Adhesion properties of soybean protein/transglutaminase/pectin composite adhesives improved by adjusting tannic acid content

Soy protein isolate is often used to make adhesives. Inspired by the adhesion mechanism of mussel proteins, this study developed a plant-based adhesive composed of soy protein isolate (SPI), low-ester pectin, tannic acid (TA), and transglutaminase (TGase) for bonding simulated fat and muscle in plant-based meat analogues. The results demonstrated that TA enhanced the viscosity, thermal stability, and fluidity of the adhesive by forming a cohesive network. Structural analyses revealed that covalent interactions between SPI and TA peaked at 2.5 wt%. The apparent viscosity results demonstrated that the TA concentration had a significant effect on the viscosity of the adhesive, lower concentrations (0-1.0 wt%) reduced the viscosity of the adhesive, whereas higher concentrations (1.5-3.0 wt%) increased it. Tensile adhesion tests showed that the mechanical properties of the adhesive reached their optimum value when the TA content was 2.0 wt%. Thermodynamic analysis indicated that TA improved the stability of the adhesive and reduced heat loss; however, excessive TA (3.0 wt%) led to aggregate formation, weakening the binding force between TA and protein molecules, and decreasing the thermal stability of the adhesive. Tannic acid content is a key factor affecting the viscosity, thermal stability, and fluidity of SPI/TGase/pect in/TA (SPTTA) adhesives. This study provides a new formulation and methodology for the development of plant-based adhesives for meat products.