Isomerization and epimerization of glucose and galactose in arginine solution and phosphate buffer under subcritical fluid conditions

Abstract

Reaction of glucose or galactose was performed in arginine solution or phosphate buffer (pH 7.0) using a batch reactor at 110 °C. The yields of products, pH, and absorbances at 280 nm and 420 nm were measured during the reaction. Fructose, mannose, and allulose were formed from glucose; tagatose, talose, and sorbose were done from galactose. The reaction proceeded more rapidly in arginine solution than in phosphate buffer. In arginine solution, yields of fructose and tagatose were 20% and 16%, respectively, after 30-min reaction; in phosphate buffer, they were 14% and 10%, respectively. However, in both reaction media, the pH drop and increase in absorbances continued even after the yield became almost constant. The absorbance increased particularly in the latter half of the reaction due to formation of browning products. Therefore, to avoid browning, the reaction should be stopped as soon as possible after the yield approaches its maximum value.

Isomerization of maltose to maltulose by microwave heating, using arginine as a catalyst

“…In addition, HPLC analysis showed unidentified peaks, as well as glucose, but the fraction of unidentified peaks was small (<1%), even with long heating times. It is possible that glucose might be further converted to other isomers, including mannose and fructose, in arginine solution (Kobayashi et al, 2023). Figure 3 shows the relationship between the yield of the product (maltulose) and A 420 , a measure of coloration, of the reaction mixture when microwave-heated at a power of 200, 500, and 700 W. Independent of power, the relationship between the two is represented…”

“…Recently, as part of our search for simple and green methods for producing rare sugars, our group has studied the feasibility of using arginine as a catalyst for producing rare ketose and aldose isomers from common monosaccharides at high temperatures (Khuwijitjaru & Adachi, 2023a, 2023bKhuwijitjaru et al, 2023;Kobayashi et al, 2023;Milasing et al, 2023). Arginine is a basic amino acid that is widely used as a food additive.…”