Lipase-catalyzed synthesis of astilbin fatty acid esters: Effect of key reaction factors on catalysis and physicochemical properties of target products

To improve the liposolubility and stability of astilbin, a series of astilbin fatty acid esters (ASE) with different carbon chain lengths were successfully synthesized through lipase-catalyzed transesterification. It was found that the substrate conversions were between 97.86 % and 99.29 % as determined by HPLC analysis. An isomerization reaction was found in the enzymatic transesterification reaction system, and the product was neoastilbin fatty acid ester. The pathway of this isomerization reaction was investigated and a high relative content of ASE (>90 %) was obtained by controlling the reaction time (24 h-48 h). Moreover, the underlying mechanism by which a high substrate molar ratio (acyl donor: astilbin/mM: mM) inhibited the hydrolysis of ASE was revealed. The products were purified using preparative thin-layer chromatography, and their structures were identified by mass spectrometry, H-1 NMR and C-13 NMR analysis. Subsequently, the liposolubility, temperature, and pH stability of ASE were explored. It was found that the liposolubility and temperature stability of ASE were higher than those of astilbin. Additionally, ASE exhibited pH-dependent stability, maintaining structural integrity in acidic conditions but undergoing significant hydrolysis, isomerization, and decomposition in alkaline conditions. This study may expand the application of astilbin in foods and functional foods.