Continuous enzymatic synthesis of lactulose in packed-bed reactor with immobilized Aspergillus oryzae β-galactosidase

Lactulose synthesis from fructose and lactose in continuous packed-bed reactor operation with glyoxyl-agarose immobilized Aspergillus oryzae beta-galactosidase is reported for the first time. Alternative strategies to conventional batch synthesis have been scarcely explored for lactulose synthesis. The effect of flow rate, substrates ratio and biocatalyst-inert packing material mass ratio (M-B/M-IM) were studied on reactor performance. Increase in any of these variables produced an increase in lactulose yield (Y-Lu) being higher than obtained in batch synthesis at comparable conditions. Maximum Y-Lu of 0.6 g.g(-1) was obtained at 50 degrees C, pH 4.5, 50% w/w total sugars, 15 mL.min(-1), fructose/lactose molar ratio of 12 and M-B/M-IM of 1/8 g.g(-1); at such conditions yield of trans-galactosylated oligosaccharides (Y-TOS) was 0.16 g.g(-1), selectivity (lactulose/TOS molar ratio) was 5.4 and lactose conversion (X-Lactose) was 28%. Reactor operation with recycle had no significant effect on yield, producing only some decrease in productivity.