16 research outputs found
Adaptation of Scheffersomyces stipitis to hardwood spent sulfite liquor by evolutionary engineering
Hardwood spent sulfite liquor (HSSL) is a by-product of acid sulfite pulping process that is rich in
xylose, a monosaccharide that can be fermented to ethanol by Scheffersomyces stipitis. However, HSSL also contains
acetic acid and lignosulfonates that are inhibitory compounds of yeast growth. The main objective of this study
was the use of an evolutionary engineering strategy to obtain variants of S. stipitis with increased tolerance to HSSL
inhibitors while maintaining the ability to ferment xylose to ethanol
Short-term adaptation improves the fermentation performance of Saccharomyces cerevisiae in the presence of acetic acid at low pH
Hybrid SSF/SHF Processing of SO2 Pretreated Wheat Straw—Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time
Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO2 as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO2 (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion
Current trends in waste valorization
This paper presents the scientific breakthroughs made in bioprocess engineering and microbial biotechnology for the conversion of wastes into products with added value and/or biofuels. The significant results obtained in the emerging fields of hybrid electrosynthesis, the role of enzymes in the degradation of plastics, polyhydroxyalkanoate and 5-aminolevulinic acid production, fermentation technology and the application of molecular engineering tools to bioprocess technology are highlighted