Phenolic Compounds and Antioxidant, Antibacterial, and α-Amylase-/α-Glucosidase-Inhibitory Activities of Plant Species from the Genera Persicaria, Polygonum, and Fallopia

The comparative analysis of extracts from eight closely related species belonging to the Polygonaceae family (Persicaria lapathifolia, Persicaria hydropiper, Persicaria maculosa, Persicaria amphibia, Persicaria minor, Persicaria bistorta, Polygonum aviculare, and Fallopia convolvulus) and growing under identical environmental conditions is presented in this study. The total contents of phenolic compounds, flavonoids, hydroxycinnamic acids, catechins, proanthocyanidins, and tannins were determined using spectrophotometric methods. The maximum concentrations of phenolic compounds were found in P. maculosa (up to 70 mg g−1); flavonoids in P. hydropiper (about 45 mg g−1); hydroxycinnamic acids in P. minor, P. bistorta, and F. convolvulus (11.7–15.5 mg g−1); catechins in P. bistorta and P. aviculare (6.2–6.4 mg g−1); proanthocyanidins in P. bistorta (about 3.6 mg g−1); and tannins in P. hydropiper and P. maculosa (5.8–6.5 mg g−1). The qualitative and quantitative composition of phenolic compounds was determined by high-performance liquid chromatography with diode-array detection (HPLC-DAD) by comparing retention times and UV spectra with those of the relevant standards. The predominance of flavonol derivatives (quercetin and kaempferol) over flavone derivatives in the species studied was revealed. P. hydropiper, P. maculosa, and P. lapathifolia were found to contain high concentrations of ellagic acid and its derivatives (about 15 mg g−1), which correlated with the higher antioxidant activity characteristic of the extracts from these species. Based on their inhibitory activity (exceeding 70%) against α-amylase and yeast α-glucosidase, P. hydropiper, P. lapathifolia, P. minor, and P. bistorta appear to be the most promising species for further studies of their antidiabetic properties using cell-based in vitro and in vivo models. The 70% aqueous ethanol extracts from P. maculosa and P. hydropiper also showed pronounced antimicrobial activity against S. aureus, B. cereus, and P. aeruginosa. Further experiments are required to investigate the dose–response relationships for the antibacterial and enzyme-inhibitory activities of extracts. A cluster analysis based on biochemical parameters showed that P. hydropiper, P. maculosa, and P. lapathifolia form a single cluster, supporting the further use of phytochemical analysis as an auxiliary tool in plant systematics.