Carbohydrate fermentation pentoses

The oldest fermentation process known uses modem technology today and produces e. from all kinds of carbohydrates (hexoses, pentoses, hydrolyzed starch, sucrose and cellulose and waste liquor from - paper pulping) in aqueous solution with the aid of living yeast (Species of Saccharo-myces, Candida and Kluyveromyces) ... 

Sixty-five percent of the carbohydrates present in QF are in the form of pentoses, which S. cerevisiae does not ferment to ethanol. We have developed a recombinant E. coli strain that is capable of fermenting arabinose,... 

Wood is about 65—75% carbohydrate and has been considered as a potential source of ethanol for fuel. The carbohydrate material can be hydrolyzed to monomer sugars, which in turn can be fermented to produce ethanol. However, wood carbohydrates are expensive to hydrolyze. Hydrolysis with acids and enzymes is impeded by the crystalline structure of cellulose. Lignin interferes with processing, and hydrolytic by-products such as furfural, acetic acid, and derivatives of lignin and extractives can inhibit fermentation. Research is still being conducted on wood hydrolysis to develop a process that is economically sound. Furfural is a useful chemical feedstock and results from the dehydration of pentose sugars. It can be obtained in 9 to 10% yield from the dilute acid hydrolysis of hardwoods (75). 

There are many publications and comprehensive handbooks on the thin-layer chromatography (TLC) of carbohydrates (e.g., Refs. 1 and 2). The reason is their great importance in life science and the great diversity of cases monosaccharide, disaccharide, trisaccharide, oligosaccharide, polysaccharide, aldose, ke-tose, triose, tetrose, pentose, hexose, as well as reducing and nonreducing sugars. In addition, when extracted from natural products or produced by fermentation, carbohydrates are accompanied by many impurities. That is why separation methods are used predominantly for their analysis. 

A potentiometric method for the determination of D-glucose, D-mannose, and D-fructose in a mixture of hexoses and pentoses employs fermentation by Streptococcus mutans. The response is based on the selective fermentation of these three carbohydrates by the organism, followed by measurement of hydronium ion. The response time is 4 min and other hexoses and pentoses do not interfere. ... 

Pentoses aldoses containing five carbon atoms. P. are an important group of monosaccharides (see Carbohydrates). Naturally occurring P. include d- and l-arabinose, L-lyxose, D-xylose, D-ribose and 2-deoxy-D-ribose, and the ketopentoses (pentuloses) o-xylu-lose and D-ribulose. P. occur chiefly in the furanose form. They are not fermented by the usual yeasts. By distillation with dilute acids, P. are converted into furfural, a reaction which serves for the detection of P. and their differentation from hexoses. 

In this chapter a number of variations employed for the metabolism of carbohydrates has been described. These illustrate the many mechanisms devised to support the metabolism of organisms at the expense of fermentation or oxidation of carbohydrate. Many more individual reactions are known. For example, several additional reactions for metabolizing various pentoses have been reported. The specificity of various enzyme systems is shown by oxidation of free arabinose by Pseudomonas, which follows the general mechanism described for glucose phosphate in this organism, but the dehydrogenase and lactonizing... 

The metabolism of carbohydrate utilization depends both on the kind of the sugar (e.g. hexoses, pentoses) and from the type of fermentation by the LAB. General, the fermentation types differ in the utilization of hexoses and pentoses. 

Continuous fermentations were described by Russian workers. A plant in Dokshukin was operated in three batteries of seven to eight fermentors of 60,000 to 70,000 gallons. The continuous cycle was 40 to 90 hours, and the flow rate through the battery was 5000 to 10,000 gal/h. The feed contained 4 to 6 percent carbohydrates. A combination of raw material was used molasses, flour, and hydrolysate containing pentoses. The continuous process gave a 20 percent productivity increase, and saved 142 lb of starch for every ton of solvents produced. 

Bioethanol is produced from the hydrolysate of lignocellulosic substrate after pretreatment and enzymatic hydrolysis. With high conversion of carbohydrates, hexose and pentose can be fermented by commercial or engineered Saccharomyces cerevisiae or other microorganisms. Depending on the feedstock and pretreatment processes, various types of growth-inhibiting compounds have been discovered to hinder the performance of fermentation. For example, HMF and furfural formed from dehydration of... 

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