Non‐sterilized fermentative production of acetoin with 2,3‐butanediol as a main byproduct from maize hydrolysate by a newly isolated thermophilic Bacillus strain

BACKGROUND Acetoin is an important biorefinery platform chemical with many industrial uses. It is mainly produced by chemical synthesis or mesophilic fermentation with high costs. RESULTS A thermophilic Bacillus strain was isolated to efficiently produce acetoin from maize hydrolysate at 50°C. The fermentation medium was statistically optimized by Plackett–Burman design. Operational conditions were then optimized using a 4.2 L fermenter conducted at 50°C without sterilization. Oxygen enriched air (65% oxygen) accelerated substrate consumption but did not increase product titer. In comparison with 600 rpm, agitation speed controlled at 400 rpm yielded less acetoin but more 2,3‐butanediol in the final products. A two‐stage pH control strategy (pH first at 6.6–7.1 then at 7.7–8.0) was applied to further increase the yield of acetoin. Finally, 50.8 g L ‐1 of acetoin and 32.1 g L ‐1 of 2,3‐butanediol were obtained from 251 g L ‐1 of degermed maize flour (dry weight). The conversion yield from sugar to the 4‐carbon compounds (acetoin and 2,3‐butanediol) was 94.4% of the theoretical value. CONCLUSION This is the first report of non‐sterilized fermentative production of acetoin. Using degermed maize hydrolysate as the main feedstock, this work sets a new titer record of acetoin fermentation among known thermophilic producing systems. © 2017 Society of Chemical Industry