Starch, whey or hemicellulosic waste can be used as a raw material for the industrial production of rare sugars. D-glucose from starch, whey and hemicellulose, D-galactose from whey, and D-xylose from hemicellulose are the main starting monosaccharides for production of rare sugars. We can produce all monosaccharides; tetroses, pentoses and hexoses, from these raw materials. This is achieved by using D-tagatose 3-epimerase, aldose isomerase, aldose reductase, and oxidoreductase enzymes or whole cells as biocatalysts. Bioproduction strategies for all rare sugars are illustrated using ring form structures given the name Izumoring.
The objective of this study was to optimize continuous acetone-butanol-ethanol (ABE) fermentation using two stage chemostat system integrated with liquid-liquid extraction of solvents produced in first stage. This minimized end product inhibition by butanol and subsequently enhanced glucose utilization and solvent production in continuous culture of Clostridium acetobutylicum B 5313. During continuous two-stage ABE fermentation, sugarcane baggase was used as cell holding material for the both stages and liquid-liquid extraction was performed using oleyl alcohol and decanol mixture. An overall solvent production of 25.32 g/L (acetone 5.93 g/L, butanol 16.90 g/L and ethanol 2.48 g/L) was observed as compared to 15.98 g/L in single stage chemostat with highest solvent productivity and solvent yield of 2.5 g/L.h and of 0.35 g/g, respectively. Maximum glucose utilization (83.21 %) at dilution rate of 0.05 1/h was observed as compared to 54.38 % in single stage chemostat.
Clostridium spp. produce n-butanol in the acetone/butanol/ethanol process. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, the low product yield, toxicity to production strain, multiple-end products and downstream processing of alcohol mixtures. This review describes the use of lignocellulosic feedstocks, bioprocess and metabolic engineering, downstream processing and catalytic refining of n-butanol.
The gradual shift of transportation fuels from oil based fuels to the alternative fuel resources and worldwide demand for energy has been the impetus for research to produce alcohol biofuels from renewable resources. Current bioethanol and biodiesel can, however, not cover an increasing demand for biofuels. Hence, there is an extensive need for advanced biofuels with superior fuel properties. The present review is focused on the developments of biobutanol, which is regarded to be superior to bioethanol in terms of energy density and hygroscopicity. Although acetone-butanolethanol (ABE) fermentation is one of the oldest large-scale fermentation processes, butanol yield by anaerobic fermentation remains sub-optimal. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, low product yield, product toxicity to production strain, multiple end-products and downstream processing of alcohol mixtures.Metabolic engineering provides a means for fermentation improvements. Different strategies are employed in the metabolic engineering of Clostridia that aim to enhance the solvent production, improve selectivity for butanol production, and increase the tolerance of Clostridia to solvents. The introduction and expression of a non-clostridial butanol producing pathway in E. coli is most promising strategy for butanol biosynthesis. Several rigorous kinetic and physiological models for fermentation have been formulated, which form useful tool for optimization of the process. Due to the lower butanol titers in the fermentation broth, simultaneous fermentation and product removal techniques have been developed to improve production economics. With the use of new strains, inexpensive substrates, and superior reactor designs, economic ABE fermentation may further attract an attention of researchers all over the world. The present review is attempting to provide an overall outlook on discoveries and strategies that are being developed for commercial n-butanol production.
Xylitol is the first rare sugar that has global markets. It has beneficial health properties and represents an alternative to current conventional sweeteners. Industrially, xylitol is produced by chemical hydrogenation of D-xylose into xylitol. The biotechnological method of producing xylitol by metabolically engineered yeasts, Saccharomyces cerevisiae or Candida, has been studied as an alternative to the chemical method. Due to the industrial scale of production, xylitol serves as an inexpensive starting material for the production of other rare sugars. The second part of this mini-review on xylitol will look more closely at the biotechnological production and future applications of the rare sugar, xylitol.
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