Antioxidants efficiency

MADSEN H L, ANDERSEN c M, JORGENSEN L v and SKIBSTED L H (2000) Radical Scavenging by dietary flavonoids. A kinetic stndy of antioxidant efficiencies, EurFood Res Technol, 211, 240-46. 

ROGINSKY v A, BARSUKOVA T K, REMOROVA A A and BORS w (1996) Moderate antioxidative efficiencies of flavonoids during peroxidation of methyl linoleate in homogeneous and micellar solutions, J Am Oil Chem, Ti, 777-86. 

As mentioned earlier, physiological concentrations of carotenoids in vivo are in the micromolar range, mainly because of limited bioavailabiUty. Also, the antioxidant efficiencies of carotenoids after absorption are probably limited. Concentrations before absorption are much higher and can justify possible antioxidant actions in vivo. To test this hypothesis, Vulcain et al. developed an in vitro system of lipid peroxidation in which the oxidative stress is of dietary origin (metmyoglobin from meat) and different types of antioxidants (carotenoids, phenols) are tested. 

Another assay that is very similar to the ABTS assay is the AGV-dimethyl-p-phenylenediamine (DMPD assay). In the presence of a suitable oxidant solution at an acidic pH, DMPD is converted to a stable and colored DMPD radical cation (DMPD +). Antioxidants capable of transferring a hydrogen atom to the radical cause the decol-orization of the solution, which is spectrophotometrically measured at 505 nm. The reaction is stable, and the endpoint is taken to be the measure of antioxidant efficiency. Antioxidant ability is expressed as Trolox equivalents using a calibration curve plotted with different amounts of Trolox (Fogliano and others 1999). This method is used to measure hydrophilic compounds. The presence of organic acids, especially citric acid, in some extracts may interfere with the DMPD assay, and so this assay should be used with caution in those extracts rich in organic acids (Gil and others 2000). 

Allam SSM. 2007. Antioxidative efficiency of some common traditional Egyptian beverages. Riv Ital Sostanze Grasse 84(2) 94-103. 

The mechanism of prooxidant effect of a-tocopherol in aqueous lipid dispersions such as LDLs has been studied [22], This so-called tocopherol-mediated peroxidation is considered in detail in Chapter 25, however, in this chapter we should like to return once more to the question of possible prooxidant activity of vitamin E. The antioxidant effect of a-tocopherol on lipid peroxidation including LDL oxidation is well established in both in vitro and in vivo systems (see, for example, Refs. [3,4] and many other references throughout this book). However, Ingold et al. [22] suggested that despite its undoubted high antioxidant efficiency in homogenous solution a-tocopherol can become a chain transfer agent in aqueous LDL... 

Tests, of antioxidant efficiency, 21 789—790 Test temperatures, in fatigue testing, 13 487-488... 

H.L. Madsen, C.M. Andersen, L.V. Jorgensen and L.H. Skibsted, Radical scavenging by dietary flavonoids. A kinetic study of antioxidant efficiencies. Eur. Food Res. Technol. 211... 

No readily acceptable mechanism has been advanced in reasonable detail to account for the decomposition of hydroperoxides by metal dialkyl dithiophosphates. Our limited results on the antioxidant efficiency of these compounds indicate that the metal plays an important role in the mechanism. So far it seems, at least for the catalytic decpmposition of cumene hydroperoxide on which practically all the work has been done, that the mechanism involves electrophilic attack and rearrangement as shown in Scheme 4. This requires, as commonly proposed, that the dithiophosphate is first converted to an active form. It does seem possible, on the other hand, that the original dithiophosphate could catalyze peroxide decomposition since nucleophilic attack could, in principle, lead to the same chain-carrying intermediate as in Scheme 4 thus,... 

L14. Liegeois, C., Lermusieau, G., and Collin, S., Measuring antioxidant efficiency of wort, malt, and hops against the 2,2 -azobis(2-amidinopropane) dihydrochloride-induced oxidation of an aqueous dispersion of linoleic acid. J. Agric. Food Chem. 48, 1129-1134 (2000). 

Plasma levels of melatonin could not be delegate of its concentration in tissues [63], and its half-life in the target tissues could be much lower than expected. The availability of new compounds having the beneficial properties of melatonin, but revealing different pharmacokinetic properties could therefore be useful in the search for good antioxidant efficiency. 

Aldol condensation of the zinc enolate of resin-bound alkyl ester 29 with aromatic aldehyde or ketone forms a P-hydroxy ester, which upon treatment with DIBAL-H leads to simultaneous reduction and cleavage of the ester moiety from the resin to give a soluble 1,3-diol 31 [31], Parallel synthesis utilizing three ester and nine carbonyl building blocks afforded a library of 27 analogs which was screened for antioxidative efficiency using a ferric thiocyanate assay. 

Contrary to monoalkyl derivatives, the presence of two alkyl groups in positions 2 and 5 (Type Ic) and 2 and 6 (Type lib) lowered the efficiency of 4-alkoxyphenols. Similar influences of substitution can be shown when comparing the activities of 4-acetoxy-2-terf-octylphenol and 4-acetoxy-2,5-di-ferf-octylphenol (Table IV). The change in the nature of alkyl groups influences the activity of Type lib antioxidants in a manner similar to that of 2,4,6-trialkylphenols the antioxidative efficiency decreased in the latter group, introducing a bulkier alkyl group into position 4, when the substituents in the positions 2 and 6 remained the same (the values of relative activities are referred to hydroquinone). 

An interesting observation was made by Davies et al. (1956) on the correlation of the fundamental vo h stretching frequencies and the antioxidant efficiencies of phenols. Still, several workers could not find any significant isotope effect (Bickel and Kooyman, 1957 Shelton and McDonel, 1958 Ingold, 1960a) and the complex mechanism was further applied (Caldwell and Ihrig, 1960 Hammond and Nandi, 1961). 

Novolaks 127 formed from p-cresol and 2-terr-butyl-4-methylphenol were studied in some details [159], Phenolic groups present in 127 are not equivalent in the reactivity with RO2. A good antioxidant efficiency was observed in PS and poly (ethylene-co-propylene), even with polycondensates having n > 15. Polycondensate 128 is an example of AO which may be used in contact with food [160]. 

The migration principle was suggested as the reason of the enhancement of the antioxidant activity of polyester-polyether elastomer-bound hindered phenol by the addition of 0.25% of an easier migrating AO, 4,4 -bis(a,a-dimethylbenzyl)di-phenylamine (5) [181] this easier migrating amine is regenerated by the immobilized phenolic moiety, by means of the principle of homosynergism [5]. Similarly, a blend of polymeric redox hydroquinone-benzoquinone AO with equal amounts of iV-phenyl-iV -(l,3-dimethylbutyl)-l,4-phenylenediamine exerted a pronounced increase of antioxidant efficiency in SBR [124]. A synergistic combination based... 

Khopde SM, Priyadarsini Kl, Venkatesan P, Rao MNA. (1999) Free radical scavenging ability and antioxidant efficiency of curcumin and its substituted analogue. Biophys Chem 80 85-91. 

Moore DE. Antioxidant efficiency of some polyhydric phenols in the photooxidation of benzaldehyde. J Pharm Sci 1976 65 1447-1451. 

Results on comparative antioxidant efficiency on crude palm oil (Table VI) again show ascorbic acid to be very active. 

Very recently a family of diphenyltin(IV) compounds was tested in vitro against human tumor cell lines to assess their cytotoxic activity, and the same family of compounds was also tested for antioxidant efficiency in rat brain homogenate, showing that there is a structure-activity relationship in the latter case. The correlation suggests that selected molecular variables are prototype tracers for the calculation of inhibitory concentrations. Moreover there seems to be an inverse structure-response behavior among activities, since the most hydrophobic organotin molecule is the least active compound for cytotoxic assays, while it is the best in anti-oxidant tests. 

Although phospholipid bilayers are better mimics of biomembranes than are micelles, there are few reliable quantitative data on flavonoid antioxidant activities in lipid bilayers. Terao and coworkers compared the antioxidant efficiency of quercetin and catechins (epicatechin and epicatechin gallate) with that of a-Toc in egg yolk PC liposomes using initiation by the water-soluble initiator, ABAP, and analysis of hydroperoxide formation and antioxidant consumption by HPLC. Based on the length of the induction periods and the profile of suppressed hydroperoxide formation, they concluded that quercetin and the catechins were more efficient antioxidants than a-Toc in these bilayers. Apparently the unique behavior of a-Toc in bUayers is responsible for these results (vide supra). In hexane and alcohols solution during suppressed peroxidation of methyl linoleate, the relative antioxidant activities reversed so that the flavonoids were 5-20 times less active... 

To sum up the state of antioxidant efficiencies of the flavonoids, a few general conclusions can be reached. 

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