Antioxidant assay

The use of real food systems for detailed studies of antioxidants is complicated by a large number of factors which are often unknown or cannot be controlled due to the complex nature of foods. Using simplified model systems, which mimic the main features of a given food system, or antioxidant assays for quantifying the antioxidant action, can be very helpful in clarifying the action of potential antioxidants (Aruoma, 1996 Moller et al, 1999 Prior and Cao, 1999 Frankel and Meyer, 2000). The extrapolation of conclusions based on the behaviour of model systems or antioxidant assays to real complex food systems should generally be done with great care, and should ideally be based on results from more than one model system or assay (Frankel and Meyer, 2000). 

A number of handbooks and monographs are available with detailed descriptions of a variety of plant products and their use (Shahidi and Naczk, 1995). From a more practical point of view, an interlaboratory comparison between six university and industry laboratories of 17 extracts of spices, teas, coffees, and grape skin and of tomato peel slurry established within the framework of an EU sponsored programme, would be of interest (Schwarz et al, 2001). In this collaboration, detailed chemical analysis of the content of different phenolic compounds is compared with six antioxidant assays for the 17 extracts including different extraction procedures. 

SCHWARZ K, BERTELSEN L H, NISSEN L R, GORDNER P T, HEINONEN M I, HOPIA A, HUYNH-BA T, LOMBELET p, MCPHAIL D, SKIBSTED L H and TIJBURG L (2001) Investigation of plant extracts for the protection of processed foods against lipid oxidation. Comparison of antioxidant assays based on radical scavenging, lipid oxidation and analysis of the principal antioxidant components, Eur Food Res Technol, 212, 319-28. 

Table 1 Some Principal Systems for Antioxidant Assay... 

FIGURE 4.10 Average responses in antioxidant assays for microoxygenated (mo) and control wines, for 4 replicates of 162 Spanish wines (n — 648). Values that are significantly different (LSD test, p = 0.05) are given different letters. Reprinted with permission from Rivero-Perez et at. (2008). Copyright 2008 Elsevier. 

The pharmacokinetic dispositions of other stilbenes that are structurally similar to resveratrol and have pharmacological activity across many anticancer, anti-inflammatory, and antioxidant assays have been studied. The pharmacokinetics was characterized in male Sprague-Dawley rats after single intravenous... 

Much less is known on the antioxidant activity of tocotrienols than tocopherols. Tocotrienols were shown to have similar reactivities to peroxyl radicals and antioxidant activities than tocopherols in solution and membranes (Yoshida et ah, 2003) also, in general, y-tocotrienol was a better antioxidant than a-tocotrienol, and tocotrienols were better than tocopherols in oil systems (Seppanen et ah, 2010). Recently, Muller et ah (2010) conducted a comparative study to investigate the four tocopherols, four tocotrienols, and a-tocopheryl acetate on their antioxidant activities in five different popular in vitro assays (FRAP, a-TEAC, DPPH, ORAC, and CL), which were adapted to nonpolar antioxidants. Most notably, they found that a-tocopheryl acetate, a popular ingredient in supplements, had no significant antioxidant activity in vitro. However, once ingested, tocol esters are hydrolyzed and antioxidant activities are retained. Overall, the eight tocols performed similarly in the five assays. The authors concluded that in vitro antioxidant assays performed in polar solvents are not a good way to predict in vivo antioxidant activity. 

Table 9 Comparison of absorbance values and percent inhibition of Knoleic add peroxidation as measured by the FTC and TBA antioxidant assays.

Antioxidative assay. Antioxidative activity was measured by DPPH method [10,11]. 

Antioxidative Activity of MaUlard Reaction Extracts. In the antioxidative assay system utilized in this study heptanal was readily oxidized to heptanoic acid in the dichloromethane solutions. However, the presence of a-tocopherol (Figure 1) inhibited this transformation in a concentration dependent manner. This system was then used to evaluate the antioxidative activity of dichloromethane extracts of several Maillard reaction model systems. Figure 2 shows the antioxidative activity of 5- iL aliquots of each pH extract from a microwave heated glucose/cysteine model system. The order of antioxidative effect of the extracts from the samples was as follows pH 9 > pH 5 > pH 2 > pH 7. The Maillard reaction is catalyzed under both slightly basic and acidic conditions and may explain this trend. Volatiles from sugar/cysteine Maillard reaction... 

Due to the presence of different antioxidant compounds which may act through different meehanisms, no single method can be used to estimate the total antioxidant capacity of finits extracts. Different antioxidant assays were used to assess the antioxidant activity, such as ferric reducing ability of plasma (FRAP), permanganate reducing antioxidant capacity (PRAC), 2,2-diphenylpiciylhydrazyl (DPPH) ass, P-carotene bleaching assay, deoxyribose method. 

All investigated Cornelian cherry genotypes showed high antioxidant capacity evaluated by all mentioned antioxidant assays [Yihnaz et al., 2009 Popovic et al., 2012 Hassanpour et... 

Because antioxidant capacity estimates are likely to vary with teehniques, the author s recommend to use of more than one antioxidant assay for the determination of antioxidant power of small fruit samples [40]. 

Flow injection methodology was used to estimate the total phenolic content of wine using acidic potassium permanganate chemiluminescence detection by Costin et al. (2003). Simple phenolic compounds such as quercetin, rutin, catechin, epicatechin, ferulic acid, caffeic acid, gallic acid, 4-hydroxycinnamic acid, and vanillin were examined analytically with chemiluminescence. Analysis of 12 different wines showed that detection limits were 2 x 10 M for caffeic acid, 3 x 10 M for ferulic acid, and 5 x 10 M for gallic acid. Comparison of the results of the chemiluminescence methodology and other total phenol/antioxidant assays showed that their correlation was good. Chemiluminescence... 

Kedare, S. B. and R. R Singh. 2011. Genesis and development of DPPFI method of antioxidant assay. Journal of Food Science and Technology 48(4) 412-422. 

Mnatsakanyan, M., T. A. Goodie, X. A. Conlan, P. S. Francis, G. P. McDermott, N. W. Barnett, D. Shock, F. Gritti, G. Guiochon, and R. A. Shalliker. 2010. High performance liquid chromatography with two simultaneous on-line antioxidant assays Evaluation and comparison of espresso coffees. Talanta 81(3) 837-842. 

Sharma, O. P. and T. K. Bhat. 2009. DPPH antioxidant assay revisited. Food Chemistry 113(4) 1202-1205. 

FIGURE 33.1 Schematic representation of the 96-well microplate distribution of experiments for antioxidant determination AO to AO5, correspond to increasing concentrations of antioxidant standard solutions, each analyzed in quadruplicate Sj to Sig, correspond to different sample solutions, each analyzed in quadruplicate. The different modes of measurement mostly used in antioxidant assays, including the absorbance, fluorescence, and chemiluminescence, are represented at the bottom. 

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