Studies on the antioxidant activity and phenolic compounds of enzyme-assisted water extracts from Du-zhong (Eucommia ulmoides Oliv.) leaves

Abstract

Enzyme-assisted water extracts (EWEDL) and ethanol extracts of Du-zhong leaves (EEDL) were evaluated for their antioxidant activities using the DPPH radical-scavenging assay, Fe²⁺-chelating assay, and inhibition ability of the linoleic acid peroxidation assay. In general, the antioxidant activity of Du-zhong leaf extracts increased with increasing concentration. Based on the two extracting methods with different antioxidative reactions, it was shown that the enzyme-assisted water extracting method was more effective for antioxidant extraction from Du-zhong leaves. By HPLC-MS analysis, the main phenolic compounds (geniposidic acid, epicatechin, and chlorogenic acid) identified in EWEDL and EEDL were similar. EWEDL and EEDL had total phenolic contents of 13.84 ± 0.11 and 14.72 ± 0.14 mg chlorogenic acid equivalents (CAE) in each gram of extract, respectively. However, there was no positive correlation between total phenolic content and antioxidant activities of EWEDL and EEDL measured by the three different assays.

Keywords::

• Antioxidant
• extraction
• enzyme
• Du-zhong leaves
• phenolic compound
• Eucommia ulmoides

Acknowledgments

The authors are thankful to Professor Jing Zhang for generously providing laboratory facilities. This work was financially supported by the Ministry of Education of P. R. China (Project No. 00118).

Declaration of interest: The authors report no conflicts of interest.