Mechanical and rheological effects of transglutaminase treatment on dense plant protein blends

Pea protein isolate (PPI) and mung bean protein isolate (MBPI) are rising alternatives for soy protein isolate in producing meat analogues. Transforming these isolates into full products is challenging due to their differences in functional properties compared with soy. Here, we report on the use of transglutaminase to improve the mechanical and rheological properties of dense MBPI and PPI dispersions. Gels from PPI and MBPI (40 wt% dry matter) were produced with 0, 0.1, 0.3, 0.5, and 0.7 wt% transglutaminase and incubation temperatures of 30, 40, 50, and 60 °C. Their mechanical and rheological properties were determined by tensile and closed cavity rheometer tests. The degree of crosslinking was determined by the OPA assay. Transglutaminase significantly increased fracture stress and strain of PPI gels, and to a lesser extent those of MBPI gels. The degree of free amino confirmed that this increase in PPI was due to formation of additional crosslinks. Amplitude sweeps identified that the rheological properties of PPI gels and MBPI gels were affected by the addition of transglutaminase, but in an opposite manner. Stress relaxation experiments showed that transglutaminase increased the elasticity of PPI gels and formed mainly small aggregates in MBPI gels. This work showed that the fibrous structure diminished when >0.1 wt% transglutaminase was added to PPI/MBPI - wheat gluten blends. To conclude, transglutaminase can be used to create intermolecular crosslinks in PPI gels, creating a full network, while mostly intramolecular crosslinks are formed in MBPI gels, leading to a cluster structure.