Diversity of volatile organic compound production from leucine and citrate in Enterococcus faecium
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Enterococcus faecium is frequently isolated from fermented food; in particular, they positively contribute to the aroma compound generation in traditional cheese. Citrate fermentation is a desirable property in these bacteria, but this feature is not uniformly distributed among E. faecium strains. In the present study, three selected E. faecium strains, IQ110 (cit−), GM70 (cit+ type I), and Com12 (cit+ type II), were analyzed in their production of aroma compounds in milk. End products and volatile organic compounds (VOCs) were determined by solid-phase micro-extraction combined with gas chromatography mass spectrometry (SPME-GC-MS). Principal component analysis (PCA) of aroma compound profiles revealed a different VOC composition for the three strains. In addition, resting cell experiments of E. faecium performed in the presence of leucine, citrate, or pyruvate as aroma compound precursors allowed us to determine metabolic differences between the studied strains. GM70 (cit+ type I) showed an active citrate metabolism, with increased levels of diacetyl and acetoin generation relative to Com12 or to citrate defective IQ110 strains. In addition, in the experimental conditions tested, a defective citrate-fermenting phenotype for the Com12 strain was found, while its leucine degradation and pyruvate metabolism were conserved. In conclusion, rational selection of E. faecium strains could be performed based on genotypic and phenotypic analyses. This would result in a performing strain, such as GM70, that could positively contribute to flavor, with typical notes of diacetyl, acetoin, 3-methyl butanal, and 3-methyl butanol in an adjuvant culture.
KeywordsEnterococcus faecium Aroma compound Leucine Citrate Rational strain selection
We are especially grateful to M.S. Gilmore for providing us E. faecium Com12. We would like to thank the Agencia Nacional de Promoción Científica y Tecnológica, Consejo Nacional de Investigaciones Cientifícas y Técnicas, and Universidad de Rosario for the financial support. MD and GPM are CONICET fellows, and VSB, ME, SHA, and CM are researchers of the same institution.
This study was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, PIP 11220150100855) and Agencia Nacional de Promoción Científica y Tecnológica (ANPyCT, PICT2014-1513 and 3482 and PICT2015-2361).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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