Endogenous 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 of Lactobacillus on 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 in Lactobacillus is 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, whereas Lactobacillus brevis 367 formed exclusively 1,2-propanediol and Lactobacillus fermentum 14931 formed both metabolites. In addition, we determined the inherent tolerance to bacteriostatic concentrations of MG among lactobacilli grown in rich media. It was found that L. brevis 367 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.

中文翻译：

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乳酸杆菌显示甲基乙二醛不依赖硫醇的代谢：对帕尔马干酪的褐变预防具有重要意义。

乳酸菌内源性生产α-二羰基会影响发酵食品和饮料的质量和稠度。帕玛森干酪中的甲基乙二醛（MG）可能会导致在低温成熟和储存条件下发生不希望的褐变，从而导致受影响干酪的经济贬值。我们证明了使用帕马森干酪提取物（PCE）外源添加的MG对褐变和挥发物形成的影响。为了确定乳杆菌对α-二羰基的影响，筛选了菌株调节PCE中MG，乙二醛和二乙酰基浓度的能力。发现乳酸杆菌中MG的主要代谢途径是不依赖硫醇的还原，由此MG分别部分或完全还原为丙酮醇和1，2-丙二醇。在PCE中生长的大多数乳酸杆菌会积累中间丙酮醇，而短乳杆菌367仅形成1,2-丙二醇，而发酵乳杆菌14931则形成两种代谢产物。此外，我们确定了富培养基中生长的乳酸杆菌对MG抑菌浓度的固有耐受性。发现短乳杆菌367仅将MG还原成1，2-丙二醇，这与其筛选PCE中的MG浓度显着降低的能力以及与之相比显着更高的对MG的耐受性有关。这些发现对乳酸菌作为减少MG介导的帕马森干酪褐变的可行解决方案具有更广泛的意义。2-丙二醇和发酵乳杆菌14931形成两种代谢物。此外，我们确定了在富培养基中生长的乳酸杆菌对MG抑菌浓度的固有耐受性。发现短乳杆菌367仅将MG还原成1，2-丙二醇，这与其筛选PCE中的MG浓度显着降低的能力以及与之相比显着更高的对MG的耐受性有关。这些发现对乳酸菌作为减少MG介导的帕马森干酪褐变的可行解决方案具有更广泛的意义。2-丙二醇和发酵乳杆菌14931形成两种代谢物。此外，我们确定了在富培养基中生长的乳酸杆菌对MG抑菌浓度的固有耐受性。发现短乳杆菌367仅将MG还原为1，2-丙二醇，这与其筛选的其他乳杆菌相比显着降低其在PCE中MG浓度的能力以及其对MG的耐受性显着更高有关。这些发现对乳酸菌作为减少MG介导的帕马森干酪褐变的可行解决方案具有更广泛的意义。与筛选的其他乳杆菌相比，这与其在PCE中显着降低MG浓度的能力以及对MG的明显更高的耐受性有关。这些发现对乳酸菌作为减少MG介导的帕马森干酪褐变的可行解决方案具有更广泛的意义。与筛选的其他乳杆菌相比，这与其在PCE中显着降低MG浓度的能力以及对MG的明显更高的耐受性有关。这些发现对乳酸菌作为减少MG介导的帕马森干酪褐变的可行解决方案具有更广泛的意义。