Acid Treatment Enhances the Antioxidant Activity of Enzymatically Synthesized Phenolic Polymers.

Maria Laura Alfieri,Federica Moccia,Marco D'Ischia,Alessandra Napolitano,Lucia Panzella,Gerardino D'Errico

doi:10.3390/polym12112544

Abstract

Phenolic polymers produced by enzymatic oxidation under biomimetic and eco-friendly reaction conditions are usually endowed with potent antioxidant properties. These properties, coupled with the higher biocompatibility, stability and processability compared to low-molecular weight phenolic compounds, open important perspectives for various applications. Herein, we report the marked boosting effect of acid treatment on the antioxidant properties of a series of polymers obtained by peroxidase-catalyzed oxidation of natural phenolic compounds. Both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated a remarkable increase in the antioxidant properties for most phenolic polymers further to the acid treatment. In particular, up to a ca. 60% decrease in the EC50 value in the DPPH assay and a 5-fold increase in the Trolox equivalents were observed. Nitric oxide- and superoxide-scavenging assays also indicated highly specific boosting effects of the acid treatment. Spectroscopic evidence suggested, in most cases, that the occurrence of structural modifications induced by the acid treatment led to more extended π-electron-conjugated species endowed with more efficient electron transfer properties. These results open new perspectives toward the design of new bioinspired antioxidants for application in food, biomedicine and material sciences.

Highlights

IntroductionPolymers of natural phenolic compounds, in particular, have attracted remarkable interest in view of their lower volatility (with reduced adverse effects), greater stability, and higher processability, and lower tendency to be released into the contact medium compared to the corresponding monomers [24,25,26,27,28,29]
We report the effects of the acid treatment on the antioxidant and radical-scavenging properties of nine polymers prepared by horseradish peroxidase (HRP)-H2 O2 -catalyzed oxidation of accessible natural phenolic compounds
Spectroscopic analysis indicated the occurrence of significant structural modifications leading in most cases to the generation of more extended π-conjugated systems, responsible for the improvement of the antioxidant properties observed

Summary

Introduction

Polymers of natural phenolic compounds, in particular, have attracted remarkable interest in view of their lower volatility (with reduced adverse effects), greater stability, and higher processability, and lower tendency to be released into the contact medium compared to the corresponding monomers [24,25,26,27,28,29]. They are usually endowed with a range of antioxidant properties which further add to the potential of this material [30]. Remarkable examples include, among others, polymerized flavonoids [31,32], lignin-inspired polymers [33], sinapic acid-derived polymers [34], catechol and gallol-type polymers [35].

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Conclusion