Antioxidant properties measurements

Mooradian (1993) has studied the antioxidant properties of 14 steroids in a non-membranous system in which the fluorescence of the protein phycoerythrin was measured in the presence of a lipid peroxyl radical generator (ABAP). Oxidation of the protein produces a fluorescent species. Quenching of fluorescence by a test compound indicates antioxidant activity. Oestrone, testosterone, progesterone, androstenedione, dehydroepian-drosterone, cortisol, tetrahydrocortisone, deoxycorti-... 

This method is also used to measure ex vivo low-density lipoprotein (LDL) oxidation. LDL is isolated fresh from blood samples, oxidation is initiated by Cu(II) or AAPH, and peroxidation of the lipid components is followed at 234 nm for conjugated dienes (Prior and others 2005). In this specific case the procedure can be used to assess the interaction of certain antioxidant compounds, such as vitamin E, carotenoids, and retinyl stearate, exerting a protective effect on LDL (Esterbauer and others 1989). Hence, Viana and others (1996) studied the in vitro antioxidative effects of an extract rich in flavonoids. Similarly, Pearson and others (1999) assessed the ability of compounds in apple juices and extracts from fresh apple to protect LDL. Wang and Goodman (1999) examined the antioxidant properties of 26 common dietary phenolic agents in an ex vivo LDL oxidation model. Salleh and others (2002) screened 12 edible plant extracts rich in polyphenols for their potential to inhibit oxidation of LDL in vitro. Gongalves and others (2004) observed that phenolic extracts from cherry inhibited LDL oxidation in vitro in a dose-dependent manner. Yildirin and others (2007) demonstrated that grapes inhibited oxidation of human LDL at a level comparable to wine. Coinu and others (2007) studied the antioxidant properties of extracts obtained from artichoke leaves and outer bracts measured on human oxidized LDL. Milde and others (2007) showed that many phenolics, as well as carotenoids, enhance resistance to LDL oxidation. 

Analysis of antioxidant properties relative to the DPPH" radical involves observation of colour disappearance in the radical solution in the presence of the solution under analysis which contains antioxidants. A solution of extract under analysis is introduced to the environment containing the DPPH radical at a specific concentration. A methanol solution of the DPPH radical is purple, while a reaction with antioxidants turns its colour into yellow. Colorimetric comparison of the absorbance of the radical solution and a solution containing an analysed sample enables one to make calculations and to express activity as the percent of inhibition (IP) or the number of moles of a radical that can be neutralised by a specific amount of the analysed substance (mmol/g). In another approach, a range of assays are conducted with different concentrations of the analysed substance to determine its amount which inactivates half of the radical in the test solution (ECso). The duration of such a test depends on the reaction rate and observations are carried out until the absorbance of the test solution does not change [4]. If the solution contains substances whose absorbance disturbs the measurement, the concentration of DPPH radical is measured directly with the use of electron paramagnetic resonance (EPR) spectroscopy. 

A number of studies have examined the antioxidant activities of chitosan from various sources. Park et al. (2004a) prepared three kinds of partially deacetylated hetero-chitosans such as 90% deacetylated, 75% deacetylated, and 50% deacetylated chitosan from crab chitin, and their antioxidant properties were measured using electron spin resonance spectrometry. Park and coworkers found that their antioxidant activities were dependent on the DD, and the 90% deacetylated chitosan showed the highest free radical scavenging activities. Yen et al. (2008) also found that a sample with more amino groups at the C-2 position showed the highest antioxidant activity. Tomida et al. (2009) examined the protective effects of seven different MW chitosans on plasma protein from oxidation by peroxyl radicals. In the ability to protect plasma protein from... 

C. Guitton, P. Gros, M. Comtat, R. Tarroux and P. Bordat, Evaluation of antioxidant properties of dermo-cosmetic creams by direct electrochemical measurements, J. Cosmet. Sci., 56 (2005) 79-90. 

Abstract. Adsorption of antioxidants (vitamins C and E) from aqueous and ethanol solutions on unmodified and partially hydrophobized nanosilica A-200 was studied using UV spectroscopy and quantum chemical methods with consideration for the solvent effects. Antioxidant power of silica nanocomposites with immobilized vitamins was evaluated by measuring the total polyphenolic index following the Folin-Ciocalteu method. It has been shown that immobilization of vitamins on silica surface leads to their stabilization. Being released from the carrier molecules of vitamins do not lose their antioxidant properties... 

Oil (Aa 4-38) determines oil content in a dried sample of oil-bearing material by extraction with petroleum ether. This method is specific for cottonseed, which first must be fumed with hydrochloric acid to prevent oil adsorption to the fiber. Additional methods exist for other oilseeds. Oxygen Stability Index (OSI) (Cd 12b-92) measures the oxidation induction period of fat sample (essentially the time for a sample to exhaust its antioxidant properties) under conditions of the test. 

In order to measure the antioxidant properties of Crataegus oxycantha extract, we used lumino 1-dependent CL. Luminol is a suitable enhancer, because it reacts with all ROS. This allows an estimation of the effect of the extract on the system for ROS generation, as well as a comparing the effects observed in the model systems. 

The ozone concentration in the troposphere during the daytime is typically about 1 pphm (parts per hundred million parts of air by volume) [20], Values up to 100 pphm were measured in some photochemical smog areas. The molecular mechanism of the ozone aging of diene based elastomers was studied in detail and is well understood [19,21], Products or intermediates different from those arising in autoxidation or photo-oxidation of polymers were identified ozonides (3), zwitterions (4), diperoxides (5), polyperoxides (6), polymeric ozonides (7) and terminal aldehydes (8). Reactivity of aminic antiozonants (AOZ) with these species accounts for the protection of rubbers against atmospheric 03. AOZ must also possess antioxidant properties, because the free radical processes are concerted with ozonation due to the permanent presence of oxygen. 

By polarographic measurements, Baltes (1964) calculated the following normal oxidation potentials, in connection with a comparison of the antioxidant properties of the tocopherols a-tocopherol 4-754 mV P-tocophcrol 4-824 mV 7-tocopherol 4-829 mV S-tocopherol 4 886 mV. 

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