Fermentation

Application of Biomass Hydrolysate in Fermentation Processes

  Sugar-rich hydrolysates from biomass can be applied in the fermentation processes as an alternative carbon source to reduce process costs. To apply and evaluate the biomass hydrolysates as a fermentation medium, composition (pentose/hexose sugars and sugar derivatives) analysis, detoxification process, concentration process, and fermentation profiling should be performed. Based on biomass type and saccharification method (e.g., catalyst, condition), sugar derivatives (including aliphatic acids and furan compounds), and phenolic compounds are generated, which can inhibit the fermentation performance of the strain. Thus, the chemical compositions of each hydrolysate should be identified and then processed with appropriate steps (detoxification) before application to the fermentation.

  The following graphical summary shows the sugar platform-based biorefinery process in which microbial fermentation is performed to produce liquid biofuels (ethanol) and platform chemicals (lactic acid):

Direct Utilization of Biomass Hydrolysate in Fermentation without Detoxification Process

  In the peanut shell biorefinery process, aliphatic acids (acetic acid and formic acid) and xylose were generated by diluted acid hydrolysis. We studied the inhibition effects of sugar derivatives on Candida tropicalis (a major xylitol producer), finding reasonable and optimal hydrolysis conditions for maximizing xylose recovery without potential inhibitions in the fermentation process. The xylitol fermentation using the peanut shell hydrolysate medium (with xylose, acetic acid, and formic acid) achieved 0.47 g/L xylitol production, which was similar to the control medium containing xylose (0.56 g/L xylitol).

  In the chestnut pericarp biorefinery process, acetic acid was generated through alkaline pretreatment and enzymatic hydrolysis processes, and the effects of acetic acid on Gluconacetobacter xylinus (a major bacterial cellulose [BC] producer) were investigated. Fermentation experiments using analytical grade acetic acid showed that BC production was enhanced up to 2 g/L acetic acid, while BC production was significantly inhibited above 4 g/L acetic acid. Fermentation using the chestnut pericarp hydrolysate medium containing 30 g/L glucose (optimal carbon feeding) and 0.4 g/L acetic acid improved BC production by 33% compared to the control medium (without acetic acid).

  To utilize biomass hydrolysates by simple processes, we will continue to evaluate the resistance of industrial strains to the sugar derivatives and their usability as an additional carbon source of the fermentation medium.