Abstract
Post-acidification during storage limits the use of multiple probiotics in fermented dairy products. In this study, the ldh gene was deleted in Lacticaseibacillus paracasei Zhang (LCZ), resulting in 45% reduction in lactic acid production. Co-fermentation of the engineered strain with commercial starters effectively controlled post-acidification, maintained a stable pH (4.5-4.3) over 28 d, and increased production of volatile compounds (acetoin, decanoic acid, and dodecanoic acid) and bioactive metabolites (acetic and succinic acids). Metabolic analysis revealed that ldh deletion activated acetoin biosynthesis (750 ng/mL) and redirected carbon flux toward malic, and acetic acids. The modification also promoted amino acid catabolism (L-alanine, L-cysteine, and L-asparagine) to pyruvic acid, enabling nitrogen-carbon co-utilization. This study presents a promising solution for developing stable probiotic dairy products and provides new insights into probiotic metabolic engineering.