Food Proteins: Interactions and Functionality

Proteins are the most abundant macromolecules found in living cells and approximate half of the cell's dry weight. They are required in the food of humans, fish, and most higher animals. Historically, food proteins have been selected for their nutritional value and can be obtained from a wide variety of naturally occurring sources. Proteins undergo a wide range of structural and conformational changes through a variety of complex interactions during processing and storage. Such changes can affect the principal purpose of dietary proteins, which is to supply nitrogen and amino acids for the synthesis of proteins in the body. It is through an understanding of these interactions and their effects on functionality that food proteins have played a major role in the food supply. The macrostructure of a protein is primarily determined by its amino acid sequence. Amino acids are essential in basic nutrition, growth, and maintenance. Nine of the 20 identified amino acids, namely, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, are considered essential. They are so classified because they cannot be synthesized by humans and must therefore be supplied in the diet. When essential amino acids are not supplied in sufficient quantity, they restrict the adequate utilization of other amino acids and are thus termed limiting amino acids. The processing of food proteins is designed to reduce microbial and enzymatic spoilage, inactivate antinutritional substances, improve the a...