Highly efficient enzymatic acetylation of flavonoids: Development of solvent-free process and kinetic evaluation

Abstract

Solubility and stability of flavonoid glycosides, valuable natural constituents of cosmetics and pharmaceuticals, could be improved by lipase-catalyzed acylation. Focus of this study was on development of eco-friendly process for the production of flavonoid acetates. By using phloridzin as model compound and triacetin as acetyl donor and solvent, 100% conversion and high productivity (23.32gl−1day−1) were accomplished. Complete conversions of two other glycosylated flavonoids, naringin and esculin, in solvent-free system were achieved, as well. Comprehensive kinetic mechanism based on two consecutive mono-substrate reactions was established where first one represents formation of flavonoid monoacetate and within second reaction diacetate is being produced from monoacetate. Both steps were regarded as reversible Michaelis-Menten reactions without inhibition. Apparent kinetic parameters for two consecutive reactions (Vm constants for substrates and products and Km constants for forward and reverse reactions) were estimated for three examined acetyl acceptors and excellent fitting of experimental data (R2>0.97) was achieved. Obtained results showed that derived kinetic model could be applicable for solvent-free esterifications of different flavonoid glycosides. It was valid for entire transesterification course (72h of reaction) which, combined with complete conversions and green character of synthesis, represents firm basis for further process development.