Characterization of edible films from skin gelatin of brownstripe red snapper and bigeye snapper

Edible films were successfully prepared from fish skin gelatin of brownstripe red snapper (Lutjanus vitta) and bigeye snapper (Priacanthus macracanthus). Films with greater protein content had higher thickness and mechanical properties (tensile strength, TS and elongation at break, EAB) but lower water vapor permeability (WVP) than those with lower protein content. Films without glycerol were mostly brittle, and became more flexible in the presence of glycerol. TS generally decreased with increasing glycerol concentration from 25 to 75%. Films prepared from bigeye snapper skin gelatin exhibited the lower mechanical properties than those of brownstripe red snapper at any glycerol concentrations used. Marked decreases of transition temperature and transition enthalpy of the films were observed with increasing glycerol content. Films from bigeye snapper skin gelatin contained the lower content of high-molecular-weight cross-links with the concomitant increased degradation peptides, compared with gelatin powder and films from brownstripe red snapper skin gelatin. The addition EDTA and soybean trypsin inhibitor into the film forming solution (FFS) of bigeye snapper skin gelatin totally inhibited and mostly retarded the degradation of gelatin components, respectively. This suggested that metallo- and serine- proteinase/collagenase actively involved in protein hydrolysis in bigeye snapper skin gelatin, especially during FFS preparation. Addition of EDTA also increased TS and EAB of film from bigeye snapper skin gelatin.