Combination of two β-galactosidases during the synthesis of galactooligosaccharides may enhance yield and structural diversity

Abstract

In this study, the combination of two β-galactosidases to synthesize prebiotic galactooligosaccharides (GOS) was evaluated in terms of total GOS yield as well as GOS structures (chain length). Two different combinations of either Aspergillus oryzae and Cryptococcus laurentii or Aspergillus oryzae and Kluyveromyces lactis were tested to examine the influence of enzyme origin. Neither consecutive nor simultaneous synthesis with A. oryzae and C. laurentii led to an increased GOS yield. However, with the latter, synthesis of higher GOS (≥3 monomer units) was enhanced from 38.5% to 40% with special emphasis of tetra- and pentasaccharides, which increased from 6.7% to 12.8% and from 0.4% to 3.3%, respectively. Additionally, due to the different preferences of the two β-galactosidases in terms of types of glycosidic linkages, the structural diversity of the final GOS product could be increased. Using K. lactis following the synthesis with A. oryzae increased the yield of total GOS from 24.6% to 33.1%, which was mainly due to the formation of GOS disaccharides. On the other hand, applying A. oryzae as the second enzyme led to a degradation of di- and trisaccharides, and thus total GOS yield was diminished, although the yield of tetrasaccharides could be enhanced. In conclusion, with both studied enzyme combinations it was possible to increase the percentage of higher GOS and reduce the residual lactose content of the final mixture, which is beneficial for subsequent purification processes. Thus, using more than one β-galactosidase during the synthesis of GOS represents an interesting research area, which should be explored in more detail in the future.