Effect of transglutaminase concentration on the properties of soy protein isolate-pectin composite edible films

Enzymes such as transglutaminase (TGase) have been used to catalyze protein cross-linking reactions to enhance protein properties. The present study investigates the effects of TGase treatment and concentration on the properties of soy protein isolate (SPI)-pectin films. SPI-pectin films were prepared by adding 0.5 %, 1 %, and 1.5 % TGase. The film with no added enzyme served as a Control. Film thickness, water activity (a_w), and antioxidant activity slightly increased (P < 0.05). Film opacity increased (P < 0.05) with the addition of TGase. Transparency significantly (P < 0.05) reduced at 1.5 % TGase concentration. The water vapor permeability (WVP) of the films declined after being enzyme-treated. Besides, increased TGase concentration affected mechanical properties; films with the highest TGase concentration, i.e., 1.5 %, were least (P < 0.05) stiff and had the lowest Young's Modulus and tensile strength. However, this film had the highest % elongation. 1 % TGase film was the toughest to break, recording the highest total area (5758 g.sec) followed by the Control (5628 g.sec). TGase cross-linked films possessed higher (P < 0.05) water holding capacity (WHC) than that of Control films. As investigated through Scanning Electron Microscopy (SEM), TGase-treated films revealed different degrees of protein cross-linking as a function of enzyme concentration. However, the 1 % enzyme concentration led to a compact film structure with no microfractures. Overall, TGase treatment can be a practical approach to enhancing protein-based film properties.