Hydrolysis of oleuropein by recombinant β-glycosidase from hyperthermophilic archaeon Sulfolobus solfataricus immobilised on chitosan matrix

Abstract

The recombinant β-glycosidase (EcSβgly) from Sulfolobus solfataricus was immobilised on chitosan to perform the enzymatic hydrolysis of commercial oleuropein (heterosidic ester of elenolic acid and 3,4-dihydroxy-phenylethanol (hydroxytyrosol)) at two temperatures (60 and 70°C). Interestingly, on the basis of the reasonable assumption that the enzyme hydrolyses only the sugar linkage, the biotransformation produces unstable aglycone species formed by oleuropein hydrolysis that, differently from some commercially available β-glucosidases tested, give rise to the formation of hydroxytyrosol, at the operative temperatures of the bioreactor. The results of the biotrasformation at 70°C showed that the main products are hydroxytyrosol, and glucose, being the oleuropein aglycone present in low amount at the end of reaction. Both in single step approach or in recycle approach the amounts of glucose and oleuropein aglycone were lightly dependent from flow rate. The amount of hydroxytyrosol, increased on decreasing the flow rate of bioreactor in recycle approach, following a non-linear trend and obtaining the highest value at a flow rate of 15 ml h −1 while in the single step approach the 3,4-dihydroxy-phenylethanol was at its maximum at higher flow rate (16 ml h −1). For the hydrolysis of the oleuropein by bioreactor at 60°C we used lower molar ratio oleuropein/enzyme only by the single step approach. In these conditions it is possible to obtain high amounts of only two products (glucose and hydroxytyrosol) in short time (2 h). The stability of the bioreactor at the operative temperatures showed a t 1/2 of 30 days at 70°C and a t 1/2 of 56 days at 60°C.