Production of a novel non-toxic γ-PGA/casein composite hydrogel using MTG and optimization by response surface methodology

Abstract The γ-PGA-based food hydrogel exhibits good biodegradability and biocompatibility, and is non-toxic to humans. In this study, a novel hydrogel (γ-PGA/casein composite hydrogel) was prepared by combining casein with γ-PGA separated from natto using microbial transglutaminase (MTG) as the crosslinker. The effects of the MTG mass concentration, gelation time, crosslinking temperature, pH, and the mass ratio of γ-PGA to casein on the crosslinking ratio of γ-PGA and swelling ratio of the γ-PGA/casein hydrogel were investigated. Furthermore, the synthesis conditions were optimized by response surface methodology to optimize three important factors, i.e. crosslinking temperature, pH and the mass ratio of γ-PGA to casein. The results of single factor experiments showed that the MTG mass concentration and crosslinking time had little impacts on the crosslinking ratio of γ-PGA and the swelling ratio the preferred MTG mass concentration, crosslinking time, temperature and pH were selected as 0.3%, 7 h, 40 °C and 7.5; and the preferred mass ratio of γ-PGA to casein was 0.1 for the crosslinking ratio of γ-PGA and 0.2 for the swelling ratio. The response surface experiment results showed that the optimum crosslinking temperature, pH and the mass ratio of γ-PGA to casein ratio were 42.4 °C, 7.33, and 0.18, respectively. Under these optimum conditions, the predicted crosslinking ratio of γ-PGA and swelling ratio reached 90.35% and 112.07%, which were highly consistent with the experimental values (88.00% and 115.87%). The γ-PGA/casein composite hydrogel developed in this study shows promising application potential in food industry, biomedical field, and cosmetic industry.