A novel process to efficiently form transglutaminase-set soy protein isolate-stabilized emulsion gels

A novel process to efficiently form soy protein isolate (SPI)-stabilized emulsion gels, induced by microbial transglutaminase (MTGase) was reported, with the enzyme added before the emulsification (instead of after the emulsification in the conventional case). The rheological behavior and microstructure of the formed emulsion gels (at a constant protein concentration of 6 g/100 mL and oil fractions (ø) of 0.2-0.6) were characterized using dynamic oscillatory measurement and confocal laser scanning microscope. The gel stiffness of the formed gels with the novel process progressively increased with increasing enzyme concentration (1.0-5.0 U/g), or with the ø increasing from 0.2 to 0.6. Interestingly, the gel stiffness at a given ø with the novel process was considerably greater than that with the conventional process, though the enzyme concentration was less (e.g., 1.0 vs 20 U/g). Furthermore, a pre-incubation (15-60 min) of the proteins with the enzyme (before the emulsification) greatly improved the gelation. The analyses of droplet size and amount of entrapped proteins within the gel matrix indicated that during the initial gel network, the bridging flocculation of oil droplets played a prominent role, but the full development of the gel stiffness mainly depended on the inter-droplet covalent cross-linking.