Download 1345107329.

FOODS AND NUTRITION
(with Science in the Home)
PAPER I
TIME: 2 HOURS
Instruction: Attempt all questions
1. (a) Describe the structure and composition of fish.
(b) What factors must be considered when buying fish?
2. (a)
(b)
(c)
(d)
Giving examples, define essential fatty acids.
Why are the essential fatty acids recommended in the diet?
Discuss the importance of lipids in the diet.
Describe how emulsifiers work.
3. (a) Outline the changes that occur during the storage of fresh eggs.
(b) What is the effect of heat on eggs?
(c) Discuss the various uses of eggs in cookery?
4. (a) (i) What do you understand by the denaturization of proteins?
(ii) Discuss the factors that are responsible for the denaturization of proteins.
(b) Explain the following terms:
(i) Biological value of proteins
(ii) Deaminisation
(iii)Write short notes on unsaturated fatty acids.
Marking guide
1. (a) Structure and composition of fish
INTERNAL STRUCTURE OF FISH
- The structure and composition of meat is similar to that of lean meat.
- Flesh of fish is composed of bundles of short muscle fibres called myome / muscle blocks.
- Muscle blocks are held together by connective tissue which is collagen.
- Fish contains les connective tissue; collagen, than meat therefore muscles of fish are not held together strongly
thus causing flakes to fall apart.
- Fish doesn’t contain tough elastin.
- Muscles are divided into flakes and bones.
- On cooking, collagen is converted into gelatin causing fish to break.
(b) Factors considered when buying fish
- Eyes should be bright red
- Scales should be plentiful and firmly attached to the skin
GAYAZA HIGH SCHOOL FOODS AND NUTRITION DEPARTMENT
Page 1
-
Gills should be bright red
Any natural colouring present should be bright e.g. orange spot on plaice
Tail should be stiff
No disagreeable colour
White fish should be pearly white in colour with no discolouration
Smoked fish should have glossy appearance
Body should be firm and not sticky
Whole fish should be plump
Buy fish which is in season
Buy medium sized fish because small fish are tasteless and have more bones.
2. (a) Essential fatty acids
Essential fatty acids are the ones that must be obtained from the food because the body cannot
synthesize them from its own use.
e.g. - Linoleic acid
- Linoleric acid
- Arachidom acid
(b) Why essential fatty acids are recommended in the diet.
Because they help to counteract the hardening effect of cholesterol on the coronary artery therefore
reducing the incident of heart attack.
(c) The importance of lipids in the diet
- Provide concentrated source of energy for various functions in the body.
- Provide the three essential fatty acids needed in the body to stop heart attacks.
- Protects delicate organs of the body like liver, lungs, kidney etc.
- Provides texture to food therefore increasing palatability.
- Are carneers of flavour in food.
- Provide long term satisfaction due to slow digestion.
- Control body temperatures as they are insulators.
- Carry fat soluble vitamins A, D, E, K.
(d) How emulsifiers work
- Molecules of emulsifiers have hydrophilic (water loving) and hydrophobic (water hating) groups.
- Hydrophilic group attaches itself to water molecules and the hydrophobic group to lipid molecules.
- At the point where oil and water touch, (oil / water) interface, emulsifiers hold them together.
- Thus the emulsifier lowers the surface tension between the two liquids and encourages them to
combine forming a stable emulsion.
3. (a) The changes that occur during the storage of fresh eggs
- Water moves from the white into the yolk
GAYAZA HIGH SCHOOL FOODS AND NUTRITION DEPARTMENT
Page 2
- The yolk membrane weakens
- The thick white becomes thinner
- The size of the airspace increases
- Moisture is lost through the shell
- Bacteria enters through the shell
- The bad smell of Hydrogen Sulphide is produced by the reaction of sulphur from the egg white and the
phosphoric acid in the egg yolk.
- The egg eventually decomposes as bacteria contaminates the content.
(b) Effect of heat on eggs
- When heated, the ovalbumin in the egg white starts to coagulate at a temperature if 600 C until the
whole white is opaque and solid.
- Protein of the egg-yolk starts to coagulate at a temperature of 700 C and continues until the egg yolk is
dry and hard.
- When heated beyond coagulation temperature, the protein structure gets denatured i.e. it becomes
too hard, tough and rubbery.
- In hard boiled eggs,a greenish-black discolouration is sometimes seen between the yolk and the white.
-If the eggs are heated too quickly, the protein will coagulate and shrink rapidly and then become tough.
- Vitamin B gets destroyed on cooking.
- Denatured egg becomes difficult to digest.
(c) Uses of eggs in cooking
- A main dish combined with other food or ingredients
- Thickening due to coagulation property e.g. it’s used for thickening custards.
- Coating; beaten eggs provide a protective covering for fried foods because albumen quickly hardens
on heating therefore, preventing the content being saturated with fat.
- Enriching; addition of a whole egg or yolk to a mixture adds nutrients to the food being cooked.
- Lightening; By means of whisking either egg-white or a whole egg, air is entangled and lightness given
to a mixture acts as a raising agent in cakes etc.
- Glazing; Brushed on top of pastries
- Garnishing; For decorating dishes e.g. chopped boiled egg whites, sliced hardboiled egg etc.
- Emulsifying; Eggs contain lecithin, a natural emulsifier.
- Clarifying e.g. Soups, stocks, home-made wines, jellies using egg-white and shell.
- Binding; meat balls, hamburgers, chaps, fish cakes etc
4. (a) (i) Denaturization of proteins is the untwisting of the protein structure due to breakage of bonds thus
leading to loss of structure.
(ii) Factors that are responsible for denaturization of proteins
- Very high temperatures
- Very low temperatures where ice is formed thus breaking the bonds
GAYAZA HIGH SCHOOL FOODS AND NUTRITION DEPARTMENT
Page 3
- Whisking eggs breaks bonds
- Addition of acids
(b) (i) Biological value of proteins
- This is a measure of how nourishing a protein is i.e. how much protein will eventually be made
available to the body for protein synthesis
- Proteins which contain all the essential amino-acids in the proportions required by the human body
have a high biological value i.e. most of their protein is available for growth and repair.
- Proteins that are deficient in one or more of the essential amino-acids are proteins of low biological
value and are mainly of plant origin.
(ii) Deaminization
is the process by which amino group of protein radical is removed from the amino-acid molecule to be
excreted by the liver in form of urea.
(iii) Short notes on unsaturated fatty acids.
- Are the fatty acids in which the hydrocarbon chain are not all surrounded by the Hydrogen atom and
therefore have 1, 2, 3 or 4 double bonds.
- If the fatty acid molecules contains only one double bond, it is non-saturated.
- If the double bond is 2 or more, it is polyunsaturated.
- Polyunsaturated acids are: - Linoleic, Linoleric and Arachidonic and have 2, 3 and 4 double bonds
respectively.
- Unsaturated acids are mainly found in plants.
- They help to counteract the hardening effect of cholesterol on the artery hence reducing the incidence
of heart attack.
GAYAZA HIGH SCHOOL FOODS AND NUTRITION DEPARTMENT
Page 4