Performing under pressure: esterification activity of dry fermented solids in subcritical and supercritical CO2.

Abstract

Lipases are often used in immobilized form, but commercial immobilized lipases are costly. An alternative is to produce lipases in solid-state fermentation, dry the solids and then use the "dry fermented solids" (DFS) directly. We produced DFS by growing Burkholderia contaminans on a mixture of sugarcane bagasse and sunflower seed meal and used the DFS to esterify oleic acid with ethanol in subcritical and supercritical CO2 at 40°C. Compared to a control without CO2 at atmospheric pressure, subcritical CO2 at 30bar improved esterification activity 1.2-fold. Higher pressures, including supercritical pressures up to 150bar, reduced activity to less than 80% of the control. At 30bar, the esterification activity was improved a further 1.8-fold with the addition of 9% water (i.e. 9g water per 100g oleic acid) to the reaction medium. A subcritical CO2 atmosphere, with the addition of a small amount of water, improved the esterification activity of DFS containing lipases of Burkholderia contaminans.