酸奶发酵过程中游离氨基酸含量的分析

Change of Free Amino Acids in Fermentation of Yoghourt

酸奶的氨基酸含量与其营养价值、风味及质构密切相关.试验研究了酸奶发酵过程中各种游离氨基酸含量的变化.结果表明,在40℃恒温发酵10h的过程中,酸奶的总游离氨基酸含量先降后升,发酵0～8 h以乳酸菌分解游离氨基酸占主导地位,8～10 h以蛋白质水解占主导地位.谷氨酸、组氨酸、蛋氨酸、两种芳香族氨基酸（酪氨酸和苯丙氨酸）和支链氨基酸（亮氨酸、异亮氨酸和缬氨酸）含量在整个发酵过程中呈现持续下降趋势且在0～4 h时下降幅度为极显著;而牛磺酸、丙氨酸、甘氨酸、苏氨酸、丝氨酸和赖氨酸含量在4～8 h时下降幅度为极显著：而精氨酸和天冬氨酸含量在整个发酵期间呈现持续上升的趋势.另外通过主成分分析发现40℃发酵10 h酸奶游离氨基酸水平进入相对稳定的阶段,结合pH检测及感官评定,选择10 h作为其发酵终点.

The amino acids in yoghourt closely related with the nutrition,flavor and texture were analyzed during yoghourt fermentation process.The resuls showed that the contents of total free amino acids first decreased and then increased during the 10 h fermentation under 40 ℃.During the fermentation from 0 to 8 hours,the catabolism reaction by lactic acid bacteria played a dominant role while during the 8 h to 10 h the total free amino acids increased mainly because the hydroxylation of casein and polypeptide.The contents of glutamate,histamine,methionine,two kinds of aromatic amino acid and branched-chain amino acids continuously decreased especially during 0 to 4 hours while the contents of taurine,alanine,glycine,threonine,serine and lysine reduced sharply during 4 to 8 hours.The level of arginine and asparate continuously increased in the process.Results of the principal component analysis showed that the contents of free amino acids in yoghourt reached relatively stable level when it was fermented under 40 ℃ after 10 hours taken as the end of fermentation by pH test and sensory evaluation.