Klein N, Maillard M B, Thierry A, Lortal S
DSM--Food Specialities B.V., Delft, The Netherlands.
J Appl Microbiol. 2001 Sep;91(3):404-11. doi: 10.1046/j.1365-2672.2001.01391.x.
Lactobacillus helveticus is an essential starter in Swiss-type cheeses such as Emmental. This study was to determine whether cell-free extracts of Lact. helveticus were able to convert free amino acids into neutral volatile aroma compounds at the pH and temperature occurring in cheese.
A mix of branched-chain (Leu, Ile, Val), aromatic (Tyr, Phe) and sulphur (Met) amino acids was incubated for 7 days, at pH 5.7 and 24 degrees C, with cell-free extracts of six strains. The amino acids were all transaminated into the corresponding keto acids when an amino group acceptor (alpha-ketoglutaric acid) was provided. Phe and Tyr were transaminated the most efficiently, followed by Leu, Met, Ile and Val. Three major volatile compounds were detected by GC-MS: benzaldehyde, dimethyl disulphide and 2-methyl propanol. Whatever the strain, benzaldehyde was produced in the highest quantity (0.25-1 micromol l(-1) mg(-1) protein).
CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacillus helveticus intracellular enzymes could significantly contribute to the production of aroma compounds from amino acid catabolism.
瑞士乳杆菌是埃曼塔尔等瑞士型奶酪中的重要发酵剂。本研究旨在确定瑞士乳杆菌的无细胞提取物在奶酪的pH值和温度条件下是否能够将游离氨基酸转化为中性挥发性香气化合物。
将支链（亮氨酸、异亮氨酸、缬氨酸）、芳香族（酪氨酸、苯丙氨酸）和含硫（蛋氨酸）氨基酸的混合物在pH 5.7和24℃条件下与6株菌的无细胞提取物孵育7天。当提供氨基受体（α-酮戊二酸）时，所有氨基酸都转氨生成相应的酮酸。苯丙氨酸和酪氨酸的转氨效率最高，其次是亮氨酸、蛋氨酸、异亮氨酸和缬氨酸。通过气相色谱-质谱联用仪检测到三种主要挥发性化合物：苯甲醛、二甲基二硫和2-甲基丙醇。无论菌株如何，苯甲醛的产量最高（0.25 - 1微摩尔·升⁻¹·毫克⁻¹蛋白质）。
研究的结论、意义和影响：瑞士乳杆菌的细胞内酶可显著促进氨基酸分解代谢产生香气化合物。
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