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611581 
Journal Article 
Formation of diacetyl and acetoin by Lactococcus lactis via aspartate catabolism 
Le Bars, D; Yvon, M 
2008 
Yes 
Journal of Applied Microbiology
ISSN: 1364-5072
EISSN: 1365-2672 
104 
1 
171-177 
Aims: 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. Methods and Results: Resting cells of L. lactis were incubated in reaction media at different pH values, containingl-aspartic acid orl-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 α-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 5·5 and above the pyruvate conversion into acetolactate was less efficient than at pH 5, and acetolactate was mainly decarboxylated to acetoin. Conclusions: Acetoin and diacetyl can be formed as a result of aspartate or alanine catabolism by L. lactis in the presence of α-ketoglutarate in the medium. Significance and Impact of the Study: 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. [ABSTRACT FROM AUTHOR] Copyright of Journal of Applied Microbiology is the property of Blackwell Publishing Limited and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts) 
ACETYLENE; HEROIN; BIOLOGICAL products; ORGANIC acids; ORGANIC compounds; PHENOLIC acids; HYDROGEN-ion concentration; METABOLISM; LACTOCOCCUS lactis; LACTOCOCCUS; acetoin; amino acid catabolism; cheese flavour; diacetyl; L-aspartic acid