d -amino acids produced by Lactobacillus are thought to contribute to the taste quality and health functions; however, no studies have comprehensively evaluated the concentrations of the D- and L-forms of amino acids separately in individual Lactobacillus strains. To gain insight into amino acid concentrations in Lactobacillus , we evaluated amino acid concentrations in culture broth of Lactobacillus separately for the D- and L-forms. Lactobacillus strains were cultured in culture broth, and the amino acid concentrations in supernatant were assessed. The amino acid concentrations obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS) were subjected to cluster analysis based on Bray-Curtis distance with Ward's minimum variance method. In the analysis of amino acid concentrations under culture with different monosaccharides, the distances among strains cultured with the same monosaccharide were significantly greater than those among cultures of the same strain under different monosaccharides (p < 0.01). The cluster analysis of amino acid concentrations under culture with the same monosaccharide suggested that strains belonging to the same phylogenetic group of Lactobacillus exhibited similar concentrations of amino acids. Data analyses of 70 strains belonging to 17 Lactobacillus taxa indicated that the concentrations of amino acids were highly dependent on the phylogenetic group of Lactobacillus and that the group differences in amino acid concentration were strongly driven by differences in l -serine and d -alanine concentrations. Our results indicate that it is important to evaluate D- and l -amino acids separately when evaluating variations in amino acid concentrations. Because d -alanine has the potential to affect taste quality, the results of this study may provide insight into the taste quality of fermented food produced by Lactobacillus .

Reduction of greenhouse gas emissions is important to limit climate change. Because ruminant animals emit greenhouse gases, the worldwide plant-based alternative market is an emerging trend for eating less meat and dairy products. To produce plant-based dairy products such as yogurt alternatives, certain lactic acid bacterial species, which are used for cow's milk fermentation, are often used. Substrate changes from cow's milk to plant-based milk caused nutritional changes, and unsaturated fatty acids are more enriched in plant-based milk alternatives than in cow's milk. Unsaturated fatty acids can lead to the formation of aldehydes, some of which are off-flavors; therefore, substrate changes have the potential to alter the suitable lactic acid bacterial species used for fermentation to control flavor formation, such as aldehyde compounds. However, differences in the effect of the fermentation processes on aldehyde compounds have not been evaluated among lactic acid bacterial species. In this study, we comprehensively evaluated the effect of lactic acid bacterial fermentation on aldehyde compounds in synthetic medium and plant-based milk alternatives using 20 species of lactic acid bacteria. Heterofermentative lactic acid bacteria such as strains belonging to Limosilactobacillus had a strong aldehyde-reducing ability, likely from differences in alcohol dehydrogenase function. Because the odor detection threshold of ethanol compounds was lower than that of their equivalent aldehyde compounds, our findings are valuable for the fermentation of plant-based milk alternatives with lactic acid bacteria with the goal of decreasing off-flavors derived from aldehyde compounds.