Chelation of Cu(II), Zn(II), and Fe(II) by Tannin Constituents of Selected Edible Nuts

The tannin fractions isolated from hazelnuts, walnuts and almonds were characterised by colorimetric assays and by an SE-HPLC technique. The complexation of Cu(II) and Zn(II) was determined by the reaction with tetramethylmurexide, whereas for Fe(II), ferrozine was employed. The walnut tannins exhibited a significantly weaker reaction with the vanillin/HCl reagent than hazelnut and almond tannins, but the protein precipitation capacity of the walnut fraction was high. The SE-HPLC chromatogram of the tannin fraction from hazelnuts revealed the presence of oligomers with higher molecular weights compared to that of almonds. Copper ions were most effectively chelated by the constituents of the tannin fractions of hazelnuts, walnuts and almonds. At a 0.2 mg/assay addition level, the walnut tannins complexed almost 100% Cu(II). The Fe(II) complexation capacities of the tannin fractions of walnuts and hazelnuts were weaker in comparison to that of the almond tannin fraction, which at a 2.5 mg/assay addition level, bound Fe(II) by ~90%. The capacity to chelate Zn(II) was quite varied for the different nut tannin fractions: almond tannins bound as much as 84% Zn(II), whereas the value for walnut tannins was only 8.7%; and for hazelnut tannins, no Zn(II) chelation took place at the levels tested

Antioxidant Activity of Faba Bean Extracts

Phenolic compounds were extracted from seeds of 22 cultivars of faba bean (Vicia faba L.) by using 80% (v/v) aqueous acetone. The total phenolic compound and condensed tannins contents of the extracts and their antioxidant activity were determined using the Folin-Ciocalteu’s phenol reagent, vanillin/HCl method, and ABTS and FRAP assays, respectively. The content of total phenolic compounds ranged from 40.7 to 66.1 mg/g extract and from 326 to 574 mg/100 g seeds. Contents of condensed tannins ranged from 2.40 to 49.9 mg/g extract and from 22.2 (FAB) to 365 mg/100 seeds. The extracts and seeds were characterized by Trolox equivalent antioxidant capacity (TEAC) values ranging from 0.550 (FAB 443) to 1.030 mmol Trolox/g extract (FAB 187) and from 4.85 (FAB 318) to 9.81 mmol Trolox/100 g seeds (FAB 187). Ferric-reducing antioxidant power (FRAP) values varied from 0.595 (FAB 443) to 0.908 mmol Fe2+/g extract (FAB 5023) and from 4.61 (FAB 297) to 7.90 mmol Fe2+/100 g seeds (FAB 187). The total phenolic content of faba bean extract was correlated with the results of the ABTS (r = 0.864) and FRAP (r = 0.862) assays. The coefficients of correlations between the contents of condensed tannins and ABTS and FRAP results were 0.543 and 0.862. We also noted a correlation between results of ABTS and FRAP assays (r = 0.795)

Effect of the Growth Stage of False Flax (Camelina sativa L.) on the Phenolic Compound Content and Antioxidant Potential of the Aerial Part of the Plant

The phenolic compound profile and antioxidant potential of the false flax (Camelina saliva L.) plant, harvested at five morphological stages, that is. from the vegetative to the ripe seed-pod stage, have been investigated. False flax extracts were prepared using 80% (v/v) methanol. and the total phenolic content (TPC), the contents of the individual phenolics and antioxidant activity, measured as the Trolox equivalent antioxidant capacity (TEAC), ferric-reducing antioxidant power (FRAP), DPPH center dot scavenging activity and the ability to inhibit the oxidation of beta-carotene-linoleic acid emulsion, were determined. The TPC of the plant, at different growth stages, ranged from 49.2 to 59.1 mg GAE/g of extract and from 1.46 to 3.10 mg GAE/g of fresh matter (FM). Four main phenolic compounds were identified (chlorogenic acid, rutin, quercetin 3-O-glucoside, and quercetin glycoside). The chlorogenic acid content and the sum of flavonoids increased in the extracts from the vegetative to the bud stage, reaching 35.9 and 49.5 mg/g of extract, respectively, and gradually decreased in the subsequent growth stages. The plant extracts at the bud and flowering stages generally had the highest antioxidant activity in the polar systems (TEAC, FRAP and DPPH assays). The ripe seed-pod stage showed the highest antioxidant potential in these conditions when the results were expressed on FM basis. The best antioxidant activity in the lipid emulsion system was shown for the false flax extracts at the flowering and ripe seed-pod stages. Our research has indicated the possibility of using the aerial part of C. saliva as a source of ingredients with protective antioxidant activity

Changes in the Total Polyphenolic Content and Antioxidant Capacities of Perilla ( Perilla frutescens

Changes in the total polyphenolics and antioxidative capacity of the perilla (Perilla frutescens L.) plant, during the growth cycle, have been analyzed in this study. These parameters were evaluated at five morphological stages. The extracts characterized by the highest total phenolic compound content were obtained at the full flowering stage. The phenolic compound profile was characterized by the presence of three major compounds, with rosmarinic acid being the most abundant. Moreover, their contents were significantly different according to the growth stage. High Trolox equivalent antioxidant capacity values were found for the last two growth stages. The lowest ferric-reducing antioxidant power value was observed for the medium vegetative stage. The highest antiradical activity against DPPH• was observed for extracts obtained from the early vegetative stage. The antioxidant activity changes during the growth cycle, and this change may be useful to determine the optimal harvest time

Effect of osmotic stress and post-stress recovery on the content of phenolics and properties of antioxidants in germinating seeds of grapevine Vitis californica

The tested material consisted of grapevine Vitis californica stratified seeds germinated under optimum conditions (+25°C in water), under osmotic stress (-0.2 MPa in PEG solution) and submitted to recovery after stress (+25°C in water). The germinating seeds were determined to contain tannins, catechins and the following phenolic acids: gallic, caffeic, p-coumaric and ferulic. The acids occurred in free, ester- and glycoside-bound forms. The dominant form of phenolic acids was the ester-bound fraction. Gallic acid was the most abundant phenolic acid in germinating seeds, while ferulic acid appeared in the smallest amounts. Our analysis of tannins demonstrated that osmotic stress depressed their concentration. Presence of catechin group compounds such as catechin and epicatechin was also determined. In each sample epicatechin was dominant. The total concentration of catechin increased under stress conditions and declined during post-stress recovery. Catechins are a constituent of tannins and their increase under osmotic stress is most probably caused by the breakdown of some tannins in seeds germinating under stress conditions. Samples submitted to osmotic stress were also found to contain less of total phenolic compounds, whereas in samples which underwent post-stress recovery the total level of phenolic compounds increased. Compared to extracts from seeds germinating under optimum conditions, osmotic stress depressed the capacity of extract to scavenge DPPH● (2,2-diphenyl-1-picrylhydrazyl) and ABTS●+ – 2,2-Azino-bis (3-etylbenzothiazoline-6-sulfonic acid) free radicals, but the antioxidant activity rose in seeds submitted to recovery after stress. Positive correlation was therefore demonstrated between the total content of phenolic acids in germinating grapevine seeds and the reducing power of extracts obtained from these seeds and their free radical scavenging activity. The results suggest that osmotic stress inhibits the activity of antioxidizing enzymes in germinating grapevine seeds. Thus, the antioxidative defence system is largely blocked under osmotic stress. It seems that a very high oxidoreductive potential in grapevine tissues prior to occurrence of osmotic stress is essential for maintaining proper homeostasis of oxidation and reduction reactions

Extracts of Phenolic Compounds from Seeds of Three Wild Grapevines—Comparison of Their Antioxidant Activities and the Content of Phenolic Compounds

Phenolic compounds were extracted from three wild grapevine species: Vitis californica, V. riparia and V. amurensis seeds using 80% methanol or 80% acetone. The total content of phenolic compounds was determined utilizing the Folin-Ciocalteu’s phenol reagent while the content of tannins was assayed with the vanillin and BSA precipitation methods. Additionally, the DPPH free radical scavenging activity and the reduction power of the extracts were measured. The RP-HPLC method was applied to identify the phenolic compounds in the extracts, such as phenolic acids and catechins. The seeds contained large amounts of tannins, catechins and gallic acid and observable quantities of p-coumaric acid. The total content of phenolic compounds and tannins was similar in the extracts from V. californica and V. riparia seeds. However, the total content of total phenolic compounds and tannins in the extracts from V. californica and V. riperia seeds were about two-fold higher than that in the extracts from V. amurensis seeds. Extracts from seeds of the American species (V. californica and V. riparia) contained similarly high concentrations of tannins, whereas extracts from seeds of V. amurensis had approximately half that amount of these compounds. The content of catechin and epicatechin was similar in all extracts. The highest DPPH• anti-radical scavenging activity was observed in the acetonic and methanolic extracts of V. californica and V. riparia seeds— while the acetonic extract from the V. californica seeds was the strongest reducing agent

Fractionation of Buckwheat Seed Phenolics and Analysis of Their Antioxidant Activity

Five fractions of phenolic compounds were obtained from the extract of common buckwheat seed (Fagopyrum esculentum Moench) using Sephadex LH-20 column chromatography with methanol as a mobile phase. The total phenolics content ranged from 19.8±1.5 (fraction I) to 164±2.2 mg (+)-catechin eq/g (fraction IV). The profiles of phenolic acids and flavonoids in the fractions were analysed using RP-HPLC-DAD. The antioxidant activity was tested as ABTS⋅+ and DPPH⋅ scavenging activity and capability to reduce the Fe(III)/2,4,6-Tris(2-pyridyl)-s-triazine complex to the ferrous form. Results were expressed as Trolox equivalent antioxidant capacity (TEAC), IC50 and ferric reducing antioxidant power (FRAP) values, respectively. The highest antioxidant activity was noted for fraction IV that was predominated by flavones. TEAC, IC50 and FRAP values were: 1.47±0.01 mmol Trolox eq/g, 0.058±0.003 mg/assay and 2.18±0.05 mmol Fe(II)/g, respectively. Rutin constituted 77.7% of the compounds identified in fraction III. The antiradical activity and reducing capability of this fraction were lower compared to fraction IV, but significantly higher than in fractions I and II. The main phenolic compounds of fractions I and II were phenolic acids (caffeic, 5-O-caffeoylquinic and p-coumaric). The antioxidant activity of fraction V was similar to that of fraction III