Xylan, fermentation

Katahira S, Fujita Y, Mizukie A, Fukuda H, Kondo A. (2004). Construction of a xylan fermenting yeast strain through codisplay of xylanolytic enzymes on the surface of xylose utilizing Saccharomyces cerevisiae cells. Appl Environ Microbiol, 70, 5407-5414. 

Morosoli R, Zalce E, Durand S. (1993). Secretion of a Cryptococcus albidus xylanase in Pichia stipitis resulting in a xylan fermenting transformant. Curr Genet, 24,94-99. 

RunUnococcus albus and Ruminococcus flavefadens. These bacteria are important cellulose-degraders found in the rumen of cattle and sheep (2). Most isolated strains ferment cellulose and xylan and all ferment cellobiose. Fermentation of glucose and some other carbohydrates depends on the particular strain. R flavefadens and B. succinogenes can ferment the highly ordered crystalline cellulosic su trates but R albus cannot. No evidence has been found for extracellular cellulase production by R albus, but Ohmiya et al. purified cellobiosidase from this culture 17). Laboratory growth of R albus has been conducted at pH 7.0 and 37 C. 

The particular wood species we chose for this study is aspen (Populus tremuloides), which is plentiful in Canada and in the northern U.S.A. The chemical composition we found to be glucan 53.4%, xylan 14.9%, total carbohydrate 79.0%, lignin 17.1% and extractives 3.8%. We would expect total fermentable sugars of about 56% in this sample of aspen in anhydro form (Timell has reported about 60% in another sample (15)) which upon hydrolysis would yield about 1,250 lb wood sugars per ton of wood (dry basis), from the stoichiometry. Theoretical conversion of this sugar to ethanol would yield 640 lb or 81.1 gallons of anhydrous... 

Hemicellulose (or polyose) is primarily composed of xylan, a branched polymer composed of five-carbon sugar, xylose. Typical polymerization degree of hemicellulose is 50 - 200, which is shorter than the cellulose molecules. The acid hydrolysis of hemicellulose, (C6H10O5)n, produces mainly xylose (C6H10O5), which can be converted to furfural, a chemical feedstock, or can be fermented to ethanol. 

The ultimate goal of the AFEX treatment is to increase the yields of fermentation products such as ethanol by increasing the digestibility of the biomass. Therefore, selected runs that showed higher glucan and xylan conversion were chosen for further SSF analysis. The best treatment temperature is to be selected based on the fermentation results, not just on enzymatic hydrolysis the fermentation results are presented later in this article. 

Note that all the runs (with one exception) with longer treatment time showed lower ethanol yield. However, the hydrolysis results of these runs all showed greater glucan and xylan conversion. As mentioned previously, perhaps during longer treatment times some inhibitory materials were produced that in turn reduced the yield of the fermentation. Based on these findings, 5 min is currently considered the best residence time for the AFEX treatment of corn stover. 

The noncellulose (1-n-glucans in hemicellulose are generally 1,3- and 1,4-bonded arabinans, xylans, arabinoxylans, arabinogalactans, etc. Their aqueous dispersions are quite viscous to the detriment of filters used to clarify cereal-based fermented beverages. Oat (3-glucans are Theologically... 

Jeanite liquid fuel from fermentation of molasses, IV, 32 Jute, xylan percentage in, V, 270 Jute fibers, diffraction pattern, V, 104... 

Another promising thermophilic Gram-positive microbe is Thermoanaero-bacterium saccharolyticum which ferments xylan and produces ethanol, acetate, lactic acid, CO2, and H2. The engineered strain TD1, in which the... 

Saraswat, V and Bisaria, V S., Biosynthesis of xylanolytic and xylan-debranching enzymes in Melanocarpus albomyces IIS 68. J Fermentation Bioeng 1997, 83 (4), 352-357. 

Bergius-Willstatter saccharification process. Process for industrial production of fermentable sugar from wood by hydrolysis of tannin and xylan-free cellulose with 40-45% hydrochloric acid. The use of concentrated acid requires acid-resistant equipment and recovery of acid. The sugar produced must be rehydrolyzed prior to fermentation. 

Galactan Mannans, xylans Plants Alcoholic fermentation reduction to alcohol... 

Xylan-based polymers show no convincing evidence for molecular interaction with, or cross-linking of, cellulose under the high dilution fermentation conditions. Whether this is also true in the less dilute cell wall environment remains to be determined. Description of hemicellulose polymers as glucan-binding may therefore not always be accurate. 

---