Isomerisation of lactose to lactulose in an aqueous solution containing arginine

In the present work, the isomerisation of lactose (5%, w/v) to lactulose in an aqueous solution containing arginine (0.1 mol/mol lactose) with an initial pH of 9.80 was investigated. The consumption of lactose, and formation of lactulose and other monosaccharides (glucose and galactose) were monitored to evaluate the effects of reaction temperature (100, 110, and 120°C) and time (0 - 20 min) on the isomerisation and hydrolysis of lactose. The results showed that lactulose was formed during heating, and that the lactulose yield reached its maximum value more rapidly at higher temperature. The highest yield, approximately 26% (w/w), was obtained after the reaction proceeded for 12 min at 120°C. The progress of the Maillard reaction was monitored by measuring the absorbances at 280, 325, and 420 nm, and these parameters increased with both reaction temperature and time, whereas the pH gradually decreased. The present work demonstrated that lactose can be conveniently isomerised into its rare isomer using an environmentally friendly process.