1. Fish as food
TYBSc Semester VI
(Applied component: Marine science)
Biren Daftary

2. Biochemical composition of Raw Fish
• Principal contents: protein, fat and water
• Protein = 20%
• Variation in fat and water
• Minerals, vitamins and enzymes
• No carbohydrate except glycogen in liver
• Water = 55 - 83%

3. Proteins
• Normal 15 - 20%
• In some species < 15% or as high as 28%
• Chains of chemical units linked together to make
a long molecule
• Each unit = amino acid (20)
• Essential in human diet for maintenance of good
health
• Lysine & Methionine are found in high
concentrations in fish proteins
• Skeletal protein = 50 – 60% of total weight of fish

4. • Protein content classified into following
groups:
a) Albumin fraction: 16 – 22%
b) Protein fraction: 75%
c) Stroma: 3%

5. Non-protein N2 components
• Peptides (Flavour)
• Free AA, Histidine (Richer in red muscle than
white)
• Bases like ammonia, trimethylamines
• Creatine, taurine, betaine, histamine, glycine,
uric acid, carnosine, etc.
• Nucleic acids

6. Fat
• Average fat content between 1-8%
• If fat > 8% fish classified as oily or fat
• Depot fats
• Brain shows highest concentration of fat
• Heart shows lowest
• Fat content determines the quality of fish and
hence its price

7. • Fatty substances: glyceride group or lipid
group of fatty acids
• Fatty acids: Straight chain monocarboxylic
forms having even no of C atoms (12-28)
• Glyceride group: Fatty acids occur on three
-OH groups of glycerol molecule

8. Fish Oil
• Marine fish oil contains larger quantities of
C18, C20 and C22
• Fresh water fish oil contains larger quantities
of C16 and C18 but less of C20 and C22
• Large applications in industries
• Shark oil rich in unsaponifiable substances

9. Minerals
• 1-2% of fish flesh composition
• Concentrated in fish bones
• Principal minerals: Ca, Mg, K, Na, P, S, Fe, Cl,
Cu, Mn, I, Br
• Trace minerals: Sr, Zn, Ba, Al, Pb, Mo, Co, Ni,
Hg, Cd

10. Vitamins
• Liver rich in B12 and B complex, A and D
• A and D: inner organs of the body
• B: liver, eyes, skin, kidney, spleen and
intestines and roe
• Eels are rich in vitamin A, mackerel in vitamin
D
• Vitamin A, D and E: Fat soluble
• Vitamins of B group: water soluble

11. Nutritional value of Raw Fish
• Nutritional value of fish meat > meat of cattle
• Less stroma protein in fish
• Excellent source of all essential AA needed in diet
• 300g of fish = ½ of total protein & fat
requirement and 1/4th of calories needed in
balanced daily diet
• This amount also provides 50% P, 30% Fe, 100%
vit A, 30% vit B1 & B2 and 50-100% of niacin req.

12. Nutritional value of preserved and
processed fish
• Exudation causes 4% loss in proteins, water soluble
vitamins are also lost
• Cooking at 60˚C causes loss in weight due to water loss
• Frying causes heavy loss of essential AA
• Steam/pressure cooking causes loss in proteins and
minerals
• Canning doesn’t affect protein and fat and heat stable
vitamins
• Canning causes considerable losses in vit B1, C,
pantothenic acid & pteroylglutamic acid
• Salting: 1-5% loss in proteins
• Smoking: 8-30% loss in proteins

13. Freezing & lyophilizing:
• Only vitamin E is destroyed
• Encourage rancidity of fat & denaturation of
proteins
• Undesired look reduces acceptability of the
product, although there is no actual loss of
proteins

14. FISH BY-PRODUCTS

15. Fish Protein Concentrate
• FPC is prepared from whole fish or its parts
• Concentration is increased by removal of water,
oil, bones and other materials
• FPC does not bear resemblance to the original
nutritive values of raw fish
• It is a gritty odourless, colourless & tasteless
powder
• Stable at room temperature for 3-4 years
• Components: Highly digestible protein + lysine +
minerals

16. • Highly nutritious
• For human consumption but not direct
• 5-10% added in bread and biscuits
• 35g/day is recommended level of use of FPC

17. Fish maws
• Fish maws is the internal gas filled organ that
helps to maintain the buoyancy of fish
• Also called swim bladder/air bladder
• In some Asian cultures fish maws are considered
a food delicacy (China)
• Served in soups or stews
• Used in the food industry as a source of collagen
• Can be made into a strong water resistant glue
• Making isinglass for the clarification of beer

19. Isinglass
• It’s a collagen derived from thin, inner shiny
silvery layer of airbladder of some fishes
• Airbladders are washed thoroughly, outer thick
fibrous layer is separated from inner layer which
is isinglass raw material
• This raw material is then purified
• Russian isinglass from sturgeons is considered as
a very high quality product
• Good substitute for gelatin in confectionary
• Swells in cold water without dissolving

20. • At high temp it produces strongly adhesive
gelatin
• Chief use is clarification of beer, vinegar, etc.
• Also used as an adhesive in the form of
cements and court plaster

22. Fish Body Oil
• Obtained from entire body of fish along with
liver
• Generated from oil sardines / less edible
varieties of fish or from wastes discarded from
canneries
• 5kg of fish = ½ kg fish body oil
• Lesser Vit A and D, less unsaponifiable matter
when compared to liver oil

23. Uses:
• Source of vit A and D for medicinal purpose
• Manufacture of paints & varnishes
• Leather and tanning industry
• Manufacture of cheap soaps
• Iron and steel industry as a tempering agent
• Manufacture of chemicals, cosmetics and candles
• Fungicides for citrus group of trees

25. Fish Liver Oil
• Rich source of vit A and D
• Fat of liver is the source of fish liver oil
Uses:
• Prophylactic & curative agent
• High vit A & D enables it to cure rickets, eye
disorders, abnormalities of skin and vertebrae
• Good growth of bone and teeth
• More resistance to counter bacterial attack

26. Methods of extraction:
• Auto fermentation
• Boiling
• Steaming (85-90˚C under 2kg/sq-cm pressure)
• Chemical digestion
• Solvent extraction
• Refinement of oil

28. Chitosan
• It is a linear polysaccharide
• Made by treating shrimp and other crustacean shells with
NaOH
• No of commercial and biomedical uses
• Used in agriculture as seed treatment & bio pesticide
• Used in wine making industry, helps to prevent spoilage
• Rapidly clots blood and hence used in bandages and
haemostatic agents
• Research going on for study which shows it limits fat
absorption in the body
• Also used in water filtration

30. Shark Fin Rays
• Valuable by-product of shark
• Shark fins are dried & soaked overnight in 10%
Acetic acid
• The scale and softened muscles are scraped
off and the rays are separated individually
• Then thoroughly washed and dried
• Essential ingredient in some exotic soups