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

Abstract

The demand for production of prebiotics at a commercial scale is rising due to the consumers’ growing health awareness. Whey, a coproduct of the dairy industries, is a suitable feed medium to produce a prebiotic lactulose through the isomerization of lactose under alkaline conditions. The aim of the present study was to compare the isomerization of lactose into lactulose in situ of whey by using electroactivation technology with the chemical isomerization method using KOH as catalysis under equivalent solution alkalinity. Electroisomerization of lactose into lactulose was performed by using whey solutions of 7, 14, and 21% (w/v) dry matter under current intensities of 300, 600, and 900 mA, respectively, during 60 min with a sampling interval of 5 min. The conventional chemical method was carried out using KOH powder as catalyst at the alkalinity that corresponded to that measured in the electroactivated whey at each 5 min interval. The results showed that lactulose production was dependent on the whey concentration, current intensity, and EA time. The highest lactulose yield of 32% was achieved under a 900 mA current intensity at 60 min for a 7% whey solution. Thereafter, the EA conditions were compared to those of a conventional chemical isomerization process by maintaining similar alkalinity in the feed solutions. However, no lactulose was produced by the chemical process for the equivalent solution alkalinity as in the EA technique. These results were correlated with the solution pH, which reached the required values in a 7% whey solution with values of up to pH 11.50, whereas the maximum pH values that were obtained at higher whey concentrations were around 10–10.50, which was not enough to initiate the lactose isomerization reaction. The outcomes of this study suggest that EA is an efficient technology to produce lactulose using whey lactose.

Contribution to the Process Development for Lactulose Production through Complete Valorization of Whey Permeate by Using Electro-Activation Technology Versus a Chemical Isomerization Process

“…This might be due to the retarding pH evolution and low alkalinity in a feed solution with higher solid concentration because of a higher resistance and buffering capacity of the solution. 21 Indeed, the solution alkalinity and pH significantly affected (p < 0.001) the formation of lactulose in the EA. For 18% WP solution, the lactulose formation was started at 50 (13.72 ± 0.40%) and 35 min (16.50 ± 0.51%), afterward gradually increased to 18.37 ± 0.76 and 23.42 ± 0.84% at the end for 300 and 600 mA, respectively (Figure 7c).…”

“…, 12% WP) was less than that obtained for 6% WP solution under a similar current intensity and reaction time. This might be due to the retarding pH evolution and low alkalinity in a feed solution with higher solid concentration because of a higher resistance and buffering capacity of the solution . Indeed, the solution alkalinity and pH significantly affected ( p < 0.001) the formation of lactulose in the EA.…”

“…However, no lactulose was produced for 300 mA in the 12 and 18% WP solutions. This could be attributed to the lack of sufficient solution alkalinity . Adequate alkalinity is usually essential for lactulose formation because the rearrangement of the molecules for lactose isomerization into lactulose demands proton acceptors, that is, OH – , that can be obtained by reaching a higher alkaline condition in the feed solution …”

“…In fact, greater activation energy was needed for an isomerization reaction to occur in the chemical method. Thus, a higher dosage of catalysts was obliged for producing and adequate degree of alkalinity, while the more concentrated solutions of WP were used as feed solutions . Indeed, the catalyst concentration is one of the critical factors to be considered during the conventional lactose isomerization process.…”

“…This could be attributed to the lack of sufficient solution alkalinity. 21 Adequate alkalinity is usually essential for lactulose formation because the rearrangement of the molecules for lactose isomerization into lactulose demands proton acceptors, that is, OH − , that can be obtained by reaching a higher alkaline condition in the feed solution. 12 The results achieved in the present study were corroborated with those obtained from a study by Kareb, et al, 16 where they produced a maximum lactulose yield of 35% at 40 min of EA under a current intensity of 400 mA using 100 mL of 7% (w/v) whey solution.…”