Effect of transglutaminase and laccase on pea protein gel properties compared to that of soybean

Enzyme cross-linking is a pivotal method for enhancing the functionality of plant proteins, offering improvements in texture, stability, and nutritional value, which are essential for food applications. Pea protein is increasingly used as it is not identified as allergenic and has fewer other negative health concerns. However, the lower gelling capacity compared with soybean protein has limited its application in plant-based meat or protein-based products. Thus, this study focused on investigating the effects of transglutaminase (TG) and laccase (LAC) and their concentrations on pea protein isolate (PPI) gelation, towards comparison with that of soybean protein isolate (SPI). Results showed that TG and LAC both contribute to the formation of PPI gels while exhibiting different action ways. As the TG content increased, the particle size of PPI significantly increased from 97.27 ± 4.61 μm to 146.67 ± 9.87 μm at 0.8% TG concentration, whereas the particle size remained constant with increasing LAC content. Both TG and LAC significantly enhanced the PPI gel properties, with 0.4% TG addition resulting in gel strength comparable to SPI and 0.8% TG content increasing PPI gel strength by approximately 4.2 times compared to the control, surpassing SPI. Moreover, PPI with TG treated demonstrated superior effects compared to LAC-treated gels at the same concentration. Water retention of gels increased from 89.37 ± 1.97% to 94.90 ± 3.86% with TG concentration increasing, while it decreased with LAC increasing. SDS-PAGE results revealed that TG promoted the formation of larger aggregates in PPI, indicating that legumin and vicilin were the main target sites for TG, while LAC was inapparent on molecular weight. The viscosity of PPI increased from 36.91 ± 2.32 Pa·s to 70.57 ± 1.00 Pa·s with 0.8% TG, while 0.8% LAC increased viscosity to 61.79 ± 1.32 Pa·s. Hydrogen bonds and disulfide bonds play a crucial role in the gel formation process facilitated by TG and LAC. Besides, TG is also expected to contribute through the formation of isopeptide bonds. These findings validated the potential of TG and LAC in improving the quality of PPI gels and provided insights for the application and development of cross-linking enzymes in the protein processing industry.