Comparison of fractionation techniques to obtain prebiotic galactooligosaccharides

Four different fractionation techniques for obtaining galactooligosaccharides (GOS) free from digestible carbohydrates were compared. Diafiltration did not show any selectivity among mono-, di- and oligosaccharides, whereas yeast treatment to remove monosaccharides allowed a high recovery of GOS and disaccharides. Activated charcoal treatment showed a different selectivity in GOS recovery depending on the concentration of ethanolic water solutions used (1–15%). Ethanolic solutions of 8% led to a high recovery of GOS (∼90%), but 20% of disaccharides were also recovered, whilst solutions with 10% ethanol allowed almost complete removal of disaccharides, but only ∼53% of GOS trisaccharides were recovered. Finally, the purest GOS fractions (degree of polymerization up to 8) were obtained using size exclusion chromatography.