Facilitatory effect of immobilized lipase-producing Rhizopus oryzae cells on acyl migration in biodiesel-fuel production

For biodiesel-fuel production by methanolysis of plant oils, Rhizopus oryzae cells producing a 1,3-positional specificity lipase were cultured with polyurethane foam biomass support particles (BSPs) in a 20 l air-lift bioreactor, and the cells immobilized within BSPs were used as whole-cell biocatalyst in repeated batch-cycle methanolysis reaction of soybean oil. The whole-cell biocatalyst had a higher durability in the methanolysis reaction when obtained from air-lift bioreactor cultivation than from shake-flask cultivation. Following repeated methanolysis reaction using the whole-cell biocatalyst, analysis of the reaction mixture composition indicated that monoglycerides (MGs) decreased and free fatty acids (FFAs) increased with increasing water content in the reaction mixture, and that MGs, diglycerides (DGs), and triglycerides (TGs) increased with increasing number of reaction cycles. The isomers of MGs and DGs generated during the 20th methanolysis reaction cycle consisted of 2-MGs and 1,2(2,3)-DGs, respectively. The hydrolytic activity of the whole-cell biocatalyst, on the other hand, was stable regardless of the number of reaction cycles. It was demonstrated thus that the whole cell biocatalyst promotes acyl migration of partial glycerides, and that the facilitatory effect is increased by increase in the water content of the reaction mixture but it is lost gradually with increasing number of reaction cycles.