Pentoses xylose

In the first stage, the pentose xylose was converted by strain Lactococcus lactis to a mixture of lactic and acetic acids. After removal of the cells, Ralstonia eutropha was inoculated in the supernatant in the same fermentor. Cost calcu-... 

As previously stated, furfural is obtained through dehydration of pentoses, xylose in particular, or hemicelluloses, at high temperatures (200-250 °C), and in the presence of mineral acids as catalysts, mainly sulfuric acid.[31] Under these... 

From the reaction between ammonium molybdate and the pentose xylose, a complex composed of a dimolybdenum core and one sugar moiety 143 [163] could be obtained. 

Figure 11 GC/MS assay of alditol hexa-acetates quantified against inositol internal standard (IS), (a) In the chromatogram shown here the monosaccharides making up a plant cell wall are being quantified as their alditol acetates, using inositol (Ino) as the (IS). The GC separation of these reduced sugars is essential for their identification. The mass spectra of the alditol acetates of the hexoses, glucose (Glc) (b), galactose (Gal) (c), and mannose (Man), are essentially identical, as are the mass spectra of the alditol acetates of the pentoses, xylose (Xyl) and arabinose (Ara), and the deoxysugars, rhamnose (Rhm) and fucose (Fuc).

Vast amounts of renewable biomass are available for conversion to liquid fuel, ethanol. In order to convert biomass to ethanol, the efficient utilization of both cellulose-derived and hemicellulose-derived carbohydrates is essential. Six-carbon sugars are readily utilized for this purpose. Pentoses, on the other hand, are more difficult to convert. Several metabolic factors limit the efficient utilization of pentoses (xylose and arabinose). Recent developments in the improvement of microbial cultures provide the versatility of conversion of both hexoses and pentoses to ethanol more efficiently. In addition, novel bioprocess technologies offer a promising prospective for the efficient conversion of biomass and recovery of ethanol. 

International Polyol Chemical Inc. (ICPl) has invested in a 200000 tonne plant which was originally planned to start in 2007 but has been delayed. The plant win produce glycols such as propylene glycol, ethylene glycol, glycerin, and butane-diol, starting from sorbitol/glucose. It also aims to use molasses or waste streams such as various pentoses (xylose/arabinose) and lactose derived from whey as feedstocks. 

Furfural is formed by dehydration of pentose. Xylose is a major aldopentose and is involved as a form of xylan in hemicelluloses. Unlike glucose, furfural can be formed from xylose by Bronsted acids alone at high temperature, although the furfural selectivity is low. A variety of Bronsted acid catalysts have been examined for furfural synthesis and they are H-type zeolites such as H-mordenite and H-Y faujasite [183], delaminated zeolite [184], H-MCM-22 [185], ion-exchange resins [186], sulfonated porous silicas [187-189], porous niobium silicate [190], metal oxide nanosheets [51], and sulfated zirconia [191]. Sulfated tin oxide (S04 /Sn02) is an effective catalyst for furfural formation [192] because of the combination of Lewis acid and Bronsted acid properties, as well as HMF synthesis. 

The first smdy on PHA biosynthesis from the pentoses xylose and arabinose stemming from the hemicellulose fraction of poplar wood was done by Bertrand et al. (1990) with Pseudomonas pseudoflava ATCC 33668 (today known as... 

PHB. In the first stage, the pentose xylose was converted by a strain of Lactococcus lactis to a mixture of lactic and acetic acids. After removal of the cells by (presumably aseptic) centrifugation, R. eutropha was used to inoculate the supernatant in the same 1-L fermentor. No nutrient deficiency was present to favor polymer synthesis, but the cells accumulated PHB to up to 55% of their CDM during growth on lactate. In 24 h, 4.7 g homopolymer L were produced. With such a strategy for PHA production, the extent to which the advantages of the use of an inexpensive substrate like xylose are offset by the additional procedures needed to separate the two micro-organisms must be carefully calculated. 

Kraus and Schwinden utilized protecting groups, especially methoxymethyl (MOM), which allowed the pentose xylose to undergo photoinduced 5-hydrogen abstraction, which produces a cyclic acetal. Acid catalysis converts the acetal carbon to an aldehyde, such that the overall process produces two epimeric hexoses, gulose and idose. The same paper provides a short review of other sugar photochemistry. 

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