ABSTRACT
This chapter explains the classification systems for proteins and their distribution in food. Proteins are made up of chains of amino acids. The dispensable amino acids can be synthesised by the attachment of an amino group (–NH2) to a metabolic intermediate in one of the metabolic pathways. Protein digestion begins in the stomach, where pepsin secreted by the chief cells and hydrochloric acid secreted by parietal cells begin protein breakdown. Proteolytic activity in the stomach is not critical to adequate protein digestion, since more powerful proteolytic enzymes produced by the pancreas are capable of achieving complete digestion of most dietary proteins in the gut. The end products of protein digestion by the pancreatic enzymes include a proportion of free amino acids, with the major part left as short chain peptides. Proteins make up a large part of the machinery of the living body and have a number of functions.
