Antioxidant effect of naturally occurring furan fatty acids on oxidation of linoleic acid in aqueous dispersion

Naturally occurring furan fatty acids were synthesized and their antioxidant activity has been studied during the oxidation of linoleic acid in the phosphate buffer, pH 6.9, in the dark. The extent of the oxidation was followed both by the accumulation of conjugated diene and by the measurement of the residual amounts of linoleic acid. The tetra-alkylsubstituted furan fatty acids were found to suppress the oxidation. The trialkylsubstituted compound also showed antioxidant activity, being about 50% as effective as the tetra-alkylsubstituted ones. The di-alkylsubstituted one revealed no significant activity. The antioxidant activity of furan fatty acids depended on the number of substituents on the furan ring. Therefore, a tetra-alkylsubstituted furan ring may be necessary for the antioxidant action of furan fatty acids. The tetra-alkylsubstituted furan fatty acids reduced 1,1-diphenyl-2-picrylhydrazyl, reacted with the peroxyl radical generated from the thermal decomposition of a radical initiator, 2,2′-azobis(2-amidinopropane)hydrochloride (AAPH), and also suppressed the AAPH-induced oxidation of linoleic acid, indicating that, by scavenging, the peroxyl radical furan fatty acids inhibit the oxidation.     

α-Tocopherol prooxidant effect in aqueous media: Increased autoxidation rate of linoleic acid

The prooxidant effect of a-tocopherol was investigated during linoleic acid autoxidation in an aqueous media, at pH 6.9. α-Tocopherol (1.25 x 10⁻⁴ M) was added to linoleic acid (2.5 x 10⁻³ M) and the linoleic acid autoxidation rate was evaluated using 2 methods: spectrophotometric measurement at 234 nm exhibited an important increase of conjugated dienes after α-tocopherol addition, especially during the first 4 days, and gas Chromatographie measurement of unoxidized linoleic acid showed an important degradation of linoleic acid in the presence of a-tocopherol. During the pro-oxidant reaction, α-tocopherol was rapidly oxidized ; it was detected as traces by thin layer chromatography after 4 days of experimentation. Two oxidation products of α-tocopherol have been identified: α-tocopherylquinone and a dimer of α-tocopherol.     

The performic acid oxidation of linoleic acid

The performic acid oxidation of linoleic acid has been shown to form 9,12-dihydroxy-trans-10,11-methylene-heptadecanoic acid (I) after hydrolysis of the formate ester. A sequence of reactions led to the identification of dimethyl-trans-1,2-cyclopropanedicarboxylate by gas liquid chromatography. Spectroscopic evidence is presented for thetrans geometry in I. Failure of the monoepoxide of linoleic acid to give the formate ester of I suggests the alternative that a homoallylic carbonium ion is formed directly upon attack of the peroxide reagent.     

Behavior of alpha,gamma, and delta tocopherols with linoleic acid in aqueous media

Tocopherols can exhibit opposite effects in aqueous media on linoleic acid autoxidation rate. The effect which was observed depended on tocopherol concentration and on the tocopherol itself. At 0.05 mole of tocopherol per mole of linoleic acid, α-tocopherol was prooxidant while in similar conditions, δ-tocopherol was anti-oxidant as well as γ-tocopherol. However, this latter one exhibited a slight antioxidant activity. When tocopherol concentration decreased (twice as weak), α-tocopherol still exhibited the same pro-oxidant activity, while the antioxidant effect of γ and δ tocopherols was increased. The study of tocopherol stability by HPLC has shown that tocopherol oxidation increased in order δ < γ < α. There was a relationship between the ability for a tocopherol to be easily oxidized by air and its prooxidant activity. Tocopherol oxidation would enhance the formation of a perhydroxyl radical ([·OOH] or one of this type [O₂0=, ·OH]) which was responsible for the prooxidant effect.     

The effect of some amino acids on the oxidation of linoleic acid and its methyl ester

Manometric studies of the effect of certain amino acids on oxidation (measured as oxygen consumption) of linoleic acid, as well as the methyl esters of linoleic acid and linolenic acid dispersed in water or phosphate buffers at pH 7 to pH 5 have shown that

1. 1.
   The amino acids tested (except cysteine) have a potential antioxidative effect.     
   
   

Catalytic oxidation of organic compounds in aqueous media

Ru, Pt and Rh catalysts supported on titania, ceria or active carbon and a Mn/Ce composite oxide catalysts were prepared and their catalytic behavior in Wet Air Oxidation ( 20 bar O₂) of phenol and acetic acid were investigated. Phenol was found to be an easily oxidizable compound as 170°C, while acetic acid was a very refractory molecule, even at 200°C. Ru(5 wt.-%)/C is a very efficient catalyst for the WAO of acetic acid without any leaching of noble metal.     

Positional and geometrical isomers of linoleic acid in partially hydrogenated oils

The geometrical and positional isomers of linoleic acid of a partially hydrogenated canola oil-based spread were isolated and identified. Through partial hydrazine reduction and mass spectral studies,cis-9,trans-13 octadecadienoic acid was identified as the major isomer. Other quantitatively important isomers characterized werecis-9,trans-12;trans-9,cis-12 andcis-9,cis-15. These four were also the major isomers in margarine based on common vegetable oils. A number of minor isomers were detected and some structures identified weretrans-9,trans-12;trans-8,cis-12;trans-8,cis-13;cis-8,cis-13;trans-9,cis-15;trans-10,cis-15 andcis-9,cis-13. The proportions of the various isomers are given for some margarines in the Canadian retail market. The amounts oftrans-9,trans-12 isomer in Canadian margarines were generally below 0.5% of the total fatty acids.     

Influence of thyme and clove essential oils on cottonseed oil oxidation

Simple model systems composed of refined cottonseed oil and thyme oil or clove oil, without additives, were designed to approximate conditions in natural oils in order to study their oxidation behavior. Three methods were used to follow cottonseed oil oxidation, i.e., coupled oxidation withβ-carotene, the TBA test and hydroperoxide number. The results illustrate that clove and thyme oils at various concentrations exhibit antioxidant activity and this phenomenon for clove oil is superior to that of thyme oil. Sensory evaluation tests indicate that the addition of thyme oil or clove oil to cottonseed oil at concentrations ranging from 50 to 1200 ppm do not affect the odor note of cottonseed oil. Therefore, thyme and clove essential oils are recommended for use as natural antioxidants to suppress lipid oxidation.     

Linoleic acid oxidation catalyzed by various amino acids and cupric ions in aqueous media

Model systems were designed to study linoleic acid oxidation in the presence and absence of various amino acids with or without cupric ions. The tested amino acids exhibited a potential prooxidant effect in linoleic acid dispersed in aqueous media. The effectiveness of various amino acids on linoleic acid oxidation decreased in the following order: cysteine > serine > tryptophan > phenylalanine > histidine > alanine. The addition of alanine, serine, phenylalanine, histidine, or tryptophan to linoleic acid showed an autocatalytic chain reaction. With cysteine, there was a linear relation between concentration of hydroperoxides and time during the early stages of oxidation. The prooxidative activity of the tested amino acids in general could be attributed to the presence of the a-amino group in the form H₃-N-R. The apparent difference in the prooxidative activity is mainly due to the functional groups attached in the β-carbon atom in the amino acid molecules. The addition of cupric ions at a concentration of 10^-5M to linoleic acid catalyzed with various a-amino acids showed that these amino acids had no significant effect. Increasing the copper concentration from 10^-5M to 10^-3M had the following effects: a shortening of the induction period of linoleic acid catalyzed by amino acids having an aromatic side chain, no effect on the induction period but an increase in the oxidation rate during the propagation step in the model systems catalyzed by alanine and serine, and in the model system containing cysteine a linear increase in the linoleic acid oxidation from the start of the reaction.     

Antioxidant activity of amino acid sodium and potassium salts in vegetable oils at frying temperatures

Previous studies reported that several amino acids had strong antioxidant activity in vegetable oils under frying conditions. In this study, amino acids were converted to their sodium or potassium salts, and a heating study was conducted with 5.5 mM amino acid salts in soybean oil (SBO) at 180°C. Sodium salts of amino acids including alanine, phenylalanine, and proline and disodium glutamate had significantly stronger antioxidant activity than the corresponding amino acids, and potassium salts had stronger antioxidant activity than sodium salts. Potassium salts of alanine and phenylalanine more effectively retained tocopherols in SBO than the corresponding amino acids during heating. Phenylalanine potassium salt had stronger antioxidant activity than phenylalanine in other vegetable oils including olive, high oleic soybean, canola, avocado, and corn oils. Phenylalanine potassium salt at 5.5 mM more effectively prevented oil oxidation than tert-butyl hydroquinone, a synthetic antioxidant, at its legal concentration limit (0.02%) indicating its feasibility as a new antioxidant for frying.     

The oxidation of glyoxal and ethylene glycol on platinum in aqueous acid mediums containing some metal salts

The oxidation of glyoxal and ethylene glycol in mediums like N NClO₄, N H₂SO₄ or M KNO₃ on a platinum anode led mainly to the formation of glyoxylic acid and to the breaking of the CC bond, giving then formic acid or fromaldehyde. The addition of metal salts (Ag, Sn, Pb, Tl) favours this latter reaction. The adsorption of glyoxal, which is an important step for its transformation into glyoxylic acid, is promoted by the lack of platinum oxides or hydroxides on the anode surface and is possible even at the oxidation potential of glyoxal.     

Antimicrobial activity of aroma chemicals and essential oils

Determination of the minimum inhibitory concen-trations (MIC) of 212 common soap fragrance raw materials demonstrated that the paper disc-petri plate technique does not reflect the relative anti-microbial activity of these materials. Commonly used soap bacteriostats were shown to be 100 to 1000 times more effective than the most active fragrance materials. Of 521 fragrance materials initially screened by the petri plate method, 44% were inhibitory against one of the three test organisms, and 15% were effective against all three(Staphylococcus aureus, Escherichia coli, Candida albicans). Of a selected number (212) of these positive materials, subsequently screened against a lipophilic diphtheroid organism(Corynebacterium sp.), 64 materials (30%) were positive against all four test organisms. However, only nine materials (4%) had a MIC as low as 50 ppm compared to the common soap bacteriostat TCC, which had a MIC of 0.08 ppm (vs.S. aureus). In hand-degerming tests, no reduction of bacterial counts was obtained with a soap containing the most active fragrance materials. These results demonstrate that creation of a practical antimicrobial soap fragrance does not appear to be possible. 1Preliminary report presented at the 1976 national meeting of the American Chemical Society, Miami Beach, FL, September 1978.     

Antioxidant activity of oat extract in soybean and cottonseed oils

A previously published method for extracting antioxidants from Noble oats with methanol was modified to improve the antioxidant activity. The extract was tested in soybean and cottonseed oils held at 30 and 60°C in the dark and at 30°C in the light. During storage, the peroxide values (PV) of the oils were generally significantly lower (P≤0.05) with the addition of the extract than was the control (no additives), and the PV were slightly higher than for oils containing TBHQ. In addition, the extract was added to emulsions of the same oils and held at 30°C in the light and at 60°C in the dark. The PV of the emulsions containing the extract were significantly lower (P≤0.05) than were the PV of those containing tertiary butylhydroquinone and the control.     

Suppressive effect of alkyl ferulate on the oxidation of microencapsulated linoleic acid

The oxidation processes of linoleic acid mixed with ferulic acid or the 1‐pentyl, 1‐hexyl and 1‐heptyl ferulates, encapsulated with gum arabic or maltodextrin, were studied. The alkyl ferulates had a higher antioxidative effect than ferulic acid, but there was no significant difference among the three alkyl ferulates. Suppression of the oxidation by 1‐hexyl ferulate or ferulic acid was more effective at the higher molar ratios of the additive to linoleic acid. The processes were analyzed using the Weibull equation to evaluate the rate constant, k, and the shape constant, n. Although the k values for linoleic acid encapsulated with gum arabic were lower than that with maltodextrin, the suppressive effect of the alkyl ferulates was more remarkable for linoleic acid encapsulated with maltodextrin than with gum arabic because of the non‐antioxidative ability of maltodextrin. Because the partition coefficient of the alkyl ferulates was much greater than that of ferulic acid, most of the alkyl ferulates would be located in the linoleic acid phase of the microcapsules and effectively suppress the oxidation of linoleic acid.     

Dietary linoleic acid and the fatty acid profiles in rats fed partially hydrogenated marine oils

The influence of the linoleic acid levels of diets containing partially hydrogenated marine, oils (HMO) rich in isomeric 16∶1, 18∶1, 20∶1 and 22∶1 fatty acids on the fatty acid profiles of lipids from rat liver, heart and adipose tissue was examined. Five groups of rats were fed diets containing 20 wt% fat−16% HMO+4% vegetable oils. In these diets, the linoleic acid contents varied between 1.9% and 14.5% of the dietary fatty acids, whereas the contents oftrans fatty acids were 33% in all groups. A sixth group was fed a partially hydrogenated soybean oil (HSOY) diet containing 8% linoleic acid plus 32%trans fatty acids, mainly 18∶1, and a seventh group, 20% palm oil (PALM), with 10% linoleic acid and notrans fatty acids. As the level of linoleic acid in the HMO diets increased from 1.9% to 8.2%, the contents of (n−6) polyunsaturated fatty acids (PUFA) in the phospholipids increased correspondingly. At this dietary level of linoleic acid, a plateau in (n−6) PUFA was reached that was not affected by further increase in dietary 18∶2(n−6) up to 14.5%. Compared with the HSOY- or PALM-fed rats, the plateau value of 20∶4(n−6) were considerably lower and the contents of 18∶2(n−6) higher in liver phosphatidylcholines (PC) and heart PC. Heart phosphatidylethanolamines (PE) on the contrary, had elevated contents of 20∶4(n−6), but decreased 22∶5(n−6) compared with the PALM group. All groups fed HMO had similar contents oftrans fatty acids, mainly 16∶1 and 18∶1, in their phospholipids, irrespective of the dietary 18∶2 levels, and these contents were lower than in the HSOY group. High levels of linoleic acid consistently found in triglycerides of liver, heart and adipose tissue of rats fed HMO indicated that feeding HMO resulted in a reduction of the conversion of linoleic acid into long chain PUFA that could not be overcome by increasing the dietary level of linoleic acid.     

Use of some essential oils as natural preservatives for butter

Thyme and cumin essential oils were used in the present study in an attempt to prevent butter deterioration during storage at room temperature. Butter oxidation and lipolysis were followed by measuring the acid, peroxide and TBA values. Lipolytic activity and total microbial and lipolytic bacterial counts were also measured. During butter storage, very little change in the peroxide and TBA values were found while a gradual increase in the acid value was noticed. The addition of cumin and thyme oils at 200 ppm to butter caused very little increase in the acid value. The data for lipolytic bacterial counts were in general agreement with the acid values. Thyme and cumin essential oils showed a greater anti-hydrolytic effect and act as superior preservatives compared to BHT.     

The oxidation of valeric acid in aqueous solution

The liquid phase oxidation of an aqueous solution of a lower fatty acid, valeric (pentanoic) acid, has been studied at high temperatures (240?325°C) and pressures (10.3-10.4 MPa) in a batch autoclave reactor. The objective of the study was to develop a mechanistic understanding of the wet oxidation of industrial wastewaters contaminated with vegetable oils. Valeric acid was chosen as the prototype molecule. High performance liquid chromatography (HPLC) has been used to identify the liquid products and estimate their concentrations as a function of the extent of oxidation. Moreover the technique of GC-MS has also been used to obtain information on specific intermediate oxidation products that could not be identified by HPLC. The gaseous products of the reaction have been also identified and quantified. A detailed reaction mechanism is proposed based on free radical reactions.