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 es terification between free acetic acid and primary alcohols (geraniol and et hanol) in organic solvent. The growth conditions to obtain high activity of mycelium-bound enzymes were firstly evaluated. A medium containing Tween 8 0 as carbon source furnished mycelium with the highest activity in the hydr olysis of alpha-naphthyl esters (alpha-N-acetate, butyrate, caprylate). Dry mycelium was employed to select suited conditions for an efficient acetyla tion of ethanol and geraniol in heptane. Maximum productions were obtained using 30 gl(-1) of lyophilized cells: 12.4 gl(-1) of geranyl acetate were p roduced at 80 degrees C starting from 75 mM geraniol and acetic acid (84% m olar conversion) and 4.1 gl(-1) of ethyl acetate at 50 degrees C from 50 mM ethanol and acetic acid (94% molar conversion) after 24 h. The stability o f the mycelium-bound carboxylesterases are notable since only 10-30% loss o f activity was observed after 14 days at temperatures between 30 and 50 deg rees C. (C) 2000 Elsevier Science Inc. All rights reserved.