Hemicellulose hydrolyzing

Buchert, J., Puls, J. andPoutanen, K. 1988. Comparison of Pseudomonas Fragi and Gluconobac-ter Oxydans for Production of Xylonic Acid from Hemicellulose Hydrolyzates. Appl. Microbiol. Biotechnol., 28, 367-372. 

Hemicelluloses hydrolyze much more easily and rapidly than cellulose. Temperatures and acid concentrations that hydrolyze the cellulose to glucose in a matter of a few hours readily convert much of the hemicellulose into simple sugars in minutes or even seconds. Under industrial conditions of hydrolysis, the sugars formed undeigo decomposition, with the pentoses decomposing more rapidly than the hexoses. Thus, the conditions of hydrolysis cause variations in the ratio and yields of the various sugars due to (1) their different rates of formation by hydrolysis and (2) their different rates of decomposition. 

Yeast Biomass Production in Brewery s Spent Grains Hemicellulosic Hydrolyzate... 

Keywords Debaryomyces hansenii Biomass Single-cell protein Hemicellulosic hydrolyzate Brewery s spent grains Agro-industrial residues upgrading Yeast extract... 

The used BSG hydrolyzate conqjosition is shown in Table 2. It has approximately 26 g F of monosaccharides and a low level of microbial inhibitors, specially aliphatic acids, and furan derivatives compared to similar hemicellulosic hydrolyzates used for SCP production, e.g., eucalyptus wood [28] and sugar cane bagasse [7,8]. Also, it has a low content of phenolic compounds. Crude protein has a concentration of about 1.2 g F. Much of this nitrogen (about half) is in ammonia form, the rest as amino acids (data not shown). 

Xylitol, a sugar alcohol, has potential use as a natural food sweetener, a dental caries reducer and a sugar substitute for diabetics. It is produced by chemical reduction in alkaline conditions of the xylose derived mainly from wood hydrolyzate (169). The recovery of xylitol from the xylan fraction is about 50-60% or 8-15% of the raw material employed. Drawbacks of the chemical process are the requirements of high pressure (up to 50 atm) and tenq>erature (80-140°C), use of an expensive catalyst (Raney-Nickel) and use of extensive separation and purification steps to remove the by-products that are mainly derived from the hemicellulose hydrolyzate (770). The bulk of xylitol produced is consumed in various food products such as chewing gum, candy, soft drinks and ice cream. It gives a pleasant cool and fresh sensation due to its high negative heat of solution. 

C). They concluded that xylitol separation by crystallization from fermented hemicellulose hydrolyzate is feasible. 

Wood chips can also be utilized as such to produce bioethanol. The cellulose and hemicellulose material is hydrolyzed in the presence of acids (H2SO4, HCl, or HCOOH) or enzymes to yield glucose and other monosaccharides [16]. Lignin is separated by filtration as a solid residue and the monosaccharides are fermented to ethanol, which, in turn, is separated from water and catalyst by distillation. Ethanol can be used not only as energy source but also as a platform component to make various chemicals, such as ethene and polyethene. Today green acetaldehyde and acetic acid from wood-derived bioethanol is manufactured by SEKAB Ab, at the Ornskoldsvik Biorefinery of the Future industrial park. 

Yundt64 obtains a crystalline xylan from the xylan-rich fraction of straw or birchwood hemicellulose. The fraction is hydrolyzed with 0.2% oxalic acid solution for five hours at 100°. Upon autoclaving the insoluble residue approximately 0.2% dissolves and precipitates as hexagonal platelets when the filtrate is cooled to 60-70°. Very likely this crystalline material is of low molecular weight. 

To break up cellulose/hemicellulose, it is treated physically (milling), with heat, and hydrolyzed (sulfuric acid + enzymes). Also in this case, improved (bio)cata-lytic hydrolysis processes for cellulose/hemicellulose are needed. The sugar can then serve as feedstock for standard fermentation plants. 

For monitoring the extent of polysaccharide hydrolysis, l.c. methods that sepeu ate and analyze the non-fermentable oligosaccharides (d.p. 3-30) derived from cellulose, hemicellulose, and pectins are useful, and have already been described (see Section III,l,c). For determination of the monosaccharide composition of completely hydrolyzed, plant polysaccharides, l.c. is especially useful and has been applied to the compositional analysis of hydrolyzed plant fiber,wood pulps,plant cell-walls,and cotton fibers.In these representative examples, the major sugars of interest, namely, glucose, xylose, galactose, arabinose, and mannose, have traditionally been difficult to resolve by l.c. The separa-... 

Endo-xylanases (1,4-p-D-xylan xylanohydrolase, EC 3.2.1.8), which hydrolyze mainly interior p-(l- 4)-D-xylosyl bonds in the plant hemicellulose xylan, have been isolated from many fungi and bacteria and occasionally from plants and invertebrates. Because xylan is one of the most common of all natural materials, and its removal or conversion is often desirable, the endo-xylanase family has high commercial as well as scientific interest. 

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