OPTIMIZATION OF GALACTOOLIGO-SACCHARIDE PRODUCTION FROM LACTOSE USING β-GLYCOSIDASES FROM HYPERTHERMOPHILES

Abstract

The maximal production of galactooligosaccharides (GOS) from lactose by (β-glycosidases from the hyperthermophilic archaea, Sulfolobus solfataricus (LacS) (derived from lacS gene) and Pyrococcus furiosus (CelB) (derived from celB gene) was optimized. The performance of these enzymes under extreme reaction conditions, temperatures up to 95°C and lactose concentrations up to 90% (w/v), were studied. The highly thermostable enzymes were shown to be very well suited for oligosaccharide synthesis. For both LacS and CelB the maximum yield of GOS increased with increasing lactose concentration, up to 70% (w/v). The maximum yield of GOS also increased with increasing temperature, and the optimal pH for synthesis was different at different temperatures. The sum of tri- and tetrasaccharides yielded 37% (w/w) in an optimally designed reaction for LacS, and a maximum yield of 40% (w/w) was attained for CelB. Compared to aqueous solution, an increase of the tetrasaccharide/trisaccharide ratio was obtained in two-phase systems with heptane and nonane. These two enzymes from hyperthermophilic organisms were shown to give higher GOS yields at high substrate concentrations than a β-galactosidase from a thermophilic/mesophilic organism (Aspergillus oryzae).

ACKNOWLEDGMENT

This work was supported by the European Commission project: FAIR-CT96-1048. The authors wishto thank the Institute of Protein Biochemistry and Enzymology, Naples, Italy and the Departmentof Microbiology, Wageningen, The Netherlands for the enzyme solution gifts and for helpful assistance. The authors thank Babinder Samra for linguistic advice.