Purification of lactulose derived-galactooligosaccharides from enzymatic reaction mixtures

This study compares two different procedures for purification of lactulose-derived galactooligosaccharides (GOS) using fresh Saccharomyces cerevisiae yeast or activated charcoal with water or ethanol/water solutions for selective removal of monosaccharides. Yeast fermentation allowed the complete removal of monosaccharides without any losses of di- and oligosaccharides; however besides ethanol, glycerol and higher alcohols difficult to remove are also produced. The presence of higher alcohols affects the sensory quality of the lactulose-derived GOS and may limit its use in certain food applications. Fractionation of these oligosaccharides using activated charcoal was compared with that of lactose-derived GOS the latter being the most strongly adsorbed. When water was utilised as solvent, all monosaccharides were removed, as well as about 20% of unreacted disaccharides. Removal of tri-, tetra- and pentasaccharides was not observed. Using water/ethanol mixtures, desorption of oligosaccharides increased with ethanol content, allowing the selective recovery of different sugar fractions.