occurring ingredients contain various amounts of proteins,
carbohydrates, fats, water and minerals. Cooking involves manipulating
the chemical properties of these substances.
Carbohydrates — These include sucrose (common table sugar or cane sugar), a disaccharide made up of the simple sugars glucose and fructose; as well as starches such as cereal flour, rice, arrowroot and potatoes. Simple carbohydrates are chemical structures comprising one or two sugars. Complex carbohydrates, such as whole grains and vegetables, contain three or more sugars and are generally rich in fibre, vitamins and minerals.
Fats — Vegetable oils, animal products such as butter and lard, as well as grain oils such as corn and linseed oils, are all types of fat. Fats can reach temperatures higher than the boiling point of water and are often used to conduct heat to other ingredients, such as in frying or sauteing.
Protein — Edible animal products, such as meat, offal, milk and eggs, contain substantial amounts of protein. Almost all vegetable matter (in particular legumes and seeds) also includes protein, although generally in smaller amounts. Mushrooms have a high protein content. Any of these may be sources of essential amino acids. When proteins are heated they become denatured and change texture. In most cases, the material becomes softer or more friable (e.g. meat). In some cases, proteins form more rigid structures when heated (e.g. the coagulation of albumen in egg whites). The beating of egg whites to form a relatively rigid but flexible structure is an important component in baking cakes and is the basis of meringue making.
Vitamins and minerals — Vitamins are organic compounds that are required for normal metabolism, although the body cannot manufacture them itself and must obtain them from external sources. Good sources of vitamins are fresh fruit and vegetables (vitamin C); carrots and liver (vitamin A); cereal bran, bread and liver (B-group vitamins); fish-liver oil (vitamin D); and fresh green vegetables (vitamin K). Small quantities of minerals such as iron, calcium, magnesium and sulphur are also essential; and copper, zinc and selenium are needed in very small quantities. The micronutrients, minerals and vitamins contained in fruits and vegetables may be destroyed by cooking. Vitamin C is especially prone to oxidation during cooking and may be completely destroyed by protracted cooking. The availability of some vitamins such as thiamin (vitamin B1), vitamin B6, niacin (vitamin B3), folic acid (vitamin B9), and carotenoids (vitamin A) increases with cooking.
Water — Stock, wine, water or other liquids containing water are added during cooking, and water is also released from some foods as they cook. Liquids are such an important ingredient that the name of the cooking method often refers to how the liquid is used (e.g. to steam, simmer, boil, braise or blanch). When liquid is heated in an open pan, the rate of evaporation rapidly increases, concentrating the remaining ingredients and intensifying flavours. This is an essential part of stewing and sauce making.Food poisoning and other illnesses may be caused by bacteria, viruses and protozoa in uncooked or inappropriately prepared food. Raw leaf vegetables, undercooked meat and non-boiled water may contain parasites. Cooking can kill such organisms, or make them harmless. The sterilising effect of cooking depends on temperature, cooking time and the technique used. However, some bacteria can form spores that survive cooking, which then germinate and grow after the food has cooled. It is therefore recommended that cooked food should not be reheated more than once in order to prevent bacteria from proliferating to dangerous levels.
Cooking prevents many food-borne illnesses and also increases the digestibility of some foods. Foods such as grains are inedible when raw, and some foods, like kidney beans, are poisonous if not properly cooked.
Food safety must also be taken into consideration during the preparation, handling and storage of ingredients. Cold foods should be stored at 4°C or less, and hot foods should be kept hot at 60°C or above to avoid the "danger zone" in which bacteria are most likely to proliferate. Good practices include washing hands and wiping down surfaces, and avoiding cross-contamination. Plastic chopping boards may be less likely to harbour bacteria than wooden ones. It is recommended to washing and sterilise chopping boards, especially after preparing raw meat, poultry or seafood.
Proponents of raw food argue that cooking has a detrimental effect on foods and increases health risks. During cooking, the vitamin C contained in vegetables and fruits dissolves in the cooking water, and the food itself is degraded through oxidation. Peeling vegetables can also substantially reduce their vitamin C content: most of the vitamin C in potatoes, for example, is contained in the skin. Some scientists claim that diets that include large amounts of raw vegetables significantly reduce the risk of breast cancer.
According to some studies, more than 30 percent of cancer deaths may be prevented by making dietary changes. Some cancers may be caused by carcinogens in food generated during cooking processes, although it is often difficult to identify the specific dietary components responsible for increased cancer risk. Many foods, such as beef and broccoli, contain low concentrations of both carcinogens and anti-carcinogens. Several studies published in recent decades indicate that cooking meat at high temperatures creates heterocyclic amines (HCAs), which are thought to increase cancer risk in humans. Microwaving meat before cooking may reduce HCAs by 90 percent. Grilling, barbecuing or smoking meat and fish increases the levels of carcinogenic polycyclic aromatic hydrocarbons (PAHs). Baking, grilling or broiling food, especially starchy foods, until a crust forms, generates significant concentrations of acrylamide, a possible carcinogen.
Heating sugars with proteins or fats can produce substances that have been linked to ageing, diabetes and obesity. Deep-fried foods may contain high levels of trans-fats, which are known to increase the risk of heart disease.
Source: Various online resources