Lipase-catalyzed synthesis of fructosyl myristic acid esters as biosurfactants in a low solvent media: Optimization of the bioconversion

Abstract

Lipase-catalyzed synthesis of fructosyl myristic acid esters as natural food biosurfactants in low solvent reaction media was investigated. The effect of chain length of fructose-based glycosides as acyl acceptors was found to be inversely proportional to the bioconversion yield. The application of molecular sieves proved unsuccessful in low-solvent media due to their saturation and mass transfer limitations. The substitution of low-solvent myristic acid reaction media with 5% oleic acid led to similar bioconversion yield than that achieved without oleic acid, while no solidification of the reaction media was observed. Response surface methodology using a 3-factor and 5-level central composite design was used to achieve a compromise between mass transfer limitations and catalytic activity of lipase in low-solvent myristic acid reaction media enriched with oleic acid. Modeling found reduced quadratic models accurately described the yield and productivity of the reaction. Maximum bioconversion yield (22%) was achieved using 0.2 mol/L of fructose and 5% (w/v) of Lipozyme® RM IM in a reaction media composed of 80% myristic acid and 10% oleic acid. Lipozyme® RM IM catalyzed successfully 5 consecutive reactions before showing reduction of its synthetic activity at the 6th cycle. The end-product profile analysis confirmed the selectivity of Lipozyme® RM IM towards saturated fatty acids over unsaturated one and the formation of fructosyl monoester and diester of myristic acids. This study lays the ground of a sustainable approach for the acylation of myristic or longer saturated fatty acids with carbohydrates for a great potential as functional ingredients.