ABSTRACTEthylphenols are strong odorants produced by microbial activity that are described as off flavors in several foods.Lactobacillus plantarumis a lactic acid bacterial species able to produce ethylphenols by the reduction of vinylphenols during the metabolism of hydroxycinnamic acids. However, the reductase involved has not been yet uncovered. In this study, the involvement in vinylphenol reduction of a gene encoding a putative reductase (lp_3125) was confirmed by the absence of reduction activity in the Δlp_3125knockout mutant. The protein encoded bylp_3125, VprA, was recombinantly produced inEscherichia coli. VprA was assayed against vinylphenols (4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol), and all were reduced to their corresponding ethylphenols (4-ethylphenol, 4-ethylcatechol, and 4-ethylguaiacol). PCR and high-performance liquid chromatography (HPLC) detection methods revealed that the VprA reductase is not widely distributed among the lactic acid bacteria studied and that only the bacteria possessing thevprAgene were able to produce ethylphenol from vinylphenol. However, all the species belonging to theL. plantarumgroup were ethylphenol producers. The identification of theL. plantarumVprA protein involved in hydroxycinnamate degradation completes the route of degradation of these compounds in lactic acid bacteria.IMPORTANCEThe presence of volatile phenols is considered a major organoleptic defect of several fermented alcoholic beverages. The biosynthesis of these compounds has been mainly associated withBrettanomyces/Dekkerayeasts. However, the potential importance of lactic acid bacteria in volatile phenol spoilage is emphasized by reports describing a faster ethylphenol production by these bacteria than by yeasts. The genetic identification of the bacterial vinylphenol reductase involved in volatile phenol production provides new insights into the role of lactic acid bacteria in the production of these off flavors. The development of a molecular method for the detection of ethylphenol-producing bacteria could be helpful to design strategies to reduce the bacterial production of vinylphenols in fermented foods.
Draft Genome Sequences of Fructobacillus fructosus DPC 7238 and Leuconostoc mesenteroides DPC 7261, Mannitol-Producing Organisms Isolated from Fructose-Rich Honeybee-Resident Flowers on an Irish Farm