Processing Optimization and Physicochemical Properties of Collagen from Skate (Okamejei kenojei) Skin

Abstract

The processing of collagen from skin of skate (Okamejei kenojei) was optimized by the response surface methodology and the central composite design. The optimal condition included the following independent variables: 0.45 N NaOH concentration, 23.4 NaOH treatment hours, 0.88% additional ratio of pepsin, and 46.8 extraction hours. The collagen content estimated under the optimal condition was 6.94%, and the actual experimental collagen content was 6.56%. Physicochemical properties of collagen extracted from skate skins were characterized by amino acid analysis, SDS-PAGE, FT-IR, solubility and denaturation temperature. Collagen from skate skin had an imino acid (Hyp+Pro) of 152 residues/1,000 amino acids. The SDS-PAGE pattern of the skate collagen indicated two different α-chains (α1 and α2), β-component and γ-component. This pattern is similar to that of calf skin collagen, but the skate collagen has a different mobility. FT-IR of collagen from skate and calf skins showed such regions of amide A, I, II and III as 3284 and 3313 cm-1 (amide A); 1650 and 1640 cm-1 (amide I); 1549 and 1547 cm-1 (amide II); 1238 and 1237 cm-1 (amide III), for collagens of skate and calf skins, respectively, exhibiting similar wave numbers to each other. Solubility of the skate skin collagen on NaCl concentration is hardly changed up to 2%, and then it was decreased from 3% to 5%. Solubility of the skate skin collagen on pH variation was high in the range of pH 3~5 and then sharply decreased up to pH 7. Denaturation temperature of the skate skin collagen was 23℃ which was lower by about 10℃ than that of calf skin collagen.