Extraction optimization and properties of collagen from yellowfin tuna (Thunnus albacares) dorsal skin

Yellowfin tuna (Thunnus albacares) dorsal skin obtained from tuna processing was used as a source of fish collagen. Optimization of collagen extraction was investigated by using a central composite design of response surface methodology. The optimal conditions were X1=0.92 N (NaOH concentration), X2=24 h (NaOH treatment time), X3=0.98% (w/v) (pepsin concentration) and X4=23.5 h (digestion time). The predicted collagen content under optimal conditions was 26.7%, and the actual experimental collagen content was 27.1%. The properties of yellowfin tuna dorsal skin collagen were characterized by amino acid analysis, SDS-PAGE, FT-IR, solubility and viscosity. The yellowfin tuna dorsal skin collagen had a 20.5% imino acid content. Electrophoresis revealed two different α (α1 and α2) chains, β-component and γ-component. FT-IR showed regions of amides A, I, II and III were 3427, 1651, 1544 and 1240 cm−1, respectively. Collagen solubility sharply decreased at over pH 4.0 and it was relatively low in the range of pH 5.0–9.0. Collagen solubility continuously decreased with increasing salt concentrations up to 4% and was little changed at higher concentrations. The viscosity of the collagen solution decreased at a constant rate until 32 °C and then decreased at a slower rate from 33 to 50 °C.