Lactobacillus demonstrate thiol-independent metabolism of methylglyoxal: Implications toward browning prevention in Parmesan cheese

摘要

ABSTRACTEndogenous production of α-dicarbonyls by lactic acid bacteria can influence the quality and consistency of fermented foods and beverages. Methylglyoxal (MG) in Parmesan cheese can contribute toward undesired browning during low temperature ripening and storage conditions, leading to the economic depreciation of affected cheeses. We demonstrate the effects of exogenously added MG on browning and volatile formation using a Parmesan cheese extract (PCE). To determine the influence ofLactobacilluson α-dicarbonyls, strains were screened for their ability to modulate concentrations of MG, glyoxal, and diacetyl in PCE. It was found that a major metabolic pathway of MG inLactobacillusis a thiol-independent reduction, whereby MG is partially or fully reduced to acetol and 1,2-propanediol, respectively. The majority of lactobacilli grown in PCE accumulated the intermediate acetol, whereasLactobacillus brevis367 formed exclusively 1,2-propanediol andLactobacillus fermentum14931 formed both metabolites. In addition, we determined the inherent tolerance to bacteriostatic concentrations of MG among lactobacilli grown in rich media. It was found thatL. brevis367 reduces MG exclusively to 1,2-propanediol, which correlates to both its ability to significantly decrease MG concentrations in PCE, as well as its significantly higher tolerance to MG, in comparison to other lactobacilli screened. These findings have broader implications toward lactobacilli as a viable solution for reducing MG-mediated browning of Parmesan cheese.