Properties of Alaska pollock skin gelatin: A comparison with tilapia and pork skin gelatins

The objective of this work was to compare the physiochemical and rheological properties of Alaska, pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some, mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (similar to 11%) or pork skin gelatin (similar to 13%). Most of the protein fractions in AG were alpha chain, beta chain, and other oligomers. The gel strength of AG was 98 gram-force at 10 C-degrees, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil-drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G' was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G and a minimum in G ''. G' was found to be a power law function of concentration for all gelatins used: G' = k x C-n. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in., a higher melting temperature and a broader melting region for all gelatin gels. For both the AG-pork and AG-tilapia mixed gels, the got melting temperatures decreased and melting regions narrowed as the AG fraction was increased.