Improvement Of Enzyme-mediated Crosslinking Modidfication For Gluten With α-polylysine And The Properties Of Gluten Films

Wheat gluten is the main protein of wheat. It has unique viscoelastic, good biocompatible and biodegradable properties. Wheat gluten is an ideal raw material for preparing protein films. The transglutaminase(TGase) is an enzyme that catalyzes an acyl-transferring reaction in which ε-(γ-glutamyl) lysine bonds are formed using the γ-carboxyamide groups of peptide-bound glutamine residues(acyl donor) and the amino groups of lysine side chains(acyl receptor). Wheat gluten is a good substrate for TGase. In this paper, wheat gluten was used as the raw material to prepare film based on the crosslinking modification induced by TGase. To improve the reaction efficiency of gluten induced by TGase, α-polylysine was introduced into the crosslinking reaction system to increase the amount of acting site in gluten. Meanwhile, the gluten/silk fibroin composite films were prepared based on the TGase-mediated crosslinking modification of gluten in the presence of silk fibroin and α-polylysine. The composite films were expected to overcome the disadvantage of poor performance of single gluten films. In this paper, the preparation method of gluten films and the catalytic conditions of TGase were discussed. The effects of α-polylysine on enzymatic reaction were investigated. The properties of the gluten films with the percentage of weight loss in water, hydrophobicity, microstructure, thermal stability and application in food preservation were measured.The results showed that the protein solution has good film forming properties when the protein concentration was 5%(g/mL) and the concentration of the glycerol was 1%(g/mL) in the film-formation solution. The tensile strength of gluten film was up to 4.36 MPa when the catalytic conditions of TGase were as follows: TGase dosage: 20 U/g gluten, pH 7.0, reaction temperature: 40 ℃and reaction time: 3 hours. The content of ammonia released into the reaction solution induced by TGase was increased significantly in gluten and gluten/silk fibroin solution with the presence of α-polylysine. SDS-PAGE proved that the content of macromolecule polymers was improved in the enzymatic reaction system after introducing α-polylysine into the solution. Gluten/silk fibroin composite films had a better mechanical property than single gluten films. The tensile strength of gluten/ silk fibroin composite films from the gluten/silk fibroin solution modified with TGase at the presence of α-polylysine reached 5.21 MPa, Meanwhile, the gluten/ silk fibroin composite films have more hydrophobic property, better thermal stabilities, lower water solubility and better storage of small tomato than gluten/ silk fibroin composite films without any modification. Scanning electron microscope(SEM) displayed a rougher surface and a more compact network structure of films modified with TGase and α-polylysine.