Soy protein isolate (SPI) was preheated at 90°C and 95°C for 3 min to obtain preheated samples, SPI 90 and SPI 95 , respectively. The preheat treatment increased protein hydrophobicity and decreased the aggregation of 11S acidic and basic subunits. The 7S and 11S soy proteins exhibited a decreased thermal stability when mixed with pork myofibrillar protein isolate (MPI). The presence of preheated SPI accelerated the disappearance of myosin heavy chain in the gelling process. Incorporation of preheated SPI significantly increased the MPI gel elasticity and hardness while native SPI showed negative effects.

Native and briefly heated (85 °C for 3 min) soy protein isolates (SPI) were partially hydrolyzed (4% DH) by Alcalase ® and Flavourzyme™ before incorporation into a pork myofibril isolate (MPI) system. The hydrolysis of soy protein enhanced its interaction with MPI, leading to a decreased thermal stability of both soy and muscle proteins. Alcalase SPI hydrolysates, when compared with nonhydrolyzed SPI, improved viscoelastic properties and hardness of MPI gels, while Flavourzyme SPI hydrolysates had an adverse effect. Hydrolyzed SPI augmented emulsifying properties of MPI; the specific efficacy depended upon the type of enzymes used, the SPI:MPI ratio, and whether SPI was heated before hydrolysis.

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Native, heated, and enzyme (Alcalase ® , Flavourzyme™)-hydrolyzed soy protein isolates (SPI, 2%) were incorporated into pork frankfurters. Both heated and hydrolyzed SPIs improved product-cooking yield. The addition of heated and Alcalase-hydrolyzed SPIs produced a fine-stranded microstructure and improved frankfurter hardness, while addition of Flavourzyme-hydrolyzed SPI resulted in a more porous gel structure with reduced hardness, cohesiveness, and breaking strength. These results indicate that functional performance of SPI in frankfurters is critically affected by its pre-application treatment.

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