Studies on the Structure and Properties of Ultrasound-Assisted Enzymatic Digestion of Collagen Peptides Derived from Chinemys reevesii Skin

This study examined the ultrasound pretreatment (UP) and simultaneous ultrasound (US) effects on the structural-functional features of collagen peptides in <i>Chinemys reevesii</i> skin collagen hydrolysates (CCHs) using a composite protease system (Trypsin: Alkaline protease, 1:1). Structural characterization revealed that UP induced the unfolding of collagen molecules, evidenced by reduced disulfide bond content and the concomitant increase in surface hydrophobicity. Consequently, ultrasound pretreatment-assisted enzymatic hydrolysis (UPH) significantly enhanced the yield of low-molecular-weight components (<0.18 kDa) and hydrophobic amino acids, which rose by 3.03% and 4.89% compared to the results of conventional enzymatic treatment (CE). UPH showed higher antioxidant activity than CE and WUH over CE and whole-process ultrasound-assisted hydrolysates (WUH). At 5 mg/mL, it displayed an ABTS radical scavenging rate of 87.59%, a DPPH scavenging rate of 53.37%, and the highest reducing power. However, WUH induced peptide reaggregation due to prolonged ultrasonication, thus exhibiting moderately lower antioxidant activity than UPH. These findings suggest that UP is an effective strategy to optimize the structure and composition of CCHs, outperforming both CE and WUH in facilitating the release of antioxidant peptides and improving antioxidant capacity.