Isolation and characterization of a thermally stable collagen preparation from the outer skin of the silver carp Hypophthalmichthys molitrix

Abstract

Currently the main sources of collagen are still the skins of cows and pigs. However, the recent outbreaks of bovine spongiform encephalopathy (BSE) have sparked the development of new, alternative sources of safe collagen for industrial uses. In this work we studied the possibilities of using silver carp Hypophthalmichthys molitrix skin waste as a potential rich source of collagen. The collagen-containing preparation extracted from silver carp skins was a homogeneous, viscous gel, free of mechanical impurities. It was transparent and had a pH of 3.64. The water content varied from 95.0 to 97.5%. Total nitrogen was 14.3%, and the hydroxyproline content was 7.2%. After hydrolysis, glycine was the major amino acid in the collagen from the silver carp skins. There were also relatively high contents of proline, hydroxyproline, alanine and glutamic acid, in decreasing order of magnitude. The isolation procedure did not eliminate non-collagenous proteins extracted under the acidic conditions that probably thermally stabilize the isolated protein. Collagen is the main protein in the preparation, with an average total protein content of 75%. The protein consisted of two α chains (α1 and α2) classified as type I collagen. The remaining 25% of the protein fraction comprises smaller fragments that appear under the α bands corresponding to molecular masses ranging from 70–150 kDa, including a probable elastin band (8%); the remainder are unknown proteins and peptides (17%). The denaturation temperature (revealing thermal stability) of collagen from silver carp skin investigated using circular dichroism spectroscopy and differential scanning calorimetry was 34.5–34.8 °C.