Assessing the Enzyme Activity of Different Plant Extracts of Biomasses from Sub-Saharan Africa for Ethyl Biodiesel Production

This work focused on identifying plant biomasses as potential sources of lipases and their use as biocatalysts for ethyl biodiesel production. To that end, plant extracts prepared from dormant and germinated seeds of eight local (Burkina Faso) oil-bearing biomasses were tested as a biocatalyst for the hydrolysis and ethanol transesterification of sunflower oil. The optimum transesterification conditions with the most active extracts were then determined. The results of the hydrolysis and transesterification tests showed that the plant extracts from germinated Jatropha curcas (JG) and Moringa oleifera (MG) seeds contained lipases whose catalytic activity could be utilized without prior purification. The highest hydrolysis yield obtained was 88% using the JG extracts and 62% with the MG extracts after 24 h of reaction at 40 degrees C and at pH 7. For transesterification, the highest ethyl ester yield obtained was 94% with the JG extracts and 48% with the MG extracts after 144 h at 37 degrees C, following two successive transesterification reactions. Using the plant extracts in transesterification called for the stepwise addition of ethanol in a TAG:ethanol molar ratio of 1:0.3 at 6 h intervals to overcome the inhibiting effect of high ethanol concentrations on the catalytic activity of the plant extracts. In addition, a study on the influence of the reaction conditions showed that water had a negligible effect on transesterification yield when its content in the ethanol was lower than or equal to 5% (v/v) and that adding silica to the reaction medium led to an increase in transesterification yield.