Twelve kinds of silica particles, with particle sizes of 1.6-700 mu m and specific surface areas of 14-620 m(2)/g support, were investigated as lipase-immobilizing supports for the production of fatty acid methyl ester (FAME). When the particle size and specific surface area of silica particles became smaller, the maximum enzymatic reaction rate was at a high level. Scanning electron microscopy revealed that the surfaces of lipase-immobilizing silica particles were coated by a lipase layer. At higher lipase loading than 20%, the lipase formed multilayers or wrinkled sheets on the silica surface and some of them peeled off. Lipase activity was proportional to the increase in the enzyme loading on silica particle until 30%, but the FAME formation rate was proportioned to the enzyme loading until 20%, and remained at a maximum level at lipase loading higher than 20%. The lipase-immobilizing silica particle did not lose activity following agitation rate at a 150 rpm for 8 h and 118 d of storage at room temperature. When lipase-immobilizing silica P-707 with at a specific surface area of 300 m2/g was used, the FAME conversion remained at 80% until the 16-20th cycle, and decreased to 20% after the 33rd cycle. The lipase immobilized on P-707 produced 57 g FAME per gram of lipase. Total FAME production increased with an increase in the specific surface area of silica particles, but it was not influenced by particle size over 40 mu m. During the progress of a long-term esterification reaction, the outer layer lipase was first inactivated, and then the inner layer of lipase was inactivated. (c) 2006 Elsevier Inc. All rights reserved.