Characterization of the volatile decomposition products of oxidized methyl arachidonate

The volatile thermal and oxidative decomposition products of methyl arachidonate were separated by capillary gas chromatography and identified by mass spectrometry. Various aldehydes, ketones, aldehyde esters, hydrocarbons and alcohols were identified. The major products included hexanal, methyl 5-oxopentanoate, pentane, methyl butanoate and 2,4-decadienal, which could be important to off-odor development in oxidized food systems containing arachidonate.     

Effect of the phenol antioxidant type on the kinetics and mechanism of inhibited lipid oxidation in the presence of fatty alcohols

A kinetic analysis of inhibited lipid autoxidation in the presence of a phenol antioxidant and a hydroxy compound is proposed. It is based on studies of the dependence of the W^ROH/W_inh ratio (between the inhibited oxidation rates in presence and absence of a hydroxy compound) on the hydroxy compound concentration. This analysis permits establishing the mechanism of action of the hydroxy compound in the presence of different types of phenol antioxidants during inhibited lipid oxidation. The kinetic analysis has been applied to the oxidation at 80°C of triacylglycerols of sunflower oil (TGSO) inhibited by 0.1 mM hydroquinone, butylated hydroxytoluene (BHT) or α-tocopherol in the presence of different concentrations of 1-tetradecanol (1-TD) and 1-octadecanol (1-OD). A linear character of this dependence is established during hydroquinone-inhibited oxidation of triacylglycerols of sunflower oil in presence of 1-TD. In the case of α-tocopherol this dependence is linear for both 1-TD and 1-OD. The equilibrium constant of interaction between the phenol antioxidant and the fatty alcohols is determined by the angle coefficient of the linear dependence. The hydroquinone-inhibited autoxidation of TGSO in the presence of 1-OD has shown a non-linear character of the dependence under consideration. A kinetic model describing simultaneous participation of 1-OD in reaction with both the phenol antioxidant and the lipid hydroperoxides is deduced. Studying the kinetics of BHT-inhibited autoxidation of TGSO in the presence of 1-OD, it has been shown that due to steric reasons there is no interaction between 1-OD and BHT, 1-OD participating in the process only by accelerating the decomposition of the lipid hydroperoxides.     

Pseudomonas spp. convert metmyoglobin into deoxymyoglobin

Meat ‘reddening’ by bacteria was observed in chilled beef. To identify the reddening bacteria, isolates were inoculated onto beef and the changes in CIE L^*a^*b^* values monitored. As a result, two Pseudomonas spp., including Pseudomonas fragi which is commonly observed in raw meat, were selected and identified as reddening bacteria. The reddening was coincidentally occurred with the appearance of slime, and the increase in thiobarbituric acid-reactive substances (TBARS) was simultaneously suppressed. In myoglobin-containing nutrient broth, it is shown spectroscopically that P. fragi converted metmyoglobin into deoxymyoglobin. It was concluded that the meat reddening was due to the formation of deoxymyoglobin, induced by the very-low-oxygen tension brought about by Pseudomonad’s oxygen consumption: This oxygen depletion simultaneously suppressed TBARS increase.     

Oxidative stability of polyunsaturated fatty acids and soybean oil in an aqueous solution with emulsifiers

The oxidative stability of polyunsaturated fatty acids (PUFA) and soybean oil homogenized with emulsifiers was investigated. Model emulsions were prepared from PUFA, including linoleic acid (LA), arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), and from soybean oil emulsified with different emulsifiers: three Tween emulsifiers (Tween 20, Tween 60, Tween 80) and two sucrose esters (S-1170 and S-1570) were used. The results showed that the emulsions prepared from LA and the various emulsifiers, oxidized at 40°C, were unstable. However, the corresponding AA, EPA, and DHA emulsions were stable, indicating that PUFA with a higher degree of unsaturation were more stable with emulsifiers than without the emulsifiers. In the soybean oil-in-water model system, the oxidation of soybean oil with various emulsifiers was less than without the emulsifiers.     

Catecholoximes as powerful antioxidants for highly unsaturated lipids

Several oximes and oximeethers of hydroxylated benzaldehydes and acetophenones were investigated for their antioxidative potential and compared with further standards. Radical scavenging activity was determined using a photometric assay based on the colored radical 2, 2‐diphenyl‐1‐picrylhydrazyl and a superoxide anion quenching assay using luminol amplified chemiluminescence. The activity against lipid autoxidation was measured by accelerated autoxidation of soybean oil, evening primrose oil, and squalene. All tested catecholoximes show good to excellent antioxidative properties. 3, 4‐Dihydroxybenzaldoxime shows the best overall performance and is a very powerful radical scavenger and lipid antioxidant.     

Hydroxy Radical,Hexanal, and Decadienal Generation by Autocatalysts in Autoxidation of Linoleate Alone and with Eleostearate

The formation of hydroxy radicals, hexanal, and 2,4-decadienal was demonstrated from the autocatalytic dimer peroxide which had been reported by us in autoxidizing linoleate (Morita and Tokita in Lipids 41:91-95, 2006). Then, autoxidizing linoleate containing eleostearate was investigated for new autocatalytic substances. The substances obtained were identified as peroxide-linked polymers consisting of both linoleate- and eleostearate-origin units with one hydroperoxy group, and also revealed activity of hydroxy-radical generation. The background of this study is as follows: the above paper reported this autocatalytic dimer peroxide as one of the real radical generators in linoleate autoxidation; this is a peroxide-linked dimer consisting of two linoleate moieties with two hydroperoxy groups, and was much more important than the main-product hydroperoxide in autocatalytic radical supply; its proposed decomposition mechanism has suggested the generation of hydroxy radicals, hexanal, and 2,4-decadienal; on the other hand, analogy to the formation mechanism of this dimer peroxide has predicted the formation of similar polymeric products from conjugated polyene components in lipids. In this study, these two predictions were successfully verified and a discussion is presented in connection with them.     

Sulfonic Acid‐Catalyzed Autoxidative Carbon‐Carbon Coupling Reaction under Elevated Partial Pressure of Oxygen

An aerobic organocatalytic oxidative C C bond formation reaction of benzylic C H bonds with various C‐nucleophiles is described. The coupling reaction proceeds by simply stirring the substrates under elevated partial pressure of oxygen in the presence of a sulfonic acid catalyst at room temperature. Elevation of the pressure enables the reaction of a broad scope of nucleophile substrates otherwise showing poor reactivity at ambient pressure. The benzylic C H bonds of xanthene, acridanes, isochromane and related heterocycles could be functionalized with nucleophiles including ketones, 1,3‐dicarbonyl compounds and aldehydes. Electron‐rich arenes could be utilized as nucleophiles at elevated temperatures. The reactions are believed to proceed via autoxidation of the benzylic C H bonds to the hydroperoxides and subsequent nucleophilic substitution catalyzed by sulfonic acids.     

Temperature dependence of the autoxidation and antioxidants of soybean, sunflower, and olive oil

Effects of temperature on the autoxidation and antioxidants changes of soybean, sunflower, and olive oils were studied. The oils were oxidized in the dark at 25, 40, 60, and 80 °C. The oil oxidation was determined by peroxide (POV) and p-anisidine values (PAV). Polyphenols and tocopherols in the oils were also monitored. The oxidation of oils increased with the oxidation time and temperature. Induction period decreased with the oxidation temperature; 87 and 3.6 days at 25 and 60 °C, respectively, for sunflower oil. The activation energies for the autoxidation of soybean, sunflower, and olive oils were 17.6, 19.0, and 12.5 kcal/mol, respectively. Olive oil contained polyphenols at 180.8 ppm, and tocopherols were present at 687, 290, and 104 ppm in soybean, sunflower, and olive oils, respectively. Antioxidants were degraded during the oil autoxidation and the degradation rates increased with the oxidation temperature of oils; for tocopherols, 2.1 × 10⁻³ and 8.9 × 10⁻²%/day at 25 and 60 °C, respectively, in soybean oil.