Lactose electroisomerization into lactulose: Effect of the electrode material, active membrane surface area-to-electrode surface area ratio, and interelectrode-membrane distance

Abstract

The aim of the present work was to study and develop an innovative, clean, and environmentally friendly process for lactulose synthesis by electroactivation of lactose. In this work, the electrode material (type 304 stainless steel, titanium, and copper), dimensionless interelectrode-membrane distance at the cathodic compartment (0.36, 0.68, and 1), and the membrane:electrode surface area ratio (0.23, 0.06, and 0.015) were considered to be the factors that could affect the kinetic conversion of lactose into lactulose. The reactions were conducted under an initial lactose concentration of 0.15mol/L at 10°C, Froude number (mixing speed) of 2.05×10(-2), and electric current intensity of 300mA for 30min. The highest lactulose formation yield of 32.50% (0.05mol/L) was obtained by using a copper electrode, interelectrode-membrane distance of 0.36, and membrane:electrode surface area ratio of 0.23. The 2-parameter Langmuir, Freundlich, and Temkin isotherm models were used for the prediction of the lactose isomerization kinetics as well as the 3-parameter Langmuir-Freundlich isotherm model. It was shown that the lactose isomerization kinetics into lactulose followed the Temkin and Langmuir-Freundlich models with coefficients of determination of 0.99 and 0.90 and a relative error of 1.42 to 1.56% and 4.27 to 4.37%, respectively.

Sustainable Valorization of Whey by Electroactivation Technology for In Situ Isomerization of Lactose into Lactulose: Comparison between Electroactivation and Chemical Processes at Equivalent Solution Alkalinity

“…Obviously, with the higher distance, the moving electrical charges/ions encounter more collisions and, therefore, the resistance might be increased. 16 Consequently, the current intensities used for higher concentrations (14 and 21%) and volume (350 mL) of whey were not adequate to create enough alkalinity for isomerization in the present study. In addition, the concentration of the electrolyte (0.5 M Na 2 SO 4 ) in the central compartment used by Kareb et al 9 was higher compared to that of the present study (0.1 M K 2 SO 4 ), which could be another reason for anomalies in lactulose production.…”

“…This is because an increase in the volume of feed solution under a constant current intensity and for the same electrode surface results in lower pH evolution due to the similar amount of OH – ions produced at the solution/cathode interface. Nevertheless, the lactulose yield is directly related to the amount of OH – ions formed in the medium because they act as proton acceptors and ensure the optimum alkalinity for lactose isomerization into lactulose. , The lower the solution volume, the higher was the alkalinity in the cathodic compartment.…”

“…Besides the types and lactose concentration of the feed solution, the activity of isomerization reaction in the EA can be affected by current intensity, time, temperature, volume of the feed solution, salt type and concentration used as electrolyte, electrode material, interelectrode−membrane distance, configuration, and geometry of the EA reactor. 10,14,16 Recently, Kareb et al 9 described the effect of feed solution concentration and volume, temperature, and current intensity on whey lactose isomerization into lactulose. They obtained a maximum yield of ∼35% using 100 mL of a 7% whey solution during 40 min of EA under a 400 mA current intensity at a 10 °C temperature.…”

“…Nevertheless, the lactulose yield is directly related to the amount of OH − ions formed in the medium because they act as proton acceptors and ensure the optimum alkalinity for lactose isomerization into lactulose. 9,16 The lower the solution volume, the higher was the alkalinity in the cathodic compartment.…”

“…Aider and Gimenez-Vidal observed that the formation of lactulose was different for whey permeate (8.84 ± 0.19%) compared to that of a pure lactose solution (25.47 ± 1.18%) even though similar experimental conditions (200 mA, 60 min, 23.1 ± 1 °C) and similar initial lactose concentration (∼5%, w/v) of feed solutions were used. Besides the types and lactose concentration of the feed solution, the activity of isomerization reaction in the EA can be affected by current intensity, time, temperature, volume of the feed solution, salt type and concentration used as electrolyte, electrode material, interelectrode–membrane distance, configuration, and geometry of the EA reactor. ,, …”