Effect of ethanolic extract of coconut husk on gel properties of gelatin from swim bladder of yellowfin tuna

The impacts of ethanolic extract from coconut husk (EECH) rich in tannic acid at different levels (0.25, 0.5, 0.75, 1, 2, 3 and 5 mg g−1 dry gelatin) on gel properties of gelatin from yellowfin tuna swim bladder were investigated. Gel strength of gelatin increased when EECH concentrations increased up to 0.5 mg g−1 (p < 0.05). Nevertheless, the gradual decrease in gel strength was found with increasing EECH levels. When EECH at different levels was incorporated, no marked changes in protein patterns determined by SDS-PAGE were observed, suggesting that most of bondings were hydrogen bond or other weak bonds. Gel matrix with uniformity and larger strands were observed with gels added with 0.5 EECH mg g−1. Gelling and melting temperatures were also increased when EECH at a level of 0.5 mg g−1 was incorporated. The color of all gelatin gels slightly increased with increasing concentrations of EECH. Therefore, ethanolic extract from coconut husk at an appropriate level could act as a natural gel enhancer of gelatin.