Study on the application of liquid ice for handling and preservation of yellowfin tuna

MINISTRY OF EDUCATION AND TRAINING
NHA TRANG UNIVERSITY

OLANREWAJU AKIN YINKA

STUDY ON THE APPLICATION OF LIQUID ICE FOR
HANDLING AND PRESERVATION OF YELLOWFIN TUNA

MASTER THESIS

KHANH HOA - 2020


MINISTRY OF EDUCATION AND TRAINING
NHA TRANG UNIVERSITY

OLANREWAJU AKIN YINKA

STUDY ON THE APPLICATION OF LIQUID ICE FOR
HANDLING AND PRESERVATION OF YELLOWFIN TUNA
MASTER THESIS

Major:

Food Technology

Code:

8540101

Topic allocation Decision

192/QĐ-ĐHNT dated 03/3/2020

Decision on establishing the Committee:

899/QĐ-ĐHNT dated 04/9/2020

Defense date:

18/9/2020

Supervisors:

Dr. Mai Thị Tuyết Nga

Chairman:

Assoc. Prof. Nguyen Thuan Anh

Department of Graduate Studies:

KHANH HOA - 2020

ii


UNDERTAKING
I undertake that the thesis entitled: “Study on the application of liquid ice for

handling and preservation of yellowfin tuna” is my own work.

The data collection was an effort of a research team led by my supervisor, Dr. Mai
Thi Tuyet Nga, who started the project KC.05.10/16-20 of Vietnam “Studying,
designing, and manufacturing a liquid ice production system for handling and
preservation of ocean tuna” since April 2018 before I began my MSc study in
Vietnam. I joint the project since January 2020, when the final phase of the project
studying on slurry ice and crushed block ice was going on, and luckily allowed to use
the data previously collected by my teammates.
The work has not been presented elsewhere for assessment until the time this thesis
is submitted.
Khanh Hoa, date 25 month 08 year 2020
Author

Olanrewaju Akin Yinka

iii


ACKNOWLEDGMENTS
First and for most, my sincere appreciation goes to God for granting me such a great
opportunity to be alive and healthy to complete this program. I specially honor the
Lord Jesus and the Holy Spirit for the deep inspiration, supernatural strength, and
great opportunity made available to be awarded a scholarship in Vietnam.
Secondly, I really want to appreciate my supervisor and promoter in the person of Dr.
Mai Tuyet Nga for her unrelenting supports and great contributions towards the
success of this research study. I acknowledge the support of the HOD, secretary of
the program and other staff in the department.
Thirdly, I would like to express the deepest appreciation to my good friend for his
immense contribution towards the success of my thesis. My good colleagues, you are
well appreciated for your love and kindness. Especially, I appreciate my family and
friends in the diaspora for your love, prayers, and support.

I would like to appreciate the support of the VLIR Network Vietnam, Nha Trang
University, Food Technology Department for the success of this research study. Food
Technology Laboratories at Nha Trang University for allowing me to carry out this
research study with their up-to-date equipment.
Last but not least, I would like to thank project KC.05.10/16-20 of Vietnam
“Studying, designing, and manufacturing a liquid ice production system for handling
and preservation of ocean tuna” for financial support and permission to use its data
for my MSc. thesis.

iv


ABSTRACT
Yellowfin tuna (Thunnus albacares) is a big species of tuna mostly found in Atlantic,
Pacific and Indian oceans. It is an important aspect of tuna fisheries worldwide and
in the major oceans, yellowfin tuna is one of the major target species for the tuna
fishery and the most commonly catch marine fish on overseas fishery. The major
objective of this study was to evaluate the suitable handling and preservation methods
that could be used for port-harvested Yellowfin tuna. Among the studied cooling and
storage media, the liquid ice of 3.5% NaCl, 48% ice content, initial temperature of 4.0°C showed the best preservation effect for yellowfin tuna sensory quality. The
second most effective medium was the liquid ice of 3.0% NaCl, 44% ice content,
initial temperature of -3.1°C. Fish chilled down either in slurry ice of initial
temperature of -4.0°C or in crushed ice, and then stored in crushed ice had the second
worst and the worst sensory quality, respectively, indicating the weakness of
traditional icing. However, no cooling or storage media effect, as well as no size
influence on TVC of tuna samples has been found so far. These results vividly
showed that liquid/slurry ice has a large scope of preservation effect and has the
potential to improve significantly the quality and as well as extends the product shelf
life. Further study on on-board cooling and salt uptake of fish stored for long period
in liquid ice is needed.

v


TABLE OF CONTENTS

UNDERTAKING ...................................................................................................... iii
ACKNOWLEDGMENTS ......................................................................................... iv
ABSTRACT ............................................................................................................... v
TABLE OF CONTENTS ........................................................................................... 1
LIST OF ABBREVIATIONS .................................................................................... 3
LIST OF FIGURES .................................................................................................... 4
LIST OF TABLES ..................................................................................................... 5
CHAPTER 1.
INTRODUCTION ........................................................................ 6
1.1. INTRODUCTION ....................................................................................... 6
1.2. MAIN OBJECTIVE .................................................................................... 9
1.3. SPECIFIC OBJECTIVES............................................................................ 9
1.4. PROBLEM STATEMENTS ....................................................................... 9
CHAPTER 2.
LITERAURE REVIEW .............................................................. 11
2.1. YELLOWFIN TUNA .................................................................................... 11
2.1.1.
Production .......................................................................................... 11
2.1.2. Habitat of Yellowfin Tuna ....................................................................... 12
2.1.3 Size, age, and growth ................................................................................ 12
1.3.4. Reproduction ........................................................................................... 13
2.2. POST-MORTEM QUALITY CHANGES OF FISH-RELEVANT FACTORS
AND VARIABLES............................................................................................... 14
2.2.1. Autolytic changes .................................................................................... 14

2.2.2. Chemical spoilage.................................................................................... 14
2.2.3. Microbiological spoilage ......................................................................... 15
2.3. HANDLING AND PRESERVATION OF FISH .......................................... 16
2.4. REFRIGERATED METHODS OF SEAFOOD PRESERVATION ............. 18
2.4.1. Icing and iced storage of fish ................................................................... 21
2.4.2. Pre-cooling and cooling by slurry ice ...................................................... 22
2.5. EVALUATION OF FRESHNESS AND QUALITY CHANGES OF FISH 24
2.5.1. Sensory analysis ...................................................................................... 25
2.5.2. Microbiological analysis.......................................................................... 27
CHAPTER 3.
MATERIALS AND METHODS ................................................ 28
3.1. MATERIALS ................................................................................................. 28
3.2 APPARATUS AND TOOLS ......................................................................... 28
3.3. METHODS .................................................................................................... 29
3.3.1. Experimental plan .................................................................................... 29
3.3.2. Experimental factors ................................................................................ 30
3.3.3. Sampling .................................................................................................. 30
3.3.4. Determination of sensory quality ............................................................ 32
3.3.5. Determination of total viable count ......................................................... 33
3.4. DATA COLLECTION AND ANALYSIS .................................................... 34
1


CHAPTER 4.
RESULTS AND DISCUSSION ................................................. 35
4.1. CHANGES OF TVC IN TUNA DURING STORAGE OF FISH................. 35
4.1.1. Changes of TVC in tuna cooled and stored in liquid ice over time ......... 35
4.1.2. Changes of TVC in tuna cooled in ice slurry and stored in crushed block
ice....................................................................................................................... 40
4.1.3. Changes of TVC in tuna cooled and stored in crushed block ice ............ 41

4.2. SENSORY CHANGES OF TUNA DURING STORAGE ........................... 43
4.2.1. Sensory changes of tuna cooled and stored in liquid ice over time ......... 43
4.2.2. Sensory changes of tuna cooled in ice slurry and stored in crushed block
ice....................................................................................................................... 47
4.2.3. Sensory changes of tuna cooled and stored in crushed block ice ............ 48
4.2.4. Comparison of sensory quality of yellowfin tuna cooled and stored in
different media ................................................................................................... 49
CONCLUSIONS AND RECOMMENDATIONS ................................................... 58
CONCLUSIONS ................................................................................................... 58
RECOMMENDATIONS ...................................................................................... 58
REFERENCES ......................................................................................................... 59
APPENDICES ....................................................................................................... - 1 -

2


LIST OF ABBREVIATIONS
°C

–

Degree Celsius

CFU -

Colony forming unit

F

-

Fish

g

-

Gram

Kg

–

Kilogram

NaCl -

Sodium Chloride

TVC -

Total viable count

3


LIST OF FIGURES
Figure 3. 1. Experimental flowchart ......................................................................... 29
Figure 3. 1. Yellowfin tuna....................................................................................... 31
Figure 3. 2. Sampling tool ........................................................................................ 31

Figure 3. 3. Procedures of TVC determination ........................................................ 33
Figure 4. 1. Changes of TVC of Fish 2 (30 kg up) during storage in liquid ice of 3.0%
of NaCl, 44% initial ice concentration, and initial temperature of -3.1°C ............... 35
Figure 4. 2. Changes of TVC in Fish 3 (20 kg up) during storage in liquid ice of 3.5%
of NaCl, 48% initial ice concentration, and initial temperature of -4.0 °C .............. 37
Figure 4. 3. Changes of TVC in Fish 4 (30 kg up) during storage in liquid ice of 3.5%
of NaCl, 48% initial ice concentration, and initial temperature of -4.0°C ............... 38
Figure 4. 4. Changes of TVC in Fish 5 (40 kg up) during storage in liquid ice of 3.5%
NaCl, 48% initial ice concentration, and initial temperature of -4.0°C ................... 39
Figure 4. 5. Changes of TVC in Fish 8 (30 kg up) cooled in ice slurry with an initial
temperature of -4.0°C and stored in crushed block ice ............................................ 40
Figure 4. 6. Sensory changes of Fish 2 (30 kg up) stored in liquid ice of 3.0% NaCl,
44% initial ice mass, and initial temperature of -3.1°C............................................ 43
Figure 4. 7. Sensory changes of Fish 8 (30 kg up) cooled in ice slurry with an initial
temperature of -4.0°C and stored in crushed block ice ............................................ 47
Figure 4. 8. Comparison of the sensory quality of all the fish at day 0 .................... 49
Figure 4. 9. Comparison of the sensory quality of all the fish at day 3 .................... 50
Figure 4. 10. Comparison of the sensory quality of all the fish at day 6 .................. 51
Figure 4. 11. Comparison of the sensory quality of all the fish at day 9.................. 51
Figure 4. 12. Comparison of the sensory quality of all the fish at day 12................ 52
Figure 4. 13. Comparison of the sensory quality of all the fish at day 15................ 53
Figure 4. 14. Comparison of the sensory quality of all the fish at day 18................ 54
Figure 4. 15. Comparison of the sensory quality of all the fish at day 21................ 54
Figure 4. 16. Comparison of the sensory quality of all the fish at day 24 ................ 55
Figure 4. 17. Comparison of the sensory quality of all the fish at day 27 ................ 56
Figure 4. 18. Comparison of the sensory quality of all the fish at day 30 ................ 56

4

LIST OF TABLES
Table 3. 1. Studied parameters of liquid ice ............................................................. 30
Table 3. 2. Cooling and storage media for tuna ....................................................... 30
Table 3. 3. Control sensory sheet 1 .......................................................................... 32
Table 4. 1. Changes of TVC in Fish 6 (40 kg up) cooled and stored in crushed block
ice ............................................................................................................................. 41
Table 4. 2. Changes of TVC in Fish 7 (30 kg up) cooled and stored in crushed block
ice ............................................................................................................................. 42
Table 4. 3. Sensory scores of Fish 3 (20 kg up) cooled and stored in liquid ice of 3.5%
NaCl, 48% initial ice concentration, and initial temperature of -4.0°C ................... 45
Table 4. 4. Sensory scores of Fish 6 (40 kg up) and Fish 7 (30 kg up) cooled and
stored in crushed block ice ....................................................................................... 48

5


CHAPTER 1. INTRODUCTION
1.1.

INTRODUCTION

Yellowfin tuna (Thunnus Albacares) part of the member of family Scombridae and
falls among the pelagic large size marine fish (Jinadasa, Galhena and Liyanage,
2015). Yellowfin tuna is a big species of tuna mostly found in Atlantic, Pacific and
Indian oceans. It is one of the specific focus species for the tuna fishing system and
the most commonly caught marine fish on overseas fishery. Yellowfin Tuna can be
seen all over the environment that is warm-temperate and major occupied with
tropical waters of all oceans staying in the environment with the temperatures
between 15oC and 31oC (Nsw, 2000).
The principal components of Yellowfin Tuna are fat, water, vitamin, minerals and

protein compounds. The protein constituents of Yellowfin Tuna is within 15- 20%
but there is variation as per the time period (Jinadasa, Galhena and Liyanage, 2015).
The spoilage processes of fish is a difficult process which existed because of the
actions of enzymes, microorganisms and chemical components (Nwaigwe, 2017).
Yellowfin Tuna is a rapidly growing fish with females reaching 5 kg after one year
and becomes matured after about 2 years at 25 kg. Yellow fin Tuna mostly feeds on
small fish, crustaceans and squids ((Nsw, 2000). According to Food Agricultural
Organizations, it reported that the post-harvest losses getting to 35%. In most of the
developing countries, fish quality and their outcomes are the most imperative concern
in the industries where fish and fish materials are produced. The losses are said to be
higher in the countries where they consume lower protein. Most of the fishermen have
realized the benefit of high standard products in view of getting good outcome of the
catch. When there are physical damages to the body of the Yellowfin Tuna, it results
to spoilage, reduce the quality and shelf life (Razak and Hassan, 2002). Yellow tuna
is commonly used in the preparation of raw cuisine such as sashimi and sushi
(Nurilmala et al., 2013).

6


Ice slurry has been seen to be a promising medium for preserving aquatic products.
Slurry ice has high benefits on local freshwater ice (block ice) and it brings down the
temperature very quickly, has faster chilling rate and causes almost no physical
damage to the fish. Slurry ice also slows down the rate of microbial development and
gives longer shelf life for many species. It was recorded that the slurry ice has
preventive effects over the multiplication of microbial loads when it is utilized for
the preservation of some species on-board storage (Zhang, 2017). Deterioration of
fish begins immediately after they die and as the degradation rate is mostly rely on
the temperature, the quicker the fish can be cooled the better. This is one of the
reasons why the fish quality is prevented for enough time when there is sufficient ice

quantity and it is distributed accordingly. Slurry ice is especially efficient for cooling
large pieces (Ronsivalli and Baker, 1981). The smaller the ice particles, the greater
the interaction between fish and ice, it has positive effect on the rate of heat removal
(Ronsivalli and Baker, 1981).
The proper handling of fish plays high role in the extension of storage life and fish
quality after catch. Any delay in fish cooling after its catch under the environmental
temperatures of 15-20oC will bring down the seafood storage life for quite a number
of days (Razak and Hassan, 2002). Some tools are required for proper handling of
fish and these include gaffs, tuna missile, fish bat or club, spike, knives, nylon
brushes, meat hook, gloves, mutton cloth or plastic body bags, ice shovel and all these
tools should be kept clean to prevent cross contamination to the fish. One of the such
good handling practices is to ensure that captured live fish are not permitted to fight
and die of asphyxia oxygen starvation (Tawari and Abowei, 2011). There are so many
factors responsible for the spoilage of fish and these includes microbiological,
enzymatic, oxidative and hydrolytic (‘Recent Developments in Fish Processing,
1953). Microorganism contamination of fresh fish is the most causative agents of fish
storage. When fish is kept under low temperature, growth of bacteria and as well as
spoilage is minimized (Tawari and Abowei, 2011). Inappropriate handling practices
and insufficient infrastructure facilities have immediate impact on the quality of
yellowfin tuna which can result in major post-harvest losses.
7


The two most common problems when it comes to selling and marketing of seafood
are their openness to deterioration and unhealthy cleaning quality. The major
objective of fish preservation is to inhibit microbial, chemical and enzymatic spoilage
and which is only possible by controlling the storage temperature, sustaining
appropriate pH, aW or through the use of preservatives. Temperature plays a main role
in fish spoilage which have major control on microbial growth and the autolytic
degradation (Co, Cn and Tk, 2016).

Preservation of fish is necessary in order to get the fish to an end user in good and
usable conditions. The necessary steps to accomplish this starts immediately before
the fishing expedition starts and do not stop until fish is eaten or processed into any
other form (Nwaigwe, 2017). When fish is stored at the temperature that is low, it can
extend its storage life and improves the quality as a result of reducing the chemical
and microbiological processes. The higher the temperature during storage, the shorter
the shelf life of fish and also affects the quality of the fish (Agustini, 2002). Freshness
quality of fish is said to be a great important factor on the overall quality of a
particular fish product. This quality included appearance, flavour, odour, skin colour
and texture of each fish product, is knowingly and unknowingly determined by every
consumer. If the fisheries item comes across the expectation of the buyer in respect
to freshness quality, it will be more likely to be purchased.
Fish that is not properly taken care of might not be noticeably bad, but it loses its
quality because of off-flavours, soft texture, or discoloration that discourage a
potential buyer from buying (Nwaigwe, 2017). The major causes of fish spoilage are
microorganism contaminations, such as bacteria, fungi, virus etc., and their growth.
It is generally stated that if fish are kept clean at low temperature, then development
of bacteria, consequently spoilage is kept at minimum (Tawari and Abowei, 2011).
Therefore, the aim of this study is to show the difference and the effect of ice slurry
and block ice on the sensory, microbiological and chemical parameters of yellowfin
tuna possessing unique attention applied to the quality deteriorations in the fish during
the chilled preservation.
8


1.2.

MAIN OBJECTIVE

To evaluate the suitable handling and preservation method that can be used for portharvested Yellowfin Tuna.

1.3.

SPECIFIC OBJECTIVES

1. To monitor and compare the sensory changes during storage of yellowfin tuna
cooled and stored by various media, namely liquid ice of different salt and
initial ice concentration, mixture of ice and salted water, crushed block ice or
combinations of those.
2. To monitor and compare the total viable counts (TVC) changes during storage
of yellowfin tuna cooled and stored by the above mentioned media.
3. To find out the suitable medium/media for post-harvested yellowfin tuna
handling and preservation.
1.4.

PROBLEM STATEMENTS

One of the most challenging demands faced by the fish industry is to maintain the
quality and improve the yield of the fish products. It is generally known that tuna has
been regarded as a palatable and valuable fish species and its freshness has become
the concern of many researchers.
Block and flake do not have direct contact with the flesh of the fish thereby limiting
the quality of the yellowfin tuna. Most of these forms of ices require a certain degree
of manual operation for transportation from one place to another, as there is an
additional income procurement which in turn affects the outcome of the final product.
The block ice possess rather sharp edges that damages a product’s surface when used
for direct contact chilling, when the sharp edges pierce through to the flesh of the
fish, this tends to open up the flesh of the fish muscle providing medium for quick
deterioration in the quality of the fish muscle by chemical, biological and
microorganism activities.
9

The crushed block ice is quite coarse and have poor heat transfer performance when
releasing their latent heat of fusion which is responsible for slow and poor distribution
of heat transfer performance and results in poor quality of the final seafood product.
The use of an ice slurry is guaranteed to maximize the surface area available for
cooling, and this will drop the core temperature of fish much faster than almost any
other media and this gives it good cooling system.

10


CHAPTER 2. LITERAURE REVIEW
2.1. YELLOWFIN TUNA
2.1.1. Production
Yellowfin tuna (Thunnus albacares) is important in tropical and subtropical season.
Near-surface schooling yellowfin tuna are mainly caught by purse seines and by poleand-line fishing, than trolling and gillnetting (Science, 2010). The most popular
fishing method for deep swimming yellowfin tuna is long lining. The total catch of
this species in 1999 was reported to be 1,258,386 t, of which Indonesia 176,320 t and
Mexico 121,884 t (Science, 2010).
Vietnam, with a long coastline of over 3,260 km, 226,000 km2 of the inland water is
about 226,000 km2, and above 1 million km2 of the Exclusive Economic Zone (EEZ),
has significant potential for seafood exploitation. Yellowfin tuna poses a mild, meaty
flavor and it can be called swordfish. Yellowfin tuna is leaner compared to Bluefin.
Fish has contributed around 50% of the total protein source for human beings
(Vietnam, 2020). Yellowfin tuna was recorded as the second dominant component of
coastal based tuna fishery and they formed about 24.5% of the overall tuna catch in
coastal fishery with an average annual production of 27,277 t during the year 20062010 (Ghosh, 2012). When the fish meat is in its raw form, it possesses bright red but
when it is cooked, it changes from brown to grayish-tan, firm and moist skin with big
flakes. There are important yellowfin tuna fisheries throughout tropical and

subtropical seas (FAO, 2010). A number of researchers have seen vertical movements
and environmental preferences with the aid of acoustic and satellite telemetry and
also archival data loggers. One of the major limitation of yellowfin tuna and all fishes
is the oxygen concentration though there is a large level of differences which occurs
for endurance to hypoxic conditions (Weng, Stokesbury and Boustany, 2018).
Vietnamese tuna fisheries, occurring mainly in Binh Dinh, Phu Yen and Khanh Hoa
provinces, use four main fishing gears, which are longline, purse seine, hand line and
11


gillnet. There were 714 and 1,678 long line fishing vessels in 2011 and 2012
respectively.
2.1.2. Habitat of Yellowfin Tuna
Yellowfin tuna (Thunnus albacares) are found mostly on the surface layer of all warm
seas of the world apart in the Mediterranean Sea. The gear types determine the
varieties of fish sizes. Most of the long liners delivers majorly fish > 100 cm, while
purse seiners (and pole-and-line boats) focus both small (40- 60 cm) and large fish
(Lehodey and Leroy, 1999).
Thermal structure of the water column affects the vertical water column distribution
of the, as is revealed by the high correlation between the susceptibility of the fish to
purse seine capture, the mixed layer depth, and the strong point of the thermocline
temperature gradient. Yellowfin tuna live mainly at the upper 100 m of the water
column with noticeable oxyclines (Science, 2010).
2.1.3 Size, age, and growth
Yellowfin tuna can reach a dimension of 280 cm long with the highest weight of 400
kg. 176.4 kg as reported by the International Game Fish Association (IGFA). This
fish species is popular in warm waters all over the Pacific and the Atlantic.
Yellowfin spawning seems to be Pacific-wide and confined in its northern and
southern extremes by the 26°C surface isotherm. While the incidence of larvae is
unceasing transversely the equatorial Pacific inside a zone nearly 10° north and south

of the equator, three areas of higher larval density have been uncertainly documented:
180-160°W, east of 110°W and 130-170°E. The occurrence of spawning in yellowfin
tuna is seen all year round, possibly with a peak in the November–April period. Some
records also recommend diverse spawning times for areas east (March–September)
and west (November–April) of 180°. The smallest female yellowfin tuna found in the
eastern pacific with mature ovaries was 84 cm, and the projected length at 50-percent
development was 95 cm. A few yellowfin tuna in the central equatorial Pacific mostly
12


reaches maturity at around 70-80 cm. According to the recent data recorded by the
University of Hawaii shows that the majority of yellowfin tuna do not mature until
they get to 100-110 cm. Nevertheless, the food supply plays important roles in
determining the time needed to reach spawning state (Lehodey and Leroy, 1999). The
optimum fork size is over 200 cm, common fork size is 150 cm. The smallest mature
fish were found within the size group from 50 to 60 cm fork length at an age of
roughly 12 to 15 months in Philippines and Central America, but within 70 and 100
cm fork length indicates that the percentage of mature individuals is much higher. All
fish reaches sexual maturity when they gets to the length over 120 cm (Science,
2010).
1.3.4. Reproduction
Yellowfin tuna sizes vary by regions, especially at the maturity stage, and differences
could also be observed between individuals seen near- and offshore. When yellowfin
reaches the state of maturity by the time they become 120 cm long at the age of about
2-3 years. However, some cases are seen where fish become mature at the size of 50
to 60 cm in fork length at an age of about 12 to 15 months. The percentage of the sex
is nearly 1:1 in immature fish and in grownup up to 140 cm. This fish shows full
sexual maturity from 50 cm upward and as well as pawn at a much smaller size at an
age of almost one year, especially in Indian waters (Ghosh, 2012).
Yellowfin tuna reproduces all year round, but it happens mostly during the summer

in each hemisphere. In the tropical water of Mexico and Central America, it has been
resolute that yellowfin spawn at minimum of two times in a year. Record shows that
the minimum temperature for yellowfin tuna fish spawning is 26oC and each female
lays multiple million eggs per year.

13


2.2.

POST-MORTEM

QUALITY

CHANGES

OF

FISH-RELEVANT

FACTORS AND VARIABLES
2.2.1. Autolytic changes
The inherent enzymes in fish remain active after the fish death and they are
responsible for self-digestion, particularly in small size fatty fish. The level of selfdigestion by enzymes can be influenced by temperature, the seasons of the year as
well as species. The enzymes actions and further relations do not instantaneously stop
in the muscle of fish muscle as at when they are dead. Self-digestion weakens the
belly wall (Mayer and Wolf, 2015).
Rough handling coupled with autolysis can cause the bursting of the belly which is
rely mostly on the storage temperature and time. Nucleotide catabolites from
autolytic changes could be responsible for fish spoilage. The major autolytic method

in the fish muscles involves carbohydrates and nucleotides. Subsequently, the process
of rigor mortis sets in, it serves as a basis for advance autolytic deterioration. The
belly of some fish (e.g. herring, capelin, sprats and mackerel) during the period of
heavy feeding is very vulnerable to tissue dilapidation and may rupture inside some
hours after the catch (Mayer and Wolf, 2015).
2.2.2. Chemical spoilage
Peroxidation occurs in Herring fillets because of high polyunsaturated fatty acids,
great level of speed up of haeme-proteins and made up of relatively small postmortem
muscle pH and this leads to susceptibility. High content of these compound in the fish
is particularly on of the major factors that brings about the quality reduction,
especially all through the post-harvest handling. They eventually plays a major role
to catalyze the development of rancidity, texture changes, pigmentation and that of
nutritional value loss (Mayer and Wolf, 2015). Oxidation of a purely chemical nature
is the major important changes that takes place in the lipid fraction and these
variations may possess serious quality depreciation challenges, which includes rancid
14


odours, flavours, and discolouration. Auto-oxidation and lipid autolysis are the two
types of rancidity found. Auto-oxidation is described as a response involving oxygen
and unsaturated lipid which is enhanced by heat and light. Lipid autolysis which is
an enzymatic hydrolysis consisting of free fatty acid and glycerol as most important
products. The breakdown of sulphur-containing ammonium acids to methyl
mercaptan, hydrogen sulphide and dimethylsulphide play major role toward the
resultant smell of the damaged fish. When peptide is broken down to ammonia, it
gives off the ammonia and sulphate odours. Due to the fact that most small and
medium sized fatty pelagic fish are caught in excessive number and they are not
gutted directly when catch which results to a challenge due to the rate at which
rancidity sets in (Mayer and Wolf, 2015).
2.2.3. Microbiological spoilage

Bacteria plays an important role in depleting the constituents present in the fish, most
especially non-protein nitrogen combinations, thereby resulting in the advancement
of abnormal odours or foul odours and flavors, most particularly seen with fish
damage (Ababouch, L., Afilal, M.E., Rhafiri, S. and Busta, 1991).
The micro-organisms number multiplies when they are subjected to a favourable
atmospheres with the help of non-protein nitrogenous compound such as volatile
nitrogen bases, ammonia, creatine, free amino acids, betaines and trimethylamine.
(Jay, 1986). The substances above lead to the formation of a substantially alkaline
condition, mostly in stored fish outputs. Some micro-organism such as some strains
of the genera Pseudomonas, Shewenella, and Alteromonas cause disintegration at a
speedy rate. The major cause of the organoleptic spoilage in raw fish is due to the
accumulations of metabolic products of bacteria thereby producing the characteristics
fishery ammonia and sulphide odour, and this affects the texture by changing it to the
pulpy and slimy features of damaged fish (Gormley, 1990).
Several researches reported important inhibition of histamine development in fish
preserved at low temperatures (Taylor, 1986). Nevertheless, the histamine
15


accumulated in mackerel stored for elongated times (14 days) at 5°C. Others
researchers have recounted on a group of psychrophilic halophiles which indicates as
part of the ordinary surface micro-flora of marine fish and can yield big volumes of
histamine at temperatures as low as 2.5°C (Okuzumi et al., 1984). These bacteria
occur artificially in the external layer of the on the gills, skin and intestine of marine
fish and several of these bacteria need proteins and amino acids for their growth
(Prescott, Harley and Klein, 1996). Spoilage micro-organism grow even at low
temperatures in refrigerated seawater (RSW) systems in the presence of NaCl because
they are modified to the environment where the fish is gathered.
2.3. HANDLING AND PRESERVATION OF FISH
Seafood spoilage is caused by a number of factors which include endogenous

enzymatic processes, lipid oxidation and processing techniques, most times the
spoilage that occurs above freezing temperature is as a result of the presence of
bacteria on the fish flesh when it is harvested. Since fish are poikilothermic, the
microflora present during the period of catch is greatly influenced by the
microorganisms in their habitat and temperature (Keys, 2015). To properly retard the
enzymatic and microbial activity after harvest, the fish should be cooled to
temperatures between 0 and -2°C as quickly as possible and even a short time of
temperature abuse can promote rapid decomposition and loss of quality (Keys, 2015).
Correct handling of fish through the aid of quick cooling and keeping on board play
major roles in dictating the quality of the fish. And also, adequate processing kinds
and methods established on capacity and demand are also the key factors for real
assistances (Mayer and Wolf, 2015).
Another major factors that can be responsible for seafood contamination and growth
of pathogenic micro-organisms is inappropriate handling and processing of seafoods.
Also, the regular incidence of aquatic bio-toxins and regular pathogenic flora of the
aquatic surroundings also have contributing impact to seafood borne diseases
(Mahmud et al., 2018). In order to improve the marketing chances regionally as
quality standards are becoming as important criteria for selling fish across borders,
16


there must be taken into considerations the improved quality and sanitation issues.
People who are involved in the fish value chain should have their capacity built
because this is important of improving standards and quality (Ward and Beyens,
2012).
One of the major factors that the body support of the fish and techniques needs is safe
handling and this in turn helps to protect against wound. The common examples of
these techniques are using wet hands and not grabbing fish by the jaws, gills or eyes.
All the necessary precautions must be adhered to such as time out of the water should
be reduced and all measures should be carried out low and on the water tub so that

should in case a fish slides off the measuring board it will fall softly into the tub of
water and not on a rigid boat outward (Hawkins, 2008). The way fish is handled
onboard the vessels i.e. how they are preserved, packed and moved from one place to
another greatly influences the quality of fish getting to the consumer or processing
factories. Personnel on board the vessels play the major role of preserving the catch
after hauling till it is unloaded at landing centers. To ensure high quality for the end
product, big tuna must be gaffed carefully, spiked, bled and then quickly placed in
the slurry in order to prevent a rise in the temperature which will later make them
prone to quick spoilage.
Preservation means putting microorganisms in an unfavorable environment of their
normal activities to delay or inhibit their growth, shorten their survival or cause their
death (Tsironi, Houhoula and Taoukis, 2020). The quality of end seafood product is
determined by the standard of raw materials. The quality lost during handling cannot
be recovered back during processing. Most of the fish produced from low quality fish
does not pose any safety risk but the quality as well as the shelf life of the final product
would be affected (Quang, 2005). In Vietnam, one of the major challenges is how to
maintain fish raw material standard. The interval frame between catching and
acceptance at the processing plants can be extended while the raw materials
temperature is not sufficiently low adequately to inhibit decomposition or

17


deterioration. The fishing sector in Vietnam has been faced with the challenges of
stagnation in catching and also deterioration in the quality of raw materials.
2.4. REFRIGERATED METHODS OF SEAFOOD PRESERVATION
The purpose of the preservation of foods by refrigerated system is to decrease and
sustain the food temperature which in turn stops, or greatly decreases the rate at which
deterioration changes take place in the food. Examples of these changes can be
microbiological (i.e. development of microorganisms), biochemical (e.g. browning

reactions, lipid oxidation, and pigment degradation), and/or physical (such as
moisture loss) physiological (e.g. ripening, senescence, and respiration) (James and
James, 2014). Some foods possess the features that enable them to be easily processed
and preserved while others, such as fresh fish, poses a challenge to retailers,
processors and consumer. Fish is highly prone to deterioration because of the
presence on inherent constituents, which are responsible for the growth of bacteria.
The quality of fish quality will become depreciated after some hours or days if
appropriate storage condition which include refrigeration or preservation treatments
(e.g. salting, heating and irradiation) are not put in place. When fish are caught offshore, special procedures are used to enable low amount of microbial counts through
processing and to assure consumer product’s safety (Barbut, 2015).
Some of the most dominant preservation methods used presently have been
established in several years ago before the knowledge science about microorganism/chemical decomposition and pathogen existence. In the past, people extend
the shelf life of food by using different preservative methods and these include
cooling, drying, freezing, heating, fermenting and adding ingredients such as salt,
sugar, etc. Today, antimicrobial compounds, produced by selected strains of
microorganisms resulted to the development of molecular biology, are used to
inactivate pathogens during fermentation of fish (Barbut, 2015). The skin outward of
not alive fish is a perfect growth medium for micro-organism, which results in fish
spoilage. When the temperature is altered, the growth of many bacteria that causes
the deterioration will be retarded but not completely eliminated (Txdolw et al., 2018).
18


Physical factors can aids either chemical or bacteriological processes such as bruising
cutting and tearing etc. can open up fish muscles to enables quick bacterial growth
and this causes blood to flow out which in turn darken the fillets and reveal greater
surface area for chemical corrosion (Txdolw et al., 2018).
To make available hygienically safe food products of high organoleptic standard
(such as smell, taste texture, appearance), sensible effort must be paid to every aspect
of the cold chain from primary freezing or chilling of the raw ingredients, packing

and transport to retail exhibition outlet handling. A competent and appropriate coldchain is made to enable the optimum conditions for retarding, or hindering these
variations (James and James, 2014).
In view to understand the degree of perishability of foods, they are often categorized
as less delicate, moderately delicate and highly delicate. Foods such as cereals, grains,
and nuts are categorized as less delicate and more stable, vegetables as moderately
delicate and seafoods as highly delicate food items. Seafoods are prone to spoilage as
a result of their high moisture content, inherent enzymes, weak connective tissue,
neutral pH and nutrients availability which enhances the growth of microorganisms
(Jiang et al., 2018). Furthermore, the quality of seafood is greatly dependent on its
initial quality, catching time, catching location or habitat, gender, body composition,
species, and methods of handling (Jiang et al., 2018). Studies shows that the
decomposition of fish occurs from three major factors: autolysis, enzymatic,
oxidation and microbial growth (Ghaly et al., 2010).
Different types of preservation methods have been used both traditionally and in
modernized ways which include drying, salting, smoking, freezing, chilling, brining,
fermentation and canning. These methods have been reported to extend the shelf life
of seafoods and meat products, although at different degrees. However, the most
common methods in the industry are the chemical and low temperature storage
techniques for controlling water activity, enzymatic, oxidative and microbial
development (Ghaly et al., 2010).
19


Principles guiding the various methods include controlling water activity, low
temperature storage and controlling oxidative spoilage, while other means of
preservations can be grouped into chemical, physical, and microbial controlling
methods. The major objective of proper handling and preservation is to control or
reduce those factors that can cause spoilage in fish and fishery products so that the
end product is wholesome and safe for the consumer. Fish and fishery products in a
well-kept situation will commonly have advanced value placed on them both at the

wholesale and retail levels and thereby gives higher profits to the seafood operators
(Txdolw et al., 2018).
Chilling plays an important role in reducing decomposition in fish if it is done
speedily and if the fish are chilled and kept cautiously and hygienically. Immediate
chilling of fish ensures high quality products. For every 10oC reduction in
temperature, the rate of deterioration decreases by a factor of 2-3 (Txdolw et al.,
2018). Chilling is obtained when the top layer of the seafood is covered with ice.
However, chilling techniques is not encouraged for a long-term preservation, because
melted ice produces excess water which may be containing washed bacteria and
therefore bring about leaching of valuable flesh content responsible for flavour and
desirable taste. Meanwhile, well-iced seafoods are able to stay six to seven days
without any difference in their taste and a freshly caught seafood. Also, antibiotics
are sometimes added to the ice used in the chilling process (Tawari and Abowei,
2011).
When a product has been chilled, the temperature must be preserved by refrigerated
storage. Cold air plays Chill stores are normally cooled by circulation of cold air
produced by mechanical refrigeration units, and foods may be stored on pallets, racks,
or in the case of carcass meats, hung from hooks (Richardson, 2001). The size of the
refrigeration system is different depending on the level of heat that needs to be
eliminated and preferably the heat capacity will be reduced. During the time of
cooling, heat will be eliminated out of the products during storage, transportation and
retailing the only means by which heat loads should gain access to the product should
20