Effect of Different Ultrasound-Assisted Process Modes on Extraction Yield and Molecular Characteristics of Pepsin-Soluble Collagen from Asian Bullfrog Skin

Different modes of ultrasound-assisted process (UAP) enhance pepsin-soluble collagen (PSC) extraction and affect characteristics of PSC. This study aimed to evaluate the efficacy and characteristics of PSC extracted from Asian bullfrog skin using different modes of UAP (pretreatment (UP) and simultaneous treatment (US)) and ultrasonication times (15, 30, and 45 min). Both UP and US increased solid yield and recovery compared with control (without UAP). The α-amino group content and surface hydrophobicity of PSC varied according to the mode used. The protein pattern revealed the type I collagen for all PSC samples. Fourier-transform infrared spectroscopy and circular dichroism spectra indicated that UAP has a significant effect on the molecular structure, with a negligible impact on the integrity of the triple helix structure. Nevertheless, the UAP conditions applied in this study affected the structural stringency by lowering the thermal stability. UP at 30 min and US at 45 min, which displayed high extraction recovery and satisfactory triple helix structure, were selected for further analyses. The difference in isoelectric point and amino acid composition was also observed between each sample. Conclusively, both UP and US applied for appropriate time periods successfully enhanced the PSC extraction efficiency with various molecular characteristics of collagen. Graphical Abstract