Purification of galacto-oligosaccharides (GOS) bythree-stage serial nanofiltration units under criticaltransmembrane pressure conditions

A purification process of galacto-oligosaccharides (GOS), using three-stage serial nanofil-tration (NF) units, operating under critical transmembrane pressure (TMPc) was designed.Three commercial flat-sheet membranes were tested at 53.5oC and 65oC, using GOS solu-tions at 20 and 40oBrix. Since one of the main drawbacks of NF for the purification of rawGOS is the removal of lactose, an enzymatic pre-hydrolysis step was also tested for produc-ing a prehydrolyzed GOS and compared with non-hydrolyzed raw GOS. An empirical modelshowed that due to the increase in the solute concentration during batch NF, TMPc mustbe decreased with time to prevent fouling effects. Using NF serial system, the maximumGOS concentration achieved for raw GOS was 241 g/L and 156.8 g/L for pre-hydrolyzed GOS.Despite filtration times of the later were shorter, after three sequential batches, similar puri-ties (~55%) were obtained with both GOS solutions. Thus, the use of pre-hydrolyzed raw GOSas substrate for NF purification had two opposite effects: an improved flux due to lower lac-tose deposition on membrane, but also a lower GOS retention by the membrane, revealinga marginal gain in purification. The purities achieved were similar to those of commercialGOS, currently obtained by using conventional processes.