Effect of the lactose hydrolysis on galacto-oligosaccharides mixtures subjected to nanofiltration: A detailed fractionation analysis

Galacto-oligosaccharides (GOS) are short oligosaccharides chains containing several galactoses and one terminal glucose. Raw GOS are mixtures containing oligosaccharides, unreacted lactose and monosaccharides; hence nanofiltration is an alternative for product purification. However, poor membrane selectivity towards separation of lactose from GOS is the main drawback. So, in order to improve the purification of enzymatically-produced GOS by nanofiltration, the incorporation of a previous lactose hydrolysis step, to convert the remaining lactose into monosaccharides, is proposed. The purification of raw and hydrolyzed raw GOS was evaluated using two nanofiltration polymeric membranes (Synder NFG and TriSep XN45) at different transmembrane pressures (8-30 bar) in a stirred dead-end cell. Results indicate that the incorporation of the lactose hydrolysis step allows increasing GOS retention and monosaccharides and lactose removal, improving GOS purification. Best operational conditions for hydrolyzed raw GOS nanofiltration were obtained with the TriSep XN45 membrane at 20 bar, 45 degrees C and 1500 rpm.