Effect of ammonium sulfate fractional precipitation on gel strength and characteristics of gelatin from bighead carp (Hypophthalmichthys nobilis) scale

Gelatin from bighead carp (Hypophthalmichthys nobilis) scale was extracted with the gel strength of 415.7 ± 9.9 g. Ammonium sulfate fractional precipitation (ASFP) with different ammonium sulfate saturations (20%, 25%, 30%, 35% and 40%, respectively) separated fish gelatin components with different gel strengths (469.7 ± 12.0 g, 419.7 ± 9.9 g, 181.9 ± 17.7 g, 83.9 ± 9.9 g and 15.3 ± 2.1 g, respectively). ASFP did not destroy characteristic FTIR peaks (amide A, amide I, amide II and amide III) and X-ray diffraction peaks (around 7° and 20–21° represented the triple-helix structure and the single left-hand helix chain, respectively) in the fish gelatin. In addition, lower ammonium sulfate saturation precipitated the fish gelatin component with stronger hydrogen bond, more triple-helix structures, higher molecular weight distribution and denser microstructure. Prominently, fish gelatin with higher gel strength had greater amount of high molecular weight components and denser microstructure.