Ion exchange membranes controlled electro-catalytic synthesis of lactulose from lactose under refrigerated conditions

• Lactulose was synthesized by electro-activation of lactose.
• Ion exchange membranes permitted the modulation of the electro-activation conditions.
• The electro-activation reactor allowed high isomerization yield.
• The electro-activation reactor allowed high lactulose purity.
• The electro-membrane reactor was energetically very efficient.

Lactulose is considered as a prebiotic because it promotes the intestinal proliferation of Bifidobacterium which is added to various milk products. Moreover, lactulose is used in pharmaceuticals as a gentle laxative and to treat hyperammonemia. This study was aimed to synthesize lactulose from lactose isomerization by using an electro-activation reactor in which the alkaline conditions were controlled by ion exchange membranes under refrigerated conditions including 0 °C. In contrast to the production of lactulose by both chemical methods, which present many problems of purification and sugar degradation, and enzymatic methods, which is very expensive, the electro-activation is a very clean, safe and an economic green electro-membrane method to produce lactulose. The effects of Froude number (Fr), working temperature (TWorking) and feed lactose concentration (CLactose) on pH, conductivity, current density and lactulose yields are evaluated in this work. Then, it is shown that the highest lactulose yield of 25 ± 1.28% with a purity of 95 ± 1.34% in the final product is obtained at Fr = 2.05 ∙ 10− 2, TWorking = 0–10 °C, CLactose = 10%, τ = 2 min, pH = 10.30, λ = 4.64 mS/cm, i = 4.86 mA/cm2 and U = 30 V. Using the experimental data given at time, τ = 10 min, sulfate sodium concentration in central and anodic compartment, CNa2SO4 = 0.3 M/L, and voltage, U = 38 V, three correlations are proposed to predict the medium alkalinity (pH), the medium conductivity (λ), and the current density (i) which have the highest significance on lactose isomerization into lactulose.Industrial relevanceLactulose is a well-known prebiotic and is mainly produced by chemical or enzymatic methods. The first is expensive and difficult to control. The end product is a mixture of different compounds that need to be purified. The second is more selective but very expensive. The application of electro-activation under near or sub-zero temperatures offers the possibility to produce high purity lactulose following electro-activation of a lactose solution. The cost of this technology can be very interesting for the industry and more lactose will thus be valorized.