BACKGROUND
Lactulose, a valuable lactose‐originated ‘bifidus factor’ product, is exclusively produced by chemical‐based isomerization commercially. A complexing agent of sodium aluminate exhibiting high conversion efficiency and strong recyclable stability is more practical for industrial applications. In this study, efficient purification of high‐purity lactulose through recycling of sodium aluminate and further desalination by nanofiltration (NF) was implemented on a pilot scale.
RESULTS
Over 99.5% of the catalyst was prior recycled in the form of Al(OH)3 precipitate by pH‐induced precipitation and centrifugation; residual aluminum was further absorbed by ion exchange resin to an acceptable level (≤10 mg kg−1). Subsequently, impurities (monosaccharides and NaCl) were ideally separated from lactulose syrup by NF based on their significant retention differences (lactulose 94.8–97.2% > lactose 86.2–93.5% > monosaccharides 36.3–48.7% > NaCl 9.5–31.1%). High‐purity (>95%) lactulose was obtained with >90% yield in both constant and variable volume diafiltration (CVD and VVD) modes when the volume dilution ratio (Vc/Vf) was 4.0 and 2.5 respectively. Both experimental and predicted results showed that the VVD mode was more water‐saving in practice.
CONCLUSION
This is the first trial purification of lactulose syrup from chemical isomerization of lactose catalyzed by sodium aluminate, and the applied methodology is a promising industrial‐scale purification strategy. © 2018 Society of Chemical Industry