Structure-function relationships of muscle proteins

Proteins, the most important functional components in muscle, confer many of the desirable physicochemical and sensory attributes of muscle foods. As already described in previous chapters. functionality of proteins in food processing refers to any property of the protein that affects palatability of the final product, and it should be distinguished from functionality of proteins in living tissues (e.g., ion transportation through the cell membrane; enzyme catalysis). Muscle proteins comprise 15-22% of the total muscle weight (about 60-88% of mass) and can be divided into three major groups on the basis of solubility characteristics: sarcoplasmic proteins (water-soluble). myofibrillar proteins (salt-soluble), and stromal proteins (insoluble). Of the three groups. myofibrillar proteins play the most critical role during meat processing as they are responsible for the formation of thermally induced cohesive structures and the firm texture of meat products. The functional behavior of myofibrillar proteins is manifested by their ability to produce three-dimensional, viscoelastic gel matrices via protein-protein interactions, to bind water, and to form cohesive and strong membranes on the surface of fat globules in emulsion systems or flexible films around the airlwater interface. These functional properties are the major factors contributing to palatability or sensory perception (tenderness, juiciness, mouthfeel, etc.) of processed meat products. A number of sarcoplasmic and stromal proteins also possess desirable functionalities, which are important for producing consumer-acceptable muscle foods. For instance. myoglobin imparts a desirable pinkishred color to meat, and the specific color is dictated by the chemical state of the heme moiety as well as the structure of globin, the protein moiety. Hydrolyzed collagen derived from the connective tissue has excellent water-binding ability and. therefore. is able to improve the water-holding capacity and tenderness of cooked meat products.