Improved menaquinone (Vitamin K2) production in cheonggukjang by optimization of the fermentation conditions

To improve the content of menaquinone (MK) in cheonggukjang by using Bacillus amyloliquefaciens KCTC11712BP, the fermentation conditions were optimized. The rate of sporulation was found inversely correlated with MK productivity in soybean extract medium during the fermentation process. The best sensory quality of cheonggukjang was appeared at 36 h of fermentation. The synthesis rate of MK was slowed down after fermented for 36 h, which may due to the accumulation of aromatic amino acids (phenylalanine, tyrosine, and tryptophan). Especially, tryptophan was found to be the most sensitive feedback inhibitor of MK biosynthetic pathway. The optimum temperature for MK production was 43°C, and supplement of 4% glycerol could significantly increase the yield of MK. The content of MK in cheonggukjang fermented by using B. amyloliquefaciens KCTC11712BP under the optimum condition reached as high as 12.47 μg/g, which was about 4-fold higher than that of commercial cheonggukjang and natto products.