Properties of gelatins from some selected Pangasius skins

Abstract

Gelatin is a gelling protein. It is mostly made from a hide of porcine and bovine. Fish skin is an alternative source of gelatin. Pangasius is one of the most important aquaculture, especially in the northeast part of Thailand.  Its skin, which is a major byproduct of the fish-processing industry, could serve as valuable source of gelatin. However, the information on physicochemical properties of gelatin from Pangasius has been rarely reported. Thus, the objective of this study was to characterize the gelatin from the skin of some members of Panasiidae family including striped catfish (Pangasius hypophthalmus), black ear catfish (Pangasius larnaudii) and diamond green fish (Pangasius larnaudii x Pangasius bocoarti). The process of gelatin preparation consisted of 6 steps: 1) cleaning with cold water, 2) removal of non-collagenous portion by soaking with 0.2 M NaOH, 3) fat removal by soaking with 10% butyl alcohol, 4) collagen swelling in 0.05 M acetic acid prior to neutralization by washing with cold water, 5) extraction of the gelatin at a ratio of swollen FS to distilled water of 1:10 for 12 h at 60^°C and 6) filter and drying at 65^°C. Proximate compositions and physicochemical properties of fish skin gelatins were evaluated. The highest yield (18.15 % dry basis) for gelatin extraction was obtained from the skin of diamond green fish. The major component of gelatins from various fish species were 89.09-91.24% dry basis of protein. Fat contents were in the range of 0.77-2.73 depended on fish species (P<0.05). The pH values of gelatins were 5.04-5.06. In comparison with commercial gelatin, the significant difference of gel strength, color and turbidity were found (P<0.05). The highest gel strength was observed for gelatin extracted from skin of striped catfish while the lowest turbidity and highest lightness was found for commercial gelatin. In addition, black ear catfish gelatin had higher foaming expansion.