Analysis of multiphasic behavior during the ethyl esterification of fatty acids catalyzed by a fermented solid with lipolytic activity in a packed-bed bioreactor in a closed-loop batch system

A fermented solid containing lipases was produced by growing Burkholderia cepacia LTEB11 on a 1:1 mixture, by mass, of sugarcane bagasse and sunflower seed meal. This fermented solid was dried and then used in a packed-bed bioreactor to catalyze the esterification of fatty acids from soybean soapstock acid oil with ethanol in a solvent-free system. The bioreactor was operated in batch mode, with the medium being recirculated from the reservoir through the bed in a closed-loop system. During the reaction, the bulk reaction medium separated into organic and aqueous phases. Additionally, up to 30% of the reaction medium was held as a sorbed phase on the fermented solids. The composition of this sorbed phase, which represents the microenvironment of the lipases, was significantly different from the compositions of the bulk organic and aqueous phases. It was predominantly polar, with water or ethanol as the major component, but also contained significant amounts of ester. Importantly, the molar ratios of ethanol to fatty acid in the sorbed phase were significantly higher than those in the bulk reaction medium; this has implications for the reaction, since ethanol is known to cause inhibition and denaturation of lipases.