Production of polysaccharide and surfactin by Bacillus subtilis ATCC 6633 using rehydrated whey powder as the fermentation medium

Abstract

The aim of this research was to assess the amounts of polysaccharide and surfactin produced by Bacillus subtilis ATCC 6633 in rehydrated whey powder (RWP) as the growth medium. One-day-old cultures of B. subtilis (∼4.6 log cfu/mL) were inoculated into 100mL of 10, 15, or 20% (wt/vol) RWP and incubated at 30°C for 72h. To analyze the effects of lactose and protein on polysaccharide and surfactin production, 6 RWP solutions containing different levels of lactose and protein were also used as media. The number of vegetative cells and spores, pH, viscosity, and the concentration of lactose were determined at 0, 24, 48, or 72h of fermentation. The levels of polysaccharide and surfactin produced after 72h of fermentation were measured using HPLC and the phenol-sulfuric acid method, respectively. During 72h of fermentation, B. subtilis populations increased from 4.6 to 10.54, 9.82, and 9.67 log 10 cfu/mL in 10, 15, and 20% RWP, respectively. The number of B. subtilis spores in 10% RWP increased from 3.91 to 4.72 log 10 cfu/mL after 48 and 72h of fermentation, respectively. The increased level of lactose or protein in RWP did not significantly change the vegetative growth. After 72h of fermentation, the pH of RWP decreased from 5.70 to 4.99 with a slight increase in viscosity. Polysaccharide levels in 10, 15, and 20% RWP after fermentation were 513.6, 613.5, and 768.3mg/L, respectively, with B. subtilis producing 0.18 to 0.29g/L of surfactin after 72h of fermentation. The polysaccharide or surfactin production was not changed significantly by addition of protein or lactose to RWP. These results indicate that RWP is a good fermentation substrate for surfactin and polysaccharide production. © 2012 American Dairy Science Association.