protein polypeptide, that is, a long chain of amino acids bound together by peptide bonds. Receptors, which receive chemical signals and identify sensory impressions such as taste and smell, are proteins. Enzymes are a particular class of proteins, whose function is to ensure that chemical reactions take place under controlled circumstances. Proteins lose their functional ability (denature) and their physical properties change when they are heated, exposed to salt and acid (for example, when cooked, salted, or marinated), or degraded by enzymes during fermentation. When proteins are broken down, smaller peptides and free amino acids, for example, glutamic acid, are formed.
