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Fermentation of xylose, arabinose, glucose, their mixtures and sugarcane bagasse hydrolyzate by yeast Pichia stipitis for ethanol production
(2020-02-01)
Phaiboonsilpa, Natthanon
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Chysirichote, Teerin
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Champreda, Verawat
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Laosiripojana, Navadol
Xylose, arabinose and glucose were studied their fermentabilities to ethanol by yeast Pichia stipitis. The experiments were conducted by using 1.0, 5.0, 10.0 and 20.0 g/l of mono-saccharide solutions in a close fermentation system at 30 °C with 100-rpm shaking rate for 120 h. Fermentabilities of mono-saccharides appeared to produce high ethanol yield when a low concentration of xylose and arabinose was applied. Glucose fermentability was, however, found to be preferable at high sugar concentration. The highest ethanol yields could be achieved at 106.27, 86.25, and 73.10%, reported as a relative % to its theoretical ethanol yield, by using 1.0 g/l of xylose, 1.0 g/l of arabinose, and 20.0 g/l of glucose solutions, respectively. The empirical equations were then established based on the fementabilities obtained to predict ethanol yield for a given concentration of mono-saccharides. A comparative study on fermentation of the mono-saccharide mixture and sugarcane bagasse hydrolyzate, of which xylose, arabinose and glucose concentrations were similar, were moreover conducted. It was revealed that the empirical equations provided an excellent estimation of ethanol concentration when the mono-saccharide mixture was used. The presence of furans and other compounds in sugarcane bagasse hydrolyzate besides the mono-saccharides, however, resulted in a lower ethanol fermentability compared with that calculated by the empirical equations. This is due apparently to an inhibition effect of these additional components to Pichia stipitis.
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Comparative study on liquefaction behaviors of xylan hemicellulose as treated by different hydrothermal methods
(2020-02-01)
Phaiboonsilpa, Natthanon
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Champreda, Verawat
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Laosiripojana, Navadol
Liquefaction behaviors of xylan were studied as treated by six different hydrothermal methods. As a comparative study, a xylan sample isolated from corn core was subjected to hot-compressed water, hot-compressed 0.01 and 0.1wt% H<inf>2</inf>O<inf>2</inf> solutions under pressurization of N<inf>2</inf> or CO<inf>2</inf> at 110–250 °C for 0 min in 10-ml batch-type reactor. Not only xylose and xylo-oligosaccharides, but also arabinose, glucose, and acetic acid were recovered as hydrolyzed products. In addition, decomposition compounds, i.e. furans and organic acids were found. The highest xylose yield could be attained at 210 °C in all the studied hydrothermal methods, except for only 0.1wt% H<inf>2</inf>O<inf>2</inf> solution under pressurization of CO<inf>2</inf>. By this strongly oxidative condition, where peroxy carbonic acid was formed in situ, the temperature that xylose could be highly recovered was at 190 °C. The highest xylose yield of 61.62wt% was obtained by 0.01wt% H<inf>2</inf>O<inf>2</inf> solution under pressurization of N<inf>2</inf>. Formation of furan compounds showed a preference to the treatments with pressurized CO<inf>2</inf>, while organic acids had a better recovery when N<inf>2</inf> was applied. Different results in the production of various liquefied products could be attributed to the degree of hydrolysis and oxidation reactions which altered under the different hydrothermal methods.
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Identification and characterization of a cellulase-encoding gene from the buffalo rumen metagenomic library
(2012-06-29)
Nguyen, Nhung Hong
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Maruset, Lalita
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Uengwetwanit, Tanaporn
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Mhuantong, Wuttichai
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Harnpicharnchai, Piyanun
Microorganisms residing in the rumens of cattle represent a rich source of lignocellulose-degrading enzymes, since their diet consists of plant-based materials that are high in cellulose and hemicellulose. In this study, a metagenomic library was constructed from buffalo rumen contents using pCC1FOS fosmid vector. Ninety-three clones from the pooled library of approximately 10,000 clones showed degrading activity against AZCL-HE-Cellulose, whereas four other clones showed activity against AZCL-Xylan. Contig analysis of pyrosequencing data derived from the selected strongly positive clones revealed 15 ORFs that were closely related to lignocellulose-degrading enzymes belonging to several glycosyl hydrolase families. Glycosyl hydrolase family 5 (GHF5) was the most abundant glycosyl hydrolase found, and a majority of the GHF5s in our metagenomes were closely related to several ruminal bacteria, especially ones from other buffalo rumen metagenomes. Characterization of BT-01, a selected clone with highest cellulase activity from the primary plate screening assay, revealed a cellulase encoding gene with optimal working conditions at pH 5.5 at 50 °C. Along with its stability over acidic pH, the capability efficiently to hydrolyze cellulose in feed for broiler chickens, as exhibited in an in vitro digestibility test, suggests that BT-01 has potential application as a feed supplement.

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