Alcalase assisted production of novel high alpha-chain gelatin and the functional stability of its hydrogel as influenced by thermal treatment

High alpha-chain (α-chain) content is associated with superior quality gelatin. In this study, a production process involving mild alcalase treatment was optimized by response surface methodology, and the α-chain was quantified based on SDS-PAGE. A novel fish skin gelatin high in α-chain (32% of total protein, 45 mg/g fish skin of yield) was produced at optimum conditions, i.e., 2.3 U/g alcalase addition to fish skin for 0.5 h at 25 °C, followed by water extraction at 67 °C for 7 h. The novel gelatin contained 34% glycine and 16% imino acids as determined by UPLC. FTIR analysis disclosed four characteristic infra-red amide absorption bands. DSC and TGA analysis revealed thermal decomposition at 215 °C. Novel gelatin hydrogel (1%, w/v) could withstand a wide range of temperatures, and exhibited high emulsifying activity and viscosity, as well as stable gel clarity from 35 °C to 80 °C. The high temperature treatment (95 °C) produced hydrogel with lower clarity and emulsifying activity but higher viscosity than at the other temperatures. All heat-treated gelatin hydrogels behaved as non-Newtonian fluids as per the Ostwald de Waele model. The novel high α-chain fish skin gelatin has potential broad application in food, pharmaceutical and biological industries.