Interaction of myofibrillar and thermally/enzymatically modified soy proteins

Soy protein, as an abundant and nutritious food ingredient, is widely used in meat processing to modify the products' physical and sensory properties and to lower production cost. Interactions between pork myofibrillar proteins and thermally/enzymatically modified soy proteins were studied to: (1) elucidate the underlying mechanism of the functional role of soy protein in processed meats, and (2) identify the effect of preparation treatments on soy protein's performance.; Brief heating (90 or 95°C, for 3 min) and limited enzyme-hydrolysis (by Alcalase or Flavourzyme to a 4% degree of hydrolysis) dissociated soy globulins and increased protein surface hydrophobicity. Incorporation of native, heated, and enzyme-hydrolyzed soy protein isolates (SPI) into pork myofibrillar proteins (in 0.6 M NaCl, 25 mM phosphate, pH 6.0) decreased thermal stability of both protein groups, resulting in an accelerated disappearance of myosin heavy chain in the thermal gelation process. Heated and Alcalase-hydrolyzed SPIs improved muscle protein gel elasticity and hardness while Flavourzyme-hydrolyzed SPIs had an adverse effect.; Enzyme-hydrolysis improved soy protein's emusifying activity but diminished the emulsion stability. Addition of soy protein hydrolysates generally improved the emusifying properties of muscle proteins and the specific efficacy depended largely upon the type of enzyme used, the protein incorporation level, and whether SPI was denatured before hydrolysis.; Pork frankfurters containing 2% heated or enzyme-hydrolyzed SPIs showed an improved cooking yield. Frankfurters with heated or Alcalase-hydrolyzed SPIs exhibited a fine-stranded microstructure and an improved hardness, while frankfurters with Flavourzyme-hydrolyzed SPIs had a somewhat porous gel structure with reduced hardness, cohesiveness, and breaking strength.; The study identified the relationship between protein-protein interaction, protein functionalities, and physical properties of comminuted muscle foods that contain soy proteins, and the results suggest that thermal/enzymatic treatments are an effective means to enhance soy protein's functional performance in muscle foods.