga telah dijalankan. Herba kering dan basah P. hydropiper dan C.asiatica menunjukkan perencatan pengoksidaan lemak yang signifikan berbandingsampel kawalan. Pada mulanya, Nilai Asid Tiobarbiturik menunjukkan tidaperbezaan yang signifikan (P


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CHAPTER 1

INTRODUCTION

1.1 Background and Problem statement

Herbs are used in many domains, including medicine, nutrition flavouring,

beverages, dyeing, repellents, fragrances, cosmetics. Many species have been

recognised to have medicinal properties and beneficial effect on health and

food such as antioxidant activity, digestive stimulation action, anti-

inflammatory, antimicrobial, hypolipedemic, antimutagenic effects and

anticarcinogenic potential (Aneta et al. , 2007). Traditional herbs of the

Malays in Malaysia (locally called ulam) comprise of more than 120

species representing various families, from shrubs to large trees. The leaves,

shoots or rhizomes of the vegetable are eaten fresh as salad or cooked. They

are consumed because of their taste, which adds variety and flavour to the

diet, as well as for health benefit. Nutritional studies have indicated that

many of these vegetables are rich in carbohydrate, proteins, minerals and

vitamins (Faridah et al. , 2006).

Although consumption of fruit and vegetables has increased, it is still lower

than in the Mediterranean countries. Therefore the incorporation of

seasoning based on herbs into everyday meals may be crucial importance.

The benefits resulting from the use of natural product rich in bioactive


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substances has promoted the growing interest of pharmaceutical, food and

cosmetic industries as well as of individual consumer in the quality of herbal

produce (Ewa et al. , 2005). Autoxidation of fats and oils in processed foods

maybe prevented by the use of oxidation inhibitors or antioxidants. Plant

extracts obtained from some fruits and vegetables have been reported to be

effective antioxidants (Vanitha et al. , 2005).

Even though many research works have proven the health benefit of herbs,

the data collection on the Malay herbs which are known as ulam in

Malaysia is still lacking. Furthermore there are no data available on the effect

of incorporating the local ulam on the storage stability of traditional food

such as Keropok Lekor.

Fish are perishable food commodities, so as fish food products. It generally

spoils faster than do other muscle foods (Wenjiao et al ., 2008). Keropok

Lekor is a product made mainly from fish and is easily spoiled during

storage at chilled temperature and normally consumed fresh. Thus it is

important to increase the shelf life of this product. The spoilage is a complex

processes in which physical, chemical and microbiological mechanism are

involved especially the deterioration due to lipid oxidation and

bacteriological activity.

1.2 Significance of study

This study will be carried out to investigate the effect of Malay herbs such as

P. hydropiper (Kesum) and C. asiatica (Pegaga) on the oxidative and the


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antimicrobial stability of Keropok Lekor stored at chilled temperature and

therefore increases the shelf life of the product. The herbs are known to

contain high antioxidative activities. Malays usually consumed local herbs as

salad, but this study will diversify the usage of these local herbs in Keropok

Lekor. If the research is successful, a new product with natural preservatives

will be obtained. This will be an opportunity for the food industry to

commercialise a healthy traditional food in the market.

1.3 Objectives

The intention of this research is to investigate the effect of Malay herbs

namely Polygonum hydropiper (Kesum) and Centella asiatica (pegaga) on

Keropok Lekor.

The objectives of this project are:

1. To compare the oxidative and antimicrobial stability of Keropok Lekor

incorporated with dry herbal mix ( P. hydropiper and C. asiatica ), wet

herbal mix ( P. hydropiper and C. asiatica ) and synthetic antioxidant

BHA/BHT.

2. To determine the shelf life of the Keropok Lekor incorporated with

local herbs.

3. To investigate the acceptability of this product by the consumer.


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CHAPTER 2

LITERATURE REVIEW

2.1 Fish

Fish are perhaps one of the most vulnerable of the world resources. For many

economically developing nations, fish are the first or second largest export

commodity. Since the freshness of fish deteriorates rapidly, freshness may be

considered a synonym for quality. The increasing demand of high quality

fresh seafood has intensified the search for methods and technologies for

better fresh fish utilization (Manju et al. , 2007), and also fish product

utilisation.

Fish provides a good source of high quality protein and contains many

vitamins and minerals. It may be classed as either white (lean), oily (fatty) or

shellfish. White fish, such as haddock and seer, contain very little fat (usually

less than 1%) whereas oily fish, such as sardines, contain between 10-25%.

The latter, as a result of its high fat content, contain a range of fat-soluble

vitamins (A, D, E and K) and essential fatty acids, all of which are vital for

the healthy functioning of the body. The composition of fish is influenced by

feeding, locality, size, age, season and species. Certain processing techniques

such as boiling leach the water-soluble vitamins into the surrounding liquid.

If this is thrown away, a great deal of nutritional value is lost (Fellows and


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Hampton, 1992). Table 2.1 shows the nutrient composition some of the main

nutritional differences between oily and white fish.

Table 2.1 The nutrient composition of oily and white fish

Composition White fish e.g. haddock Oily fish e.g. herringEnergy (KJ) 321 970Protein (g) 17 17

Fat(g) 07 18Water (g) 82 64

Calcium (mg) 16 33Iron (mg) 0.3 08

Vitamin A (mg) 0 45Thiamine (mg) 0.07 0

Source: Fellows and Hampton (1992).

Fish is one of the most highly perishable food products. During handling and

storage, quality deterioration of fresh fish rapidly occurs and limits the shelf

life of the product. Shelf life is defined as the period of time, under defined

condition of storage, for which food products remains safe and fit for use. In

other words, during this period, it should retain its desired sensory, chemical,

physical, functional or microbiological characteristic (Khalid, 2007). Table

2.2 shows the shelf life of fish products stored at different temperature.

Table 2.2 Predicted shelf life of fish products stored at differenttemperatures

Shelf life in days of product stored in ice

(0C)

Shelf life at chill temperatures (days) 5C 10C 15C

6 2.7 1.5 110 4.4 2.5 1.614 6.2 3.5 2.218 8 4.5 2.9

Source: Huss (1995).


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2.1.1 Fish Muscle

There are three types of muscles: striated muscles which constitute the

livestock meat or fish meat, smooth muscles which constitute mollusks or

visceras, and the heart muscle which is more or less an intermediate structure

between the other two. Livestock meat and fish meat are basically striated

muscles which are formed by group of muscle fibers with striation. Fish

muscle can be divided into ordinary muscle (white meat) and dark muscle

(dark meat).

Dark muscle lies along the side of the body under the skin. The shape and

volume of the dark muscle can be classified in three types according to the

fish species (Suzuki, 1981). There are many differences in the chemical

composition of the two muscle types, some of the more noteworthy being

higher levels of lipids and myoglobin in the dark muscle. From a

technological point of view, the high lipid content of dark muscle is

important because of problems with rancidity (Huss, 1995).

The muscle fiber lies parallel to one another within myotome, divided by the

membrane consisting of the mycommata. The myotome of the back and belly

are arranged in concentric circles. Muscle fiber, smaller unit of muscle, are

bound together by connective tissue (endomysium) and covered with

mycommata. Muscle fiber consists of many myofibril which lie parallel, and

sarcoplasm which fills the space. There is more connective tissue around the

muscle fibers in dark muscle than in ordinary muscle meat (Suzuki, 1981).


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2.1.2 Shortfin Scad Fish

Scad belong to the family Carangidae. They resemble mackerel in flavor, but

a little milder and without so much oil. Shortfin Scad or Round Scad

( Decapterus macrosoma) is an Indo-Pacific scad and is also found in the

East Pacific from the coast of Baja California to Northern Peru. They can

grow to over 14 inches, but the ones popular are about 6-1/2 inches and

weigh 2 ounces (http://www.mexfish.com). In Malaysia, Shortfin scad is

known as Selayang, Curut, Sardin or Basung (Ismail et al., 2004).

This fish is excellent for frying whole. It has a strong enough flavor to be

interesting hot or cold and, while the head and spine are too hard to eat, it has

no bone or fin problems otherwise. Table 2.3 shows the nutrient composition

of Shortfin scad fish.

Table 2.3 Nutrient composition of Shortfin scad fish

Type Weight

(g)

Nutrient composition

En

(Kcal)

Water

(g)

Protein

(g)

Fat

(g)

CHO

(g)

Fiber

(g)

Ash

(g)

1 piece,

tail

portion

48 43 28.6 8.5 0.9 0.0 0.0 0.6

1 whole,

small

81 41 27.7 8.3 0.9 0.0 0.0 0.6

1 whole

medium

105 54 36.2 10.8 1.2 0.0 0.0 0.7

Source: Tee, et al . (1997).


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2.1.2.1 Keropok Lekor

Keropok lekor is a popular traditional Malay snack food in the East Coast

Malaysia which has a resemblance to a sausage in appearance. They are

marketed in variable sizes such as those with a diameter of 4.0-6.0 cm and

1.5 2.0 cm. The bigger size Keropok Lekor are normally sliced to a

thickness of 1.0 1.5 cm or to a thickness of 2.0 2.5 mm prior to deep

frying. The smaller ones are normally slit and fried whole. The main

characteristics of fried Keropok Lekor are the crunchiness on the surface

and chewiness in the inner part of the product.

The two essential ingredients in Keropok Lekor making are starch and fish.

Fish such as Ikan Parang ( Chirocentrus dorab ), Ikan Tamban beluru

(Clupea leiogaster ) and Ikan Selayang ( Decapterus macrosoma ) are

preferred although other fishes are also used for making Keropok Lekor.

Tapioca or sago starch is used but sago starch is said to give the best product

in terms of texture and flavour (Muhammad Redza, 2004). Every food

products final profile will be established by the ingredients and processing

(Modi et al. , 2006).

This food product can be eaten as soon as it is boiled and together with chili

sauce. Keropok Lekor usually has a short shelf life. When stored in the

fridge especially at chilled temperature the Keropok Lekor does not last

long. After a few days, it will have a slimy layer and people usually just

wash the slimy layer and add a bit of salt then boiled and then fry it. As it is

known the slimy layer is due to bacteriological deterioration.


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2.1.3 Chilled fish

The appearance of fish stored under chilled condition without ice does not

change as much as for iced fish, but the fish spoil more rapidly and an

evaluation of cooked flavour will be necessary. Temperature for chilling is

usually between 0-25C. It is well known that both enzymatic and

microbiological activities are greatly influenced by temperature. However, in

the temperature range from 0 to 25C, microbiological activity is relatively

more important, and temperature changes have greater impact on

microbiological growth than on enzymatic activity. Many bacteria are unable

to grow at temperatures below 10C and even psychrotrophic organisms

grow very slowly, and sometimes with extended lag phases, when

temperatures approach 0C.

Several studies have been carried out on the quality changes of ready-made

seafood products. One of them was performed by Akkus et al. (2004) on fish

balls that were preapared using boiled and raw anchovy. These authors

discovered that the shelf-life of the fish balls was 9 days at 41C. G koglu

(1994) used sensory, physical, chemical and, and microbiological analysis to

study fish balls made from mackerel that were prepared using boiling (pre-

cooking) method and stored at a refrigerated temperature. In this study, a

shelf-life of up to 8 days and spoilage after 10 days were reported for fish

balls stored under refrigerated temperature.

The microflora responsible for spoilage of fresh fish changes with changes in

storage temperature. At low temperatures (0-5C), Shewanella putrefaciens,


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Photobacterium phosphoreum, Aeromonas spp. and Pseudomonas spp . cause

spoilage. However, at high storage temperatures (15-30C) different species

of Vibrionaceae, Enterobacteriaceae and Gram-positive organisms are

responsible for spoilage. For tropical fish, however, the average relative rate

of spoilage of a large number of species stored at 20-30C was

approximately 25 times higher than at 0C (Huss, 1995).

Minced fish is commonly used for product of surimi-based or traditional,

ready-to-eat, pre-cooked products such as fish balls or burger patties. Three

types of fish mince from whiting ( Merlangius euxinus ) which is plain mince

commonly used in Turkey for producing fish balls and requires no washing

steps, surimi commonly used for making ready-made products and the type

produced from boiled fish which is used in household preparation of fish

balls. All mince was stored under refrigerated conditions (at 41 C) for 15

days. Increasing amounts of TVB-N, TMA-N and TBA were found in all

types of mince with increasing storage time. The results of measured

chemical parameter, plain mince retained its consumable properties up to 11

days of storage; surimi was acceptable for consuming up to 13 days of

storage. Pre-cooked product was still consumable up to the end storage time.

However, sensory attributes showed only 7 days of storage life for all types

of products (Sevim et al ., 2006).

If quality criteria of chilled fish during storing are needed, sensory assessment

of the cooked fish can be conducted. A characteristic pattern of the

deterioration of fish stored in ice can be found and divided into the following


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four phases, in phase 1 the fish is very fresh and has a sweet, seaweedy and

delicate taste. The taste can be very slightly metallic. In cod, haddock,

whiting and flounder, the sweet taste is maximized 2-3 days after catching.

For phase 2 there is a loss of the characteristic odour and taste. The flesh

becomes neutral but has no off-flavour. The texture is still pleasant. As for

phase 3 there is sign of spoilage and a range of volatile, unpleasant-smelling

substances is produced depending on the fish species and type of spoilage

(aerobic, anaerobic). One of the volatile compounds may be trimethylamine

(TMA) derived from the bacterial reduction of trimethyl-aminoxide (TMAO).

TMA has a very characteristic "fishy" smell. At the beginning of the phase

the off-flavour may be slightly sour, fruity and slightly bitter, especially in

fatty fish. During the later stages sickly sweet, cabbage-like, ammonia,

sulphurous and rancid smells develop. The texture becomes either soft and

watery or tough and dry. And at phase 4 the fish can be characterized as

spoiled and putrid (Huss, 1995).

2.2 Spoilage in Fish

Fish is an extremely perishable food. For example, most fish become inedible

within twelve hours at tropical temperatures. Spoilage begins as soon as the

fish dies, and processing should therefore be done quickly to prevent the

growth of spoilage bacteria. Fish is a low acid food and is therefore very

susceptible to the growth of food poisoning bacteria. This is another reason

why it should be processed quickly. Some methods of preservation cause

changes to the flavour and texture of the fish which result in a range of

different products. These include cooking (for example, boiling or frying),


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lowering the moisture content (by salting, smoking and drying collectively

known as curing), lowering the pH (by fermentation) and lowering the

temperature with the use of ice or refrigeration also preserves the fish, but

causes no noticeable changes to the texture and flavour (Fellows and

Hampton, 1992).

Fish are perishable food commodities, which generally spoil faster than do

other muscle foods. Deterioration of fish mainly occurs as a result of

bacteriological activity leading to loss of quality and subsequent spoilage.

The spoilage of fish is a complex process in which physical, chemical and

microbiological mechanisms are implicated (Wenjiao et al. , 2008). Fish tissue

is characterized in being rich in protein and non-protein nitrogen (e.g. amino

acids, trimethylamine-oxide (TMAO), creatinine, but low in carbohydrate

resulting in a high post mortem pH


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faster particularly in fatty and semi-fatty species like horse mackerel, in

whose muscle has large amount of hemoglobin a well known activator of

lipid oxidation and lipid coexist (Snchez-Alonso et al. , 2008). Table 2.4

shows the causes of the various types of spoilage.

Table 2.4 The causes of the various types of spoilage in fish

Signs of spoilage

Causes of fish spoilage

Microbiological Chemical

(oxidation)

Autolytic Physical

Off odours/ off flavours+ + + -

Slime formation + - - -

Gas formation + - - -

Discolouration + + + +

Change of texture + - + +

Source: Huss (1995).

2.2.1 Microbiological spoilage

Initial loss of quality of fresh lean or fatty fish species, chilled or not chilled,

is caused by autolytic changes, while spoilage is mainly due to the action of

bacteria. During storage a characteristic flora develops, but only a part of this

flora contribute to spoilage. The specific spoilage organisms (SSO) are

producers of the metabolites responsible for the off odours and off flavours

associated with spoilage.

Shewanella putrefaciens is typical for the aerobic chill spoilage of many fish

from temperate waters and produces trimethylamine (TMA), hydrogen

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The Effect of Malay Herbs on the Storage Stability of Chilled Keropok Lekor