Download Fish Classification White Oily Shell Cod, Whiting Salmon, Trout

Fish
Classification
White
Oily
Shell
Cod, Whiting Salmon, Trout
Prawns, Crab
Plaice, Sole
Tuna, Herring Lobster, mussels
Nutritive Value/Composition
•Protein HBV, Easily digested. 17-20%
•Lipid Polyunsaturated fatty acids, omega3 associated with
lowering risk of heart disease. Oil in liver of white fish, in liver
and fibres’ of oily fish. 0.5% white, 10-20% Oily
•Carbohydrate None due to glycogen converted to lactic acid
during struggle when caught. Serve with rice/potatoes
•Vitamins B group in all and Vitamins A+D in oily fish
•Minerals Iodine, fluorine + iron. Calcium in bones of tinned
fish e.g. salmon
•Water High in white fish , less in shell + oily. 65-80%
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Dietetic Value
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One or two portions should be eaten every week to help lower
cholesterol and prevent heart attacks. Omega 3 fatty acids are
important for brain development in unborn babies
and may help to alleviate skin problems and high
blood pressure
Easily digested suitable for children, elderly and
invalids
Low in fat so very suitable for low fat diets. White fish
contains fat in the liver which is removed to make
supplements..cod liver oil. Fat in oily fish gives it more
flavour than white fish.
Good substitute for meat and is high in HBV proteins
Main source of HBV protein and B vitamins in the diet of a Pesco
vegetarian.
Should be eaten with rice/potatoes as does not contain any
carbohydrates
Spoilage of Fish
• When fish are caught they struggle and use up
their stores of glycogen. There is no glycogen left
to be converted to lactic acid to preserve
the fish
• Bacteria multiply very quickly and break down the protein in
fish flesh
• Protein is converted to a nitrogen compound ( trimethylamine) which has a very strong smell
• Fish also go off because of enzyme activity and oxidative
rancidity
• Polluted waters may contaminate shell fish
Fish Structure
• Fish is composed of bundles of short fibres called
myomers. These are held together by the connective
tissue called collagen.
• Collagen changes to gelatine during cooking, this allows the
fish fibres to fall apart.
• As the fibres in fish are short the fish cooks very quickly
and are very easy to digest.
Shell fish have coarser fibres so are
more difficult to digest
Cuts of fish
Fish can be sold whole, in fillets, steaks
or cutlets
Buying Fish
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Buy fish in season, they are better quality and cheapest
Fish should smell fresh
Flesh should be firm and moist
Fillets, steaks and cutlets should show no sign of
discolouration
Medium size fish have a better flavour than large fish
Colour should be correct for type of fish
Eyes should be bright and clear
Molluscs should not be open
Frozen fish should be frozen solid
Storage
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Fish should be covered before being
refrigerated. The odour from fish will quickly
taint other food e.g. egg/milk. Covering the
fish will also prevent the fish from drying out
Use fish on the day of purchase
Frozen fish should be placed into the freezer
immediately
Tinned fish should be used up immediately
Effects of Cooking on Fish
• Protein coagulates and shrinks between 60oC and
70oC and flesh becomes opaque
• Fish shrinks slightly
• Fibres are short so the fish will cook quickly. The
connective tissue changes to gelatine making the
fish break up easily
• Some B Vitamins are lost
• If the fish is cooked in water or milk this liquid
should be used for a sauce so that the leached
nutrients are not lost
• Bacteria and parasites are destroyed
Methods of Cooking
Baking, frying, grilling, poaching,
steaming, stewing and microwaving
Processing
• Canning. Loss of B vitamins. Calcium available as the
bones are softened and edible. Can be canned in oil
or brine
• Freezing. Blast frozen at –30oC. Very little change
in nutritive value. Can be processed into
fish fingers, fish in batter, etc.
• Smoking. Can be done naturally(cold smoked
at 30oC or hot smoked at 110oC) or
artificially (dyed and flavoured). Bacteria are
destroyed, fish changes colour and a smoky
flavour develops