Reversibility of the gel, rheological, and structural properties of alcohol pretreated fish gelatin: Effect of alcohol types

The reversibility of gel property of alcohol (methanol, ethanol)-pretreated fish gelatin (FG) were investigated through removing alcohol solutions by freeze drying. Results showed that the gel strength and the hardness of FG could be retained (1%, 40%) or even improved (1% methanol) using low or high concentration alcohol solutions, while decreased in medium concentration alcohol solutions. Compared with untreated FG, rheology results showed that, all alcohol solutions pretreated FG had lower apparent viscosity, while higher alcohol solutions pretreated ones decreased the gel and melt points and shorten the gelation time. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis showed that methanol pretreated FG had the higher alpha contents than those of ethanol pretreated. Circular dichroism spectra results indicated that beta-sheet could be decreased after removing ethanol solutions, whereas the beta-sheet increased after removing the methanol solutions. Moreover, low field nuclear magnetic resonance relaxation test showed that pretreated FG had lower transverse relaxation times of internal water (T-21 and T-22) compared to that of the untreated FG. Overall, FG still retains higher gel properties after removing the low or high alcohol concentrations.