Identification and Antioxidant Activity of Bioactive Peptides Derived from Zhongdian Yak Milk Casein

The enzymatic hydrolysate of Zhongdian yak milk casein was fractionated by ultrafiltration into two fractions: molecular mass > 3 kDa and < 3 kDa. The cell proliferation activity and antioxidant activity of the two fractions were determined. The bioactive peptides derived from yak milk casein were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), bioinformatics and molecular docking. The results showed that the proliferation rate of RAW264.7 cells was above 80% in the presence of either the molecular mass > 3 kDa or < 3 kDa fraction. Both fractions had the ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) cation radical. The cell proliferation and free radical scavenging activity of the molecular mass < 3 kDa fraction were better than those of the > 3 kDa fraction. A total of 895 peptides were identified from the molecular mass < 3 kDa fraction, of which 96 were known bioactive peptides, mainly antioxidant peptides (39.6%) and angiotensinconverting enzyme inhibitory peptides (30.2%), indicating that Zhongdian yak casein is an important source of bioactive peptides. Based on their activity and hydrophobicity, antioxidant peptides GYF and RPW were selected from the predicted 20 potential antioxidant peptides. The results of molecular docking showed that the binding energies of GYF and RPW with ABTS cation and DPPH radicals were all negative, indicating that they had binding potential and exerted antioxidant activity mainly by forming hydrogen bonds and hydrophobic interactions.