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.
Highlights
With the world population growing and available land becoming scarce, energy problems are an increasing concern
The products go through the phosphate pentose pathway (PPP), which is involved in the EMP pathway, in order to complete the use of five- and sixcarbon sugars
In order to investigate the fermentation potential of the mutant strain, we studied on its fermentation parameters and the results were showed in Tables 2, 3
Summary
With the world population growing and available land becoming scarce, energy problems are an increasing concern. Ethanol Production from Cassava Residue the costs of grain soaring, the production of ethanol from the fermentation of grain is becoming unsustainable leading to an urgent need for a cheap raw material replacement. In this respect, the biotransformation of cellulose is of great significance and could help to address the current worldwide energy crisis (Ebrahimi et al, 2017), grain shortages, and environmental pollution. China’s annual use of raw fibrous materials is about 7 × 108 t, primarily from agriculture, forestry, industry, and urban waste (Alves et al, 2015; Kang et al, 2015; Khare et al, 2015). The main product of cellulose hydrolysis is glucose and other sixcarbon sugars, while hemicellulose hydrolyzatesare mainly xylose and other five-carbon sugars (Brienzo et al, 2009; Kamoldeen et al, 2017)
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