Antibacterial effect and hydrophobicity of yak κ-casein hydrolysate and its fractions

The antibacterial effects of yak κ-casein hydrolysate and its fractions on Escherichia coli were determined. Their surface hydrophobicity and amino acid profiles were also evaluated. Compared with intact yak κ-casein, yak κ-casein hydrolysate obtained with trypsin (YCHT) over 4 h of hydrolysis, permeate of YCHT obtained with 10 kDa cut-off membrane and permeate-F2 obtained from Sephadex G-25 gel filtration of permeate, exhibited a significantly higher antibacterial effect. Compared with YCHT and its permeate, permeate-F2 showed higher surface hydrophobicity when using PRODAN as a probe. Compared with native κ-casein, YCHT and permeate-F2 have a higher content and ratio of Lys, Pro, Phe and Leu residues. In contrast to its antibacterial effect, YCHT showed no cytotoxicity to mouse leukaemic monocyte macrophage RAW 264.7 cells at the concentrations used from 0 mg mL−1 to 4 mg mL−1. Therefore, yak κ-casein hydrolysate and its fractions may be used as potential inhibitors of E. coli.