A Novel Leuconostoc mesenteroides Direct-Vat-Set Starter with High Nitrite-Degrading Activity for Safe and High-Quality Fermentation of Chinese Dongbei Suancai

Dongbei suancai is a popular traditional fermented vegetable in Northeast China. However, the conventional production methods often lead to nitrite accumulation and quality fluctuations, which to some extent constrain the development towards health and scale. To address this, a novel Direct-Vat-Set (DVS) starter was developed based on L. mesenteroides AA001, a strain isolated from traditional fermented foods and possessing high nitrite-degrading capability. By optimizing the culture medium and cryoprotectant formulation, the cell density and freeze-drying survival rate were significantly enhanced. Crucially, the freeze-drying process did not impair the core degradation function of the strain, with the nitrite degradation rate remaining above 90%. The DVS starter was applied to Dongbei suancai fermentation, effectively inhibiting nitrite accumulation while simultaneously increasing organic acid content and optimizing the proportion of essential amino acids. It simultaneously suppressed the growth of undesirable bacteria and, under low-temperature conditions, steered the microbial community toward metabolic activities, ensuring the controllability and safety of the fermentation process. Therefore, inoculation with the L. mesenteroides AA001 DVS starter effectively inhibits nitrite accumulation, enabling a highly efficient, stable, and clean fermentation process that significantly improves the quality of Dongbei suancai.