Promotion or suppression of glucose isomerization in subcritical aqueous straight- and branched-chain alcohols

Abstract

The influence of water-miscible alcohols (methanol, 1-propanol, 2-propanol, and t-butyl alcohol) on the isomerization of glucose to fructose and mannose was investigated under subcritical aqueous conditions (180–200 °C). Primary and secondary alcohols promoted the conversion and isomerization of glucose to afford fructose and mannose with high and low selectivity, respectively. On the other hand, the decomposition (side-reaction) of glucose was suppressed in the presence of the primary and secondary alcohols compared with that in subcritical water. The yield of fructose increased with increasing concentration of the primary and secondary alcohols, and the species of the primary and secondary alcohols tested had little effect on the isomerization behavior of glucose. In contrast, the isomerization of glucose was suppressed in subcritical aqueous t-butyl alcohol. Both the conversion of glucose and the yield of fructose decreased with increasing concentration of t-butyl alcohol. In addition, mannose was not detected in reactions using subcritical aqueous t-butyl alcohol.

Promoted isomerization of aldoses to ketoses in subcritical aqueous acetonitrile

“…Although the yield of fructose was increased by ∼ 7 % upon changing the solvent from subcritical water to 0.2 g/g (20 wt%) aqueous acetonitrile, it was increased by only ∼4 % in going from 0.2 to 0.6 g/g (20 to 60 wt%) aqueous acetonitrile. This was quite different from the results in subcritical aqueous primary and secondary alcohols, in which yield of fructose rapidly increased as a concave function of the alcohol concentrations and exceeded 30 % at a residence time of 500 s at 180 °C . The dependence of the selectivity for fructose on acetonitrile concentration was also different from that of the yield.…”

Production of keto-disaccharides from aldo-disaccharides in subcritical aqueous ethanol

“…We reported that subcritical aqueous ethanol could be used as an excellent solvent for aldohexose to ketohexose isomerizations. [13][14][15] Our kinetic analysis showed that, compared to the decomposition steps, the isomerization steps accelerated when changing reaction solvent from subcritical water to subcritical aqueous ethanol. 15) Besides, the chemical equilibrium constant was high (ca.…”

“…Cellobiose and melibiose have been shown to undergo isomerization to their ketoses in subcritical water or in aqueous alkaline solutions, 2,22) and we have reported the promotion of aldose to ketose isomerization in subcritical aqueous ethanol. [13][14][15] Therefore, the formation of cellobiulose and melibiulose could be assured.…”

Engineering aspects of rate-related processes in food manufacturing

“…111) Under subcritical aqueous conditions, primary and secondary alcohols promoted the conversion and isomerization of glucose to afford fructose and mannose with high and low selectivity, respectively. 112) Extraction with subcritical water Defatted rice bran has been treated in subcritical water at various temperatures, after which each extract was evaluated for yield, radical scavenging activity, molecular mass distribution, antioxidative activity, and carbohydrate, protein, total phenolic, and furfural content. 113−118) Fig.…”