Synergistic metabolism of Limosilactobacillus fermentum and Acetobacter pasteurianus combined with nutrition supplementation regulating γ-aminobutyric acid biosynthesis in solid-state fermentation of cereal vinegar.

γ-aminobutyric acid (GABA) is one of the important functional compounds in vinegar. However, the underlying GABA biosynthesis mechanisms and regulating strategy in the solid-state fermentation of vinegar remain unclear. Limosilactobacillus fermentum was identified as key microorganism for producing glutamate decarboxylase (GAD). However, the metabolic activity of L.fermentum was limited due to high ethanol and acid stress, resulting in low GAD activity. Meanwhile, the temperature was positive with GABA, while ethanol was negative with it. Therefore, synergistic bioaugmentation combined with nutrient supplementation was proposed. Nutrient supplementation combined with co-bioaugmentation of L.fermentum and A. pasteurianus diminishes the ethanol stress and improves the fermentation temperature, meanwhile, improving the expression of GAD and acid tolerance of L.fermentum. Ultimately, the GABA content was improved by 120.94% compared with the control group. These results provide a value reference for the targeted regulation of the GABA in the solid-state fermentation of cereal vinegar.