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 (23.32 gl(-1) day(-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 con-secutive 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 (V-m 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 (R-2 gt 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 (72 h of reaction) which, combined with complete conversions and green character of synthesis, represents firm basis for further process development.