Fermentation Process and Metabolic Flux of Ethanol Production from the Detoxified Hydrolyzate of Cassava Residue

Abstract

With the growth of the world population, energy problems are becoming increasingly severe; therefore, sustainable energy sources have gained enormous importance. With respect to ethanol fuel production, biomass is gradually replacing grain as the main raw material. In this study, we explored the fermentation of five- and six-carbon sugars, the main biomass degradation products, into alcohol. We conducted mutagenic screening specifically for Candida tropicalis CICC1779 to obtain a strain that effectively used xylose (Candida tropicalis CICC1779-Dyd). By subsequently studying fermentation conditions under different initial liquid volume oxygen transfer coefficients (kLα), and coupling control of the aeration rate and agitation speed under optimal conditions, the optimal dissolved oxygen change curve was obtained. In addition, we constructed metabolic flow charts and equations to obtain a better understanding of the fermentation mechanism and to improve the ethanol yield. In our experiment, the ethanol production of the wild type stain was 17.58 g·L−1 at a kLα of 120. The highest ethanol yield of the mutagenic strains was 24.85 g·L−1. The ethanol yield increased to 26.56 g·L−1 when the dissolved oxygen content was optimized, and the conversion of sugar into alcohol reached 0.447 g·g−1 glucose (the theoretical titer of yeast-metabolized xylose was 0.46 g ethanol/g xylose and the glucose ethanol fermentation titer was 0.51 g ethanol/g glucose). Finally, the detected activity of xylose reductase and xylose dehydrogenase was higher in the mutant strain than in the original, which indicated that the mutant strain (CICC1779-Dyd) could effectively utilize xylose for metabolism.

Adaptive Laboratory Evolution for Multistress Tolerance, including Fermentability at High Glucose Concentrations in Thermotolerant Candida tropicalis

“…C. tropicalis UFMGBX12 consumed 35% of xylose in a medium containing 2 g•L −1 xylose and 18 g•L −1 glucose [45]. C. tropicalis CICC1779 utilized 55.8% of xylose in a medium containing 30 g•L −1 xylose and 30 g•L −1 glucose [46] and K. marxianus DMKU 3-1042 utilized 35% of xylose in a medium containing 20 g•L −1 xylose and 20 g•L −1 glucose [14]. Therefore, it is likely that C. tropicalis X-17 and X-17.2b are less sensitive in xylose utilization to glucose repression.…”

Cost‐effective process for the production of Monascus pigments using potato pomace as carbon source by fed‐batch submerged fermentation

“…Enzymatic hydrolysate solution and residual cellulose were separated by filtration after boiled for 5 min to extinguish enzymes. Afterward, the residual cellulose was hydrolyzed according to the method of Li et al (Li et al., 2017 ). The main hydrolysis process is as follows: The residual cellulose was soaked into the 1.8% (w/v) H 2 SO 4 solution with the mass/volume ratio as 1:10 and hydrolyzed at 220℃ for 5 min.…”

Potential of Candida glabrata from ragi as a bioethanol producer using selected carbohydrate substrates

“…At the later stage of fermentation, the ethanol concentration decreased in most of the fermentation because the yeast required energy to maintain growth. According to Li et al (2017), the yeast consumed some ethanol to obtain energy due to the small amount of residual sugars in the media. From Figure 4, low ethanol yield was observed in the fermentation using sucrose, with the peak production of only 1.64 g/L at 6 h. On the other hand, no ethanol was detected in fermentations using maltose throughout the 5 days of incubation.…”