Effect of ultrasound pre-treatment on the characterization and properties of collagen extracted from soft-shelled turtle (Pelodiscus sinensis)

•Collagen yield was increased by 33.6% from calipash by ultrasound treatment.•Ultrasound did not disrupt the triple-stranded helical structures in collagen.•Solubility of collagen by ultrasound was superior to the other at the same pH.•Collagen had higher hydrolysis efficiency and antioxidant activity in digestion.

The aim of the present study was to evaluate the effect of ultrasound pre-treatment on the characterization and in-vitro digestion properties of collagen from turtle calipash and the antioxidant activity of its hydrolysates. The results showed that ultrasound significantly increased the collagen yield compared with that from conventional extraction (ASC, P < 0.05). Containing α1 and α2 chains, acid-soluble collagen (ASC) and the collagen with ultrasound pre-treatment (UASC) were characterized as type I collagen in SDS-PAGE patterns and UASC also maintained their structural integrity in the circular dichroism spectra. At the same pH, UASC had smaller particle size and larger absolute value of net charge than ASC. Moreover, ultrasound could induce apparent physical changes as looser, more porous and homogenous in microstructures imagines. Influenced by various pH, UASC showed higher solubility than ASC. Additionally, UASC was more prone to enzymolysis in vitro digestion and their hydrolysates showed significant increases antioxidant properties over ASC (P < 0.05), indicating that UASC would be a potential substrate to generate bioactive peptides. These results suggested that UASC would be a potential new material for biomedical applications and functional supplement in food industries.