Lactulose production from efficient isomerization of lactose catalyzed by recyclable sodium aluminate

•High-purity (≈95%) lactulose was obtained catalyzed by recyclable NaAlO2.•Al(OH)3 precipitation through pH adjustment simplified the recovery of catalyst.•Al(OH)3 precipitation provide an efficient and economic decolorization method.•NaAlO2 was repeatedly used in 5 cycles and presented high stability in catalysis.•Lactulose yield was up to 85% (w/w) with the highest concentration ever reported.

An efficient strategy for the synthesis of high-purity lactulose through chemical isomerization of lactose was developed using recyclable catalyst sodium aluminate. Maximum yield of 85.45 ± 1.79% was obtained from 35% (w/v) of lactose using a 1:1 M ratio of NaAlO2-lactose after reaction at 60 °C and pH 12 for 50 min, with a purity ratio (Pu) of approximately 95%. Al(OH)3 precipitation from lactulose syrup through pH adjustment showing a superior decolorizing efficiency was implemented, which simplified the removal of catalyst and provided a convenient approach to achieve catalyst recovery. After dilution by 5 folds, nearly 98.5% of catalyst was removed through centrifugation and 85.50 ± 1.81% of lactulose was recovered. Modified recycle use of catalyst without lactulose loss was carried out, after five consecutive recycles, total yield of lactulose (TYLactulose) and new yield of lactulose (NYLactulose) were of 80.44 ± 1.05% and 73.87 ± 0.50%, respectively, reflecting a high stability by using this recyclable methodology.