Synergistic Antioxidant Activity Research Articles

Antioxidant/pro-oxidant properties of model phenolic compounds. Part II: Studies on mixtures of polyphenols at different molar ratios by chemiluminescence and LC–MS

Abstract The behaviour of four known antioxidants (quercetin, ascorbic acid, catechin and caffeic acid) and their mixtures at different molar ratios was studied in view of elaborating predictions over an eventual pro-oxidant or synergistic antioxidant activity. The Co(II)–EDTA luminol chemiluminescence showed that the mixture of quercetin and ascorbic acid at ratio 2:1 had the most pronounced antioxidant activity, while that of quercetin and caffeic acid at ratio 1:2 showed the least antioxidant activity, which may be interpreted as a strong propensity for pro-oxidant behaviour. The LC–MS analysis for the two mixtures revealed a significant amount of unoxidised quercetin in the case of quercetin with ascorbic acid, whereas in the case of quercetin with caffeic acid this amount was negligible. This observation supports the fact that the first combination was more antioxidant than the second, through efficient quercetin recycling (reduction of the quinone by ascorbic acid; redox cycling of quinones).

Comparison of antioxidant activity of compounds isolated from guava leaves and a stability study of the most active compound

In the present study, quercetin (QT), morin (MR), and quercetin-3-O-glucopyranoside (QG) isolated from guava leaves were comparatively tested for antioxidant activity using DPPH, ABTS, and FRAP methods. QT was the most active among them. The free radical scavenging activity of QT was approximately four times higher than MR and two times higher than QG. The reducing power of QT was eight times higher than MR and two times higher than QG. A mixture of QT with MR or QG showed interesting combination effect. The synergistic antioxidant activity was obtained when QT was mixed with MR whereas the antagonistic effect was found when mixed with QG. The stability study of QT in liquid preparations indicated that the decomposition reaction rate of QT could be explained by a kinetic model assuming a first-order chemical reaction. The aqueous solution of QT was rapidly decomposed with t1/2 of approximately five days whereas QT entrapped in chitosan nanoparticles was five times longer. It was concluded that QT was the most active antioxidant from guava leaves. Entrapment of QT in chitosan nanoparticles could significantly enhance its stability.

Stabilization of Emulsion and Butter like Products Containing Essential Fatty Acids Using Kalonji Seeds Extract and Curcuminoids

Owing to the tendency of essential fatty acids (EFAs) to undergo autoxidation, their storage becomes a key problem. Generally, they are stabilized by synthetic antioxidants like TBHQ that are toxic in nature. Recently many studies were reported where these EFAs are stabilized by natural antioxidants. In the present study, curcuminoids and kalonji seeds ethanol extract (KEE) were used to stabilize these EFAs in refined sunflower oil (RSFO), water-in-oil (w/o) emulsion and butter like products (BLPs). In RSFO, though curcuminoids alone exerted pro-oxidant effect, KEE and curcuminoids showed synergistic antioxidant activity that was comparable to TBHQ. KEE exhibited good antioxidant activity in emulsions and BLPs, providing fine physical properties like slipping point, dropping point and spreadability. EFAs increased the nutritional value of BLPs and antioxidants added for their stabilization provided their medicinal benefits.

Porcine Hemoglobin Hydrolysate Prepared with Pepsin: Antioxidant Activities and Their Mechanisms

Different antioxidant assays were employed in order to evaluate antioxidant activities of porcine hemoglobin hydrolysate (PHH) prepared with pepsin and compared with natural and synthetic antioxidants. Molecular weight distributions of PHH polypeptide components were determined. PHH exhibited DPPH/superoxide/hydroxyl radicals scavenging (EC50 0.95 ± 0.01 mg/ml, 20.34 ± 2.83 mg/ml, 7.90 ± 0.58 mg/ml, respectively); reducing power (EC50 3.02 ± 0.91 mg/ml); and metal chelating activity (EC50 2.59 ± 0.05 mg/ml) in a dose-dependent manner. Hydroxyl radicals scavenging activity of PHH was equivalent to ascorbic acid. Relatively less active of PHH exhibited strong synergistic antioxidant activity with α-tocopherol (TOH). Tested combinations (2:1 and 1:1 of PHH:TOH) showed significantly higher antioxidant activities (P < 0.05) compared to combinations with low PHH rates (1:2 and 1:4 of PHH:TOH). The main synergistic antioxidant mechanism could be due to the regeneration of TOH by PHH. Radicals scavenging mechanism, more than metal chelation, could play a major role in the antioxidant process of PHH.

In vitro synergistic anti-oxidant activities of solvent-extracted fractions from Astragalus membranaceus and Glycyrrhiza uralensis

Our study estimated the in vitro anti-oxidant activities of the solvent-extracted fractions from Astragalus membranaceus (AME), Glycyrrhiza uralensis (GU) and the combination of them (AG), using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging assay and ferric reducing anti-oxidant power (FRAP) assay. Different solvent extracts have different anti-oxidant activities. As to the herb pair (AG), the highest anti-oxidant capacity and total phenolic/flavonoid content were observed in the ethyl acetate fraction, which were exhibited in different solvent fractions of the individual herbs. The ethyl acetate extract of herb pair (EA–AG) showed significantly higher anti-oxidant capacity than the theoretical sum of two single herbs, and presented better cytoprotection and induced higher activity of anti-oxidant enzymes than the single herbs. Moreover, there’s a linear correlation between the increment of total phenolics/flavonoids and anti-oxidant capacities, especially between polyphenol content and TEAC values (correlation coefficient = 0.9∗). These indicated that the phenolic and flavonoid may be the main compounds which caused the synergistic anti-oxidant capacity and cytoprotection in the combination of AME and GU.

Synergistic antioxidant activity of green tea with some herbs

Cardiovascular diseases, cancer, arthritis, etc. are caused by free radicals that are byproducts of metabolic pathways. Selected plants namely Vitis vinifera, Phyllanthus emblica L., Punica granatum, Cinnamomum cassia, Ginkgo biloba L., and Camellia sinensis Linn. are reported to produce antioxidant property. This study is undertaken to support the hypothesis that formulation of a polyherbal combination of these plants shows a synergistic effect with green tea. The extracts of each drug were characterized by phytochemical studies and tests for phenolics and flavonoids. In vitro antioxidant activity for individual drug and its combination was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide, and nitric oxide free radical scavenging methods. Our results suggest that a combination of all these herbs with green tea can synergistically enhance antioxidant activity and thus lower doses of each herb with green tea may be used. Antioxidant potential of polyherbal combination was also comparable to that of standard ascorbic acid. Studies showed that selected individual plants contained abundant quantity of phenolics and flavonoids and their polyherbal combination with green tea was found to produce best antioxidant activity among all individual extracts. This will help in avoiding undesirable side effects due to higher doses of single herb.

Synergistic and antagonistic effects on oxidation stability of antioxidants in a synthetic ester based oil

Synergistic and antagonistic effects have been observed with the four sulfur-, phosphorus- and heavy metal-free antioxidants, hindered bis-phenol, octylated diphenylamine, octylated phenyl-alpha-naphthylamine and tolutriazole derivative, on the oxidation stability, thermal and physicochemical properties of dioctyl sebacate oil. The oxidation stability was evaluated using a rotary bomb oxidation tester. The results from isothermal and catalytic RBOT oxidation tests suggested that ODPA has an antagonistic effect on the OIT. The combination of HP:OPANA:TZ exhibited the highest and most synergistic antioxidant activity. Furthermore, synergism was observed in terms of both oxidation and thermal stabilities through thermogravimetric analysis (TGA).

Potential Antioxidant Activity of γ‐Oryzanol in Rice Bran as Determined Using an In Vitro Mouse Lymph Axillary Endothelial Cell Model

ABSTRACTA mouse lymphatic endothelial cell (SVEC4‐10) in vitro model was developed and found to be effective in the study of antioxidant activity of γ‐oryzanol in rice bran. The critical and vital parameters in developing these cell models included the emulsion preparation of hydrophobic compounds, the consistent management of cell culture, and the selection of cell viability detection methods compatible with the cell lines and the test substances. The SVEC4‐10 cell line had a fast metabolism and consequently could be used to determine antioxidant activity of a test substance in a relatively rapid manner. Results showed that γ‐oryzanol, ferulic acid, and α‐tocopherol could interact with cells such that oxidative damage induced by tert‐butyl hydroperoxide on cellular mitochondrial activity lessened, and in some situations, γ‐oryzanol was a more effective antioxidant than α‐tocopherol. The results also suggested different antioxidant mechanisms among γ‐oryzanol, ferulic acid, and α‐tocopherol. The three major components of γ‐oryzanol generally had higher antioxidant activity than γ‐oryzanol, with 24‐methylene cycloartanyl ferulate relatively more effective. Synergistic antioxidant activity among γ‐oryzanol, ferulic acid, and α‐tocopherol was also found.

Synergistic Antioxidant Activities of Eight Traditional Chinese Herb Pairs

Many Chinese therapeutic herbs that are traditionally used in combination demonstrate significantly better pharmacological effects when used in the combination than when used alone. However, the pharmacological mechanism for this synergism is still not well understood. In the present study, the antioxidant activities of six herbs ((Paeonia lactiflora (PL), Atractylodes macrocephala (AMA), Angelica sinensis (AS), Astragalus membranaceus (AME), Glycyrrhiza uralensis (GU) and Rheum officinale (RO)), which were historically combined into eight traditional Chinese herb pairs (TCHPs) (AME-AS, AME-AMA, AME-RO, AME-GU, AME-PL, PL-AS, PL-AMA and PL-GU), were investigated in vitro by assessing the 1,1-diphenyl-2-picryl hydrazine (DPPH)-radical scavenging abilities of the herbs. The results of this study showed that all eight TCHPs had a significantly larger scavenging capacity than would be expected from the theoretical sum of those of the respective constituent herbs (p<0.05). Furthermore, the AME-GU, AME-PL and AME-AMA pairs not only showed a significant synergistic effect in the DPPH scavenging assay, but they also demonstrated similar results in hydroxyl radical and superoxide radical anion scavenging assays. Interestingly, the AME-AMA combination had a significantly higher superoxide anion (0.2 g/ml) and hydroxyl radical scavenging ability than the AME or AMA. The changes in the total phenolic and flavonoid contents were also investigated. Our study showed a significant correlation between the rate of enhancement in antioxidant capacity and the rate of increase in flavonoid content. Thus, the flavonoids are likely responsible for the synergistic effects present in TCHPs.

Synergistic antioxidant and antibacterial activity of rosemary plus butylated derivatives

Abstract Antioxidant and antibacterial activity of a methanol rosemary extract (RE) containing 30% carnosic acid (CA), 16% carnosol (COH) and 5% rosmarinic acid (RA) was studied in vitro alone and in combination with the antioxidant food additives butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). The antioxidant efficiency of the extract, CA, and RA, was determined by a kinetic analysis of the 2,2-diphenyl-2-picrylhydrazyl hydrate radical (DPPH·) scavenging activity. RE showed two different rate slopes in the reduction of DPPH· vs. time curve, which correlated with the distinct behaviours of RA and CA; pure RA reached the plateau more rapidly than CA. A synergistic antioxidant effect between RE and BHT was demonstrated by isobolographic analysis and a synergistic interaction of RE with BHA to inhibit Escherichia coli and Staphylococcus aureus growth was observed. Therefore, rosemary not only enhances the antioxidant efficiency of BHA and BHT, but also the antibacterial effect of BHA; allowing a decrease from 4.4 to17 folds in the amounts of the synthetic compounds used.

Structure−Activity Relationship and Mechanism of the Tocopherol-Regenerating Activity of Resveratrol and Its Analogues

The present study investigated the mechanism of the synergistic antioxidant activity of alpha-tocopherol with resveratrol (3,5,4'-trihydroxy-trans-stilbene, 3,5,4'-THS) and its synthetic analogues, that is, 3,4-dihydroxy-trans-stilbene (3,4-DHS), 4,4'-dihydroxy-trans-stilbene (4,4'-DHS), 4-hydroxy-trans-stilbene (4-HS), and 3,5-dihydroxy-trans-stilbene (3,5-DHS). The reaction kinetics of alpha-tocopheroxyl radical with resveratrol and its analogues were studied in sodium dodecyl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB) micelles using the stopped-flow electron paramagnetic resonance (EPR) technique. It was found that resveratrol and its analogues could regenerate alpha-tocopherol with rate constants (k(REG)) in the order of 3,4-DHS > 4,4'-DHS > resveratrol > or = 4-HS > or = 3,5-DHS in SDS and CTAB micelles. It was found that the analogues bearing o-dihydroxyl groups (3,4-DHS) and p-dihydroxyl groups (4,4'-HS) exhibited remarkably higher alpha-tocopherol-regenerating activity than those bearing no such groups (resveratrol, 4-HS, and 3,5-DHS). In addition, the alpha-tocopherol-regenerating activity of resveratrol and its analogues was correlated with their electrochemical behaviors, suggesting that electron transfer might play a critical role during the regeneration reaction.

Conjugation of gallic acid onto chitosan: An approach for green and water-based antioxidant

A novel derivative of chitosan, chitosan–gallic acid (chitosan–GA), obtained from a simple conjugating condition with gallic acid using carbodiimide is proposed. The conjugation with gallic acid brings the water-solubility or water swelling property to chitosan. The studies on the free radical scavenging of chitosan–GA clarify its significant antioxidant activity on free radicals, i.e. carbon-centered radicals and hydroxyl radicals. Chitosan–GA clearly shows a synergistic antioxidant activity on hydroxyl radical scavenging where iron metals were involved. The work demonstrates how chitosan–GA can be a potential natural-compound-based antioxidant.

Unravelling the Total Antioxidant Capacity of Pinotage Wines: Contribution of Phenolic Compounds

The total antioxidant capacity (TAC) and phenolic composition of 139 Pinotage wines (2002 and 2003 vintages) were determined using the 2,2'-azino-di(3-ethylbenzo-thialozine-sulfonic acid) scavenging assay and high-performance liquid chromatography, respectively. The contribution of individually quantified phenolic compounds to the wine TAC was calculated using their concentrations and Trolox equivalent antioxidant capacity (TEAC) values. The TEAC values of quercetin-3-galactoside, isorhamnetin, and peonidin-3-glucoside are reported for the first time. Between 11 and 24% of the measured TAC of Pinotage wines was explained by the sum of the calculated contributions of their quantified phenolic compounds comprising monomeric phenolic compounds and procyanidin B1. Ultrafiltration was carried out to attempt separation of monomeric and polymeric phenolic compounds. Analysis of ultrafiltration permeates and retentates enabled estimation of the TAC contribution of large molecular weight (MW) unknown compounds (46%) (>50 kDa), including oligomeric and polymeric phenolic compounds and small MW unknown compounds (34%) (<50 kDa). Three mixtures, containing 12 phenolic compounds in typical concentrations expected in Pinotage wines, exhibited 16-23% synergistic antioxidant activity. This suggests that synergy between phenolic compounds does play a role in the wine TAC but that it does not explain the large discrepancy between measured and calculated TAC values.

Synergistic Anti-Oxidative Effects of Lycopene with Other Bioactive Compounds

Lycopene belongs to the carotenoid family, which has more than 700 members. In human serum, only 14 caroteinoids have been identified, and, among these, lycopene was the most abundant. Lycopene is regarded as one of the most efficient singlet oxygen quencher and peroxyl radical scavenger of all the carotenoids and may represent an important defense mechanism in the human body. Singlet oxygen and free radicals can cause biological damage to important macromolecules and membrane constituents, and the presence of natural antioxidants may help to control these degradative reactions.The oxidation of low density lipoproteins (LDL) has been implicated in the development of atherosclerosis which makes the antioxidants that protect LDL potential antiatherogenic agents. There is growing evidence that certain combinations of natural antioxidants have synergistic antioxidant activity, that is, the actual inhibitory activity of the mixture is greater than the additive activities of the individual antioxidants. Lycopene on its own can retard the oxidation of LDL, but in combination with vitamin E, a synergistic effect is observed. There is clear evidence that lycopene in association with α-tocopherol synergistically inhibits the proliferation of two prostate carcinoma cell lines. Polyphenols are very potent antioxidants found in tomatoes and many other fruits, vegetables, and herbs. The polyphenols glabridin, rosmarinic acid, and carnosic acid, when used in combination with lycopene, inhibited the oxidation of LDL to a greater extent than the additive values by 32%, 32%, and 15%, respectively. Extracts and powders containing mixtures of antioxidants also showed synergism. Tomato oleoresin produced a 5-fold increase in antioxidant activity against LDL oxidation when compared to pure lycopene at the same concentration. A 33% increase in LDL inhibition was observed when lycopene was used with garlic powder. Of the six major carotenoids found in human blood and tissue, lycopene plus lutein produced the greatest synergistic effect against oxidation of multilamellar liposomes. It also has been shown that low concentrations of 1,25-dihydroxylvitamin D3 and lycopene synergistically inhibit cell proliferation and differentiation in HL-60 leukemic cells. A number of hypotheses have been put forward to explain the synergistic effects between lycopene and other natural antioxidants. It has been suggested that the synergistic effects may be related to their physicochemical properties and or their location within the biomembrane or LDL particle; that one antioxidant is able to regenerate the second antioxidant; or that vitamin E and lycopene affect different signal transduction pathways leading to the synergistic inhibition of cell proliferation.

Synergistic inhibition of lipid peroxidation by vitamin E and a dopamine agonist, cabergoline

We examined antioxidant activity of cabergoline, a dopamine agonist, during the aerobic oxidation of phosphatidylcholine liposomes at 37°C. Cabergoline retarded the oxidation initiated with a lipid-soluble initiator significantly better than that with a water-soluble initiator, suggesting that cabergoline locates in the lipid layer of liposomal membranes. Cabergoline inhibited the oxidation of liposomal membranes synergistically with endogenous antioxidants such as ascorbic acid, ubiquinol-10 and vitamin E, and vitamin E was the most efficient synergist. These results suggest that cabergoline may have a neuroprotective effect on the substantia nigra of Parkinsonian patients because of its synergistic antioxidant activity with vitamin E as well as its action on dopamine receptor.

Antioxidative properties of lycopene and other carotenoids from tomatoes: Synergistic effects

Lycopene is the major carotenoid in tomatoes. Tomatoes contain a matrix of many bioactive components, including vitamin C, vitamin E, other carotenoids (a-, beta-, gamma- carotene, lutein), and flavonoids. Their synergistic interactions, when used in combination, may be responsible for the observed beneficial effects of tomato-based products. This study investigated the synergistic antioxidant activity of lycopene in combination with beta-carotene, vitamin E, and lutein. A liposome system was used to test the synergistic antioxidant activity. The carotenoid mixtures were more efficient in protecting liposome from oxidation than the individual carotenoid. Mixtures of lycopene and vitamin E appear to have the greatest synergistic antioxidant activity.

Enhanced oxidative stability of a hydrophilic arginine‐conjugated linoleic acid complex

The application of conjugated linoleic acid (CLA) as a functional food ingredient has been limited due to its high cost of purification and insolubility in water. Recently, we reported a method to produce high-purity CLA using two-step urea-inclusion crystallization and a hydrophilic arginine-CLA (Arg-CLA) complex. The present study compared the oxidative stability and antioxidant activity of CLA and Arg-CLA. Hydroperoxide production from CLA increased about 12-fold at 10 hr after heat treatment at 100(R)C, whereas Arg-CLA did not exhibit significant hydroperoxide production. Furthermore, the Arg-CLA complex showed synergistic antioxidant activity in a 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical scavenging assay. Arg-CLA at 20 mM scavenged 89% of ABTS radicals in 3 h, whereas CLA alone quenched only 48% under the same conditions. Our results indicate that a hydrophilic Arg-CLA exhibits enhanced oxidative stability and antioxidant activity, which could expand the scope of CLA application in various food industries.

Are Water-Soluble Natural Antioxidants Synergistic in Combination with &amp;alpha;-Tocopherol ?

α-Tocopherol, ascorbic acid, catechins ((+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate), furanones (2,5 dimethyl-4-hydroxy-3(2H)-furanone and 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone), pyrogallol, hydroxyhydroquinone and resveratrol donated hydrogen atoms to stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) in a biphasic solvent system. When ascorbic acid, (-)-epicatechin gallate or (-)-epigallocatechin gallate was combined with α-tocopherol, the mixtures donated hydrogen atoms more than those calculated. Most of these water-soluble antioxidants inhibited the formation of thiobarbituric acid-reactive substances in the radical initiator-induced oxidation of methyl linoleate in a homogeneous system. However, the water-soluble antioxidants except for ascorbic acid showed no significant synergistic antioxidant activities when they were combined with α-tocopherol. In this system, ascorbic acid strongly inhibited α-tocopherol decomposition, whereas other water-soluble antioxidants slightly. Interestingly, α-tocopherol slightly inhibited decomposition of most of these water-soluble antioxidants. It is unlikely that water-soluble antioxidants except for ascorbic acid regenerate α-tocopherol and acts as synergists in combination with α-tocopherol.

Antioxidant activity of selected Indian spices

Spices and vegetables posses antioxidant activity that can be applied for preservation of lipids and reduce lipid peroxidation in biological systems. The potential antioxidant activities of selected spices extracts (water and alcohol 1:1) were investigated on enzymatic lipid peroxidation. Water and alcoholic extract (1:1) of commonly used spices (garlic, ginger, onion, mint, cloves, cinnamon and pepper) dose-dependently inhibited oxidation of fatty acid, linoleic acid in presence of soybean lipoxygenase. Among the spices tested, cloves exhibited highest while onion showed least antioxidant activity. The relative antioxidant activities decreased in the order of cloves, cinnamon, pepper, ginger, garlic, mint and onion. Spice mix namely ginger, onion and garlic; onion and ginger; ginger and garlic showed cumulative inhibition of lipid peroxidation thus exhibiting their synergistic antioxidant activity. The antioxidant activity of spice extracts were retained even after bioling for 30 min at 100°C, indicating that the spice constituents were resistant to thermal denaturation. The antioxidant activity of these dietary spices suggest that in addition to imparting flavor to the food, they possess potential health benefits by inhibiting the lipid peroxidation.

Cholesteryl Ester Hydroperoxide Formation in Myoglobin-Catalyzed Low Density Lipoprotein Oxidation: Concerted Antioxidant Activity of Caffeic and p-Coumaric Acids with Ascorbate

Two diet-derived phenolic acids, caffeic and p-coumaric acids, interplayed with ascorbate in the protection of low density lipoproteins (LDL) from oxidation promoted by ferrylmyoglobin. Ferrylmyoglobin, a two-electron oxidation product from the reaction of metmyoglobin and H 2O 2, was able to oxidize LDL, degrading free cholesterol and cholesteryl esters. Upon exposure to ferrylmyoglobin, LDL became rapidly depleted of cholesteryl arachidonate and linoleate, which turn into the corresponding hydroperoxides. Cholesteryl oleate and cholesterol were, comparatively, more resistant to oxidation. Caffeic (2 μM) and p-coumaric (12 μM) acids efficiently delayed oxidations, as reflected by an increase in the lag times required for linoleate hydroperoxide and 7-ketocholesterol formation as well as for cholesteryl linoleate consumption. At the same concentration, ascorbate, a standard water-soluble antioxidant, was less efficient than the phenolic acids. Additionally, phenolic acids afforded a protection to LDL that, conversely to ascorbate, extends along the time, as inferred from the high levels of cholesteryl linoleate and cholesteryl arachidonate left after 22 hr of oxidation challenging. Significantly, the coincubation of LDL with ascorbate and each of the phenolic acids resulted in a synergistic protection from oxidation. This was inferred from the lag phases of cholesteryl linoleate hydroperoxide (the major peroxide found in LDL) formation in the presence of mixtures of ascorbate with phenolic acids longer than the sum of individual lag phases of ascorbate and the phenolic acids. A similar description could be drawn for the accumulation of a late product of oxidation, 7-ketocholesterol. It is concluded that ferrylmyoglobin induces a typical pattern of LDL lipid peroxidation, the oxidation rate of cholesteryl esters being a function of unsaturation; furthermore, there is a synergistic antioxidant activity of diet-derived phenolic acids with ascorbate in the protection of LDL from oxidation, a finding of putative physiological relevance.