Integrated multi-omics reveals niacin's regulatory mechanism in suppressing post-acidification to enhance yogurt stability

Yogurt undergoes post-acidification during low-temperature storage due to ongoing acid production by Lactobacillus delbrueckii subsp. bulgaricus , compromising its storage quality. Preventing post-acidification during yogurt storage remains a key challenge for the dairy industry. Our prior work demonstrated that niacin, a food additive, exhibits inhibitory effects on yogurt post-acidification; however, its mechanism required further investigation. Here, we constructed a mutant library of Lactobacillus bulgaricus and isolated weak post-acidification strains via LDB_RS00370 expression screening, followed by niacin-sensitive mutants using the same approach. Integrated transcriptomic and volatile metabolite analyses demonstrated that downregulating LDB_RS00370 inhibits post-acidification by remodeling pyruvate metabolism and disrupting the NADPH/NADP + redox balance. Notably, niacin and upregulated pyruvate oxidase genes in sensitive strains, redirecting pyruvate flux to inhibit post-acidification. We propose that redirecting pyruvate metabolism toward fatty acid biosynthesis enhances acid tolerance in Lactobacillus bulgaricus by strengthening cell membrane rigidity and efficiently degrading misfolded proteins via upregulated peptidase expression. These mechanistic insights provide foundational knowledge for developing fermentation strategies targeting metabolic pathways to extend yogurt shelf life. • Niacin curbs yogurt post-acidification by redirecting pyruvate metabolism and disrupting NADPH/NADP+ balance in L. bulgaricus . • Multi-omics integration shows niacin enhances membrane rigidity and proteostasis to boost microbial acid tolerance. • High-throughput mutagenesis enables rapid screening of niacin-sensitive strains via biomarker LDB_RS00370 . • Mechanistic insights yield solutions for extending yogurt shelf life through targeted metabolic engineering.