M. Kaieda et al., Biodiesel fuel production from plant oil catalyzed by Rhizopus oryzae lipase in a water-containing system without an organic solvent, J BIOSCI BI, 88(6), 1999, pp. 627-631
A new enzymatic method of synthesizing methyl esters from plant oil and met
hanol in a solvent-free reaction system was developed. It is anticipated th
at such plant oil methyl esters can be used as a biodiesel fuel in the futu
re. Lipase from Rhizopus oryzae efficiently catalyzed the methanolysis of s
oybean oil in the presence of 4-30 wt% water in the starting materials; how
ever the lipase was nearly inactive in the absence of water. The methyl est
er (ME) content in the reaction mixture reached 80-90 wt% by stepwise addit
ions of methanol to the reaction mixture. The kinetics of the reaction appe
ars to be in accordance with the successive reaction mechanism. That is, th
e oil is first hydrolyzed to free fatty acids and partial glycerides, and t
he fatty acids produced are then esterified with methanol. Although R. oryz
ae lipase is considered to exhibit 1(3)regiospecificity, a certain amount o
f 1,3-diglyceride was obtained during the methanolysis and hydrolysis of so
ybean oil by R. oryzae lipase solution. Therefore, the high ME content in t
he reaction mixture is probably attributable to the acyl migration from the
sn-2 position to the sn-l or sn-3 position in partial glycerides.