Effects of autumn coloration of <i>Acer palmatum</i> leaves on their polyphenolic components and antioxidant activity

This study aimed to determine the changes in polyphenols associated with autumn coloration of Acer palmatum leaves. A. palmatum leaves harvested in July (before autumn coloration: BAC) and November (after autumn coloration: AAC) were boiled in water. The AAC extract showed higher antioxidant activity than the BAC extract in assays measuring DPPH radical scavenging and superoxide dismutase-like activity. High-performance liquid chromatography analysis showed that the two extracts exhibited similar peak patterns for major polyphenols, with AAC extract exhibiting a large peak for compound I. After the two extracts were fractionated, the compound I-rich fraction (AAC Fr. 2) showed the strongest antioxidant activity among the obtained fractions. Finally, compound I was identified as mallotinic acid by liquid chromatography-mass spectrometry and nuclear magnetic resonance analyses. Our study revealed that the antioxidant activity of A. palmatum leaves is enhanced and mallotinic acid is accumulated during autumn coloration.