Efficient media for high menaquinone-7 production: response surface methodology approach

The aim of this study was to assess the effect of nutrients on the production of menaquinone-7 and determine the optimum conditions to achieve a high concentration of this product. Bacillus subtilis natto was fermented at 40°C for a period of six days. Design of experiments was used for screening the most effective nutrients, and central composite face design was employed for the optimization. The optimum media consisted of 5% (w/v) yeast extract; 18.9% (w/v) soy peptone; 5% (w/v) glycerol and 0.06% (w/v) K 2 HPO 4 . The pH, bacterial growth, concentrations of amino acids, glycerol and menaquinone-7 were measured at the optimum fermentation media each day. Total free amino acids concentration increased 1.7-fold during the fermentation. Lysine and glutamic acid were the most abundant whereas arginine, asparagine and serine were the limiting amino acids at the end of fermentation period. The menaquinone-7 concentration approached 86% of the final value in the third day of fermentation, where the bacteria growth was at exponential phase. At this condition the concentration of glycerol as carbon source and asparagine, serine and arginine as the amino acid sources were dramatically diminished in the fermentation media. The optimum menaquinone-7 concentration was in good agreement with the predicted value by the model (96% validity). The maximum menaquinone-7 concentration of 62.32 ± 0.34 mg/L was achieved after six days of fermentation; this value is the highest concentration reported in the literature.