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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 °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 IC 50 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 IC 50 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•, OH• 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. [Display omitted] • Ultrasound-assisted enzymatic digestion of Tibetan sheep placenta. • Ultrasound-assisted enzymatic hydrolysis improves hydrolysis and antioxidant activity of peptides. • Identification and analysis of antioxidant peptide sequences in Tibetan sheep placenta. • The possible involvement of the peptide in antioxidant pathways was verified by molecular docking analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Araloside A and L-ascorbic acid had a synergistic antioxidant effect. • Araloside A and L-ascorbic acid synergistically increased Nrf2 nuclear translocation. • The combination of Araloside A and L-ascorbic acid elevated the expression of CAT. • Nrf2/CAT pathway was synergistically activated by Araloside A and L-ascorbic acid. The synergistic effect of different antioxidants has potential application prospect in alleviating oxidative injury. Araloside A is the most abundant active ingredient of Aralia elata (Miq.) Seem, which exhibits multiple biological activities, including antioxidant, et al. This study investigated the interaction between Araloside A and several natural antioxidants, and explored the mechanism of the combination with synergistic antioxidant effect. The results showed that only the combination of Araloside A and L-ascorbic acid (A + Vc) exhibited synergistic effects in alleviating oxidative damage. A + Vc enhanced the expression levels of NF-E2-related factor 2 (Nrf2) and Catalase (CAT) in a time-dependent and dose-dependent manner. However, the Nrf2 inhibitor-ML385 and CAT inhibitor-Pyocyanin impaired the protective effect of A + Vc. To conclude, A + Vc could ameliorate H 2 O 2 -induced oxidative injury via synergistic antioxidative effects originated from Nrf2/CAT pathway activation. Hence, dietary intake of A + Vc may be a practical, safe approach to prevent diseases associated with oxidative damage. [ABSTRACT FROM AUTHOR]