Functionality of Proteins in Meat Products

Quality attributes of meat and meat products are often described in terms of protein functionality, i.e., any inherent or process-generated property of proteins that affects physical and sensory characteristics of raw and finished products. For example, in comminuted meats, the ability of a muscle mince to form a three-dimensional gel matrix, to emulsify fat, and to retain natural and added water are some of the most important functional properties. These physicochemical processes greatly influence product texture, integrity, physical stability, cooking yield, appearance, and hence, palatability and consumer acceptance. Processed meats are heterogeneous systems composed of muscle itself and various nonmuscle ingredients including polysaccharides, flavor agents, salt, and phosphates. It is well established that proteins are largely responsible for the functional characteristics of muscle foods. This conclusion is based on the pioneering research conducted by Fukazawa and coworkers in the early 60’s (Fukazawa et al., 1961) and on numerous studies that subsequently followed (for review, see Acton, et al., 1983; Asghar et al., 1985, Gordon Barbut, 1992; Xiong, 1997). Today, two questions are still frequently asked by meat processors: 1) what are the major factors affecting meat protein functionality, and 2) how can we predict product quality from functional properties of raw material constituents? Data generated from model systems are sometimes difficult to extrapolate to in situ conditions of processed meats, because the environment of model systems is usually oversimplified from that of processed meats in order to address specific questions. Nevertheless, it is generally agreed that functional behaviors of proteins in processed meats and in isolated systems are controlled by the same factors, e.g., characteristics of the protein itself, temperature, pH, and ionic conditions. For example, emulsification and gelation properties of isolated myofibrillar proteins can explain most, if not all, of the stability issues relevant to raw and cooked meat batters (Galluzzo Regenstein, 1978; Jones, 1984; Barbut, 1995). The hydration properties of salted meat clearly reflect protein-water interaction and salt-induced structural changes in the myofibrillar matrix (Offer Trinick, 1983; Parsons Knight, 1990). Similarly, bind strength and thus, texture and integrity of restructured meat products can be largely accounted for by the gel-forming properties of salt-soluble proteins extracted to the meat particle surface or added to the product formulation (Fukazawa et al., 1961; Siegel Schmidt, 1979; Kenney et al., 1992; Xiong et al., 1993). Despite extensive research conducted in the field of muscle protein functionality, meat scientists are constantly challenged by new questions and pressing issues. For example, we have changed the traditional way of making sausage with up to 30% fat to new practices of making sausage with less fat (low or no fat) but up to almost 40% added water. This change translates into a lower ionic strength for the aqueous solution (in which proteins are bathed) from about 0.82 to 0.50, assuming muscle contains 75% water, and 2.5% salt is added to both types of products. The minimal ionic strength for solubilizing and extracting myofibrillar proteins is near 0.6. Therefore, how would protein behavior be affected by the reduced ionic strength, and what should meat processors be concerned about in making low-fat products with a much diluted salt concentration? In this reciprocation session, we will try to address some of the questions and concerns, and hopefully this will stimulate follow-up discussion about the topic of muscle and protein functionality. In particular, we will focus our discussion on the influence of various factors, inherent to muscle and processing, on the functionality of proteins. Methods that may be used to measure protein functionality will also be discussed.