Lactulose synthesis by electro-isomerization of lactose: Effect of lactose concentration and electric current density

Abstract

In the present work, electro-isomerization of lactose into lactulose has been studied. Effect of lactose concentration (5 and 10%) and applied DC-electric field (100 and 200 mA) on the electro-isomerization of lactose into lactulose and on process efficiency was investigated. Total cathode area of 21.5 cm2 was used; giving electric current density of 4.65 mA/cm2 and 9.30 mA/cm2, respectively. Milk whey permeate (4.7 ± 0.15% lactose) obtained by ultrafiltration was also used as feed solution in the electro-activation reactor. Effect of the processing time on lactose electro-isomerization rate (lactulose formation yield), by-product (glucose, galactose, epilactose and fructose) formation and global electric resistance of the electro-activation reactor has been investigated. The process was run during 60 min and samples were taken every 10 min. The obtained results showed the high effectiveness of the developed electro-activation technology to convert lactose into lactulose. After 60 min electro-activation at ambient temperature (23 ± 1 °C), 25% electro-isomerisation yield was obtained. By excluding lactose, the end product purity was 96.28 ± 0.18%, which is similar to the pharmakopoeia requirements for lactulose powder. Moreover, no epilactose was formed. Not systematically, galactose was detected in some samples (< 1.5%) and only some traces of fructose were detected (< 0.31%). The global electric resistance of the electro-activation reactor decreased as the electro-activation time was increased indicating the high energetic effectiveness of this new electro-isomerization technology. From industrial application, electro-activation can be successfully used as reagentless technology to self-generate high alkalinity of the reaction medium for lactose isomerization into lactulose. By this way, important energetic savings can be made.