The antioxidant activity and contents of various polyphenol classes in the seeds of seven soybean varieties of different seed color and one yellow seed cultivar, representing a reference genotype, were evaluated. Total polyphenols and tannins were determined after extraction of plant material with 70% aqueous acetone, and total flavonoids were extracted with methanol and acetic acid, whereas anthocyanins were extracted with 20% aqueous ethanol. In addition, isoflavone content and composition were determined using high-performance liquid chromatography analysis. Antioxidant activity of seed extracts was evaluated by the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity assay. A positive linear correlation between antioxidant activity and contents of total polyphenols and anthocyanins was established. The highest antioxidant activity was observed in the extracts of black and brown varieties, which also showed high levels of all polyphenol classes examined. Yellow seed had the highest total isoflavone content (3.62 mg/g of dry material). The highest concentration of total daidzein was determined in black seeds (>2.0 mg/g of dry material), and the highest total glycitein and genistein contents occurred in the yellow cultivar (0.53 and 1.49 mg/g of dry material, respectively). According to our results, varieties of black and brown seeds could be of special interest not only for their large content of total polyphenols, ranging from 4.94 to 6.22 mg of gallic acid equivalents/g of dry material, but also for their high content of natural antioxidants such as anthocyanins.

The aim of this study was to select Vicia genotypes with higher polyphenol contents and increased antioxidant activity, and to compare them with soybean, the most widespread and utilized legume species grown in the region. The examined legumes showed similar contents of total polyphenolics and tannins in between specimen, but differed greatly in their flavonoids and proanthocynidins levels. The content of total polyphenols ranged from 1.6 to 6.09 catechin/g dry seeds, and tannins from 0.26 to 2.98 mg of catechin/g dry seeds. The flavonoids levels in Vicia species were much higher compared with soybean, while the content of proanthocyanidins ranged from 1.5 (in soybean) to 62.3 mg of leucoanthocyanidin/g dry seeds (in vetches). The gallic and trans-cinnamic acids were identified as major monomeric phenolic compounds, and quercetin among flavonoids was found in all specimens. Catechin was detected in faba bean and vetches but not in the soybean. The values of the DPPH-test varied in a range between 21.1 and 89.6% of neutralized radicals, which correlated with the total polyphenolics and tannin contents. The faba bean specimens showed favourable traits – high total polyphenolic, flavonoid and proanthocyanidin contents, low total tannin content, and high DPPH-radical scavenging ability.

The oxidative stress and antioxidant systems in soybean leaves and roots infected with plant pathogen Aspergillus niger were studied following treatment with different concentrations of cholic acid. Several oxidative stress parameters were analyzed: production of superoxide (O2 ·−) and hydroxyl radicals (·OH), lipid peroxidation (LP), and superoxide dismutase (SOD; EC 1.15.1.1) activity, as well as the content of reduced glutathione (GSH). Results showed that inoculation with A. niger led to the increase of O2 ·− production and GSH quantities in leaves and ·OH in roots. The highest activity of SOD occured in infected plants treated with cholic acid in concentrations of 40 and 60 mg L−1 which ultimately led to a decrease in O2 ·− production. Inoculation with Aspergillus in combination with elevated cholic acid concentrations also increased ·OH production which is correlated with increased LP. These results may support the idea of using cholic acid as an elicitor to trigger hypersensitive response in plant cells. Use of cholic acid may also actively contribute to soybean plants defense response against pathogen attack.

Soybean [Glycine max (L.) Merr.] cultivars (Meli, Alisa, Sava and 1511/99) were grown up to V1 phase (first trifoliate and one node above unifoliate) and then inoculated with Sclerotinia sclerotiorum (Lib.) de Bary under controlled conditions. Changes in L-phenylalanine ammonia-lyase (PAL) activity and isoflavone phytoalexins were recorded 12, 24, 48 and 72 h after the inoculation. Results showed an increase in PAL activity in all four examined soybean cultivars 48 h after the inoculation, being the highest in Alisa (2-fold higher). Different contents of total daidzein, genistein, glycitein and coumestrol were detected in all samples. Alisa and Sava increased their total isoflavone content (33.9% and 6.2% higher than control, respectively) as well as 1511/99, although 48 h after the inoculation its content decreased significantly. Meli exhibited the highest rate of coumestrol biosynthesis (72 h after the inoculation) and PAL activity (48 h after the inoculation). All investigated cultivars are invariably susceptible to this pathogen. Recorded changes could point to possible differences in mechanisms of tolerance among them.