Differences between antioxidant capacity of Japanese knotweed (Fallopia japonica), Sakhalin knotweed (F. sachalinensis) and their hybrid Czech knotweed (F. x bohemica) were examined in this research. We prepared ethanol extracts of different tissues by extraction in water bath and by ultrasonic extraction. We measured antioxidant capacity (AOC) with ABTS method. The highest AOC was detected in rhizome sheaths of Japanese knotweed, 3 mmol TEAC/g, while the lowest was detected in stems of Japanese knotweed, 0,23 mmol TEAC/g. Prooxidant activity was determined by reduction of Fe3+ and the highest ability to reduce iron ions was determined in rhizome sheaths and flowers of all taxons (about 2 mmol of ascorbic acid equivalent). The presence of resveratrol, polydatin, catechin and epicatechin was detected by a HPLC/DAD system in all taxons of knotweed, and content of each was quantified. Czech knotweed flower is the richest source of resveratrol (476 µg/g),while Japanese knotweed rhizome sheaths are the richest source of polydatine (23,3 mg/g) and has even exceeded values of the mentioned polyphenols in red grapes. The reachest source of catechin (13,3 mg/g) are Sakhalin knotweed rhizomes, and epicatechin (27,1 mg/g) flowers of Czech knotweed. Finally, we examined stability of resveratrol and polydatine as a function of temperature and time. It turned out, that both compounds are stable up to 48 hours at temperatures up to 60 °C. Outcomes of this research may help to develop new dietary supplements.
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