Le Bars D, Yvon M
Unité de Biochimie Bactérienne, UR477, INRA, Jouy-en-Josas, France.
J Appl Microbiol. 2008 Jan;104(1):171-7. doi: 10.1111/j.1365-2672.2007.03539.x.
To verify whether diacetyl can be produced by Lactococcus lactis via amino acid catabolism, and to investigate the impact of the pH on the conversion.
Resting cells of L. lactis were incubated in reaction media at different pH values, containing L-aspartic acid or L-alanine as a substrate. After incubation, the amino acid and metabolites were analysed by HPLC and GC/MS. At pH 5 about 75% of aspartic acid and only 40% of alanine was degraded to pyruvate via a transamination step that requires the presence of alpha-ketoglutarate in the medium, but diacetyl was only produced from aspartic acid. Three per cent of pyruvate was transformed to acetolactate of which 50% was converted into diacetyl. At pH 5 x 5 and above the pyruvate conversion into acetolactate was less efficient than at pH 5, and acetolactate was mainly decarboxylated to acetoin.
Acetoin and diacetyl can be formed as a result of aspartate or alanine catabolism by L. lactis in the presence of alpha-ketoglutarate in the medium.
Lactic acid bacteria exhibiting both glutamate dehydrogenase activity and high aspartate aminotransferase activity are expected to be good diacetyl producers during cheese ripening at pH close to 5.
验证乳酸乳球菌是否可通过氨基酸分解代谢产生双乙酰，并研究pH对该转化过程的影响。
将乳酸乳球菌的静止细胞在含有L-天冬氨酸或L-丙氨酸作为底物的不同pH值反应培养基中培养。培养后，通过高效液相色谱法（HPLC）和气相色谱-质谱联用仪（GC/MS）分析氨基酸和代谢产物。在pH 5时，约75%的天冬氨酸和仅40%的丙氨酸通过需要培养基中存在α-酮戊二酸的转氨步骤降解为丙酮酸，但双乙酰仅由天冬氨酸产生。3%的丙酮酸转化为乙酰乳酸，其中50%转化为双乙酰。在pH 5.5及以上，丙酮酸向乙酰乳酸的转化效率低于pH 5时，且乙酰乳酸主要脱羧生成乙偶姻。
在培养基中存在α-酮戊二酸的情况下，乳酸乳球菌通过天冬氨酸或丙氨酸分解代谢可形成乙偶姻和双乙酰。
在pH接近5的奶酪成熟过程中，兼具谷氨酸脱氢酶活性和高天冬氨酸转氨酶活性的乳酸菌有望成为良好的双乙酰生产者。
