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Autoxidation model systems

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). [Pg.373]

Pedersen on the effect of various chelating agents upon the autoxidation of petroleum (a useful model system) catalysed by various transition metals. The deactivating efficiency is the percentage restoration of the original induction period observed with a control sample of petroleum without metal or deactivator. Only iV" -tetrasalicylidenetetra(aminomethyl)methane was effective... [Pg.141]

The speed of autoxidation was compared for different carotenoids in an aqueous model system in which the carotenoids were adsorbed onto a C-18 solid phase and exposed to a continnons flow of water saturated with oxygen at 30°C. Major products of P-carotene were identified as (Z)-isomers, 13-(Z), 9-(Z), and a di-(Z) isomer cleavage prodncts were P-apo-13-carotenone and p-apo-14 -carotenal, and also P-carotene 5,8-epoxide and P-carotene 5,8-endoperoxide. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates lycopene > P-cryptoxanthin > (E)-P-carotene > 9-(Z)-p-carotene. [Pg.182]

Second-derivative spectrophotometry has been used to monitor the time-dependent production of cis,tmns-(Xmax 242 nm) and trans, tram- (Xmax 232 nm) diene conjugates of microsomal PUFAs following the exposure of rats to carbon tetrachloride (CCU) (Corongui et al., 1986). These signals have been postulated to be derived from mixtures of peroxidized substrates. Previous studies using chemical model systems have established that autoxidation of linolenic or arachidonic acid results in the production of cis, trans- and tmns, trawr-conjugated diene... [Pg.14]

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid. Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.
The interaction of carotenoids with cigarette smoke has become a subject of interest since the results of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study Group 1994 (ATBC) and CARET (Omenn et al. 1996) studies were released. P-Carotene has been hypothesized to promote lung carcinogenesis by acting as a prooxidant in the smoke-exposed lung. Thus, the autoxidation of P-carotene in the presence of cigarette smoke was studied in model systems (toluene) (Baker et al. 1999). The major product was identified as 4-nitro-P-carotene, but apocarotenals and P-carotene epoxides were also encountered. [Pg.219]

Rodriguez, E. B. and D. B. Rodriguez-Amaya (2007). Formation of apocarotenals and epoxycarotenoids from beta-carotene by chemical reactions and by autoxidation in model systems and processed foods. Food Chem. 101(2) 563-572. [Pg.227]

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. [Pg.863]

Metal ions play an important role as catalysts in many autoxidation reactions and have been considered instrumental in regulating natural as well as industrial processes. In these reactive systems, in particular when the reactions occur under environmental or in vivo biochemical conditions, the metal ions are involved in complicated interactions with the substrate(s) and dioxygen, and the properties of the actual matrix as well as the transport processes also have a pronounced impact on the overall reactions. In most cases, handling and analyzing such a complexity is beyond the capacity of currently available experimental, computational and theoretical methods, and researchers in this field are obliged to use simplified sub-systems to mimic the complex phenomena. When the simplified conditions are properly chosen, these studies provide surprisingly accurate predictions for the real systems. In this paper we review the results obtained in kinetic and mechanistic studies on the model systems, but we do not discuss their broad biological or environmental implications. [Pg.396]

We have used the reaction of m-chloroperbenzoic acid with Co/Mn/Br as a model system to attempt to understand the nature of this important autoxidation catalyst. Using stopped-flow and UV-VIS kinetic techniques, we have determined the step-wise order in which the catalyst components react with each other. The cobalt(II) is initially oxidized to Co(III) by the peracid, the cobalt(III) then oxidizes the manganese to Mn(III), which then oxidizes the bromide. The order of these redox reactions is the opposite to that expected from thermodynamics. Suggestions will be made of the relationship of this model to the known characteristics of autoxidation processes. [Pg.81]

Various methods have been employed to measure the extent of autoxi-dation in lipids and lipid-containing food products. For obvious reasons, such methods should be capable of detecting the autoxidation process before the onset of off-flavor. Milk and its products, which develop characteristic off-flavors at low levels of oxidation, require procedures that are extremely sensitive to oxidation. Thus methods of measuring the decrease in unsaturation (iodine number) or the increase in diene conjugation as a result of the reaction do not lend themselves to quality control procedures, although they have been used successfully in determining the extent of autoxidation in model systems (Haase and Dunkley 1969A Pont and Holloway 1967). [Pg.241]

It is interesting to consider the concentrations of free radicals that result from lipid hydroperoxides in an in vitro model system. For example, my group has been studying the autoxidation of linoleic acid in SDS micelles at 37°C. We initiate the autoxidation by the decomposition of an initiator, as shown in Equation 3. [Pg.90]

It has been known for many years that Maillard Reaction products can behave as antioxidants in food systems (13,14), and they have been shown to inhibit warmed-over flavor development in cooked meat which is caused by the autoxidation of lipids, especially phospholipids. There has been a significant amount of research examining the Maillard reaction products and intermediates from model systems which may have antioxidative properties. [Pg.444]

Mansuy, D., P. Battioni, and J.-P. Battioni. Chemical model. systems for drug-metabolizing cytochromc-P-450-dependent monooxygenases. Eur. J. Biochem. 184 (1989), 267-285. Miller, D. M., G. R. Buettner, and S. D. Aust. Transition metals as catalysts of autoxidation reactions. Free Radical Biol. Med. 8 (1990), 95-108. [Pg.588]

Hydroxylation Induced during the Autoxidation of N-benzyl-1,4-dihydronicotinamide. Oxygen was bubbled through the aromatic compound suspended in an aqueous solution of N-benzyl-l,4-dihydronico-tinamide and ferric chloride. Four compounds were oxidized by this model system benzene to phenol and no biphenyl toluene to benzyl alcohol, cresols, phenol, and no bibenzyl anisole to phenol and methoxyphenols fluorobenzene to phenol and fluorophenols. Even under optimum... [Pg.268]

It is the purpose of this review to (a) briefly outline the various radical reactions occurring during the course of autoxidation, (b) discuss the use of model systems in the study of the effects of lipid autoxidation on food ingredients, particularly proteins, and (c) assess the potential mutagenicity of autoxidation products. [Pg.64]

Labuza, T.P., J.F. Maloney, M. Karel, Autoxidation of methyl linoleate in freeze-dried model system II. Effect of water on cobalt catalyzed oxidation, J. Food Sci., 31, p. 885, 1966. [Pg.196]

Autoxidation is quite complex and involves a great number of interrelated reactions of intermediates. Hence, autoxidation of food is usually imitated by the study of a model system in which, for example, changes of one unsaturated fatty acid or one of its intermediary oxidation products are recorded in the presence of oxygen under controlled experimental conditions. [Pg.191]

The autoxidation of acridan esters has been of great value in the elucidation of the mechanism of luciferin oxidation, and is discussed as a model system for bioluminescence (Chap. (XII)). The following series of compounds which react in a related way summarises the main features which lead to moderately high light emission from the autoxidation of carbonyl compounds. The alkoxycarbamoyl furanones [37], whose chemiluminescent reactions are depicted in the scheme below, show the following useful features. [Pg.28]

It should be emphasized that clear-cut situations described in Schemes 1-3 are uncommon and typically the combination of these models needs to be considered for kinetic and mechanistic description of a real system. However, even when one of the limiting cases prevails, each of these models may predict very different formal kinetic patterns depending on where the rate determining step is located. For the same reason, different schemes may be consistent with the same experimental rate law, i.e. thorough formal kinetic description of a reaction and the analysis of the rate law may not be conclusive with respect to the mechanism of the autoxidation process. [Pg.399]


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Autoxidation aqueous model system

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