Mycelium-bound carboxylesterase from Aspergillus oryzae: an efficient catalyst for acetylation in organic solvent

Dry mycelium of a strain of Aspergillus oryzae efficiently catalyzed the esterification between free acetic acid and primary alcohols (geraniol and ethanol) in organic solvent. The growth conditions to obtain high activity of mycelium-bound enzymes were firstly evaluated. A medium containing Tween 80 as carbon source furnished mycelium with the highest activity in the hydrolysis of α-naphthyl esters (α-N-acetate, butyrate, caprylate). Dry mycelium was employed to select suited conditions for an efficient acetylation of ethanol and geraniol in heptane. Maximum productions were obtained using 30 g l−1 of lyophilized cells: 12.4 g l−1 of geranyl acetate were produced at 80°C starting from 75 mM geraniol and acetic acid (84% molar conversion) and 4.1 g l−1 of ethyl acetate at 50°C from 50 mM ethanol and acetic acid (94% molar conversion) after 24 h. The stability of the mycelium-bound carboxylesterases are notable since only 10–30% loss of activity was observed after 14 days at temperatures between 30 and 50°C.