Acid-Enzyme Modification And The Film Forming Properties Of Wheat Gluten

Wheat gluten, byproduct in the production of flour, is a cheap and abundant protein source. Due to its poor water solubility, wheat gluten is limited in the application in the food industry. However, because of the unique viscoelasticity and good biodegradability, wheat gluten films become a new type of green packaging materials. In this study, wheat gluten was modified by the combined treatment of citric acid and alkaline protease in order to improve the properties of wheat gluten film. In addition, effects of the addition of Micro-fibrilled cellulose (MFC) on the properties of MFC-WG films was also studied.The results showed that citric acid-alkaline protease treatment significantly improved the solubility of gluten, which increased from 4.35±0.05g/L to 16.90±0.19g/L. Further, the foaming ability of gluten with 22% deamidation degree and 5% hydrolysis degree significantly increased (increased 239.5% by volume), and the emulsion properties of 5% hydrolysis degree aslo increased from 230.3m2/g to 829.1m2/g. Fourier transform infrared spectroscopy(FTIR) spectras showed that the molecules of the modified protein was not changed, but the content of the molecules. The results of differential scanning calorimetry (DSC) and thermal analysis showed that the denaturation temperature and denaturation enthalpy of the protein decreased due to the modification. Rheological measurements showed that the modified protein’s solution viscosity increased with share rate which namely shear thickening.Wheat gluten film prepared with glycerin and investigated.The results showed trans-mittance was 28.44%; oxygen transmission rate was 49.8meq/kg; water vapor transmission rate was 3.75 ×10-6 g · m · m-2 · s-1 · Pa-1; tensile strength was 2.54MPa, and the elongation at break was 80.45%. Generally, gluten films has inferior in many properties,such as transmittance, oxygen barrier and mechanical properties.As MFC was added into the gluten films, the thickness, the light transmittance and tensile strength of the films gradually increased, whlie the oxygen permeability and water vapor permeability decreased.Film transmittance increased to 60.14%; oxygen transmission rate reduced to 26.9meq/kg; permeability reduced to 1.05 × 10-6 g · m · m-2 · s-1·Pa-1. When the content of MFC was 60%, the elastic modulus and tensile strength of the films were the highest, which were1935.83 ± 5.12MPa and 49.75 ± 2.67MPa, and the elongation at break decreased to 25.97 ± 0.16%. Because of the addition of MFC, the films had good mechanical properties and barrier properties. In addition, from the analysis of FTIR and DSC, C=N covalent bond generates in MFC and gluten’s blending process, resulting in a film mechanical enhancements. Further, the SEM results also gave an intuitive explanation. Since the MFC-WG films had good mechanical properties and barrier capacity, they could be applied to the food packaging industry in the future.