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ABSTRACT
Knotweed is an invasive plant that creates high compact growth when uncontrolled that can suppress the growth of native plants and thus reduce biological diversity. These invasive plants contain many antioxidants that require identification and quantification. In this work, aqueous 2% acetic acid, 50% ethanol in aqueous 2% acetic acid, and pure butanol extracts of young leaves, old leaves, rhizomes, stalks, and flowers from the three European knotweed species of Fallopia japonica, Fallopia sachalinensis, and Fallopia × bohemica were prepared and analyzed for their antioxidant capacities. Four methods were used for these analyses: chemiluminescence, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid [ABTS], Folin–Ciocalteu, and 2,2-diphenyl-1-picrylhydrazyl radical [DPPH•] assays. The chemiluminescence assay correlated strongly with the ABTS assay across all of the extraction media. However, correlation between the chemiluminescence assay and the Folin–Ciocalteu assay was strong only for the acidified water and acidified ethanol extracts, with moderate correlation for the butanol extracts. Similarly, the DPPH• assay strongly correlated with the chemiluminescence assay for the acidified water and acidified ethanol extracts, with weak correlation for the butanol extracts. For the overall antioxidant capacity, all of these knotweed species represent rich sources of antioxidants, particularly F. sachalinensis. The highest antioxidant activities were obtained using acidified ethanol, and the lowest using butanol. The antioxidants were most abundant in the flowers, whereas the stalks contained the lowest levels. This study also indicates that these antioxidants are synthesized during spring and early summer, and that they decrease during late summer.