Purification, microstructure, functional properties and antioxidant activity of peptides from Chinese pond turtle hydrolysate

Chinese pond turtle muscle peptide's molecular features, purification, structural characteristics, and antioxidant activity were investigated. The Flavourzyme hydrolysate demonstrated greater relative crystallinity (37.53%) than other hydrolysates using X-ray diffraction. The fourier transform infrared spectroscopy spectral changes, the second derivative spectroscopy in the amide-I region (1620–1650 cm⁻¹). Zeta-potential measurement was used to determine the surface charge ranging from − 32.73 to − 28.23 mV. Trypsin hydrolysate obtained the highest solubility (98.72% at pH 1.0) and emulsifying activity (182.81 m² g⁻¹ at pH 7.0), respectively. The Flavourzyme hydrolysate was separated by Sephadex G-10 filtration column chromatography, and three fractions (FH-1, FH-2, and FH-3) were obtained. The molecular weight was < 150 Da in fractions FH-3, FH-2, and FH-1, which were 93.25%, 85.22%, and 76.76%, respectively. The antioxidant activity showed the highest DPPH activity (71.32%) at 7 mg/mL in Fraction FH-2. SEM had a different shape (ball-drop) at FH-2 than the fractions protein (FH-1 and FH-3).