Sugar xylose

SPS could be degraded by the cruder, aaikalus preparation Pectinex Ultra-SP, giving a product consisting mostly of the monomeric sugars xylose, galactose, fucose, arabinose and... 

This model has been reinforced by kinetic studies. The five-carbon sugar xylose, stereochemically similar to glucose but one carbon shorter, binds to hexokinase but in a position where it cannot be phosphorylated. Nevertheless, addition of xylose to the reaction mixture increases the rate of ATP hydrolysis. Evidently, the binding of xylose is sufficient to induce a change in... 

PENTOSAN. A complex carbohydrate (hemicellulose) present with the cellulose in many woody plant tissues, particularly cereal straws and brans, characterized by hydrolysis to give five-carbon-atom sugars (pentoses). Thus the pentosan xylan yields the sugar xylose (HOH,C CHOH CHOH CHOH CHO) that is dehydrated with sulfuric acid to yield furfural (C5H4O2). 

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 second kind of commercial cocoa substitute consists of roasted food products. Clearly, whether intentionally or not, they employ Maillard technology in the same way in which it is employed in producing cocoa and coffee. The ingredients disclosures suggest that no effort has been made to modify or to enhance the flavors by the addition of amino acids or of special sugars (xylose, for example). At least three of these products are worth mentioning. 

Investigations on the ethanolic extract from the bark of T. yunnanensis led to the isolation of two new neolignans. One of them was named taxuyunin A, and has a neolignan structure containing a sugar xylose, while the other neolignan, taxuyunin B, carries a rare C-3 side chain [87]. 

Rooney et al (45) reported that the rate of carbonyl formation varied with the molecular structure of sugar. Xylose was most reactive as it produced the greatest quantity of carbonyls, followed by glucose, then maltose. In the presence of these sugars isoleucine was more reactive than phenylalanine. In a study on the Strecker degradation of valine-carbonyl, diacetyl showed the greatest reactivity followed by sorbose> arabinose>xylose>fructose>glucose>sucrose>rhamnose, Self(46). 

In the pentoses and hexoses there are again sugars that are reduced to meso alcohols and some that are reduced to C2 symmetric alcohols. The C5 sugar xylose has the same stereochemistry as glucose from C2 to C4 but lacks the CH2OH group at C6. 

Xylitol is obtained by hydrogenation of the pentose sugar xylose. It is as sweet as sucrose, and new relatively inexpensive methods have been devised for its production. Xylulose occurs naturally on the pathway by which breakdown products of gluconic acid (page 232) are fed into the pentose phosphate shunt. When administered, xylitol is readily metabolized but differs from glucose in the initial steps prior to the point at which it enters the glycolytic pathway. 

Xylitol is the sugar alcohol formed by reduction of the five-carbon sugar xylose, an isomer of ribose. It is of interest because, so far from promoting dental caries, as does sucrose (section 7.3.3.1), xylitol has an anti-cariogenic action. The reasons for this are not well understood, but sucking sweets made from xylitol results in a significant reduction in the incidence of caries — such sweets are sometimes called Tooth-friendly because of this. 

Xylitol is a sugar alcohol. The aldehyde group (C = O) of the pentose sugar—5-carbon sugar—xylose is replaced by a hydroxyl group (OH). It can be made from birchwood chips, berries, leaves and mushrooms. Xylitol is commercially produced in Finland from birchwood chips hydrolyzed by acid to xylose. In the body, xylitol is formed as an intermediate during the formation of xylulose. Ingested xylitol is also converted to xylulose. Xylulose then enters the pentose-phosphate cycle of carbohydrate metabolism. 

Figure 18.2 Metabolic pathways for the utilization of the pentose sugar xylose. XR xylose reductase and XDH xylitol dehydrogenase.

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