ORAC assay

The on-line measurement of reducing capacity can be performed with either a single or a series of electrochemical detectors, and linear correlations have been demonstrated between total antioxidative activities determined by the electrochemical detection and those determined by DPPH- reduction or by the ORAC assay (Guo et al, 1997 Peyrat-Maillard et al, 2000). The reducing capacity must also be quantified by post-column reactions, either with DPPH- or by the reduction of phosphomolybdenum complexes followed by UV-VIS-detection (Bandoniene and Murkovic, 2002 Cardenosa et al, 2002). A combination of HPLC and semi-automatic ORAC analysis has also been described (Caldwell, 2001). 

Orange (Citrus sinensis) was found to be more active than pink grapefruit (Citrus paradisi) in scavenging peroxyl radicals, whereas grapefruit juice was more active than orange juice, when the oxygen radical antioxidant capacity (ORAC) assay was used... 

Yellow and red onions (Allium cepa) were reported to be poor antioxidants toward oxidation of methyl linoleate (Kahkonen and others 1999) in contrast to their high antioxidant activity toward oxidation of LDL (Vinson and others 1998). Garlic (Allium sativum L) was reported to have four times more antioxidant activity than onions when using the ORAC assay (Cao and others 1996). 

ORAC Assay (Oxygen-Radical Absorbance Capacity)... 

The ORAC assay proposed by Ou and others (2001) is limited to hydrophilic antioxidants because of the aqueous environment of the assay. However, lipophilic antioxidants play a critical role in biological defense systems. Huang and others (2002) expanded the assay to the lipidic fraction by introducing a randomly methylated 13-cyclodextrin (RMCD) as a water-solubility enhancer for lipophilic antioxidants. Various kinds of foods, including fruit juices and drinks, fruits, vegetables, nuts, and dried fruits, have been evaluated with this method (Zhou and Yu 2006 Wu and others 2004 Kevers and others 2007 Wang and Ballington 2007 Almeida and others 2008 Mullen and others 2007). 

Thaipong K, Boonprakoba U, Crosby K, Cisneros-Zevallos L and Byrne DH. 2006. Comparison of ABTS, DPPH, FRAP, and ORAC assays for estimating antioxidant activity from guava fruit extracts. J Food Compos Anal 19(6-7) 669-675. 

Many methods of determination of TAC have been automated. Automatization of the ORAC assay by using the COBAS Fara II analyzer with fluorescence and robotic attachment permits 24 parallel analyses per mn (C15). A semiautomated version of the ORAC assay has been proposed for determination of 45 simultaneous analyses (Cl). 

Fluorescein (FL) (3, 6 -dihydroxyspiro[isobenzofuran-l[3H], 9 [9H]-xanthen]-3-one) was used for the ORAC assay. Excitation and emission filters of 490 and 520 nm, respectively, were used. A stock solution of 1.2 mM FL was diluted to a working solution of 94 nM made up in 0.75 mM phosphate buffer (pH 7.4). Two pipettors, which were part of the microplate... 

ORAC assay uses )3-phycoerythrin fluorescence decay, AAPH [2,2 -zobis(2-amidinopropane) dihydrochloride] as inducer and Trolox as reference. 

Folch-Cano, C., C. Jullian, H. Speisky, and C. Olea-Azar. 2010. Antioxidant activity of inclusion complexes of tea catechins with beta-cyclodextrins by ORAC assays. Food Res. Int. 43(8) 2039-2044. 

Furthermore, the oxygen radical absorbance capacity (ORAC) assay has been used to evaluate the total antioxidant activity of polyaniline/ PE blends by monitoring the oxidation of fluorescein, a fluorescence probe, into non-fluorescent products by the peroxy radicals generated in the analysis mixture [3]. The relative ORAC values, converted to trolox equivalents, indicated the antioxidant efficacy of the blend samples. As shown in Figure 4.6, the ORAC values and hence the total antioxidant activity, of the blend samples increased with increasing polyaniline content in the blend. 

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