Abstract
To stabilize the lipase activity of Rhizopus oryzae cells as whole-cell biocatalysts, the effect of cell-membrane fatty acid composition on biodiesel-fuel production was investigated. The fatty acid composition of the cell membrane was easily controllable by addition of various fatty acids to the culture medium. Oleic or linoleic acid-enriched cells showed higher initial methanolysis activity than saturated fatty acid-enriched cells, among which palmitic acid-enriched cells exhibited significantly greater enzymatic stability than unsaturated fatty acid-enriched cells. It was assumed that fatty acids significantly affect the permeability and rigidity of the cell membrane, and that higher permeability and rigidity lead to increases in methanolysis activity and enzymatic stability, respectively. When the optimal fatty acid ratio of 0.67, indicated by Rf [= oleic acid/ (oleic acid + palmitic acid)], was adopted for repeated methanolysis reactions, both methanolysis activity and enzymatic stability were maintained at significantly elevated levels, with methyl ester content of around 55% even in the tenth batch cycles.
