Efficient Conversion of D-Glucose to D-Fructose in the Presence of Organogermanium Compounds

Abstract

INTRODUCTIONThe isomerized sugar known as high fructose syrup is a mixture sugar that is manufactured by conversion of half of the content of D-glucose into D-fructose using an enzymatic reaction catalyzed by glucose isomerase. Recently, D-fructose produced by this isomerization reaction has been used not only in sweeteners but also as a promising chemical intermediate from biomass. 1) Therefore, efficient conversion reactions for isomerized sugars are being investigated as a method for increasing the synthesis of such products.During the production of sweeteners, isomerization is generally stopped after conversion of approximately 42 % of the original substrate, to prevent changes in color and breakdown of the components. The reaction solution is then passed through an ion exchange resin, and the fructose content is concentrated to approximately 90 %. This concentrated mixture is then combined with D-glucose, normally yielding a product with 55 % isomerized sugar content. Therefore, improvement in the conversion ratio during the isomerization reaction is critical for the production of isomerized sugar.The reaction equivalent constant of glucose isomerase is approximately 1.0 (isomerization ratio of 50 %) at 60 C, but it increases to 1.348 (isomerization ratio of 57.4 %) at 100 C.2) The polarity of the reaction solvent also affects the isomerization ratio; for example, reaction in 85 % ethanol (v/v) yields an isomerization ratio of 55.9 %.3) However, isomerization at 100 C is not feasible because of inactivation of the enzyme, and reaction in ethanol-containing solutions proceeds only with 6 12 % D-glucose and at a temperature of 30 C. Therefore, neither of these modifications to the standard reaction conditions is effective. Some researchers have attempted to shift the equivalence to D-fructose by using reagents with different affinities for the isomers. For example, sodium borate and germanate (i.e., germanium dioxide) can be used as affinity reagents after solubilization under alkaline conditions. Indeed, addition of borate has been reported to increase the isomerization ratio to 88 %, 4) and addition of germanate has been reported to increase the isomerization ratio to 90 %. 5) However both of these compounds are associated with toxicity; thus, their use is limited.

The Organogermanium Compound THGP Suppresses Melanin Synthesis via Complex Formation with L-DOPA on Mushroom Tyrosinase and in B16 4A5 Melanoma Cells

“…Specifically, THGP suppresses the influx of Ca 2+ by interacting with adrenaline and ATP, which have cis -diol structures. Other studies have demonstrated that THGP interacts with adenosine, D-glucose, and D-fructose [14,32]. These results suggest that the physiological activities of THGP are mediated by binding to cis -diol structures.…”

Efficient Alkaline Isomerization of Lactose to Lactulose in the Presence of an Organogermanium Compound

“…To elucidate the mechanism through which the THGP structure promotes alkaline isomerization, the K s values for lactose and lactulose with DM-THGP were measured, as described previously. 4) First, the complex formation ratios for lactose and lactulose in the presence of DM-THGP were measured using 1 H-NMR spectroscopy under the following conditions: constant sugar concentration of 0.10 M, DM-THGP concentrations of 0.0250, 0.0375, 0.0500, 0.0750, 0.100, and 0.125 M, and neutral pH (near 7.0). Subsequently, the 1 H-NMR integral values of the sugar (0.10 M constant concentration) were used to correct the concentration of DM-THGP.…”

“… 2) 3) We previously described the effective promotion of the conversion of D-glucose into D-fructose using organogermanium compounds with a 3-(trihydroxygermyl)propanoic acid (THGP) structure, in both enzymatic and alkaline isomerization reactions. 4) …”

“…In alkaline isomerization, however, the conversion from lactose to lactulose is very low (21.4 %). 10) Therefore, in the present study, we applied the method 4) of alkaline isomerization in the presence of THGP to increase the conversion of lactose to lactulose. THGP can be obtained by hydrolyzing the organogermanium compound poly- trans -[(2-carboxyethyl)germasesquioxane] (Ge-132) in aqueous solution.…”

Efficient Continuous Production of Lactulose Syrup by Alkaline Isomerization Using an Organogermanium Compound

“…We previously reported 6) 7) that the organogermanium compound poly- trans -[(2-carboxyethyl)germasesquioxane] (commonly known as Ge-132) significantly promoted the isomerization of an aldose to a ketose, such as glucose to fructose, or lactose to lactulose, with an isomerization ratio of approximately 80 %. Ge-132 is a water-soluble polymer having the formula [(GeCH 2 CH 2 COOH) 2 O 3 ] n and is hydrolyzed to 3-(trihydroxygermyl)propanoic acid (THGP) monomers in aqueous solution.…”