Bacillus subtilis-Derived Postbiotics as a Multifunctional Bio-Catalyst for Enhancing Lactic Acid Bacteria Viability and Yogurt Quality

This study demonstrates that <i>Bacillus subtilis</i> GDAAS-A32-derived postbiotics (BSP) enhance yogurt production by optimizing lactic acid bacteria (LAB) viability and functionality. BSP enhanced the growth kinetics and biomass accumulation of <i>Streptococcus thermophilus</i> and <i>Lactobacillus bulgaricus</i> in both an anaerobic and aerobic pure system. The addition of BSP significantly increased the viable cell counts of <i>S. thermophilus</i> and <i>L. bulgaricus</i>, milk-clotting activity, sensory properties, and extracellular polysaccharide content and improved the rheological properties. Moreover, BSP elevated viable counts of <i>S. thermophilus</i> and <i>L. bulgaricus</i> to 6.18 × 10⁸ CFU/g and 1.03 × 10⁸ CFU/g, respectively, by day 7-representing 11.3-fold and 9.3-fold increases versus controls at 20% supplementation. Metabolomic signatures confirmed peptidoglycan reinforcement and flavor enhancement. Mechanistically, BSP supplementation might reduce urate and H₂O₂ toxicity through NH₃-mediated proton neutralization and oxygen scavenging, while establishing a pyrimidine salvage network and redirecting one-carbon metabolism, resulting in enhanced stress tolerance and significant improvements in bacterial viability.