Abstract: Liquid chromatography-mass spectrometry was employed to determine the change of free amino acid contents in hard yak cheeses with different salt levels during 6 months of ripening. The results showed that a total of 23 free amino acids were detected, the major ones being aspartic acid, glutamic acid, isoleucine, leucine, phenylalanine, threonine and cysteine, together representing 94% to 95% of the total free amino acid content. The content of each free amino acid showed an increasing trend between months 1 and 6. In the late stage of maturation, the contents of threonine, asparaginate, aspartic acid, valine, proline and phenylalanine increased with increasing salt addition, the contents of alanine, histidine, arginine and tyrosine decreased, and the contents of leucine, isoleucine, serine, glycine and tryptophan first increased and then decreased. The contents of of glutamic acid, leucine, isoleucine, aromatic amino acid, cysteine, glycine and serine were significantly higher in long-ripened cheese with 1.3% salt addition than in those with higher salt contents. This study provides theoretical support for the development of low-salt hard yak cheese.

Key words: sodium chloride addition; yak milk; hard cheese; free amino acid

摘要： 利用液相色谱-质谱联用系统测定不同氯化钠添加量牦牛乳硬质干酪成熟过程中的游离氨基酸含量变化。结果表明：不同氯化钠添加量牦牛乳硬质干酪中共检出23 种游离氨基酸，主要为Asp、Glu、Ile、Leu、Phe、Thr、Cys，这7 种游离氨基酸占游离氨基酸总含量的94%～95%；在1～6 个月成熟过程中，牦牛乳硬质干酪中各种游离氨基酸含量均呈现增加趋势，而且在成熟后期，氯化钠添加量的增加使得干酪中Thr、Asn、Asp、Val、Pro、Phe等含量呈现增加趋势，Ala、His、Arg、Tyr等含量呈现减少趋势，leu、Ile、Ser、Gly、Trp等含量呈现先增加后减少趋势；然而，当氯化钠添加量为1.3%时，成熟时间长的牦牛乳硬质干酪中Glu、Leu、Ile、芳香族氨基酸、Cys、Gly、Ser等含量明显高于其他氯化钠添加量较高的干酪。该研究可为开发低盐牦牛乳硬质干酪提供理论支持。

关键词: 氯化钠添加量；牦牛乳；硬质干酪；游离氨基酸