Lactulose formation catalysed by alkaline-substituted sepiolites in milk permeate

Alkaline-substituted (Na+, K+) sepiolites were used as catalysts for the formation of lactulose in milk permeate. Besides lactose and lactulose, other carbohydrates, such as galactose and epilactose, produced in side reactions, were determined. The effect of different washing cycles of sepiolite on the isomerisation of lactose and the exchange of cations with the permeate were also investigated. In general, the activity of the sodium sepiolite was higher than that of potassium form. Twenty per cent of lactulose formation (≈1000 mg/100 ml), with respect to the initial lactose, was obtained after 150 min of reaction, using sodium sepiolite washed during 10 cycles. Under these conditions, 25% of lactose degradation was detected, whereas small amounts of epilactose and galactose were formed. The exchange of Na+ between sepiolite and permeate decreased considerably with the number of washing cycles. The present work shows an appropriate method for obtaining lactulose in milk permeate with acceptable yields and without complicated purification steps.