Preparation, purification and identification of antioxidant peptides from the placenta of Tibetan sheep

In this study, the placenta of Tibetan sheep (PTS) was employed to prepare antioxidant peptides. Ultrasonic pretreatment was employed to enhance the degree of hydrolysis (DH, %), with the optimal hydrolysis parameters being as follows: enzymolysis time of 4.9 h, ultrasonic temperature of 35.5 degrees C, ultrasonic power of 435 W, ultrasonic time of 22 min, and DH was 4.62 +/- 1.58%. In the in vitro antioxidant activity assay, the IC50 value of the hydrolysate for DPPH radicals was found to be 2.83 mg/mL, which is comparable to the effect observed with the positive control BHT. The IC50 value for hydroxyl radicals was determined to be 0.94 mg/mL, demonstrating superior efficacy compared to that of BHT. The second fraction (F-2) isolated from the hydrolysate exhibited the highest antioxidant activity, with a DPPH radical scavenging rate of 85.7% at a concentration of 0.60 mg/mL and a hydroxyl free radicals scavenging rate of 84.46% at the concentration of 10 mg/mL. Twenty-seven novel peptides were identified from F-2 using Nano-ESI-LC-QTOF-MS/MS. A significant proportion of the peptides identified from F-2 had some antioxidant properties, which were attributed to the presence of hydrophobic and highly antioxidant amino acids in specific proportions at specific locations. The identified sequences demonstrate the potential of PTS as a source of antioxidant peptides. Molecular docking analyses showed that 27 peptide sequences were able to interact positively with DPPH center dot, OH center dot and BHT through hydrogen bonding. In addition, the analysis predicted an interaction between KTLPVAFK (K-8-K) and Keap1, suggesting that K-8-K has some antioxidant activity and may be involved in the Keap1-nrf2 pathway.