Molecular mechanisms of high aldehyde dehydrogenase production for improved beany flavour regulated by the LuxS/AI-2 quorum sensing system in Limosilactobacillus fermentum A119

Aldehydes cause beany flavor, which is one of the factors limiting the further development of plant-based fermented milks. Limosilactobacillus fermentum (L. L. fermentum) ) A119, which has the LuxS/AI-2 quorum sensing (QS) system and producing aldehyde dehydrogenase (ALDH), improves the beany flavor of soy protein-based fermented milk. However, the precise mechanism underlying the production of ALDH and its improvement on the beany flavor remains unclear. The test results indicate that cell density content and ALDH activity were up- regulated with increasing autoinducer-2 (AI-2) signaling molecule. This suggests that ALDH synthesis in L. fermentum A119 may be regulated by the LuxS/AI-2 QS system. Subsequently, the 4D-data-independent acquisition (DIA) proteomics results revealed a total of 378 differentially expressed proteins (DEPs) after 24 h of incubation compared to 2 h incubation. Among them, 236 DEPs were up-regulated, including s-ribosylhomocysteinase (LuxS) and ALDH. Additionally, Western blot analysis confirmed that LuxS/AI-2 QS system successfully mediates the expression of ALDH. Finally, under the catalysis of ALDH, the beany flavor-metabolites benzaldehyde was converted to benzoic acid, which improved the flavor of soy protein-based fermented milk. This study reveals the mechanism of ALDH regulation through the LuxS/AI-2 QS system, provide new insights for reducing beany flavor in soy protein-based fermented milk.