Antioxidant antioxidants, measurements

Quantification of antioxidant action usually relies on the reducing ability of antioxidants, measured either by electron transfer, reaction [16.15], or by hydrogen atom transfer reactions, reaction [16.16] ... 

At least some of the antioxidant nutrients are essential to human health, and others (such as carotenoids) may be highly beneficial, particularly in preventing cancer (e.g. Block et /., 1992). However, we do not yet know what dietary intakes are optimal. In principle, this could be investigated by varying the dietary intake of antioxidants and measuring free-radical damage in the human body. This is one of our current research directions. 

For many decades, the standard technique for measuring carotenoids has been high-pressure liquid chromatography (HPLC). This time consuming and expensive chemical method works well for the measurement of carotenoids in serum, but it is difficult to perform in human tissue since it requires biopsies of relatively large tissue volumes. Additionally, serum antioxidant measurements are more indicative of short-term dietary intakes of antioxidants rather than steady-state accumulations in body tissues exposed to external oxidative stress factors such as smoking and UV-light exposure. 

Corral-Aguayo R, Yahia EM, Carrillo-Lopez A and Gonzalez-Aguilar G. 2008. Correlation between some nutritional components and the total antioxidant capacity measured with six different assays in eight horticultural crops. J Agric food Chem 56 10498-10504. 

Sun T and Powers JR. 2007. Antioxidants and antioxidant activities of vegetables. In Shahidi F, Ho C-T, editors. Antioxidant Measurement and Applications. Washington, DC American Chemical Society, pp. 160-183. 

Figure 11.1. Effect of storage temperature (0, 5, 10°C) on (I) total anthocyanins (mg/100 g FW), (II) total phenols (mg/100 g FW), and (III) antioxidant capacity measured as ORAC (p.mol TE/g FW) of strawberry fruit (cv. Chandler). Bars show the final values after treatments. Different letters on top of the bars indicate statistical differences among treatments (p < 0.05).

Analysis of antioxidants (antioxidant status) for characterization of the anti-oxidative homeostasis in organisms by selective measurement of the ACP can be very meaningful for efficient supervision of antioxidant therapy as well. 

At best, then, consumption of green tea beverage or capsules containing the concentrated catechins as a cytoprotective and antioxidant measure is logical and supported by much data. At worst, this is a pleasant custom which appears to do no harm in the vast majority of cases. 

There are few direct comparisons of total phenol values and antioxidant measurements, although some do exist (e.g., Baderschneider... 

Asharani et al. (2010) compared the antioxidant activity (measured as a-tocopherol units per gram) of methanolic extracts from different varieties of finger millet ( . coracana), little millet (P. sumatrense), foxtail millet (S. italica), and proso millet (P. miliaceum). Extracts from ragi averaged 15.3 0.6 while those of little millet, foxtail millet, and proso millet were 4.7 1.1,5.0 0.4, and 5.1 0.8, respectively. The total tocopherols in these millets were 4.1 0.2,1.3 0.2,1.2 0.008, and 3.6 0.1 mg/lOOg flour. 

The definition of an antioxidant suggests a functional assay of antioxidants by measuring inhibition of appropriate (easy to study) oxidation reactions. Such assays can be called inhibition assays for antioxidants (Fig. 2). Various oxidants are used in TAC assays. In many cases, thermal decomposition of 2,2 -azobis (2-amidopropane) (ABAP) is the source of oxidizing radicals. ABAP undergoes temperature-dependent homolysis. The primary radicals produced by thermal decomposition of the initiator react with oxygen to produce peroxyl and alkoxyl radicals, which are oxidizing species in the system (Fig. 3). The amount of free radicals formed in an aqueous medium by decomposition of ABAP at pH 7.4 and at 37°C equals 1.36 x 10-6 [ABAP] x t, where t is time in seconds and [ABAP] is in mol L-1 (N8). 

Thyroid hormones and their structural analogs showed lower DPPH-scavenging activity in comparison with butylated hydroxytoluene (BHT) as a standard compound. 3,5,3, 5 -tetraiodothyroacetic acid, 3,3,5 -triiodo-L-thyronine, and thyroxine showed the highest antioxidant activity measured by DPPH reduction, 3,5,3 5 -tetraiodothyroacetic acid having over 20% of the activity of BHT (05). 

A9. Alho, H., and Leinonen, J., Total antioxidant activity measured by chemiluminescence methods. Meth. Enzyntol. 299, 3-14 (1999). 

To evaluate the activity of antioxidants, we measured the time needed for the absorption of 0.2, 0.5, 1.0, and 1.5 ml. of oxygen in 20 mg. of stabilized polypropylene at constant conditions. The values were denoted r0.2, r0.5, ri.0, and ri.5, respectively. The scattering of the values of r0.2 and especially of the values of r measured at oxygen absorption lower than 0.2 ml. 02 per 20 mg. polypropylene was considerably greater than that of to.5. Figure 1 shows that evaluating antioxidants at to.jt-ti.s values leads to the same conclusions about structural influences. It is advantageous to use more exact data. Therefore, the value of t0. 5 is used in the tables because it illustrates the initial phase of the reaction and it is less influenced by the apparatus error than the value of t02. 

In the second experiment, mice were irradiated with the highest dose from the dose-response experiment. Concentrations of lipid hydroperoxides and lipophilic antioxidants were measured simultaneously on single skin samples from irradiated and non-irradiated sides of each mouse. The lipid hydroperoxide assay directly measured lipid peroxidation and thus was superior to the TBARS assay, which is indirect. Lipid-peroxyl radicals have been linked to chemically induced cutaneous carcinogenesis [31] as well as to UV-light-induced cutaneous carcinogenesis [32],... 

More recently, studies on the absorption of flavonoid glycosides typical of berries and grapes are reported. Lapidot et al. (1998) traced anthocyanins in human urine after the intake of 300 ml red wine, corresponding to 218 mg of anthocyanins. Totals of 1.5-5.1% of the anthocyanins were recovered in the urine within 12 h after wine consumption, two compounds were unchanged, whereas other compounds seemed to have undergone molecular modifications. The anthocyanin levels of the urine reached a peak within 6 h of consumption. Serafini et al. (1998) tested the effects of the intake of the nonalcoholic fraction of red or white wine on plasma antioxidant capacity, measured as total radical-trapping parameter (TRAP), and on... 

The utility of antioxidants in terrestrial animals has received relatively little attention so far. In earthworms, inhibition of CAT and glutathione peroxidase but not SOD have been demonstrated in E.fetida exposed to lead and uranium (Labrot et al., 1996). However, SOD and CAT activity were not induced in E. veneta and E.fetida exposed to Zn, Cu and Hg and the herbicide paraquat (Honsi et al., 1999). Antioxidant enzyme measurement therefore cannot be considered a reliable biomarker of exposure in soil invertebrates. 

As indicated in the previous sections, the antioxidant content in plastic material is often determined by chromatographic methods. Another widely used technique for polymer characterization is thermal analysis with differential scanning calorimetry (DSC). When the oxygen induction time (OIT) for a sample containing a phenoHc antioxidant is measured, a significant oxidative exothermic response is obtained in the DSC when all the phenolic antioxidant in a sample is consumed. The OIT is thus directly related to the antioxidant content in the material and to the stabihzing function, i.e. the antioxidant efficiency in the sample, if the consumption of phenolic antioxidants obeys zero-order kinetics at the temperature used [44]. Table 1 shows the amount of the antioxidant Irganox 1081 in polyethylene (PE) determined by HPLC and extraction by microwave assisted extraction (MAE),... 

Common antioxidants in hydraulic fluids are measured over the region 3700-3595 cm The left baseline, high wave number side, is taken as the minima in the region of 4000-3820 cm and a right baseline, low wave number side, as the minima in the region of 2200-1800 cm For polyol ester fluids, antioxidants are measured over the region of 3400-3320 cm using the same baseline correction. 

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