Phenolic antioxidants – radical‐scavenging and chain‐breaking activity: A comparative study

Fifty phenolic antioxidants (AH) (42 individual compounds and 8 binary mixtures of two antioxidants) were chosen for a comparative analysis of their radical‐scavenging (H‐donating) and chain‐breaking (antioxidant) activity. Correlations between experimental (antiradical and antioxidant) and predictable (theoretical) activities of 15 flavonoids, 15 hydroxy cinnamic acid derivatives, 5 hydroxy chalcones, 4 dihydroxy coumarins and 3 standard antioxidants (butylated hydroxytoluene, hydroquinone, DL ‐α‐tocopherol) were summarized and discussed. The following models were applied to explain the structure‐activity relationships of phenolic antioxidants of natural origin: (a) model 1, a DPPH assay used for the determination of the radical‐scavenging capacity (AH + DPPH? → A? + DPPH‐H); (b) model 2, chemiluminescence of a model substrate RH (cumene or diphenylmethane) used for the determination of the rate constant of a reaction with model peroxyl radicals (AH + RO₂? → ROOH + A?); (c) model 3, lipid autoxidation used for the determination of the chain‐breaking antioxidant efficiency and reactivity (AH + LO₂? → LOOH + A?; A? + LH (+O₂) → AH + LO₂?); and (d) model 4, theoretical methods used for predicting the activity (predictable activity). The highest lipid oxidation stability was found for antioxidants with a catecholic structure and for their binary mixtures with DL ‐α‐tocopherol, as a result of synergism between them.     

Stability and radical‐scavenging activity of heated olive oil and other vegetable oils

The effect of heating at 180 °C on the antioxidant activity of virgin olive oil (VOO), refined olive oil (ROO) and other vegetable oil samples (sunflower, soybean, cottonseed oils, and a commercial blend specially produced for frying) was determined by measuring the radical‐scavenging activity (RSA) toward 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH^?). The RSA of the soluble (polar) and insoluble (non‐polar) in methanol/water fractions of olive oil samples was also measured. The stability of heated oils was assessed by determining their total polar compound (TPC) content. VOO was the most thermostable oil. Total polar phenol content and the RSA of VOO heated for 2.5 h decreased by up to 70 and 78%, respectively, of their initial values; an up to 84% reduction in RSA of VOO polar and non‐polar fractions also occurred. Similar changes were observed in the RSA of ROO and its non‐polar fraction after 2.5 h of heating. The other oils retained their RSA to a relatively high extent (up to 40%) after 10 h of heating, but in the meantime they reached the rejection point (25–27% TPC). The results demonstrate that VOO has a remarkable thermal stability, but when a healthful effect is expected from the presence of phenolic compounds, heating has to be restricted as much as possible.     

Antioxidant activity of pilot‐plant alcoholic and supercritical carbon dioxide extracts of thyme

Leaves and flowering tops of thyme (Thymus vulgaris L.) were extracted with ethyl alcohol and supercritical carbon dioxide. Antioxidant activity was measured in sunflower oil at 0.3, 0.6 and 1% concentrations of extracts by oven test and Rancimat method. The activities of extracts were compared to those of butylated hydroxytoluene at 0.01 and 0.1% level. The ethanolic extract showed a slightly higher antioxidative effect than that obtained by supercritical fluid extraction. The effectiveness of both extracts added at 0.6% level were equal to that of 0.1% of butylated hydroxytoluene.     

Antioxidant efficiency of oregano in frying and storage of fried products

The effect of oregano on the oxidative stability of cottonseed oil during frying of potato chips and on the storage stability of the products was studied. The ground spice or an ethanol‐derived extract was added to the oil before frying. The results showed that both additives decreased the rates of accumulation of conjugated dienes, polar compounds, polymerized triacylglycerols, dimeric triacylglycerols and the p‐anisidine value of the frying oil, while the hydrolytic compounds were not affected. The major decrease was observed in the accumulation of polymerized and dimeric triacylglycerols. The storage stability of the produced chips was estimated by the rate of increase of the peroxide value and of the conjugated dienes in the oil absorbed by them. Both rates were depressed when oregano was added to the frying oil, with the protective action of oregano extract being considerably greater than that of ground oregano. The protective action of oregano extracts obtained by successive extractions with petroleum ether (PE), diethyl ether (EE) and ethanol (EtOH) and added to the chips after frying was also examined. The results showed that the EE and EtOH extracts were very effective against oxidative deterioration.     

Antioxidant activity of blackcurrant seeds extract and rosemary extracts in soybean oil

The objective of this research was to investigate the antioxidative properties of extract from blackcurrant seeds (BCSs) and commercially available rosemary extracts (Stabiloton OS, oil‐soluble and WS, water soluble) in soybean oil (SO). The antioxidant activity of plant extracts was compared with those of α‐tocopherol and butylated hydroxytoluene (BHT). The results of present research reveal differentiation of action of investigated extracts toward primary (peroxide value (PV), conjugated dienes (CDs)) and secondary (measured as anisidine value (AV), hexanal) oxidation products in SO. WS and OS rosemary extracts show high efficiency in delaying primary and secondary oxidative changes. BCSs extract markedly retards oxidation, nevertheless its activity falls down with formation and succeeding deterioration of primary products. Although the use of BCSs, residues of fruit processing, as a source of antioxidants would be reasonable because of economic and environmental reasons, it may be limited by low activity toward secondary oxidation products in certain lipid substrates. Taking primary oxidative changes into consideration, all extracts studied perform better than used standard antioxidants – BHT and α‐tocopherol.     

Antioxidant activity of methanolic extracts of peanut hulls from various cultivars

The antioxidant activities of methanolic extracts of peanut hulls (MEPH) from various cultivars (Spanish, Valencia, Runner, and Virginia) were investigated. The luteolin content in MEPH for Spanish, Valencia, Runner, and Virginia was 3.16, 2.47, 0.95, and 0.75 mg/g of hulls, and the total phenolic content was 10.2, 10.1, 6.6, and 4.2 mg/g of hulls, respectively. MEPH from various cultivars showed similar and strong antioxidant activity as a result of a high content of total phenolic compounds. Based on these results, the hulls of Spanish cultivar were selected as the best antioxidant material among the four cultivars because of the cultivar’s highest content in both luteolin and total phenolic compounds.     

Antioxidant activity of grape extracts in a lecithin liposome system

Extracts of 14 different grapes were tested for their antioxidant activities in a copper-catalyzed lecithin liposome oxidation assay and analyzed for their phenolic components by high-performance liquid chromatography (HPLC). The total phenolic contents of the grape extracts varied from 176 to 1236 mg gallic acid equivalents (GAE)/L. Extracts of red wine grape varieties contained higher concentrations of phenolics than other varieties. When compared at the same 20 μM GAE basis, the grape extracts inhibited formation of conjugated diene hydroperoxides by 25.1 to 67.9%, and hexanal formation by 49.3 to 97.8%. Extracts of red table grape varieties Red Globe and Emperor and white wine grape varieties Chardonnay and Sauvignon Blanc gave the highest antioxidant activities. The relative percentage inhibition of conjugated dienes and hexanal correlated with total phenols (r=0.86 and 0.89). HPLC analyses showed that anthocyanins were the most abundant phenolic compounds in extracts of red grapes, and flavonols were most abundant in extracts of white grapes.     

Antioxidant activity of some plant extracts of the family labiatae

The antioxidant activities of methanol extracts of oregano, dittany, thyme, marjoram, spearmint, lavender and basil were tested in lard stored at 75°C. The concentration of extracts in lard varied from 0.01 to 0.20%. Oregano extract was found to be the most effective in stabilizing lard, followed by thyme, dittany, marjoram and lavender extracts, in a decreasing order. The induction period of lard increased with antioxidant concentration. After the induction period, peroxide formation proceeded rapidly, following pseudo-zero order reaction kinetics. The rate of the reaction decreased slightly with increasing plant extract concentration. Combined addition of plant extracts in lard showed a low synergistic action between thyme extract and spearmint extract.     

Correlation between physicochemical analysis and radical‐scavenging activity of vegetable oil blends as affected by frying of French fries

The main goal of the present work was to compare and correlate the results of physicochemical parameters and antiradical performance of some oil blends during deep‐frying, which will be an initial indicator for applying antiradical tests for monitoring deep‐frying oils. Two oil blends were prepared. The first blend was a mixture (1 : 1, wt/wt) of sunflower seed oil and palm olein (SO/PO) and the second was a mixture (1 : 1, wt/wt) of cottonseed oil and palm olein (CO/PO). The oil blends were evaluated during intermittent frying of French fries on two consecutive days for 16 h, with oil replenishing after 8 h. Changes in the fatty acid profile and some physicochemical parameters (peroxide value, color index, viscosity, total polar compounds and UV absorbance at 232 and 270 nm) were used to evaluate the alterations during frying. A quick spectrophotometric method was developed to assess deep‐frying oil quality. With the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) method, the neutralization of the stable radical DPPH by antioxidants present in the oil during frying was measured. Radical‐scavenging activity (RSA) of both oil blends was recorded during frying, wherein the results showed that the SO/PO blend had the highest RSA. It was evident from the results that a proportional correlation and positive relationship existed between the levels of fatty acids and the physicochemical characteristics of the vegetable oil blends and their RSA. The initial results obtained allow us to suggest that antiradical measurements could be used to quantify the oxidative and hydrolytic deterioration of vegetable oils upon frying.     

Antioxidant activity in soybean oil of extracts from thompson grape bagasse

The phenolic compounds of Thompson grape bagasse were extracted using a 95:5 (vol/vol) ethanol/water mixture. Measurement of the antioxidant activity in refined soybean oil of bagasse grape extract was performed by using two different methods, the Rancimat method and the Schaal oven method in conjunction with peroxide value determination. The antioxidant activity of the extract was compared to the tertiary butyl hydroquinone (TBHQ) and butylated hydroxyanisole (BHA) activity. The bagasse grape extract showed similar antioxidant activities in both methods employed. At all concentrations tested [0.1, 0.3 and 0.5% of total phenols (TP)] the extract exhibited appreciable activity, which exceeded the activity of BHA. At some concentrations (0.3 and 0.5% TP) the extract exhibited activity comparable to that of TBHQ. Bagasse is a byproduct with a high content of phenolic compounds and is a good source of natural antioxidants.     

Antioxidant activity of extracts from six different Sudanese plant materials

Methanolic extracts obtained by manual solvent extraction (MSE) and accelerated solvent extraction (ASE) of different Sudanese plant materials (Sclerocarya birrea leaves, Salvadora persica bark and leaves, Combretum hartmannianum leaves, Guiera senegalensis leaves and roots) were investigated for their antioxidant activity. There was no significant difference between the two extraction methods (p < 0.01) regarding the total amount of phenolic compounds expressed as gallic acid equivalents (GAE) (52.6–166.7 mg GAE/g total extractable compounds for MSE and 53.1–169.3 mg GAE/g for ASE). In comparison to a control without extract, the extracts were remarkably effective in the β‐carotene bleaching method, whereas the effectiveness was half or less in comparison to Trolox as standard antioxidant. Also using the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) method antioxidant activity could be shown in comparison to a control, however, the extracts were less effective than Trolox. No significant difference was found between the two extraction methods. The increase of the peroxide value of sunflower oil during storage at 70°C was markedly lower after addition of the extracts in comparison to the control, but in the Rancimat test (120°C) the extracts showed only a small stabilization factor (F = 0.9–1.4) especially in comparison to Trolox (F = 5.8).     

Free radical scavenging capacity as related to antioxidant activity and ginsenoside composition of Asian and North American ginseng extracts

Different Panax species derived from Asia (Panax ginseng C.A. Meyer) and North America (Panax quinquefolium L.) were extracted by methanol and evaluated for relative ginsenoside composition and antioxidant activities. Ginseng root contained a greater proportion of total ginsenoside compared to ginseng hair analyzed by high-performance liquid chromatography. North American ginseng root was characterized with undetectable ginsenoside Rf and greater Rb₁/Rb₂ than Asian ginseng root. Panax quinquefolium exhibited a relatively higher (P<0.05) affinity to scavenge free radical than panax ginseng using the 2,2-azobis (3-ethylbenzothine-6-thine-6-surfonic acid) radical model. In a bilayer lamella suspension oxidation model induced by peroxyl radicals, ginseng samples exhibited notable antioxidant activity. Specifically, however, the P. quinquefolium extracts delayed lipid peroxidation longer (P<0.05) than the P. ginseng extracts. Ginseng extracts from both Panax species protected human low-density lipoprotein against cupric ion-mediated oxidation. Similar protection was observed against peroxyl radical-induced supercoiled DNA breakage. A pure ginsenoside standard (e.g., Rb₁) produced similar results. The antioxidant activities of different ginseng species and specific plant parts include free radical scavenging and may be related to ginsenoside Rb₁/Rb₂ content.     

花椰菜中异硫氰酸酯提取物抗氧化活性研究(英文)

Isothiocyanates(ITCs) extracts were prepared from fresh broccoli.Their antioxidant properties were evaluated by using the in vitro bioassays,including superoxide anion radical( 2 O·-) ,hydroxyl radical(HO·-) and 2,2-diphenyl-1-picrylhydracyl(DPPH·) radical-scavenging methods,lipid peroxidation assay,and reducing power assay.The ITCs extracts exhibited significant dose-dependent antioxidant activities(P0.01) .Its antioxidant-stability was affected by temperature and storage condition,although it was more stable than vitamin C(Vc) .GC-MS iden-tified sulforaphane in the ITCs extracts.The antioxidant activity of sulforaphane was approximately one tenth to one fifth of that of Vc.Sulforaphane was experimented to be one of dominating contributors to antioxidant capacity of ITCs extracts.However,there was no direct antioxidant activity found for benzyl isothiocyanate(BITC) in vitro. Therefore,it could be concluded that the general group(-N=C=S) was not the essential part for the antioxidant activity of sulforaphane.It is suggested that the ITCs extracts from broccoli can be developed into a promising food additive for healthy food.     

New Insights into the Anti‐Inflammatory and Antioxidant Properties of Nitrated Phospholipids

Nitro‐fatty acids (NO₂‐FA) have been widely studied with regard to their identification, structural characterization, and biological actions. NO₂‐FA could also be present endogenously esterified to phospholipids (PL), and NO₂‐PL were already detected in cardiac mitochondria from diabetic rats and cardiomyoblasts subjected to starvation. However, the biological actions of NO₂‐PL have been overlooked. In this study, we evaluate the antioxidant and anti‐inflammatory potential of the nitrated 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC) formed in vitro by incubation with NO₂BF₄, in a well‐recognized mimetic model of nitroxidative stress. Nitrated POPC showed anti‐radical ability to reduce both 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH^?) (IC₂₀ = 225 ± 4 μg/mL; Trolox equivalent (TE) = 86 ± 6 μmol Trolox/g lipid) and 2,2′‐azino‐bis‐3‐ethylbenzothiazoline‐6‐sulfonic acid radical cation (ABTS^?+) (IC₅₀ = 124 ± 2 μg/mL; TE = 152 ± 9 μmol Trolox/g lipid). Also, higher lag times were achieved in oxygen radical absorbance capacity (ORAC) assay for nitrated POPC, indicating a faster reaction with oxygen‐derived radicals (TE = 1.03 ± 0.22 and TE = 1.30 ± 0.16 mmol Trolox/g lipid for nonmodified and nitrated POPC, respectively). Nitrated POPC showed the ability to inhibit lipid oxidation induced by the hydroxyl radical generated under Fenton reaction conditions, monitored by electrospray ionization (ESI) mass spectrometry (MS) using phosphatidylcholine (PtdCho) liposomes as a model of cell membrane. Nitrated POPC showed anti‐inflammatory potential, as assessed by the inhibition of inducible nitric oxide synthase (iNOS) expression in RAW 264.7 macrophages activated by the Toll‐like receptor 4 (TLR4) agonist lipopolysaccharide (LPS) in a well‐described in vitro model of inflammation. Altogether, this study provides new clues regarding the antioxidant and anti‐inflammatory potential of nitrated POPC, which should be explored in depth.     

Effect of Chain Length on the Micellization,Antibacterial, DPPC Interaction and Antioxidant Activities of l‐3,4‐Dihydroxyphenylalanine (l‐DOPA) Esters

l ‐DOPA (l ‐3,4‐dihydroxyphenylalanine) has been widely used as a drug in the clinical treatment of Parkinson's disease. In this report, the systematic study of the effect of chain length on the critical micelle concentration (CMC), antibacterial and antioxidant activity of esters derived from the aromatic amino acid l ‐3,4‐dihydroxyphenylalanine as surfactants are accounted for the first time. The antibacterial activity displayed a cut‐off effect at C₁₂ with respect to both gram positive and gram negative bacteria (except for Pseudomonas aeruginosa where the cut‐off was displayed at C₁₀). Correlation of the CMC with the minimum inhibitory concentration (MIC) shows that the DOPA esters exist in micellar form at the MIC. An increase in chain length of the DOPA esters induces greater binding with phospholipid vesicles 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine. The C₁₂ ester possessed highest radical scavenging ability among the esters tested against both 2,2‐diphenyl‐1‐picrylhydrazyl and 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid) showing that antioxidant activity of the DOPA esters is also affected by chain length. This study showed that DOPA esters are promising candidates as antibacterial agents as well as good antioxidants.     

Antioxidant activity of extracts of defatted seeds of niger (<Emphasis Type="Italic">Guizotia abyssinica</Emphasis>)

Niger (Guizotia abyssinica) seed was ground and then defatted with hexane. The meal remaining after oil extraction was tested as a source of antioxidants. Three solvent systems, A [80∶20 (vol/vol) ethanol/water], B [80∶20 (vol/vol) acetone/water], and C (water) were evaluated as extraction media. Crude extracts were examined for their antioxidant activity in a β-carotene-linoleate and a meat model system. Extract A exhibited superior antioxidant activity, compared to extracts B and C, and its composition was studied further by using column chromatography and HPLC. Four fractions (I–IV) were obtained, of which fractions III and IV showed activity in the β-carotene-linoleate model system. Fraction IV was also highly effective in scavenging the 2,2-diphenyl-1-picrylhydrazyl radical but was less active when used in a bulk oil model system. Preparative TLC showed fraction IV as consisting of two components. UV spectroscopy suggested that the major active component pressent was a chlorogenic acid-related compound. Furthermore, HPLC analysis established that chlorogenic acid was dominant in the free phenolics fraction (2.6 mg/g). Upon hydrolysis, however, a substantial amount of caffeic acid (42.8 mg/g) was released, presumably from esterified and glycosylated chlorogenic acid. Thus, niger extracts derive their antioxidant activity, at least in part, from the chlorogenic acid-related compounds.     

Antioxidant activity in leaves of some mediterranean plants

Hexane and methanol leaf extracts of sixteen Mediterranean plant species were obtained by percolation. Higher yields were observed for methanol (16.4–47.8%) than for hexane extracts (1.3–13%). Antioxidant activity of these extracts was determined by a rapid spectrophotometric method involving the combined oxidation of beta-carotene and linoleic acid. Leaf extracts were thus characterized by an Antioxidant Activity Coefficient (AAC) ranging from 0 to 1000. Hexane extracts gave much higher AAC values than the corresponding methanol extracts. In both cases, myrtle (Myrtus communis) showed the best antioxidant effectiveness.