Monosaccharides acid hydrolysis, losses

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). 

To correct for the relatively small amount of decomposition of monosaccharides liberated under the conditions presented in Fig. 1, it is possible to subject a mixture of monosaccharides to identical conditions of hydrolysis and to measure the decomposition compared to that of a mixture not subjected to acid hydrolysis, in order to obtain a correction factor for losses by hydrolysis. Alternatively, in order to measure decomposition, hydrolysis may be continued for an extended period of time, and the concentration of monosaccharide may be extrapolated back to time zero. 

Subjecting monosaccharides to conditions of acid hydrolysis is only of importance in measuring the expected hydrolysis losses during hydrolysis of oligo- and poly-saccharides. Hydrolysis losses may be predicted, based on either the absolute or the relative decomposition of monosaccharides. Absolute decompositions are based on decomposition of monosaccharides. Relative decompositions are based on studies wherein several methods of hydrolysis were applied to the same samples for various lengths of time in this Section, these are classified under the type of acid that causes the least decomposition (that is the largest yield of monosaccharides liberated), because this acid is usually the one of principal concern in the particular study. 

A kinetic study of the hydrolysis of woods and purified plant polysaccharides in 75 % sulphuric acid was monitored by electrical conductivity measurements. The coefficients of resistance of all polysaccharide substrates increased with increasing hydrolysis time. From these measurements, the degrees of polymerization of cellulose, xylan, and inulin were estimated to be 1900, 66, and 16 respectively. The polysaccharide components of various woods and pulps can be hydrolysed with trifluoracetic acid which, in contrast to sulphuric acid hydrolysis, does not require a neutralization step since trifluoracetic acid is volatile. The presence of lignin in the wood samples impeded the hydrolysis of the polysaccharides, requiring longer reaction times and correction factors to compensate for loss of monosaccharide by degradation reactions. 

These derivatives of the monosaccharide structural units are then qualitatively and quantitatively analyzed by gas chromatography on capillary columns. In more difficult cases, a preliminary separation of acidic and neutral polysaccharides on an ion exchanger is recommended. Methanolysis or hydrolysis of polysaccharides containing uronic acids and anhydro sugars are critical due to losses of these labile building blocks. 

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