Microbial transglutaminase-modified protein network and its importance in enhancing the quality of high-fiber tofu with okara.

Introducing okara to develop high-fiber tofu (HFT) can effectively increase the utilization of soy residues as well as enhance the nutrition of tofu. However, okara degrades the glucono-δ-lactone (GDL)-induced tofu quality. Current results showed that microbial transglutaminase (TGase) remarkably enhanced the gel strength, water holding capacity and viscoelasticity of HFT. During heating of soymilk, AB and A1,2,4 subunits of 11S were more prone to aggregate via disulfide (SS) bonds to form larger soluble protein aggregates under neutral condition, while the SS-mediated insoluble aggregates were formed under acid condition by GDL and predominantly contributed to the structure of tofu without TGase. TGase-induced intermolecular ε-(γ-glutamyl) lysine strengthened protein network and contributed the most to HFT structure. TGase promoted formation of protein aggregates more orderly, and okara was well-wrapped by protein network. These results demonstrated that the macro-protein aggregates crosslinked by TGase conspicuously strengthened the gel network and significantly elevated the HFT quality.