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 angiotensin-converting 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.

Spray-dried whey protein powders were produced from whey obtained as a by-product in the production of milk cake and milk fan as ethnic dairy products in Yunnan, and their main components and processing characteristics were analyzed. The results showed that the main components of whey protein powder obtained from the by-product of milk cake were protein 39.0%, fat 6.0%, moisture 4.1%, total ash 7.7%, acidity 23.2 °T, and pH 5.61, and the processing characteristics were 99.52% solubility, less than 3.2% precipitation at different temperatures, and emulsifying activity index (EAI) and emulsion stability index (ESI) both greater than 42.7% at different pH values. The main components in whey protein powder obtained from the by-product of milk fan were protein 72.0%, fat 19.8%, moisture 4.6%, total ash 8.1%, acidity 58.3 °T, and pH 5.20, and its processing characteristics were 98.70% solubility, less than 3.5% precipitation at different temperatures, and EAI and ESI both higher than 50% at different pH values. The sensory scores of yogurts with the two whey protein powders were 70.7 and 72.7 out of 100 points, respectively, indicating that both can be used as an ingredient in yogurt.