Basics of Food Chemistry

Food is the body's source of nutrients, which serve two broad purposes: some are burned as fuel to supply energy, and others regulate growth and maintain or repair body tissues. Nutrition science groups these nutrients into six classes -- carbohydrates, lipids (fats and oils), proteins, vitamins, minerals, and water. Different food groups supply different nutrients: grains, fruits and vegetables are the main sources of carbohydrates and vitamins; meat, fish, eggs, dairy products and pulses are the main sources of proteins (and also supply vitamins); and vegetable oils, dairy products and animal fats are the main sources of lipids. Chemically, most of these nutrients are large organic molecules, and two of the major classes -- proteins and carbohydrates -- are themselves polymers, built from repeating smaller units. During digestion, enzymes break these polymers down into their constituent monomers: proteins break down into alpha-amino acids, and carbohydrates break down into glucose. Cooking assists this process before digestion even begins. During cooking, the large polymer molecules of protein and carbohydrate in raw food are partly hydrolysed into smaller polymer fragments, and in the process the food itself changes physical character: an uncooked food mixture behaves as a heterogeneous suspension, while …