β-Glucosidase catalyzed synthesis of octyl-β-d-glucopyranoside using whole cells of Pichia etchellsii in micro aqueous media

Octyl-β-d-glucopyranoside was synthesized by transglucosylation between p-nitrophenyl β-d-glucopyranoside (pNPG) and octanol as an acceptor using whole cells of thermo tolerant yeast Pichia etchellsii displaying cell wall bound β-glucosidase. Effect of several parameters such as glucosyl donor concentration, enzyme units and initial water activity was studied to optimize product yield. An initial water activity interval of 0.33–0.64 was favorable and increase in total enzyme units had marginal effect on conversion yield. An empirical model was developed to describe the relationship between various parameters and octyl glucoside yield. These factors were combined in a batch replacement strategy whereby octyl-β-d-glucopyranoside was synthesized in 4 h to a concentration of 30 mM (9.25 mg/ml) with a conversion yield of nearly 70% with pNPG as a glucosyl donor. Quantitative analysis was done by a highly reproducible reverse-phase high-performance liquid chromatography (RP-HPLC) method and detection was achieved using refractive index detector. The structure of the product was confirmed by 13C and 1H NMR spectroscopy. Additional products like octyl diglucoside were also formed, the structure of which was confirmed by mass spectrometry.