Antioxidants, analysis

Lussier [71] has given an overview of Uniroyal Chemical s approach to the analysis of compounded elastomers (Scheme 2.2). Uncured compounds are first extracted with ethanol to remove oils for subsequent analysis, whereas cured compounds are best extracted with ETA (ethanol/toluene azeotrope). Uncured compounds are then dissolved in a low-boiling solvent (chloroform, toluene), and filler and CB are removed by filtration. When the compound is cured, extended treatment in o-dichlorobenzene (ODCB) (b.p. 180 °C) will usually suffice to dissolve enough polymer to allow its separation from filler and CB via hot filtration. Polymer identification was based on IR spectroscopy (key role), CB analysis followed ASTM D 297, filler analysis (after direct ashing at 550-600 °C in air) by means of IR, AAS and XRD. Antioxidant analysis proceeded by IR examination of the nonpolymer ethanol or ETA organic extracts. For unknown AO systems (preparative) TLC was used with IR, NMR or MS identification. Alternatively GC-MS was applied directly to the preparative TLC eluent. 

H Indyk, DC WooIIard. Antioxidant analysis in edible oils and fats by normal-phase high-performance liquid chromatography. J Chromatogr 356 401-408, 1986. 

Keywords Phenolic acid phenolic HPLC GC antioxidant analysis... 

Antioxidant activity 842-845 practical Unlit to 899, 900 Antioxidants—see also Co-antioxidants analysis of 941, 947, 949, 955, 956, 960, 961, 981, 982 as food preservatives 982 biologicaUy active 913 calculations on 895-899 chain-breaking 840, 874 efficiency of 850-895, 900 media effects on 876-895 structural effects on 859-876 future prospects for 899-901 hydrogen atom donating abiUty of 865-867 in aircraft fuel 990 in alcohoUc beverages 973 in drinking water 963 induction period for 843 in foodstuffs 925 inhibition rate constants of 992 in Upid membranes 884-895... 

Also we have made a study of the antioxidants analysis in the seven samples of walnuts from the various producers using the amperometric method. The amperometric method is based on the measurement of electric current, which are come insight at the electrochemical oxidation of the substance or mixture of substances on the surfece of working electrode with the certain potential. The detector registers the change of current, which flows through the cells due of the changes in the concentration of antioxidants. 

Scheele and co-workers [73,74] have found extensive agreement between conductiometric and UV spectroscopic methods of quantitative antioxidant analysis. 

A related technique also very useful for antioxidant analysis in plastic materials is near infrared spectroscopy (NIR) [5], which utilizes the... 

The main reason for using induction time data for the determination of antioxidant concentration in polymers is the frequently observed linear relationship between induction time and antioxidant concentration [131]. In view of the aforementioned considerations great caution should be exercised in quantitative estimation of antioxidant levels in polymers. Wight [181] and others [143] have used quantitative differential thermal analysis (QDTA), in particular for determining the degree of oxidative stability of polyolefins for QC purposes in the wire and cable industry in lieu of a direct antioxidant analysis. Application of the basic purpose of a QC test... 

Table 13.1 lists the electrochemical methods developed for antioxidant analysis in several samples, including the details of sample preparation. The hardest challenge to adapt these methods to flow systems is the sample preparation step, especially for solid samples. The following paragraphs discuss some examples of electroanalytical methods associated with FIA applied to antioxidant (BHA, BHT, and TBHQ) analysis in food samples. 

TABLE 13.1 Electrochemical Methods Developed for Antioxidant Analysis in Several Samples, Including the Details of Sample Preparation... 

Table 13.2 lists the FIA methods with amperometric detection developed for antioxidant analysis in food samples including the antioxidant type, sample, and limit of detection. 

All electroanalytical methods, including the ones associated with FIA, devoted to antioxidant analysis in food samples require a prior sample treatment step such as... 

TABLE 29.4 Flow Methods with Spectrophotometric Detection for Antioxidant Analysis in Food Samples... 

Antioxidants have been shown to improve oxidative stabiHty substantially (36,37). The use of mbber-bound stabilizers to permit concentration of the additive in the mbber phase has been reported (38—40). The partitioning behavior of various conventional stabilizers between the mbber and thermoplastic phases in model ABS systems has been described and shown to correlate with solubiHty parameter values (41). Pigments can adversely affect oxidative stabiHty (32). Test methods for assessing thermal oxidative stabiHty include oxygen absorption (31,32,42), thermal analysis (43,44), oven aging (34,45,46), and chemiluminescence (47,48). 

Solvent extraction followed by gas chromatographic analysis is used to determine paraffin wax antioxidants (qv), ie, butylated hydroxyanisole and butylated hydroxytoluene and other volatile materials. Trace amounts of chlorinated organic compounds, eg, polychlorinated biphenyls, can be deterrnined by using a gas chromatograph with an electron-capture detector (22). 

M.15 In addition to determining elemental composition of pure unknown compounds, combustion analysis can be used to determine the purity of known compounds. A sample of 2-naphthol, C)0H7OH, which is used to prepare antioxidants to incorporate into synthetic rubber, was found to be contaminated with a small amount of LiBr. The combustion analysis of this sample gave the following results 77.48% C and 5.20% H. Assuming that the only species present are 2-naphthol and I.iBr, calculate the percentage purity by mass of the sample. 

Thermoanalytical techniques such as differential scanning calorimetry (DSC) and thermogravi-metric analysis (TGA) have also been widely used to study rubber oxidation [24—27]. The oxidative stability of mbbers and the effectiveness of various antioxidants can be evaluated with DSC based on the heat change (oxidation exotherm) during oxidation, the activation energy of oxidation, the isothermal induction time, the onset temperamre of oxidation, and the oxidation peak temperature. 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

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). 

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. 

SINGLETON v L, ORTHOFER R and LAMUELA-RAVENTOS R M (1999) Analysis of total phenolics and other oxidation substrates and antioxidants by means of Folin-Ciocalteu reagent, Meth Enzymol, 299, 152-78. 

Nutrient analysis of stabilized rice bran and its derivatives indicates that it is a good source of protein, dietary fiber and carbohydrates, in addition to several valuable phytonutrients, antioxidants, vitamins and minerals (Table 17.1). SRB and its water-soluble and water-insoluble derivatives contain all the nutrients at different levels. They are gluten and lactose free and do not give rise to any food allergy. 

Paganga, G. et al.. The polyphenolic content of fruit and vegetables and their antioxidant activities what does a serving constitute Free Radical Res., 30, 153, 1999. Maatta, K.R. et al.. High-performance liquid chromatography (HPLC) analysis of phenolic compounds in berries with diode array and electrospray ionization mass spectrometric (MS) detection Rihes species, J. Agric. Food Chem., 51, 6736, 2003. 

Beekwilder, J. et al.. Antioxidants in raspberry on-hne analysis links antioxidant activity to a diversity of individnal metabolites, J. Agric. Food Chem., 53, 3313, 2005. 

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