The effects of transglutaminase on soy protein isolate (SPI) film forming solution and films were investigated by rheological behavior and physicochemical properties based on different manufacturing conditions (enzyme treatments, enzyme incubation times, and protein denaturation temperatures). Enzymatic crosslinking reaction and changes in molecular weight distribution were confirmed by viscosity measurement and SDS-PAGE, respectively, compared to 2 controls: the nonenzyme treated and the deactivated enzyme treated. Films treated with both the enzyme and the deactivated enzyme showed significant increase in tensile strength (TS), percent elongation (%E), and initial contact angle of films compared to the nonenzyme control film due to the bulk stabilizers in the commercial enzyme. Water absorption property, protein solubility, Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopy revealed that enzyme treated SPI film matrix in the molecular structure level, resulted in the changes in physicochemical properties. Based on our observation, the enzymatic treatment at appropriate conditions is a practical and feasible way to control the physical properties of protein based biopolymeric film for many different scientific and industrial areas.
Practical application: Enzymes can make bridges selectively among different amino acids in the structure of protein matrix. Therefore, protein network is changed after enzyme treatment. The behavior of biopolymeric materials is dependent on the network structure to be suitable in different applications such as bioplastics applied in food and pharmaceutical products. In the current research, transglutaminase, as an enzyme, applied in soy protein matrix in different types of forms, activated and deactivated, and different preparation conditions to investigate its effects on different properties of the new bioplastic film.
Keywords: Soy protein isolate; biopolymeric film; packaging; rheological behaviour; transglutaminase.
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