Optimized enzymatic synthesis of (epi)gallocatechin (EGC) monolaurate and the antioxidant evaluation of its ester analogs

Abstract

The fatty acid ester of catechins such as (epi)gallocatechin (EGC) occur naturally in green tea but reports on their enzymatic synthesis and antioxidant evaluation is scarce. In this study, EGC esters were prepared via a one-step enzymatic transesterification. The main O-acylation products were 8 EGC monoesters consisting of varying acyl groups ranging from 2 to 18 carbon atoms (acetate, butyrate, caproate, caprylate, caprate, laurate, myristate, and stearate). The dimyristate and distearate esters of EGC were also exemplified as minor production during EGC's enzymatic esterification. LC-ToF and NMR HSQC were used to characterize the structures of purified EGC esters. Besides, the antioxidant activity of purified EGC esters were evaluated and systematically compared via several classical chemical (DPPH, ABTS, FRAP, Fe2+ chelation assays), food (β-carotene bleaching assay), and biological (LDL and DNA oxidation assays) methods/models. The lipophilicity of EGC derivatives increased upon O-acylation and was found to positively correlate with the chain length of their acyl groups. The dual effect of acyl chain length on altering EGC monoesters' antioxidant efficacies also corresponded well with previous data of the fatty acid esters of quercetin, gallic acid, EGCG, and resveratrol. Finally, response surface design was used to optimize the reaction condition to achieve the ultimate reaction yield of EGC monolaurate in a laboratory scale. Overall, the study results support that the acylated EGCs can serve as functional/health-beneficial ingredients for use in lipid-based matrices of cosmetics, supplements, and nutraceuticals. The enzymatic synthesis with optimized reaction conditions may be utilized for further pilot-scale manufacturing of similar analogs of EGC monolaurate.