HOME STUDY FOOD AND NUTRITION CERTIFICATE
The food and drink that we consume each day have a direct bearing on our state of health. It is important to vary our intake of foods so that we are deriving the full range of nutrients and other substances that the body needs. Too much of one or two food types, even healthy foods, is not recommended for long-term health.
In addition to being more healthful, a varied diet is also a lot more interesting for the taste buds. A balanced and adequate diet is essential to our wellbeing. The extra time and thought needed to prepare good quality meals is easily rewarded with increased stamina and alertness, better resistance to illness, and clear and healthy skin, eyes and hair. However, to maximize the health benefits of what we eat, we need to understand some basic nutrition requirements and principles.
This course will introduce the student to a range of theoretical concepts, and practical skills that can be applied in a range of contexts. The student has the opportunity to specialise in the area of their choice. Such as:
- Nutrition for children
- Sports nutrition
- Therapeutic nutrition
- Growing organic produce
Note that each module in the Qualification - Certificate in Food and Nutrition is a short course in its own right, and may be studied separately.
The nutritive value of food depends not only upon what and how much is consumed, but also, how it is prepared. Also, given that food is unlikely to be eaten unless it is appetising, its preparation is very important to maintaining good nutrition, as is its content.
Cooking involves the application of heat, using moist or dry methods, and may in the process:
1. Increase palatability and appearance of food by:
- Enhancing and conserving natural flavours
- Blending flavours (e.g. in cakes, casseroles etc)
- Producing the most suitable colour, form and texture.
2. Improve digestibility (eg. tough meat should be more tender and easier to chew after cooking).
3. Add variety to the diet, and so encourage foods to be eaten.
4. Improve the safety of food by destroying pathogenic microorganisms.
5. Bring about changes in the nutrient value of food, for example:
- Some fat is absorbed when foods are fried, increasing their energy value
- In grilling, some fat may be lost
- Nutrients may be lost by chemical breakdown, or by being leached into cooking waters.
Cooking may therefore affect the nutrient value of food, either beneficially or negatively.
COOKING TIPS WITH SOME TYPES FOOD
Humans could digest most foods of animal origin raw, but raw meats are particularly unpalatable. Cooking makes them easier to chew, so that the digestive juices gain more rapid access to protein. At the same time, particularly with meat, an appetising aroma develops.
Meat is important in the diet for its good quality protein, iron and B group vitamins. When the muscle tissue is heated, protein coagulates and is denatured, but only at very high temperatures will it be destroyed. Should carbohydrates be present, an additional loss of nutritive value in the food occurs at high temperatures, due to non-enzymic browning. Some loss of the amino acid, lysine occurs in this way during the roasting of meat, but the amount is small. Non-enzymic browning also accounts for the development of flavour, colour and aroma. The protein of connective tissue, collagen, is not denatured on heating, but moist cooking methods softens and converts collagen to gelatine.
During the cooking of meat, shrinkage occurs, causing extrusion of meat juices. These form the 'drip' during the roasting of meat, and if this is not used in making gravy, extractives, iron and thiamine may be lost. During moist methods of cooking, these go into the cooking liquor, and as the meat is generally eaten with the liquor of stews, casseroles etc., there is no loss. Fat melts during cooking, and the higher the cooking temperature, the greater the loss of fat into the roasting tin, or cooking liquor.
The loss of B group vitamins during cooking meat is significant, especially as meat supplies about 20% of thiamine in the average diet. The loss is proportional to the cooking temperature, and about 30-60% may be lost during roasting. Minerals are stable and not affected by heat.
The Structure of Meat
Cuts of meat are made up mostly of muscle, but it does include some connective and fatty tissues as well as bone and skin. Connective tissue is closely associated with muscle, and is found in the muscle itself or within the muscle sheath. Cooking can break down the white connective tissue (collagen), but the yellow elastic tissue (elastin) found in ligaments and tendons is not affected by heat.
Fat is an important component of meat as it improves the tenderness, moisture content or juiciness, and flavour of the meat. Fat is also a source of Vitamins A, D, E and K, and prevents meat from becoming dry.
Meat quality is a broad term that can be broken down into three factors: appearance, palatability (tenderness, juiciness and flavour), and nutritive value. Other factors that contribute to palatability are breed, sex, age of the animal, finish and cooking.
Collagen and elastin increase in content with age and work and result in tougher cuts. Muscle bundle size also increases with age up to four years and causes coarseness of meat. In beef cattle, tenderness is more than 60% heritable (passes on from parent to offspring) and this may be associated with the family trait of docility.
Rigor mortis becomes evident six hours after death and reaches a maximum stiffness by 24 hours. Anaerobic breakdown of muscle glycogen causes contraction of the muscle fibres and lactic acid is produced. Then the actin and myosin filaments fuse. Hanging the carcass during the process of rigor mortis stretches the muscles, preventing the toughening of meat by shrinkage. Immediate freezing does not prevent rigor mortis - it merely delays it till the carcass is thawed.
Excitement and stress affect tenderness by depleting the animal's glycogen content. To ensure animals are in a state of physiological balance at slaughter, they should be fed and watered as usual up to 12 hours before slaughter to restore the level of muscle glycogen.
Meat is tenderised by the natural process of autolysis (self digestion), due to certain enzymes present in the muscles. (Meat tenderisers are preparations of these enzymes). The muscle proteins become denatured and the bonds binding the molecules together are broken down. These actions are favoured by a slightly acidic pH and by elevated temperatures. Temperatures above 5 degrees centigrade permit the multiplication of ever-present bacteria. Aging of carcasses up to 40 days increases tenderness, but longer periods have an undesirable effect on palatability.
This depends on the water-holding capacity and the amount of fat embedded in the meat. Marbled meats are favoured (where the fat runs in seams through the muscle tissue) over cuts where there is a layer of fat at the edge, which is generally bulkier and doesn’t impart as good a flavour.
Certain chemicals (amino acids and fatty acids) impart the characteristic flavour to meat. Age and muscle activity improve flavour due to the larger amounts of derivatives and aromatics (myo-globin and connective tissue). Meat with a low pH and with muscle glycogen has better flavour. Autolysis also improves flavour. Heating releases flavour but, in excess, can drive away or destroy substances.
Cuts and Joints of Meat
Once the animal has been slaughtered, skinned, and the head, hooves and offal have been removed, what is left is called the carcass. This is halved, quartered and sold to the butcher who cuts it up into smaller joints and sells it to the public.
The changes that occur during cooking of fish are similar to those in meat. Shrinkage is less, and fish is not an important source of thiamine in the diet. Fatty fish contain vitamins A and D in the fat; these are heat stable, but may be lost in any fat lost during the cooking process.
When meat is heated, the protein lactalbumin coagulates and, with the fat of the milk, forms a "skin". If this skin is removed, the nutritive value of the milk is reduced. The main process of coagulation occurs when milk goes sour, or when acidified milk is treated with rennet as in cheese making.
A tough wall of cellulose, which is little disrupted by chewing, surrounds most plant cells. Digestive juice will not penetrate this cellulose wall. Cellulose is softened by moist methods of cooking, enabling digestive juices to penetrate the cell wall and reach the cell contents. When starch granules are heated in the presence of water, water passes through the walls of the granules causing swelling. The cell walls surrounding the starch granules are softened, and the starch gelatinised. In this form the starch is easier to digest.
Fruits and green vegetables may be eaten raw in limited amounts, but cereals, roots and pulses (legume seeds) containing a greater amount of starch are not easily digested unless cooked. Fruits and vegetables are of importance in the diet because of their mineral element and vitamin content. A great deal of these, however, may be lost, due to their being heat liable, water soluble, or sensitive to alkaline media. Losses of thiamine and vitamin C in particular, occur these ways. Wastage of the outer darker green leaves of vegetables can also cause losses of carotene and vitamin C in the diet. Apart from these losses of nutrients during the preparation and cooking of vegetables, cooking may result in the loss of colour, especially in green vegetables. The rate at which colour change takes place depends on the pH, cooking temperature and cooking time. Sodium bicarbonate added to water increases the pH and improves the colour, but has a detrimental affect on thiamine and vitamin C, and is not recommended.
Many cereal grains, particularly wheat in the U.K., are reduced to flour before being eaten, and in the milling process the percentage of flour produced from a given weight of grain can vary. This percentage is known as the extraction rate, and the higher the extraction rate, the fewer materials have been removed from the original grain.
When white flour is produced, the bran (husks), germ (reproductive element - good source of fibre) and scutellum (outer shell) of the grain are removed. The bran contains a high proportion of B group vitamins and about 50% of the mineral elements (calcium and iron mainly) of the whole grain. The germ is rich in fat, protein, B group vitamins, vitamin E and iron. The scutellum is extremely rich in thiamine.
How Does Cooking Affect Vitamins?
Some vitamins are more stable (less affected by cooking and processing) than others. Water soluble vitamins (B-group and C) are more unstable than fat soluble vitamins (K, A, D and E) during food processing and storage.
The most unstable vitamins include:
- Folate (Vitamin B9)
- Thiamine (Vitamin B1)
- Ascorbate (Vitamin C)
More stable vitamins include:
- Niacin (vitamin B3)
- Vitamin K
- Vitamin D
- Biotin (vitamin B7)
- Pantothenic acid (vitamin B5).
Many things can affect a food's nutrient content, from the growing, harvesting, storing and preparing of food. Here we will look at cooking and preparation.
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