Influence of Initial Xylose Concentration, Agitation, and Aeration on Ethanol Production by Pichia stipitis from Rice Straw Hemicellulosic Hydrolysate

• Published in: Applied biochemistry and biotechnology 2010-11, Vol.162 (5), p.1306-1315
• Main Authors: Silva, João Paulo A, Mussatto, Solange Inês, Roberto, Inês C
• Format: Article
• Language: English
• Subjects: Aeration; Aerobiosis - drug effects; Biochemistry; Biological and medical sciences; Biotechnology; Biotechnology - methods; Carbohydrates; Chemistry; Chemistry and Materials Science; Ethanol; Ethanol - metabolism; Fermentation; Fermentation - drug effects; Fundamental and applied biological sciences. Psychology; Hydrolysis - drug effects; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology; Oryza - chemistry; Oryza sativa; Pichia - cytology; Pichia - drug effects; Pichia - metabolism; Pichia stipitis; Polysaccharides - metabolism; Rice straw; Waste Products - analysis; Xylose - pharmacology; Yeast; Yeasts
• ISSN: 0273-2289; 1559-0291
• DOI: 10.1007/s12010-009-8867-6

Rice straw hemicellulosic hydrolysate was used as fermentation medium for ethanol production by Pichia stipitis NRRL Y-7124. Shaking bath experiments were initially performed aiming to establish the best initial xylose concentration to be used in this bioconversion process. In the sequence, assays were carried out under different agitation (100 to 200 rpm) and aeration (V flask/V medium ratio varying from 2.5 to 5.0) conditions, and the influence of these variables on the fermentative parameters values (ethanol yield factor, Y P/S; cell yield factor, Y X/S; and ethanol volumetric productivity, Q P) was investigated through a 2² full-factorial design. Initial xylose concentration of about 50 g/l was the most suitable for the development of this process, since the yeast was able to convert substrate in product with high efficiency. The factorial design assays showed a strong influence of both process variables in all the evaluated responses. The agitation and aeration increase caused a deviation in the yeast metabolism from ethanol to biomass production. The best results (Y P/S = 0.37 g/g and Q P = 0.39 g/l.h) were found when the lowest aeration (2.5 V flask/V medium ratio) and highest agitation (200 rpm) levels were employed. Under this condition, a process efficiency of 72.5% was achieved. These results demonstrated that the establishment of adequate conditions of aeration is of great relevance to improve the ethanol production from xylose by Pichia stipitis, using rice straw hemicellulosic hydrolysate as fermentation medium.