The influence of the addition of transglutaminase at different phase on the film and film forming characteristics of whey protein concentrate-carboxymethyl chitosan composite films

To reveal how transglutaminase (TG) affects the forming characteristics of whey protein concentrate (WPC)-carboxymethyl chitosan (CMCS) composite films and to develop the optimum approach for TG-modifying WPC-CMCS composite films, TG was added at different phases to WPC-CMCS composite films, and the properties and structural characteristics of the composite films and their film-forming solutions were investigated. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) results confirmed that TG could promote protein intermolecular polymerization to form macromolecular substances. TG could improve the mechanical and rheological properties of WPC-CMCS composite films, which depended on the TG addition phase during film preparation. The results from the film characterization showed that the mechanical properties and rheological property of WPC-TG-CMCS films are better than those of WPC-CMCS-TG films, which indicated that TG had stronger cross-linking ability with whey protein in WPC-TG-CMCS films. FTIR analysis showed that TG caused conformational changes in whey protein in composite films. X-ray diffraction analysis suggested that TG could promote the polymerization of protein molecules and reduce the porosity of the protein network structure, thus improving crystallinity. All the results suggested that the suitable addition phase of TG had a positive effect on the film-forming characteristics of WPC-CMCS composite films, and the films can be applied as an alternative for some petroleum-based packaging materials.