Aldo/keto reductase regulates L-lactate dehydrogenase activity as a key target for yogurt post-acidification

Post-acidification during refrigeration is a critical determinant of yogurt quality. Although it is known that niacin (NA) can influence this process via aldehyde-ketone reductase (AKR) in Lactobacillus bulgaricus, its precise regulatory mechanism remains unclear. By non-targeted metabolomics analysis revealed that nicotinic acid reshapes the metabolic profile during storage, significantly reducing the accumulation of organic acids such as L-lactic acid, fumaric acid, and succinic acid. This indicates that post-acidification processes are inhibited through relevant metabolic pathways. Concurrently, the yeast two-hybrid screening identified 21 proteins interacting with AKR, confirming L-lactate dehydrogenase (L-LDH) as a key interaction partner of AKR. This enzyme directly regulates L-LDH activity. Subsequent enzyme activity assays and AKR mutation confirmed that niacin acts as a potent inhibitor of L-LDH activity by promoting the formation of an AKR-L-LDH-NA ternary complex. Regulation of L-LDH activity by AKR without altering the structure and intrinsic catalytic properties of L-LDH is expected to realize the AKR-L-LDH-NA ternary complex as a key target for the future regulation of the post-acidification process. Our study establishes a technological method to accurately regulate the post-acidification of yogurt, which provides a theoretical basis for controlling acidity in lactic acid fermented foods.