Physicochemical analysis during co-fermentation of saccharified potato natto with Bifidobacterium animalis subsp. lactis and Bacillus subtilis

Natto is a functional food rich in nattokinase. It is produced by fermenting soybeans with Bacillus subtilis var. natto , typically with added simple sugars to support microbial growth. Potatoes and soybeans offer complementary nutrition, and saccharified potato solution supplies readily available sugars, amino acids, vitamins, and minerals. Here, potatoes were enzymatically saccharified and used to soak soybeans, and "potato natto" was produced by co-fermenting Bifidobacterium animalis subsp. lactis BLH16 with Bacillus subtilis var. natto GUTU09. The results showed that mixed-culture fermentation significantly increased nattokinase (EC 3.4.21.62) activity to 390 ± 39.68 FU/g (a 59 % increase compared with single-strain fermentation). It also elevated amino acid nitrogen, total phenolics, total flavonoids, soluble peptides, and antioxidant activity. Correlation analysis revealed a significant positive correlation between most metabolites and antioxidant capacity indices. BLH16 promoted GUTU09 to secrete nattokinase, which degraded the proteins in natto and gradually converted them into amino acid nitrogen and soluble peptides. The study confirmed the synergistic proliferation between GUTU09 and BLH16, indicating a mutually beneficial interaction. In conclusion, mixed culture fermentation can effectively enrich potato natto's nutritional and functional components, providing a theoretical basis for developing high-activity functional natto. • Synergistic metabolic mechanisms in bacterial co-culture are revealed • Co-culture raises amino acid nitrogen, phenolics, flavonoids, and other nutrients • Co-culture boosts nattokinase activity by 59 % to 390 ± 39.68 FU/g • Co-culture fermentation markedly enhances antioxidant capacity • Co-culture provides actionable insights for developing novel fermented foods