Lipase-catalyzed acylation of konjac glucomannan (KGM) with vinyl acetate in organic media was successfully conducted using Novozym 435 as a biocatalyst. The degree of substitution (DS) of the modified KGM was used to evaluate the extent of acylation. The influences of various factors, such as water activity (a(w)), organic media, reaction temperature, shaking rate, enzyme dosage and the molecular weight of KGM, on the reaction were investigated. The water activity of the reaction system played a key role in the acylation of KGM. tert-Butanol (t-BuOH) was thought to be the most suitable reaction medium by taking DS of the modified KGM into account. The optimum water activity, shaking rate, reaction temperature and enzyme dosage were 0.75, 200 r/min, 45-50 degrees C and 250 U/ml, respectively, under which the DS of product was as high as 0.71. It has also been found that the DS of modified KGM sample decreased with increasing molecular weight of KGM. Additionally, Novozym 435-catalyzed acylation of KGM was proved to be highly regioselective, with C6-OH being acylated. (c) 2006 Elsevier Ltd. All rights reserved.