Zbigniew Sroka

Hydrogen peroxide scavenging, antioxidant and anti-radical activity of some phenolic acids

Some water-soluble phenolic acids were investigated as antioxidants, scavengers of hydrogen peroxide (H(2)O(2)) and scavengers of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(*)). The strongest antioxidant, scavenging of H(2)O(2) and DPPH(*) radical activity was exhibited by 3,4,5-trihydroxybenzoic (gallic) acid and 1,2,3-trihydroxybenzene (pyrogallol) with three hydroxyl groups bonded to the aromatic ring in an ortho position in relation to each other. Phenolic acids with two hydroxyl groups bonded to aromatic ring in the ortho position, such as 3,4-dihydroxycinnamic (caffeic), 3,4-dihydroxybenzoic (protocatechuic) and 2,3-dihydroxybenzoic (o-pyrocatechuic) acids, showed strong antioxidant and anti-radical activity; however, it was lower than that of 3,4,5-trihydroxybenzoic acid or 1,2,3-trihydroxybenzene. 3,5-Dihydroxybenzoic (alpha-resorcylic) and 2,4-dihydroxybenzoic (beta-resorcylic) acids with two hydroxyls bonded in the meta position in relation to each other showed moderate antioxidant and low DPPH(*) and hydrogen peroxide scavenging activity. Compounds with one hydroxyl group such as 3-hydroxybenzoic, 4-hydroxyphenylacetic and 2-hydroxybenzoic (salicylic) acids, exhibited the lowest anti-radical and antioxidant activity. The results obtained show that the antioxidant and anti-radical activity of phenolic acids correlated positively with the number of hydroxyl groups bonded to the aromatic ring. The model of an ortho substitution of hydroxyl groups to the aromatic ring seems to be adequate for antioxidant and H(2)O(2) or DPPH(*) scavenging activity of phenolic acids.

Antioxidative and Antiradical Properties of Plant Phenolics

The plant phenolic compounds such as flavonoids, tannins and phenolic acids appeared to be strong antiradical and antioxidant compounds. The number of hydroxy groups and the presence of a 2,3-double bond and orthodiphenolic structure enhance antiradical and antioxidative activity of flavonoids. The glycosylation, blocking the 3-OH group in C-ring, lack of a hydroxy group or the presence of only a methoxy group in B-ring have a decreasing effect on antiradical or antioxidative activity of these compounds. Tannins show strong antioxidative properties. Some tannins in red wine or gallate esters were proved to have antioxidative effect in vivo. The number of hydroxy groups connected with the aromatic ring, in ortho or para position relative to each other, enhance antioxidative and antiradical activity of phenolic acids. The substitution of a methoxy group in ortho position to the OH in monophenols seems to favour the antioxidative activity of the former.

The antiradical activity of some selected flavones and flavonols. Experimental and quantum mechanical study

The aim of the study was to examine the antiradical and antioxidant activity of some flavones and flavonols with different models of hydroxylation and methoxylation. Antiradical activity was measured using ABTS and DPPH radicals and ferric ions (FRAP test). The reduction potential of the compounds was also investigated by determination of minimal hydrogen abstraction energy for each of the hydroxyl hydrogens of all compounds using quantum chemistry methods. Quercetin appeared to be a strong antioxidant when the FRAP test was performed and the strongest for ABTS and DPPH tests whereas genkwanin was the weakest antioxidant for three tests (FRAP, ABTS, and DPPH). Flavonols appeared to have much stronger antiradical activity than flavones. An exception was luteolin, which belongs to flavones but exhibited antiradical activity comparable to that of flavonols, probably due to the presence of a hydroxyl group in the B ring at the 3′ position next to another hydroxyl group at position 4′. The study using UB3LYP/6-31G(d,p) model chemistry of density functional theory (DFT) showed the lowest hydrogen abstraction energy (HAE) for the hydroxyl group situated at 3′ or 5′ of myricetin. Based on the experimental results and computational studies, we conclude that the hydroxyl group situated at 4′ in the B ring in flavonoids, and to a lesser at the 3′ and 3 position in flavonols is the most important for antioxidant activity of flavonoids. We observe strong negative Spearman’s rank order correlations between minimal HAE and antiradical activity of flavonoids in all three tests and double-tailed rejection P values are less than 0.001.

Antiradical and anti-H2O2 properties of polyphenolic compounds from an aqueous peppermint extract.

Polyphenolic compounds such as eriocitrin, luteolin-7-O-rutinoside, diosmin, hesperidin, narirutin, isorhoifolin, rosmarinic and caffeic acids were identified in an aqueous extract (Ex) obtained from peppermint leaves (Menthae × piperitae folium). The content of polyphenols in Ex was as follows: eriocitrin 38%, luteolin-7-O-rutinoside 3.5%, hesperidin 2.9%, diosmin 0.8%, isorhoifolin 0.6%, narirutin 0.3%, rosmarinic acid 3.7% and caffeic acid 0.05%. The strongest antiradical activity (determined as DPPH• scavenging features) was observed for luteolin-7-O-rutinoside, eriocitrin and rosmarinic acid. Caffeic acid and hesperidin revealed a lower antiradical activity while isorhoifolin, narirutin and diosmin showed the lowest activity. The strongest anti-H2O2 activity was observed for eriocitrin, a little lower for rosmarinic acid. The rate of hydrogen peroxide scavenging activity displayed by luteolin-7-O-rutinoside and caffeic acid was lower than that of rosmarinic acids. Hesperidin appeared to be a very weak scavenger of hydrogen peroxide. Almost no anti-H2O2 activity was demonstrated for diosmin, narirutin and isorhoifolin. Among examined flavonoids, the strongest antiradical and anti-H2O2 activity was shown for compounds with two hydroxy groups bound to the Bring in ortho position in relation to each other. Replacement of one hydroxy group in the Bring with a methoxy group or removing one hydroxy group leads to decrease of antiradical and anti-H2O2 activity of flavonoids. Our results suggest that eriocitrin is a powerful peppermint antioxidant and a free radical scavenger.

Antioxidant activity of selected phenols estimated by ABTS and FRAP methods.

INTRODUCTION Phenols are the most abundant compounds in nature. They are strong antioxidants. Too high level of free radicals leads to cell and tissue damage, which may cause asthma, Alzheimer disease, cancers, etc. Taking phenolics with the diet as supplements or natural medicines is important for homeostasis of the organism. MATERIALS AND METHODS The ten most popular water soluble phenols were chosen for the experiment to investigate their antioxidant properties using ABTS radical scavenging capacity assay and ferric reducing antioxidant potential (FRAP) assay. RESULTS AND DISCUSSION Antioxidant properties of selected phenols in the ABTS test expressed as IC50 ranged from 4.332 μM to 852.713 μM (for gallic acid and 4- hydroxyphenylacetic acid respectively). Antioxidant properties in the FRAP test are expressed as μmol Fe2+/ml. All examined phenols reduced ferric ions at concentration 1.00 x 10-3 mg/ml. Both methods are very useful for determination of antioxidant capacity of water soluble phenols.

The activity of lipase from Rhizopus sp. in native form and after immobilization on hollow-fiber membranes

The activity of immobilized and native lipase and the stability of immobilized enzyme at various temperatures were determined. The highest activity of native enzyme occurred at 30°C and the maximal initial activity of immobilized enzyme was observed at 45° C. The best stability of immobilized enzyme was at 30° C. The activity decreased with 0.8% per 24 h. The hydrolysis of sunflower oil by immobilized and native Rhizopus sp. lipase in the presence of surfactants, proteins and metals was studied. The native enzyme lost activity in the presence of cetylpyridinium bromide, Triton X-100, and sodium dodecyl sulphate (SDS) at concentrations of 0.1, 0.75, and 4 mM, respectively. The immobilized lipase was more resistant to inhibition than the native one. Bovine serum albumin, soybean trypsin inhibitor and ovalbumin had a small influence on the activity of the native lipase. However, BSA inhibited the immobilized enzyme. Cd2+, Zn2+, Hg2+ and Cu2+ inhibited the native enzyme while Cd2+ and Cu2+ strongly inhibited the immobilized one.

Antioxidative effect of extracts from Erodium cicutarium L.

Extracts from Erodium cicutarium L. (EC) and some standard substances present in EC extracts were tested for their antioxidative properties during Fe2+-induced triglyceride oxidation. Hydrophobic fractions such as petroleum ether (PEE), benzene (BE) and chloroform I (ChE I) extracts as well as hydrophilic fractions i.e. water (WE) and ethyl acetate (EAE) showed an antioxidative effect. Among the tested substances vitamin C and some polyphenolic compounds; tannin, (+)-catechin and gallic acid exhibited antioxidative activity, stronger than the one of the mentioned extracts.

Antiradical activity of hydrolyzed and non-hydrolyzed extracts from Helichrysi inflorescentia and its phenolic contents.

A methanol extract was obtained from defatted (petroleum ether) inflorescence of Helichrysum arenarium (L.) Moench (perennial herb native to Middle and Southeast Europe). The extract was evaporated under reduced pressure and the dry residue was dissolved in hot water. The aqueous solution was stored for 6 d at 4 °C and the precipitate discarded. The remaining solution was divided into three aliquots a, b and c. Part a was extracted with ethyl acetate to obtain extract (A), part b was extracted with diethyl ether to obtain extract (B) and part c was subjected to alkaline hydrolysis and then extracted with diethyl ether to obtain extract (C). Extracts (A), (B) and (C) were evaporated under reduced pressure to obtain the dry residues A, B and C which were further investigated for phenolic compound content by TLC and HPLC and for antiradical activity with 2,2-diphenyl- 1-picrylhydrazyl radical (DPPH•) as a substrate. Residue C exhibited stronger antiradical properties than non-hydrolysed residues A and B. HPLC analysis showed a great increase of caffeic acid in residue C. We concluded that the hydrolysis process led to a significant increase of free caffeic acid (strong antioxidant) concentration resulting in increased antiradical activity of residue C.

Antiradical activity and amount of phenolic compounds in extracts obtained from some plant raw materials containing methylxanthine alkaloids

Summary Raw materials containing methylxanthine alkaloids such as yerba mate, guaraná, white and green tea, coffee seeds, chocolate and cacao seed powder and extracts obtained from these raw materials were investigated for their antioxidant features and the amount of phenolic compounds. The level of phenolic compounds was measured with the colorimetric method using Folin-Ciocalteu’s phenol reagent and antioxidant features was determined with the use of DPPH (2,2-diphenyl-1-picrylhydrazyl radical). Amounts of phenolic compounds were presented in percentages per mass of extracts and mass of raw materials. Antiradical potential was shown as the number of TAUDPPH units per mg of extracts and g of raw materials. The highest number of antiradical units TAUDPPH as well as the amount of phenolic compounds was calculated for white tea and its extracts and lowest for chocolate. The correlation coefficient between the content of phenolics and antiradical features of raw materials is equal to r=0.994.

The antiradical activity of some plant raw materials and extracts obtained from these raw materials.

INTRODUCTION Free radicals and reactive oxygen species are compounds usually present in healthy organisms as natural products of many metabolic pathways, and they are important in cell signaling and homeostasis. As a source of reactive oxygen species one can mention phagocytic cells and enzymes such as xanthine oxidase. Sometimes the level of reactive oxygen species strongly increases. This may lead to damage of very important cell structures such as nucleic acids, proteins or lipids. In this situation one should provide the organism with powerful antioxidants as a medicine or in the diet. A rich source of strong antioxidants such as phenolic compounds is plant raw materials, which are the subject of our study. MATERIAL/METHODS Antiradical potential of extracts was measured with DPPH radical (2,2-diphenyl-1-picrylhydrazyl) and was expressed as the number of units per mg of extracts (TAU(515/mg)) and per g of raw material (TAU(515/g)). The amount of phenolic compounds was determined colorimetrically using Folin-Ciocalteu phenol reagent (3H₂O • P₂O5 • 13WO₃ • 5MoO₃ • 10H₂O). RESULTS The strongest antiradical activity was noted for extracts obtained from Cinnamomi cortex; the number of antiradical units per mg of extract (TAU(515/mg)) was 10.31±1.052. The lowest antiradical features were exhibited by extract from Zingiberis rhizoma (0.28±0.174) and extract from Cichorii radix (0.38±0.669). The highest amount of phenolic compounds was measured for extracts from Bistortae rhizoma, with a value (in percentage) of 78.6±13.5. The correlation coefficient between the number of antiradical units in extracts and amount of phenolic compounds in these extracts was 0.7273. When the number of antiradical units was calculated per g of raw material (TAU(515/g)) the strongest antiradical properties were noted for Bistortae rhizoma (1406±274.9), the weakest for Cichorii radix (122±158.3).