牦牛乳硬质干酪苦味肽的分离与特征鉴定

为了探究牦牛乳硬质干酪中苦味肽组成特征，采用氯仿-甲醇法提取苦味肽，通过Sephadex G-25葡聚糖凝胶色谱进行分离纯化，并利用液相色谱-串联质谱（liquid chromatography-mass spectrometry/mass spectrometry，LC-MS/MS）对其分离的苦味较强组分进行特征鉴定。结果表明：经Sephadex G-25葡聚糖凝胶色谱分离得到3 个不同分子质量的组分，组分Ⅱ具有明显苦味。LC-MS/MS鉴定出组分Ⅱ中存在14 种苦味肽，主要为氨基酸残基数目7～17 个、分子质量小于2 000 D的小肽，苦味肽序列中存在的疏水性氨基酸主要有脯氨酸、缬氨酸、亮氨酸、苯丙氨酸、异亮氨酸，800～1 500 D苦味肽占64.29%，源自β-酪蛋白（β-casein，β-CN）降解产物的苦味肽占92.86%。因此，干酪成熟过程中源自β-CN的具有较强疏水性、分子质量小于2 000 D的混合多肽的积累可能对干酪苦味的产生有较大影响。

Separation and Characterization of Bitter Peptides from Hard Cheese Made from Yak Milk

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.