Comprehensive investigation of the enzymatic oligomerization of esculin by laccase in ethanol : water mixtures

Abstract

The enzymatic polymerization of phenolic compounds arouses increasing interest due to the production of derivatives with improved biological activity. The reaction yield, the molecular mass, the structure and the properties of synthesized polymers can be controlled by the reaction conditions such as solvent and type of enzyme and substrate. In this study, the oxidative oligomerization of esculin by laccase from Trametes versicolor was performed in the presence of ethanol, a biocompatible co-solvent for food and nutraceutical applications. The formation of a precipitate was associated with the oligomerization reaction except for the medium with 50% (v/v) ethanol, due to the low reaction yield. The evaluation of antioxidant activity of the monomer and products showed that the pellet fraction from the reaction with esculin at 2 g L⁻¹ in acetate buffer led to the highest activities. The presence of esculin oligomers was confirmed by MALDI-TOF analysis, which identified a repetition unit of 338 Da with a degree of polymerization up to 9 as well as other oligomers, mainly in the pellet fraction, with a repetition unit of 176 Da which are attributed to be esculetin oligomers. Additionally, size exclusion chromatography (SEC) and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the products.