Free and Bound Phenolics of Buckwheat Varieties: HPLC Characterization, Antioxidant Activity, and Inhibitory Potency towards α-Glucosidase with Molecular Docking Analysis

Abstract

Free and bound phenolic fractions from six buckwheat varieties were investigated for their compositions, antioxidant activities, and inhibitory effects on α-glucosidase. The results showed that different buckwheat varieties have significant differences in phenolic/flavonoid contents, and these contents were found in higher quantities in free form than in bound form. HPLC results revealed that rutin, quercetin, and kaempferol-3-O-rutinoside were the most abundant components in free and bound forms, whereas dihydromyricetin was found only in the bound form. Free phenolics showed higher antioxidant activities of DPPH, ABTS+, OH•, and FRAP than those of bound phenolics. Strong inhibitory effects against α-glucosidase by the free/bound phenolic fractions were found in all buckwheat varieties, and free phenolics showed stronger α-glucosidase inhibition than that of the corresponding bound phenolics. More importantly, the main phenolic compounds observed in the buckwheat varieties were subjected to molecular docking analysis to provide insight into their interactions with α-glucosidase. The contributions by individual phenolics to the observed variation was analysed by Pearson correlation coefficient analysis and principal component analysis. The present study provides a comprehensive comparison for the phenolic fractions of buckwheat varieties and identify the main contributors to antioxidant and α-glucosidase inhibitory activity.

Breeding Buckwheat for Nutritional Quality in the Czech Republic

“…From Slovakia the variety 'Ballada', for example, had from 0.01 to 0.03 ug/g d.w. and 1.438 mg/g d.w. [52]. In contrast to our results is the result of HPLC characterization of Chinese buckwheat samples, where apigenin and kaempferol were found at high levels, which could be due to differences in genotypes and environmental factors affecting growth [58]. Kaempferol has been detected in F. tataricum and F. cymosum and furthermore in low levels in buckwheat microgreens [59].…”

“…The maximum value for 2019 was recorded in 'MC039' at 14.18 ± 0.08 ug/g d.w. and for 2020 in 'Zita' at 20.72 ± 0.23 ug/g d.w. of gallic acid. However, the values obtained were much lower than those found in Chinese buckwheat genotypes [58]. Here, more than half of the accessions had higher levels of gallic acid in 2020.…”

Concentrations of Phenolic Acids Are Differently Genetically Determined in Leaves, Flowers, and Grain of Common Buckwheat (Fagopyrum esculentum Moench)

“…In contrast, Zielińska et al [35] determined a higher rutin content in the grains of common buckwheat (16 mg/g d.w.) than was determined in our samples. Our results agree with those obtained by Zhu et al [45], who determined the rutin content in the grains of six buckwheat samples from China in the range 1.29-6.29 mg/g d.w. Anyway, these authors determined a higher kaempferol content (0.101-0.140 mg/g d.w.) compared to our values.…”

Germinated Buckwheat: Effects of Dehulling on Phenolics Profile and Antioxidant Activity of Buckwheat Seeds

“…In general, these data for AA also concur with previous studies on buckwheat seeds and germinated buckwheat seeds [ 24 , 49 , 50 , 51 ]. However, it needs to be noted that detailed comparisons of the data in the present study with the data in the literature can be difficult, as previous studies were mainly related to buckwheat seeds either before germination [ 52 ] or as sprouts [ 53 ], without consideration of the effects of dehulling on the levels of the bioactive compounds and the antioxidative potential.…”

“…In the present study, LC-MS analysis of the extracts of the germinated seeds (i.e., sprouts) identified several phenolic compounds, most of which were flavonoids in glycosylated and aglycone forms. In contrast to cereals (i.e., the Poaceae family) where the majority of phenolic compounds are bound to cell walls [ 54 ], the buckwheat seed phenolic compounds are mostly in free forms [ 52 ].…”