Liquid-phase theoretical antioxidant activity trend of some cinnamic acid antioxidants

The trend in antioxidant activity of four cinnamic acid antioxidants, derived on the basis of their liquid-phase phenolic O H bond dissociation enthalpies, is determined theoretically, with the aid of the polarizable continuum model at the density functional theory level. Three solvents, differing in their hydrogen-bonding ability and polarity—n-heptane, acetonitrile, and ethanol—were used to model different environmental situations. The trends in solution-phase antioxidant activity appeared different in each solvent; still, the theoretical antioxidant activity trend derived in n-heptane was in excellent agreement with the experimental one in the lipid systems and the gas-phase system. Different ortho substituents show notably different solvent effects. These results could lead to the determination of reliable antioxidant activity trends in real-solution environments of interest in food or biological science frameworks.     

Flavonoids as stabilizers of fish oil: An alternative to synthetic antioxidants

The antioxidant activities against fish oil oxidation of six commercially available flavonoids and of five flavonoids purified from two Chilean native plants were compared to those ofdl-α-tocopherol and of two synthetic antioxidants, butylated hydroxytoluene and butylated hydroxyanisole. Among the commercial flavonoids, catechin, morin and quercetin showed a higher activity when fish oil oxidation (either spontaneous or Fe²⁺-induced) was assessed from the formation of peroxides or thiobarbituric acid-reactive substances. Among the native flavonoids, the 5,3′,4′-trihydroxy-7-methoxy flavanone (designated as Pt-2) showed the highest antioxidant activity. Mixtures of quercetin or of Pt-2 withdl-α-tocopherol produced better inhibitory effects when compared to that of each substance assayed by itself. Also, when Pt-2 and quercetin were assayed in combination (0.3 g/kg oil and 0.7 g/kg oil, respectively), a synergistic antioxidant effect was observed. Results indicate that several flavonoids could be used as natural antioxidants as a means to replace those synthetic antioxidants, the use of which has been questioned.     

Thermal stability of some flavonoids and phenolic acids in sheep tallow olein

In this study, the thermal stability of some phenolic antioxidants including flavonoids (quercetin and catechin) and phenolic acids (gallic acid, tannic acid, ellagic acid and caffeic acid) in tallow olein was investigated. Tallow olein fractionated from sheep tallow fat was used as a medium to study the antioxidant activity at 120, 140, 160 and 180°C. In order to extract tallow olein, a three‐stage fractionation method was performed on sheep tallow fat at the constant temperatures of 25, 15 and 5°C using acetone as a solvent. The results suggested that quercetin and ellagic acid had the highest thermal stability amongst others, while gallic acid and caffeic acid exhibited the least thermal stability. Practical applications: The sheep tallow fat has been primarily used in soap manufacturing and its application as an edible fat has been limited due to its high content of saturated fatty acids. Extraction of the liquid phase of tallow fat (tallow olein) by fractionation reduces its long‐chain saturated fatty acid content to an acceptable level for edible consumption. The fractionation process, as negatively affects the stability to autoxidation, should be followed by stabilisation with antioxidants. The recent interest in natural antioxidants encouraged the authors to investigate the thermal stability of phenolic antioxidants in tallow olein. It is necessary to determine the thermal stability of antioxidants to predict their appropriateness to be used in high‐temperature applications such as deep frying. Fractionation and stabilisation with appropriate antioxidants are the important steps to utilise tallow olein as an edible oil for different applications in salad formulations, cooking and frying.     

Selection of theoretical parameter characterizing scavenging activity of antioxidants on free radicals

Semiempirical quantum chemistry method Austin Model 1 (AM1) was employed to calculate the theoretical parameters of 15 antioxidants. Such parameters as bond order, bond length, and the difference of heat of formation (ΔHOF) between the antioxidant and its phenolic free radicals were obtained. Through correlating with previous experimental results ΔHOF was proven to be a proper parameter (r=0.9491) to characterize the free radical-scavenging activity of antioxidants, but bond order and bond length were not able to represent the antioxidant’s ability to scavenge free radicals. By comparing the results calculated by different semiempirical methods, including AM1, Modified Neglect of Diatomic Overlap, and Parametric Method 3, AM1 was found to be the best for calculating ΔHOF.     

The kinetics of the oxidation of several antioxidants in oxidizing fats

Summary The deterioration of hydroquinone, catechol, NDGA (nordihydroguaiaretic acid), and gallic acid in lard oxidizing at 100° C. has been quantitatively studied. Initial concentrations of 0.02, 0.1, and 0.5% were used. The results indicate that, in general, the deterioration of phenolic antioxidants in oxidizing fats does not occur as a single low order reaction but is complicated by products formed in the oxidation of the fat and possibly also of the antioxidant. The deterioration curves for gallic acid are quite different from those of the other three antioxidants. This is tentatively explained on the basis of the synergistic action of gallic acid upon itself. There is an increasing catalytic effect with increasing initial concentrations of all of these antioxidants on the formation of peroxides during the early stages of the autoxidation of lard. Presented at a meeting of the American Oil Chemists’ Society, Chicago, Oct. 30–Nov. 1, 1946.     

Ascorbate and phenolic antioxidant interactions in prevention of liposomal oxidation

Efficient prevention of membrane lipid peroxidation by vitamin E (α-tocopherol) may involve its regeneration by vitamin C (ascorbate). Conceivably, the efficacy of antioxidants designed as therapeutic agents could be enhanced if a similar regeneration were favorable; thus, a model membrane system was developed which allowed assessment of interaction of phenolic antioxidants with ascorbate and ascorbyl-6-palmitate. Ascorbate alone (50–200 μM) potentiated oxidation of soybean phosphatidylcholine liposomes by Fe²⁺/histidine-Fe³⁺, an effect which was temporally related to reduction of Fe³⁺ generated during oxidation. Addition of 200 μM ascorbate to α-tocopherol-containing liposomes (0.1 mol%) resulted in marked, synergistic protection. Accordingly, in the presence but not absence of ascorbate, α-tocopherol levels were maintained relatively constant during Fe²⁺/histidine-Fe³⁺ exposure. Probucol (4,4′-[(1-methylethylidine)bis(thio)]bis[2,6-bis(1,1-dimethylethyl)]phenol), and antioxidant which prevents oxidation of low density lipoproteins, and its analogues MDL 27,968 (4,4′-[(1-methylethylidene)bis(thio)]-bis[2,6-dimethyl]phenol) and MDL 28,881 (2,6-bis(1,1-dimethylethyl)-4-[(3,7,11-trimethyldodecyl)thio]phenol) prevented oxidation but exhibited no synergy with ascorbate. Ascorbyl-6-palmitate itself was an effective antioxidant but did not interact synergistically with any of the phenolic antioxidants. Differential scanning calorimetry revealed significant differences among the antioxidants in their effect on the liquid-crystalline phase transition of dipalmitoyl phosphatidylcholine (DPPC) liposomes. Both α-tocopherol and MDL 27,968 significantly reduced the phase transition temperature and the enthalpy of the transition. MDL 28,881 had no effect while probucol was intermediate. The potential for ascorbate or its analogues to interact with phenolic antioxidants to provide a more effective antioxidant system appears to be dictated by structural features and by the location of the antioxidants in the membrane.     

多乙烯多胺桥联受阻酚类抗氧剂的合成及其清除DPPH·性能

以二乙烯三胺和三乙烯四胺为桥联基,β-(3,5-二叔丁基-4-羟基苯基)丙酰氯为抗氧化功能基团,通过酰胺化缩合反应合成了两类具有不同对位桥联基团的受阻酚类抗氧剂。采用傅里叶红外光谱和核磁共振氢谱证实了合成的多乙烯多胺桥联受阻酚类抗氧剂的化学结构。DPPH法研究了多乙烯多胺桥联受阻酚类抗氧剂清除自由基的性能,并探索了酚羟基个数和对位桥联基结构对受阻酚类抗氧剂清除自由基性能的影响。结果表明,多乙烯多胺桥联受阻酚类抗氧剂具有良好的清除DPPH·能力,且随着抗氧剂分子中酚羟基个数的增加,清除DPPH·的活性增加,分子中含有4个酚羟基的三乙烯四胺受阻酚类抗氧剂的抗氧化效率（AE）达到2.65×10^-2 L/(mol·s)。对位桥联基结构对受阻酚类抗氧剂清除DPPH·能力有较大影响,季戊四醇为桥联基的受阻酚类抗氧剂1010清除DPPH·能力最强,其抗氧化效率（AE）为3.08×10^-2L/(mol·s);乙二胺为核的1.0代树枝状受阻酚类抗氧剂清除DPPH·能力最弱,其抗氧化效率（AE）为2.60×10^-2 L/(mol·s)。     

Tests of refractory products of the magnohrom company at the novolipetsk metallurgical works JSC

The largest Yugoslavian producer of refractory materials Magnohrom — Kraljevo Company developed a program for manufacturing periclase-carbon products with an additive of molten periclase, corundum, and antioxidants in the early 1990s. Full-scale tests at the NLMK JSC (Novolipetsk Metallurgical Works) and the Izhorskie Zavody JSC have shown that the endurance of refractory products of Magnohrom — Kraljevo Company are at the level provided by the leader of European refractory production RADEX.     

Comparison of antioxidants for fats on an equivalent molar basis

Summary An oven incubation method for determining the relative effectiveness of antioxidants is described, which has yielded results with an over-all average variation of 2.07%. The antioxidants were compared on an equivalent molar basis, and potencies are expressed as a “catechol index”. The catechol index of a given antioxidant is defined as the ratio of its antioxidant activity to that of an equivalent molar concentration of catechol. It provides a quantitative measure of the relative effectiveness of various antioxidants, which takes into consideration the concentration of antioxidant, the induction periods of the stabilized sample and control substrate, and, at least to some extent, the substrate used. Catechol indexes of 28 phenolic compounds are given and discussed, and several relationships between structure and antioxygenic activity are pointed out. Journal paper no. 981, Purdue Agricultural Experiment Station.     

Unexploited Thapsia garganica,Orlaya maritima,and Retama raetam Seeds: Potential Sources of Unsaturated Fatty Acid and Natural Antioxidants

Total lipid contents, fatty acid compositions, phenolic profiles and antioxidants activities of seeds from Thapsia garganica, Orlaya maritima, and Retama raetam were investigated. The oil values were more than 26 %, except seeds of R. raetam (ca. 3 %). Unsaturated fatty acids accounted for the majority of the fatty acids (more than 75 %). Oleic and linoleic acid were the predominant fatty acids. Total phenolic compounds (24–104 mg GAE g^?1 DR), total flavonoids (4–102 mg QE g^?1g DR), total tannins (28–85 mg GAE g^?1 DR) and condensed tannins (0.62–131 mg CE g^?1 DR) were also determined. The antioxidant activities using different assays were evaluated. The predominant detected classes were the phenolic acids (42–85 %) and the flavonoids (11–48 %). The major phenolic acids were caffeic, trans‐4‐hydroxy‐3‐methoxycinnamic, p‐coumaric, and gallic acid. The predominant flavonoids were quercetin, luteolin, naringin, apigenin, and kaempferol. This study brings attention to the medicinal importance of these species as a source of oil and antioxidant molecules.     

Stabilisation of edible oils with natural antioxidants

Natural antioxidants have recently gained increased interest because of the belief that natural food ingredients are better and safer than synthetic ones. The review presents the results on stabilisation of the main edible oils with different types of natural antioxidants. Sources of natural antioxidants are spices, herbs, teas, oils, seeds, cereals, cocoa shell, grains, fruits, vegetables, enzymes, proteins. Researchers concentrate on ascorbic acid, tocopherols and carotenoids as well as on plant extracts containing various individual antioxidants such as flavonoids (quercetin, kaemferol, myricetin), catechins or phenols (carnosol, rosmanol, rosamaridiphenol) and phenolic acids (carnosic acid, rosmarinic acid). Ascorbyl palmitate is regarded as a 'natural' antioxidant because it is hydrolysed in the body to ascorbic and palmitic acids. Among the herbs of the Lamiaceae family, rosemary has been more extensively studied and its extracts are the first marketed natural antioxidants. Oregano, which belongs to the same family, has gained the interest of many research groups as a potent antioxidant in lipid systems. The review concerns the following main topics: stabilisation of oil with individual natural antioxidants, interaction of antioxidants with synergists, stabilisation of oil with extracts or dry materials from different plant sources (e.g. herbs and spices), stabilisation at frying temperatures and in emulsions.     

Fat oxidation at lwo oxygen pressure: II. Kinetic studies on linoleic acid oxidation in emulsions in the presence of antioxidants

Earlier reported kinetic studies on the dependence of lipid oxidation on oxygen pressure in emulsions were continued by studying this relationship in the presence of antioxidants. The substances tested represented two types of antioxidants, phenolic inhibitors (α-tocopherol, BHA, PG) and amino acid-retarders (glycine, alanine, histidine, tryptophane). The inhibiting effect of the first mentioned group, i.e., the formation of an induction period was, in general, not dependent on oxygen pressure, while the retardation caused by amino acids was stronger at low oxygen pressure than in air. The effect of lowering oxygen pressure was practically the same, when phenolic inhibitors were added as without such addition. It was, however, enhanced by the addition of amino acid-retarders. When representatives of these two types of antioxidants were added in combination, their synergistic effect was considerably enhanced at low oxygen pressure.     

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.     

An antagonistic effect with antioxidants for unsaturated fats

Summary α-and γ-tocopherol act as pro-oxidants with marine oils containing the antioxidant EMQ. The term “antagonism” is suggested for such phenomena. Antagonism was also demonstrable in purified unsaturated fatty ester acids and triglycerides. Nitrogenous inhibitors (EMQ, DPPD, ADA) are more affected by added tocopherols than are the phenolic antioxidants examined (BHT, BHA, PG, NDGA). Phenolic antioxidants other than tocopherols do not show marked antagonism with EMQ. This research was supported by funds made available through the Saltonstall-Kennedy Act and administered by means of a collaborative agreement between the U. S. Fish and Wildlife Service and the University of California.     

Antioxidant Property Enhancement of Sweet Potato Flour under Simulated Gastrointestinal pH

Sweet potato is known to be rich in healthful antioxidants, but the stability of its antioxidant properties under gastrointestinal pH is very much unknown. Hence, this study aimed to evaluate the changes in antioxidant properties (total contents of phenolics and flavonoids as well as antioxidant activity) of sweet potato flour (SPF) under simulated gastrointestinal pH conditions. It was found that the yield of SPF crude phenolic extract increased from 0.29 to 3.22 g/100 g SPF upon subjection to gastrointestinal pH conditions (p < 0.05). Also elevated significantly were the total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity of SPF (p < 0.05). In summary, the antioxidant properties of SPF were enhanced under gastrointestinal pH conditions, suggesting that SPF might possess a considerable amount of bound phenolic and other antioxidative compounds. The antioxidant properties of SPF are largely influenced by pH and thus might be enhanced during the in vivo digestive process.     

Antioxidant activity of flavonoids isolated from Scutellaria rehderiana

The present study examined the antioxidant activity in heated canola oil of hexane, acetone, and methanol extracts of dry roots of gansu huangqin (Scutellaria rehderiana) as well as six flavonoids isolated from the acetone and methanol extracts. The oxidation was conducted at 95°C by monitoring oxygen consumption and decreases in both linoleic and α-linolenic acids. The acetone extract was most effective in inhibiting oxidation of canola oil, followed by the methanol extract. The antioxidant activity of gansu huangqin acetone extract was dose-dependent. Among the six flavonoids, baicalein and ganhuangenin were more effective than butylated hydroxytoluene (BHT) in protecting canola oil from oxidation. The present results suggest that the acetone extract of this root may be a potential source of natural antioxidants for use in processed foods.     

Antioxidant Activity of Added Phenolic Compounds in Freeze-Dried Microencapsulated Sunflower Oil

This study was aimed at evaluating the effectiveness of phenolic antioxidants with a similar structure but having a different polarity in dried microencapsulated sunflower oil. The antioxidants tested were, on one hand, α-tocopherol and its water soluble analogue, Trolox, and on the other, gallic acid and its ester derivatives, propyl gallate and dodecyl gallate. At a moderate temperature (40 °C), the samples were oxidized under accelerated conditions by using Cu(II) as an oxidation catalyst. The progress of oxidation was followed up over time in the free and encapsulated oil fractions. The peroxide value, the total content of polymers and, when appropriate, the content of α-tocopherol were determined. Quantitative analysis of the total fraction of the non-volatile oxidation products and their distribution in oligomers, dimers and monomers was applied to samples to obtain a complete evaluation of oxidation. Finally, as a complementary measure, the antioxidants were also assessed by direct application of the Rancimat test at 100 °C on the dried microencapsulated oil samples. Results showed that the antioxidants of lower polarity in each series, i.e. tocopherol and dodecyl gallate, were to a great extent the most protective antioxidants. The results obtained by the Rancimat test were consistent with those found during oxidation at moderate temperature. Furthermore, the addition of Cu(II) reduced proportionally the oxidative stability index of the dried microencapsulated samples.     

Hydrophilic antioxidants of virgin olive oil. Part 1: Hydrophilic phenols: A key factor for virgin olive oil quality

Virgin olive oil (VOO) consumption is increasing all over the world due to its excellent organoleptic and nutraceutical properties. These beneficial traits stand from a prominent and well‐balanced chemical composition, which is a blend of major (98% of total oil weight) and minor compounds including antioxidants. The main antioxidants are phenolic compounds, which can be divided into lipophilic and hydrophilic phenols. While lipophilic phenols such as tocopherols can be found in other vegetable oils, most hydrophilic phenols in olive oil are exclusive of the Olea europaea species endowing it with a chemotaxonomic interest. This review is focused on VOO antioxidant profile and, particularly, on hydrophilic phenols that are divided into different sub‐families such as phenolic acids and alcohols, hydroxy‐isochromans, flavonoids, secoiridoids, lignans and pigments. Analytical methods for qualitative and/or quantitative determination of these compounds are assessed. The implementation of efficient sample preparation protocols, separation techniques such as liquid chromatography, GC and capillary electrophoresis, as well as detection techniques such as ultraviolet absorption, fluorescence or MS are critical to succeed in the quality of the results. The effects of hydrophilic phenols on increasing VOO stability, its nutraceutical interest and organoleptic properties are also considered.     

Fatty Acid Composition, Antioxidant Properties, and Antiproliferative Capacity of Selected Cold-Pressed Seed Flours

Cold-pressed seed flours from pumpkin, parsley, mullein, cardamom, and milk thistle were examined for total oil, fatty acid profile of the oil, total phenolic content (TPC), scavenging activities against peroxyl (ORAC), hydroxyl (HOSC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) (RDSC) radicals, and antiproliferative capacity against HT-29 human colon cancer cells. The cold-pressed parsley seed flour contained a very high concentration of total oil—17.6 g/100 g flour—with primarily C18:1 fatty acid at 86.2 g/100 g fatty acids. All other flour oils had relatively high levels of saturated fats, ranging from 39.0 to 62.9 g/100 g fatty acids. The tested seed flours demonstrated significant TPC and free radical scavenging activities. Milk thistle seed flour had the highest TPC value of 25.2 mg gallic acid equivalent per g flour (GAE mg/g) followed by that of parsley seed flour at 8.1 GAE mg/g. Milk thistle seed-flour extract also had significantly higher antioxidant activities than all other extracts against all tested radicals. The milk thistle seed-flour extract had an ORAC value of 1131 μmol trolox equivalents (TE) per g flour (TE μmol/g), a HOSC value of 893 TE μmol/g, and an RDSC value of 61 TE μmol/g. Also, ORAC, HOSC, and TPC values were significantly correlated (P < 0.01) under the experimental conditions. The cold-pressed milk thistle seed flour inhibited the proliferation of HT-29 cancer cells in a dose-dependent manner. Results from this study suggest that these cold-pressed seed flours may serve as natural sources of antioxidants and may be used to improve human health.     

Relative inhibitory potencies of flavonoids on 12-lipoxygenase of fish gill

The relative efficacy of 10 flavonoid compounds and some common antioxidants in inhibiting 12-lipoxygenase of fish gill was determined. Lipoxygenase activity was measured by oxygen consumption with polarography and formation of hydroxy fatty acid using thin layer chromatography with autoradiography. Generally, the inhibition of 12-lipoxygenase by flavonoids was noncompetitive. The lipoxygenase product pattern did not change in the presence of flavonoids. Fisetin (3,3′,4′,7-tetrahydroxyflavone) and quercetin (3,3′,4′,5,7-pentahydroxyflavone) were the most potent inhibitors of 12-lipoxygenase, with IC₅₀'s of 0.25 and 0.4 μM respectively. These were compared with IC₅₀'s values of 5, 1000 μM for BHA (t-butylhydroxyanisole) and BHT (t-butylhydroxytoluene) respectively. Possible inhibitory mechanisms and relationships between flavonoid structure and inhibitory potencies are discussed.