Glycerol production by microbial fermentation: A review

Microbial production of glycerol has been known for 150 years, and glycerol was produced commercially during World War I. Glycerol production by micro bial synthesis subsequently declined since it was unable to compete with ch emical synthesis from petrochemical feedstocks due to the low glycerol yiel ds and the difficulty with extraction and purification of glycerol from bro th. As the cost of propylene has increased and its availability has decreas ed especially in developing countries and as glycerol has become an attract ive feedstock for production of various chemicals, glycerol production by f ermentation has become more attractive as an alternative route. Substantial overproduction of glycerol by yeast from monosaccharides can be obtained b y: (1) forming a complex between acetaldehyde and bisulfite ions thereby re tarding ethanol production and restoring the redox balance through glycerol synthesis; (2) growing yeast cultures at pH values near 7 or above; or (3) using osmotolerant yeasts. In recent years, significant improvements have been made in the glycerol production using osmotolerant yeasts on a commerc ial scale in China. The most outstanding achievements include: (1) isolatio n of novel osmotolerant yeast strains producing up to 130 g/L glycerol with yields up to 63% and the productivities up to 32 g/(L day); (2) glycerol y ields, productivities and concentrations in broth up to 58%, 30 g/(L day) a nd 110-120 g/L, respectively, in an optimized aerobic fermentation process have been attained on a commercial scale; and (3) a carrier distillation te chnique with a glycerol distillation efficiency greater than 90% has been d eveloped. As glycerol metabolism has become better understood in yeasts, op portunities will arise to construct novel glycerol overproducing microorgan isms by metabolic engineering. (C) 2001 Elsevier Science Inc. All rights re served.