Continuous Isomerization of Galactose to Rare Isomers in Arginine Solution Using Microwave Heating

ABSTRACT Tagatose is a low‐calorie alternative sweetener with several health benefits. This study is the first demonstration of continuous‐flow microwave‐assisted isomerization of galactose using arginine as an alkaline catalyst, which enabled precise residence time control under pressurized conditions. With a microwave power of 800 W and a residence time of 3.18 min (flow rate of 0.5 mL/min), a tagatose yield of 10.9% was obtained using 0.2 M galactose and 10 mol% arginine, together with a small amount of talose and sorbose. Increasing arginine concentration from 2.5 to 15 mol% significantly increased the yield to the highest value of 14.9%, but the yield decreased at 20 mol%. Initial galactose concentration from 0.1 to 0.6 M with 15 mol% arginine did not enhance tagatose yield, but productivity increased to the highest value of 254.4 g/L h. Acid formation and browning increased with the galactose concentration. Lower galactose concentration (0.2 M) provided lower productivity (101.4 g/L h), but also much lower browning, which is an advantage for further downstream purification. Overall, this study shows the potential of this novel continuous process using microwave heating, which is more energy‐efficient than the conventional batch method and provides a novel and sustainable rare sugar production approach.