Niven G W, Knight D J, Mulholland F
Institute of Food Research, Reading Laboratory, Earley Gate, UK.
J Dairy Res. 1998 Feb;65(1):101-7. doi: 10.1017/s002202999700263x.
Analysis of the concentrations of free amino acids in milk during growth of Lactococcus lactis subsp, lactis revealed a biphasic pattern of change during the logarithmic phase. During the first period there was little overall change in the total concentration of amino acids in the medium. The second phase was characterized by increased net liberation of free amino acids. There were also qualitative differences in the amino acids that were taken up and utilized during each period. The concentrations of Val, Leu and Ile decreased only during the early phase, while those of Ser, Arg, Thr and Met decreased only during the second phase. Gly and Ala were utilized throughout logarithmic growth. Gly uptake appeared to be greater during the second period and accounted for the largest proportion of free amino acid utilization at this time. It is possible that the biphasic nature of amino acid nutrition was due to increased consumption in late log phase of peptides derived from milk proteins by proteolysis. Increased activity of the arginine deiminase pathway during late log phase was inferred from increased utilization of Arg and liberation of citrulline and ornithine.
对乳酸乳球菌乳酸亚种生长过程中牛奶中游离氨基酸浓度的分析表明，在对数生长期，氨基酸浓度变化呈双相模式。在第一阶段，培养基中氨基酸的总浓度总体变化不大。第二阶段的特征是游离氨基酸的净释放增加。在每个阶段摄取和利用的氨基酸也存在质的差异。缬氨酸、亮氨酸和异亮氨酸的浓度仅在早期阶段下降，而丝氨酸、精氨酸、苏氨酸和蛋氨酸的浓度仅在第二阶段下降。甘氨酸和丙氨酸在整个对数生长期都被利用。在第二阶段，甘氨酸的摄取似乎更多，此时占游离氨基酸利用的最大比例。氨基酸营养的双相性质可能是由于对数后期通过蛋白水解作用增加了对牛奶蛋白衍生肽的消耗。从精氨酸利用增加以及瓜氨酸和鸟氨酸的释放推断，在对数后期精氨酸脱亚胺酶途径的活性增加。
