Purification of heterooligosaccharides by microbial treatment and nanofiltration

Summary Various methods can be applied for the purification of oligosaccharides such as galactooligosaccharides (GOS), fructooligosaccharides (FOS) or heterooligosaccharides (HOS). In the present work, two methods (microbial treatment and nanofiltration (NF)) for purification of an enzymatically synthesised HOS mixture were investigated and compared. With the microbial fermentation, the monosaccharides including glucose, galactose and N ‐acetylglucosamine (GlcNAc) could be completely removed whereas lactose was only partially consumed. However, ethanol and acetate were produced as the result of microbial fermentation, which may be considered as an additional problem. The purification yield and the purity of the resulting HOS mixture were 79.4 and 59.3%, respectively. Applying NF with a molecular weight cut‐off (MWCO) of 400 Dalton, the yield and the purity of the HOS mixture were 78.0 and 54.9%, respectively. The resulting product mixture (retentate) obtained after nanofiltration is significantly more concentrated than that of fermentation (257 vs. 106 g L −1 of HOS), however, GlcNAc could not be removed.