• Quality means the level of good or bad on
something, the degree or level of quality. Quality
means that something has a quality or good
• According to Philip B Crosby quality is
compliance with requirements or standards. In
other words, a product is considered qualified if
its specifications comply with predetermined
• According to ISO 2000, the notion of quality is
the totality of the characteristics of a product
(goods or services) that support its ability to
satisfy specified or defined needs.
● The proportion of fish flesh to total body weight varies between 40% and 65%,
depending of species, shape, age and the physiological status of the fish. Fish with
more elliptical cross sections (tuna, herring and salmon) exhibit a much higher
proportion of the edible part than flatfish species or species with very big heads
such as monkfish.
● Fish flesh consists of light and dark musculature. Both types can be differentiated
by chemical composition, physiological importance and nutritional value. Most
species have more light than dark muscle.
• The light musculature is used for rapid, sudden
movements and obtains energy mainly from anaerobic
glycolysis. For continuous swimming, fish use their
• This type of muscle is therefore well developed in
pelagic species (herring, mackerel, tuna), well supplied
with blood and rich in myoglobin. The metabolism of
dark muscle is aerobic; energy is provided by lipids
• The fat content of fish varies greatly in quantity and fatty acid composition. The
protein content is almost constant. The fat content is mainly dependent on
biological state of maturity, but also on nutritional status, age, catching ground
• The fat is not homogeneously distributed in the body. In lean fish species, it is
located in the liver as an energy reservoir; in fatty species, it is deposited in the
muscle tissue, as a subcutaneous layer under the skin or in the intestines.
• Lean fish species have a higher proportion of polar lipids (phosphatidylcholine
• The highly unsaturated character of these fatty acids is the reason why they are
susceptible to lipid oxidation and oxidative degradation. Fatty fish species
therefore have a tendency to exhibit rancid tastes and odours after limited
● The vitamin contents in fish are species specific.
They can vary considerably within one species
with age, size, sex, season, diet, state of health
and geographic location.
● In fish farmed by aquaculture, the contents of
vitamins reflect the composition of the
corresponding components in the fish feed.
Therefore, the vitamin content of wild and
farmed fish can be different.
• The liver of fish is a rich source of fat-soluble vitamins (A, D, E and K). In
fish flesh, dark muscle contains more fat-soluble vitamins than white
muscle because of its higher fat content.
• The flesh of fatty fish still contains moderate amounts of vitamin A, but
lean fish contain only trace amounts. Fish and fish products are
commonly regarded as the most important natural food sources of
• Vitamin E functions as a natural antioxidant to prevent lipids from
becoming rancid. Fish flesh is only a low to modest source of vitamin E.
• Relatively few values for the vitamin K content of fish are available. The
highest concentrations are found in muscle of marine and freshwater
fish with high fat content, and in the liver.
● Most fish species cannot synthesise vitamin C (ascorbic acid). The average
vitamin C content of fish ranges from 1 to 5 mg per 100 g.
● The natural thiamin (vitamin B1) content of most fish and fishery products is
relatively low. A special problem with some fresh- and seawater fish species is
the occurrence of thiaminases. These enzymes cleave the thiamin molecule.
They ooccur especially in the viscera of fish.
● For example, carp, mackerel and mussels have high thiaminase activity. The
enzymes can act during food storage, but they are inactivated by heat, so
cooking and smoking destroy them.
Quality parameters of fishery products
• Good quality → Fresh fish
• Fresh fish → looks,
smells, tastes, as well as
Fresh fish category
• Fresh fish caught and not
experiencing process preservation
or further processing yet.
• Fish that haven’t go through
physical or chemical changes/
which still has properties same
Factors determining the quality of fresh
1. How to catch fish
2. Fishing port
3. Various other factors, starting from
the public sale, packing,
transportation and processing
Fish classified into four quality classes
Very good once
Spoilage of Fresh Aquatic Products
• Fish and other aquatic products are among the world’s
most perishable commodities. Spoilage in aquatic
products begins soon after death. Following the death of
fish, blood circulation stops resulting in a series of
changes within the muscle.
• The spoilage of fresh fish is complicated process for
which no single factor is responsible, but, rather it is a
combination of several interrelated processes.
● The flesh of the fish is sterile (free from bacteria) when they are
alive, but large numbers of bacteria are normally present in the
surface slime, on the gills, and in the guts.
● Freshwater fishes bacteria: mesophilic-gram positive. – 3 layers of
cell wall and purple in color. Example: Micrococcus, Bacillus,
● Marinewater fishes bacteria: Psychrotrophic gram-negative- 2
layers of cell wall and pink in color. Example: Pseudomonas,
alteromonas, acinetobacter, flavobacterium, cytophaga and vibrio.
● Bacterial spoilage does not start until the passage of rigor mortis.
● Enzymes are protein substances present in the muscle and in the
gut of fish that initiate or speed up chemical reactions.
● At the death of fish, the normal regulation system stops to
function and the supply of oxygen and energy production ceases.
● The cells begin a new sequence of processes characterized by the
breakdown of glycogen (this process known as Glycolysis) – the
degradation of energy-rich compounds.
● After death, the enzymes naturally act on the food in the gut
● Autolysis – the self-breakdown or selfdigestion that results the
weakening, softening and discoloration of fish tissues.
Spoilage of fish due to chemical changes mainly occurs during
storage in ice or in frozen condition.
3 factors in chemical changes or rancidity of lipids:
1. Lipid autolysis – enzymatic hydrolysis with fatty acids, and glycerol as
2. Auto-oxidation – the reaction of unsaturated lipid with oxygen.
● Oxidative rancidity in fish can result to serious quality problems such
as rancid flavors and odors as well as discoloration.
3. Denaturation of proteins during frozen storage resulting to tough, dry
and fibrous texture.
Post mortem changes in fish muscle
The quality and
Type of fish species, physiological
condition, killing procedures
The freshness of the fish can be seen by the simple
method, by looking at the physical condition:
● External appearance; Fresh fish, bright appearance and not dull.
There are no biochemical changes. Metabolism in the fish's body is
still running perfectly.
● Flexibility of fish flesh; Fresh fish flesh is quite pliable and will return
to its original shape when pressed.
● Eye condition; Changes in the freshness of the fish will cause a
noticeable change in it’s brightness.
● Condition of gills and scales; Fresh fish bright red, while the fish are
not fresh dark brown. For fish scaly if the scales are still firmly
attached, no easily released from the body means fish it's still fresh.
Chemical freshness determination of fish
Fish meat pH analysis
• Fish that is not fresh has a high pH (alkaline) compared to fresh
fish. Due to the presence of alkaline compounds ex: ammonia,
trimethylamine, and compounds other volatiles.
Analysis of hypoxanthine content
• Hypoxanthine comes from ATP breakdown, the higher the
content hypoxanthine then the degree of freshness low fish
Analysis of dimethylamine, trimethylamine/ammonia levels.
• Protein decomposition produces the above compounds, if the
freshness of the fish has decreased then volatile nitrogen content
enhancement. Patterns of protein breakdown in fresh water fish
produce ammonia, while sea fish produce dimethylamine and
Dephosphorylation of Inosine Monophosphate (IMP)
• IMP is related to changes in the taste of meat fish and fish
freshness, so it can be used to determine the freshness of the fish.
Microbiological Determination Method
• Fish naturally carry microorganisms. Dominant
microorganisms cause damage in the form of
bacteria because of its high protein, water
content and the pH of the fish meat is close to
neutral making it a suitable medium for growth
• Microbiological testing of fish can be done by
determination of the Total Plate Count (TPC).
• Only counting the total number of bacterial
colonies and then comparing it to the quality
standards of fresh fish, the test can take place
Sensory Fish Determination Method
• This method is easier and faster (using sensory tools)
• Sensory testing is more towards observation visually
• Sensory testing in the form of color appearance, mind taste
• The fresher the fish analyzed the score will be the higher it
• Its nature is very subjective just rely on panelist senses (e.g.
discriminating between foul odor with ammonia or indole
• The panelists will give a score on observed samples
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