Abstract:

The intention of this work was to investigate the structural characteristics of bitter peptides in hard cheese made
from yak milk. Bitter peptides were extracted with chloroform-methanol mixture and isolated by using gel chromatography,
and the more bitter fractions were identified by liquid chromatography-mass spectrometry (LC-MS-MS). The results showed
that three fractions named as fractions I, II and III were obtained through Sephadex G-25 column chromatography and
fraction II tasted the most bitter among these and had a flavor described as slightly bitter. Fourteen peptides were identified
in fraction II and these peptides were composed of 7–17 amino acid residues in a molecular weight range less than 2 000 D.
Hydrophobic amino acids such as proline, valine, leucine, phenylalanine and isoleucine constituted these bitter peptides. The
bitter peptides in a molecular weight range of 800 –1 500 D accounted for 64.29% and bitter peptides derived from β-casein
(β-CN) accounted for 92.86%. Therefore, polypeptides derived from β-casein with high hydrophobicity and molecular
weight below 2 000 D may have a significant influence on the bitterness of cheese.

Key words: hard cheese made from yak milk, bitter peptide, characteristic, β-casein