Formation of polyol–fatty acid esters by lipases in reverse micellar media

Abstract

The synthesis of polyol-fatty acid esters has strong implications in such industries as foods, cosmetics, and polymers. We have investigated these esterification reactions employing the polyols ethylene glycol, 2-monoglyceride, and sugars and their derivatives with the biocatalyst lipase in water/AOT/isooctane reverse micellar media. For the first reaction, 50-60% conversion was achieved and product selectivity toward the monoester over the diester shown possible by employing lipase from Rhizopus delemar. A simple kinetic model based on the formation of acyl-enzyme intermediate accurately predicted the effect of polyol concentration but not the effect of fatty acid or water concentration probably due to the model exclusion of partitioning effects. The success of this reaction in reverse micellar media is due greatly to its capacity to solubilize large quantities of glycol despite the media's overall hydrophobicity. The second reaction, investigated for its potential for production of "mixed" glycerides, also achieved about 50% conversion but had only a small portion of triglyceride in its product distribution. Also, isomerization of the 2-monoglyceride to 1-monoglyceride, followed by hydrolysis of the latter, unfortunately occurred to a significant extent. Attempts at esterification with hexoses and their derivatives such as glucose and mannitol produced no conversion.