Initial Stages Of Autoxidation Research Articles

Suplementação com ácido linoléico conjugado: estabilidade oxidativa dos suplementos e correlações com conteúdo dos lípides totais hepáticos e indicadores da oxidação dos lípides biológicos de ratos Wistar

OBJETIVO:O objetivo do trabalho foi avaliar a estabilidade oxidativa de misturas comerciais de ácido linoléico conjugado e buscar possível correlação entre a suplementação e o conteúdo total de lípides hepáticos, e também de alguns indicadores da oxidação lipídica em ratos. MÉTODOS:Um ensaio biológico com 30 ratos divididos em três grupos (n=10) caracterizando os grupos controle e suplementados com as misturas comerciais AdvantEdge® e One® foi realizado. A concentração administrada foi de 2% em relação ao consumo de dieta e os animais foram suplementados durante 42 dias. O conteúdo total de lípides do fígado foi determinado e a morfologia do órgão foi examinada por meio de microscopia ótica. Índice de peróxido e malondialdeído foram determinados para avaliar a estabilidade oxidativa dos suplementos in vitro. Índice de peróxido, malondialdeído, 8-iso-PGF2α isoprostana e catalase foram determinados como indicadores da oxidação dos lípides biológicos. RESULTADOS: Os resultados demonstraram baixa estabilidade das misturas comerciais à oxidação in vitro. As associações entre o consumo de ácido linoléico conjugado e malondialdeído (r=-0,7914, p<0,0001) e catalase (r=-0,5991, p=0,008) foram moderadas, negativas e significantes, demonstrando que o ácido linoléico conjugado reduziu a oxidação lipídica in vivo. O conteúdo dos lípides totais hepáticos não aumentou (22,42%, DP=1,40%) e a morfologia do órgão permaneceu íntegra. CONCLUSÃO:Embora esse protocolo de suplementação com ácido linoléico conjugado tenha reduzido a oxidação lipídica, há que considerar a tendência para o aumento de 8-iso-PGF2α isoprostana e de peróxidos como perspectiva de continuidade das pesquisas sobre a reinvestigação do efeito antioxidante do ácido linoléico conjugado.

Reactions of Sperm Whale Myoglobin with Hydrogen Peroxide: EFFECTS OF DISTAL POCKET MUTATIONS ON THE FORMATION AND STABILITY OF THE FERRYL INTERMEDIATE

Distal pocket mutants of sperm whale oxymyoglobin (oxy-Mb) were reacted with a 2.5-fold excess of hydrogen peroxide (HOOH) in phosphate buffer at pH 7.0, 37 degreesC. We describe a mechanism composed of three distinct steps: 1) initial oxidation of oxy- to ferryl-Mb, 2) autoreduction of the ferryl intermediate to ferric metmyoglobin (metMb), and 3) reaction of metMb with an additional HOOH molecule to regenerate the ferryl intermediate creating a pseudoperoxidase catalytic cycle. Mutation of Leu-29(B10) to Phe slows the initial oxidation reaction 3-fold but has little effect on the rate of ferryl reduction to ferric met-aquo-myoglobin. In contrast, the Val-68(E11) to Phe mutation causes a small, 60% increase in the initial oxidation reaction and a much larger 2. 5-fold increase in the rate of autoreduction. Double insertion of Phe at both the B10- and E11-positions (L29F/V68F) produces a mutant with oxidation characteristics of both single mutants, slow initial oxidation, and rapid autoreduction, but an extraordinarily high affinity for O2. Replacing His-64(E7) with Gln produces 3-4-fold increases in both processes. Combining the mutation H64Q with L29F results in a myoglobin with enhanced resistance to metMb formation in the absence of antioxidant enzymes (i.e. catalase and superoxide dismutase) due to its own high pseudoperoxidase activity, which rapidly removes any HOOH produced in the initial stages of autoxidation. This double substitution occurs naturally in the myoglobin of Asian elephants, and similar multiple replacements have been used to reduce selectively the rate of nitric oxide (NO)-induced oxidation of both recombinant MbO2 and HbO2 blood substitute prototypes without altering O2 affinity.

Structural studies of polar dimers in autoxidized methyl linoleate during the initial stages of autoxidation.

Structural studies of polar dimers in autoxidized methyl linoleate during the initial stages of autoxidation.

Formation of dimers during the initial stage of autoxidation in methyl linoleate.

The formation of dimers in the initial stage of methyl linoleate (ML) autoxidation was demonstrated. The oxidation profile of freshly prepared ML was followed by TLC during autoxidation by aeration at 30°C for 192 hr. After 24 hr of autoxidation, the peroxide value of ML was still 0.6, and two unknown polar spots appeared besides intact ML and methyl linoleate hydroperoxides (MLHPO). These two spots were identified as dimers by successive gel and high performance liquid chromatographic separations and by molecular weight determination. The ratio of dimers/MLHPO reached a maximum (0.74) after 96 hr of autoxidation. This result indicates that the formation of dimers in the initial stage of autoxidation was slightly less than that of MLHPO. The dimers were linked through -C-O-O-C- bonds and contained hydroperoxy and/or carbonyl groups and conjugated dienes.

Structures of dimers produced from methyl linoleate during initial stage of autoxidation.

A structural investigation on the main fraction of dimers formed during the induction period of autoxidation in methyl linoleate (ML) was carried out. The dimeric fraction (A2), which was isolated from the autoxidized ML (POV= 18) by various Chromatographic techniques and gave a single spot on TLC, was further separated into four major components (components 1–4) by high performance liquid chromatography (HPLC). The mean molecular weights of these components were found to be 643–655 and component 4 gave the parent peak 652 on an FD-mass spectrum which corresponded to 2 × ML + 4O. The reduced products of each component with stannous chloride were identified in common as methyl 9- or 13-hydroxy octadecadienoate and methyl 9,13-dihydroxy octadecenoate by GC-MS. These results show that all of these dimers contained a peroxide bridge linking between a pair of MLs across C-9 or C-13 on one of the MLs and C-9 or C-13 on the other, with a hydroperoxy group.

PENTANE FORMATION AND RANCIDITY IN VEGETABLE OILS AND IN POTATO CHIPS

ABSTRACTSPentane formation during initial stages of autoxidation is indicative of rancidity in aged vegetable oils and potato chips. Pentane in the headspace gas of oils and chips was measured by gas chromatography. An 18‐member taste panel evaluated the samples for development of rancid odors and flavors. Significant linear correlations were obtained between the amount of pentane developed and the number of rancid descriptions. Samples needed only 0.08 ppm pentane in the headspace to be described as rancid by 90% of the panel. Both oils and chips were more stable to the development of pentane as the linoleate content and the iodine value decreased.

The initial stages of autoxidation

AbstractThe autoxidation of polyunsaturated lipids is initiated by a discrete reaction occurring prior to the formation ofstable hydroperoxides. The products of the initiating reaction were detected by thin‐layer chromatography and by ultraviolet spectral analysis. The reaction initiating autoxidation does not necessarily involve interactions with metals, although it is catalyzed by some heavy metals when these are present in sufficient concentrations. ॅ‐Tocopherol does not inhibit the initiation reaction, and in general, the stability of preparations of esters of polyunsaturated fatty acids is related to the content of prooxygenic substances resulting from this reaction. By taking special precautions to remove these prooxygenic substances, methyl esters containing as many as six double bonds were prepared having significant induction periods at 40C during which there was no measurable uptake of oxygen.

Formation of peroxides in fatty esters. II. Methyl linoleate: application of the polarographic and direct oxygen methods

SummaryThis study of the prolonged autoxidation of methyllinoleate at 80°C. has included polarographic identification and determination of hydroperoxides, the direct determination of oxygen contents, and catalytic micro‐hydrogenation for the determination of unsaturation. The polarographic method has further substantiated the observations of other workers that the principal peroxidic substance formed during the autoxidation of methyl linoleate at 80°C. is a hydroperoxide. The direct oxygen measurements have shown that most of the oxygen absorbed in the initial stages of autoxidation can be accounted for as hydroperoxide. During the latter stages there was a continuous increase of oxygen uptake, half of which can be accounted for as free acid and half as forms other than hydroperoxide, ester, or free acid. By means of the catalytic micro‐hydrogenation method it has further been shown that as the autoxidation progresses there is a continuous decrease in unsaturation.