Abstract
To enhance the value-added use of methanol-containing raw glycerol derived from biodiesel fuel production, the effect of methanol supplementation on glyceric acid (GA) production by Gluconobacter spp. was investigated. We first conducted fed-batch fermentation with Gluconobacter frateurii NBRC103465 using raw glycerol as a feeding solution. GA productivity decreased with increasing dihydroxyacetone (DHA) formation when the raw glycerol contained methanol. The results of this experiment and comparative experiments using a synthetic solution modeled after the raw glycerol indicate that the presence of methanol caused a change in the concentrations of GA and DHA, two glycerol derivatives produced during fermentation. Other Gluconobacter spp. also decreased GA production in the presence of 1% (v/v) methanol. In addition, purified membrane-bound alcohol dehydrogenase (mADH) from Gluconobacter oxydans, which is a key enzyme in GA production, showed a decrease in dehydrogenase activity toward glycerol as the methanol concentration increased. These results strongly suggest that the observed decrease in GA production by Gluconobacter spp. resulted from the methanol-induced inhibition of mADH-mediated glycerol oxidation.
Highlights
Biodiesel fuel (BDF), a class of renewable energy, is widely used to conserve fossil fuels and reduce carbon dioxide emissions
Based on the raw glycerol composition, a synthetic solution modeled after the raw glycerol was prepared with the following pure reagents: glycerol, 66% (w/v); methanol, 30% (w/v); and sodium hydroxide, 1 M
Fed-batch glyceric acid (GA) fermentation by G. frateurii NBRC103465 using raw glycerol derived from BDF production and its modeled solution Previously, Habe et al (2009a) demonstrated that fedbatch fermentation using glycerol in an alkaline feeding solution resulted in considerable improvement in GA production by G. frateurii NBRC103465, indicating a potential use for raw glycerol derived from BDF production, which contains both alkali metals and methanol
Summary
Biodiesel fuel (BDF), a class of renewable energy, is widely used to conserve fossil fuels and reduce carbon dioxide emissions. One method of BDF production involves transesterification between triacylglycerols, which are present in plant oils and animal fats, and methanol under alkaline conditions. This reaction forms glycerol as a byproduct at 10% of the initial amount of triacylglycerol. Raw glycerol derived from BDF production has diverse properties that depend on the initial raw materials (e.g., origin of triacylglycerol), reaction conditions, and manufacturing process. The transesterification of triacylglycerol with methanol requires excess methanol for efficient BDF production, resulting in an impure, methanol-containing raw glycerol. Raw glycerol after purification has relatively high purity and represents a useful raw material for chemical production, whereas impure raw glycerol is often wasted. It is important to investigate the effects of impurities in raw glycerol, methanol, on chemical production
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