Antioxidant Activity of Selected Phenolic Acids-Ferric Reducing Antioxidant Power Assay and QSAR Analysis of the Structural Features.

Phenolic acids are naturally occurring compounds that are known for their antioxidant and antiradical activity. We present experimental and theoretical studies on the antioxidant potential of the set of 22 phenolic acids with different models of hydroxylation and methoxylation of aromatic rings. Ferric reducing antioxidant power assay was used to evaluate this property. 2,3-dihydroxybenzoic acid was found to be the strongest antioxidant, while mono hydroxylated and methoxylated structures had the lowest activities. A comprehensive structure-activity investigation with density functional theory methods elucidated the influence of compounds topology, resonance stabilization, and intramolecular hydrogen bonding on the exhibited activity. The key factor was found to be a presence of two or more hydroxyl groups being located in ortho or para position to each other. Finally, the quantitative structure-activity relationship approach was used to build a multiple linear regression model describing the dependence of antioxidant activity on structure of compounds, using features exclusively related to their topology. Coefficients of determination for training set and for the test set equaled 0.9918 and 0.9993 respectively, and Q2 value for leave-one-out was 0.9716. In addition, the presented model was used to predict activities of phenolic acids that haven't been tested here experimentally.

High Antimicrobial Efficacy, Antioxidant Activity, and a Novel Approach to Phytochemical Analysis of Bioactive Polyphenols in Extracts from Leaves of Pyrus communis and Pyrus pyrifolia Collected During One Vegetative Season.

Dried leaf samples of Pyrus communis L. var. 'Conference' and Pyrus pyrifolia Burm. f. (Nakai) var. 'Shinseiki' were subjected to the successful extraction procedures using various solvents, followed by filtering and/or drying liquid plant preparations under reduced pressure. As a result of this, for each Pyrus leaf sample examined, four dried residues were obtained, including methanolic (EA), ethyl acetate (EC), water (EB), and the residue obtained from aqueous solution (ED). Antiradical activity of these preparations was measured using the ABTS+• assay, and antimicrobial activity was examined using various strains of bacteria and yeasts. The highest antiradical activity was observed for EC from leaves of P. communis var. 'Conference' collected in May, but the highest average antibacterial activity was noted for EC residues from P. pyrifolia var. 'Shinseiki' collected in May. Antibacterial activity positively correlated with concentration of hydroquinone in extracts. No antifungal activity was observed for any extract. In addition, qualitative and quantitative analyses of active polyphenolic components in extracts from Pyrus were performed. Hydroquinone and hydroxycinnamic acid derivatives were analyzed using a new optimized method comprising reversed-phase high-performance liquid chromatography (RP-LC) coupled with simultaneous photodiode-array and fluorescence detection.

Profile of Polyphenolic and Essential Oil Composition of Polish Propolis, Black Poplar and Aspens Buds.

In this work, we studied similarities and differences between 70% ethanol in water extract (70EE) and essential oils (EOs) obtained from propolis, black poplars (Populus nigra L.) and aspens (P. tremula L.) to ascertain which of these is a better indicator of the plant species used by bees to collect propolis precursors. Composition of 70EE was analyzed by UPLC-PDA-MS, while GC-MS was used to research the EOs. Principal component analyses (PCA) and calculations of Spearman's coefficient rank were used for statistical analysis. Statistical analysis exhibited correlation between chemical compositions of propolis and Populus buds' 70EE. In the case of EOs, results were less clear. Compositions of black poplars, aspens EOs and propolises have shown more variability than 70EE. Different factors such as higher instability of EOs compared to 70EE, different degradation pattern of benzyl esters to benzoic acid, differences in plant metabolism and bees' preferences may be responsible for these phenomena. Our research has therefore shown that 70EE of propolis reflected the composition of P. nigra or complex aspen⁻black poplar origin.

Analysis of Polyphenolic Compounds in Extracts from Leaves of Some Malus domestica Cultivars: Antiradical and Antimicrobial Analysis of These Extracts.

In this study, methanol, ethyl acetate, water extracts, and precipitate were obtained from leaves of Malus domestica cultivars: Golden delicious, Jonagold, Elstar, Ligol, and Mutsu. Antiradical activity of these extracts was measured using the ABTS+∙ radical, and antimicrobial activity was measured with the disk-diffusion method. Phenolic compounds were measured with the colorimetric method and identified with high performance liquid chromatography (HPLC). The highest antiradical activity was observed for the Jonagold variety, and in particular strong activity was noted for ethyl acetate extracts. Antimicrobial activity was observed against strains of Staphylococcus aureus, Enterococcus faecalis, and the fungus Candida glabrata. Particularly susceptible to the extracts activity appeared to be Staphylococcus aureus, but the growth of Candida glabrata was inhibited in the presence of ethyl acetate extracts. With the HPLC method we identified a high amount of phloridzin (above 500 mg per g of ethyl acetate extracts), lower amounts of hyperoside, isoquercitrin, and quercitrin, and traces of p-hydroxybenzoic and chlorogenic acids. The contribution of phloridzin to antiradical activity of methanol and ethyl acetate extracts was very high (above 90%). In water extract the contribution of phloridzin was between 38.9 and 55.2%, chlorogenic acid 22.7 and 36.1%, and hyperoside 12.2 and 13.3%.