- Processing Food -

Cooking

Cooking can be both detrimental and beneficial to the nutrient content of food.

Beneficial effects of cooking

Cooking is important in food processing. Although cooking results in the loss of some nutrients, it can also convert other nutrients into a form that would otherwise not be used by our bodies. Cooking also produces the desired texture, flavour and palatability we want in our food.

Starchy foods such as potatoes, corn, beans, and lentils are made more digestible by cooking. The nutritive value of the protein in legumes such as soya beans, lima beans, lentils and chick peas is also improved by cooking. Heating these foods destroys substances that would otherwise interfere with the digestibility of the protein. Adequate cooking of the foods is particularly important when they comprise the main source of protein. Other substances in soya beans, kidney beans and lentils can produce toxic effects unless cooked prior to eating. Egg whites and some fish, unless cooked, are not an effective source of the vitamins biotin and vitamin B-1 respectively. Heating flour during baking increases the amount of niacin that can be utilized by the body.

Cooking is also necessary to ensure that food is free from harmful levels of micro-organisms. As well as causing undesirable flavours and odours in food these organisms can sometimes lead to illness.

Nutrient loss during cooking

Losses of protein and carbohydrate during cooking are generally small. The amount of fat in food may be either reduced or increased depending on the method of cooking. Generally, grilling will lower the fat content and frying will increase it. The smaller the size of the pieces being fried, the greater the amount of fat that will be absorbed per 100 grams. The largest vitamin loss during cooking is usually due to destruction of vitamin C, and to a lesser extent vitamin B-1 and the other water-soluble vitamins. A few simple guidelines for maximizing vitamin retention during cooking are listed in Figure 31.

Pressure cooking

Pressure cooking involves cooking at higher temperatures for shorter times compared with normal boiling. Because the vegetables are in contact with steam rather than boiling water, less of the water-soluble vitamins dissolve in the cooking water. Generally, pressure cooking will retain more nutrients than normal boiling. However, food steamed or boiled in a small amount of water in a tightly covered saucepan is likely to be as nutritious as food cooked in a pressure cooker.

Microwave ovens

Microwave cooking is much quicker than conventional cooking. The microwaves preferentially heat the water in food so that the cooking process is essentially similar to that of steam cooking. With meat, the differences in vitamin B-l and vitamin B-2 retention between microwave cooking and conventional grilling or roasting are small. With vegetables, the vitamin C in microwave-cooked food is similar to that achieved by cooking with steam or using a small amount of water in a tightly covered saucepan. Generally, microwave cooking retains nutrients as well as conventional methods.