1,3-Diacylglycerol (1,3-DAG) production by esterification of fatty acids (FA) and glycerol in a packed bed bioreactor using a 1,3-regioselective immobilized lipase was studied. Esterification was effectively performed by circulating the reaction mixture between a packed bed column and a water removal vessel. The rate of 1,3-DAG synthesis was increased with increase in temperature up to 50 degreesC. Higher vacuum conditions also increased 1,3-DAG production, and under vacuum condition of 0.4 kPa a maximum 1,3-DAG content of around 70% was obtained when the molar ratio of fatty acid to glycerol was higher than 2.0. Shortening the residence time decreased the water content at the reactor outlet and led to an increase in the rate of 1,3-DAG esterification. The effect of the linear flow velocity on the 1,3-DAG esterification rate was found to be negligible. (C) 2004 Elsevier Ltd. All rights reserved.