Abstract
BackgroundAcetoin (3-hydroxy-2-butanone), the precursor of biofuel 2,3-butanediol, is an important bio-based platform chemical with wide applications. Fermenting the low-cost and renewable plant biomass is undoubtedly a promising strategy for acetoin production. Isothermal simultaneous saccharification and fermentation (SSF) is regarded as an efficient method for bioconversion of lignocellulosic biomass, in which the temperature optima fitting for both lignocellulose-degrading enzymes and microbial strains.ResultsA thermotolerant (up to 52 °C) acetoin producer Bacillus subtilis IPE5-4 which simultaneously consumed glucose and xylose was isolated and identified. By compound mutagenesis, the mutant IPE5-4-UD-4 with higher acetoin productivity was selected. When fermenting at 50 °C in a 5-L bioreactor using glucose as the feedstock by strain IPE5-4-UD-4, the acetoin concentration reached 28.83 ± 0.91 g L−1 with the acetoin yield and productivity of 0.34 g g−1 glucose and 0.60 g L−1 h−1, respectively. Furthermore, an optimized and thermophilic SSF process operating at 50 °C was conducted for acetoin production from alkali-pretreated corncob (APC). An acetoin concentration of 12.55 ± 0.28 g L−1 was achieved by strain IPE5-4-UD-4 in shake flask SSF, with the acetoin yield and productivity of 0.25 g g−1 APC and 0.17 g L−1 h−1. Meanwhile, the utilization of cellulose and hemicellulose in the SSF approach reached 96.34 and 93.29%, respectively. When further fermented at 50 °C in a 5-L bioreactor, the concentration of acetoin reached the maximum of 22.76 ± 1.16 g L−1, with the acetoin yield and productivity reaching, respectively, 0.46 g g−1 APC and 0.38 g L−1 h−1. This was by far the highest acetoin yield in SSF from lignocellulosic biomass.ConclusionsThis thermophilic SSF process provided an efficient and economical route for acetoin production from lignocellulosic biomass at ideal temperature for both enzymatic hydrolysis and microbial fermentation.
Highlights
Acetoin (3-hydroxy-2-butanone), the precursor of biofuel 2,3-butanediol, is an important bio-based platform chemical with wide applications
Isolation and identification of thermotolerant acetoin‐producing strains Thirty-eight isolates with the ability to produce acetoin were obtained from the soil samples by colorimetric reaction screens on agar plates at 50 °C
The concentration of acetoin reached the maximum of 22.76 ± 1.16 g L−1 when fermenting at 50 °C in a 5-L bioreactor for 60 h, but decreased to 19.14 ± 1.56 g L−1 at 72 h
Summary
Acetoin (3-hydroxy-2-butanone), the precursor of biofuel 2,3-butanediol, is an important bio-based platform chemical with wide applications. Acetoin (3-hydroxy-2-butanone), with a natural pleasant cream aroma flavor, abundantly exists in dairy foods and some fruits. It was widely used as food flavor enhancer in food industry [1] and applied as an important intermediate in drug and chemical synthesis and multifunctional materials [2, 3]. Some efforts have been made to develop biotechnological production methods including enzymatic conversion and microbial fermentation [2]. Microbial fermentative process displays advantages in environmental-friendly sources of raw materials, and has benefits in lowering productive costs
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