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The aim of this study was to optimize the extraction method for caffeic acid from the leaves of Dendropanax morbifera using response surface methodology (RSM), and subsequently determine the polyphenolic content and antioxidant capacity of the D. morbifera leaves extracts. The extraction process considered operating variables such as solvent concentration, extraction temperature, and extraction time, which were optimized via Box–Behnken experimental design. In addition, the antioxidant capacity was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The optimal extraction conditions of 41.23% (v/v) methanol concentration, at 88.61 °C, and 1.86 h produced a maximum caffeic acid (CA) yield of 20.35 mg/g. Additionally, total polyphenols, total tannins, and total flavonoids contents in the leaves extracts of D. morbifera were 32.48 ± 2.05 mg GAE (gallic acid equivalents)/g, 17.61 ± 2.61 mg GAE/g, and 9.14 ± 0.17 mg QE (quercetin equivalents)/g, respectively. The results showed that methanol extracts exhibited an IC50 of approximately 14.3 mg AAE (ascorbic acid equivalent)/g. The results suggested that the extracts of D. morbifera leaves contain potential antioxidant activity, and could be a good source of functional food and used in medicinal applications.

Acer pseudoplatanus (maple) is a widely grown ornamental plant. In addition to its ornamental and ecological value, it also has potentially high economic value. It is a rich source of polyphenols and exhibits antioxidant activity. However, the relationship between polyphenol content and antioxidant activity in maple leaves of different colors (green, yellow, and red) has not yet been investigated. In this study, the total polyphenol (TP), total flavonoid (TFlav), tannin (TET), chlorophyll a and b (Chl a and b), total anthocyanin (TAN), and total carotene (TAC) contents in maple leaves of different colors were evaluated. Their antioxidant activities were determined based on the inhibition of lipid oxidation, DPPH scavenging, ferric ion-reducing antioxidant power, and iron-chelating abilities. The concentrations of TP, TET, TFlav, TAN, and TAC in red maple leaves were higher than those in green and yellow maple leaves. In addition, red maple leaves showed a higher antioxidant effect than the leaves of the other two colors. We observed that antioxidant activity was positively correlated with TP, TFlav, and TAN and negatively correlated with Chl a and b. Finally, we analyzed the metabolites of the different colored (i.e., green, yellow, and red) maple leaves using gas chromatography/mass spectrometry (GC/MS) and found that the metabolite profile significantly varied between the different colors. These results suggest that red leaves are a good source of polyphenols and antioxidants and have potential use in the development of functional foods and medicinal applications.