Hydrolysis to monosaccharides

Dietary Polysaccharides and Disaccharides Undergo Hydrolysis to Monosaccharides... 

Certain aerobic organisms, notably of the Pseudomonas genus but also algae and yeasts, are capable of oxidizing lactose to lactobionic acid without hydrolysis to monosaccharides (Stodola and Lockwood 1947). Lactose dehydrogenase oxidizes lactose to lactobionic-5-lactone in the presence of a hydrogen acceptor the lactose is then hydrolyzed to lactobionic acid by lactonase (Nishizaka and Hayaishi 1962). 

Assay methods are available for most of the carbohydrates ranging from glycogen, starch, and cellulose to the monosaccharides and their monophosphates. Concentration determination of complex carbohydrates usually depends on their enzymatic hydrolysis to monosaccharides and determination of monosaccharide concentration via an enzymatic reaction. For example, starch is hydrolyzed to glucose by glucoamylase, and the... 

Surface Activation. Acid Activation. Acid treatment of cellulose and hemicelluloses generally leads to hydrolysis to monosaccharides, which can subsequently dehydrate and condense to form furan-type compounds such as furfural and its 5-hydroxymethyl adduct. Further reactions lead to polymeric materials of dark color as well as to monomers such as levulinic acid, formic acid, and angelica lactones. Various condensation and solvolysis reactions also accompany the acid treatment of lignin 123). The hydrolysis, dehydration, and condensation reactions have been used to explain formation of covalent bonds between surfaces (85), increase in water resistance (85, 124), and weakening of wood (75) in nonconventional plywood or particle board production. However, very little factual information is available on how far, in terms of the consecutive reactions mentioned, and in what direction, in terms of the parallel reactions mentioned, does the surface of lignocellulosic materials actually change... 

Sugar is destroyed by pH extremes, and inadequate pH control can cause significant sucrose losses in sugar mills. Sucrose is one of the most acid-labile disaccharides known (27), and its hydrolysis to invert is readily catalyzed by heat and low pH prolonged exposure converts the monosaccharides to hydroxymethyl furfural, which has appHcations for synthesis of glycols, ethers, polymers, and pharmaceuticals (16,30). The molecular mechanism that occurs during acid hydrolysis operates, albeit slowly, as high as pH 8.5 (18). 

Methylation analysis Permethylation of intact oligosaccharides Hydrolysis of glycosidic linkages Reduction to monosaccharide alditols Acetylation of free hydroxyl groups previously involved in link-... 

The methylation technique consists of total methylation of the oligosaccharide, followed by hydrolysis to the partially methylated monosaccharide units, and determination of the unmethylated positions in each unit, these being the positions of linkage between units. 

To determine the correction factors, an internal standard is generally added to each of the mixtures and the detector response measured relative to the internal standard. If the ratio of a monosaccharide to the internal standard decreases after hydrolysis of a test mixture of monosaccharides, decomposition has occurred and a recovery factor should be determined. The internal standard must either be resistant to decomposition during hydrolysis or should be added after hydrolysis it is usually better to add the internal standard after hydrolysis, to be on the safe side. The internal standard must not appear in the samples and must be resolved from other components in the sample, as with any internal standard. 

Hydrolysis of complex molecules In the first stage, complex molecules are broken down into their component building blocks. For example, proteins are degraded to amino acids, polysaccha rides to monosaccharides, and triacylglycerols to free fatty acids and glycerol. 

The first of these methods involves the reaction of triphenyl phosphite methiodide with methyl 3-0-methyl-2-0-p-tolylsulfonyl-a-D-glucopyrano-side, hydrogenation of the resulting 4,6-diiodo derivative, and hydrolysis,186 as adapted to monosaccharides by Kochetkov and coworkers.1,0 In another approach,281 ethyl 2,3-anhydro-4,6-dideoxy-D-nbo-hexopyranoside, obtained from desosamine, was treated with sodium methoxide, to give a mixture of 2- and 3-methyl ethers. After fractionation and separation of side products,288 the 3-methyl ether was hydrolyzed, to give crystalline chalcose. McNally and Overend800 have described another synthesis, starting from methyl 4-deoxy-D-xj/Zo-hexoside.107... 

Unlike starch or cellulose, BSG hemicellulose has a complex structure, which is still present, in part, on its autohydrolysis products. Oligosaccharides from BSG hydrolysis consist mainly of branched arabino-xylo-glucurono oligosaccharides that are not highly acetylated when compared to other xylans, such as from Eucalyptus wood (31). The action of several enzymatic activities including endo-l,4-P-xylanase P-xylosidase and accessory activities such as acetyl xylanesterase, a-glucuronidase, and a-arabino-furanosidase is therefore required for the complete hydrolysis of OCL to monosaccharides. 

Dilute-acid hydrolysis is therefore the main choice for the hydrolysis of hemicellulose to monosaccharides once it is a fast and efficient method (19). However, a careful optimization of operational conditions used for hydrolysis is important to ensure high monosaccharide recovery and minimize coformation of microbial inhibitors. 

The high pentose yields obtained in the current study are favorable when compared to those previously reported for dilute-acid hydrolysis in batch processes (28-31). However, the hemicellulosic sugar yield reported in the literature is often expressed as xylose equivalents, which is difficult to compare to monosaccharide recovery. The highest monosaccharide recovery was obtained with low CS values, which is in agreement with previous findings for sulfuric acid-catalyzed steam explosion, in which also better hemicellulosic sugar recoveries were obtained at relatively low severities (28,32) of <2.2 (22). 

Polysaccharides A class of high-molecular-weight carbohydrates that can be broken down to monosaccharides on hydrolysis... 

Today (2000), GC/MS is still the method of choice for the determination of the monosaccharide composition of oligosaccharides and is widely used. The analysis starts with the hydrolysis or alcoholysis of the oligosaccharide to monosaccharides, which after derivatization (mostly by trimethylsilylation) are analysed by GC/MS. [221] Monosaccharide identification is based on comparison of retention time and fragmentation pattern with references. 

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