Assay antioxidative processes

The antioxidant activity of individual tea polyphenols in different model assays showed a proportional relationship to the number of hydrogen radical donors of catechins. A synergistic effect was observed between tea catechins and caffeine, ascorbic, citric, malic, and tartaric acids and tocopherols (153). Formation of oxidation products of (+)-catechin dirring the antioxidative process has been observed in oxidation model studies. According to the proposed mechanism, (+)-catechin can scavenge four radicals per molecule (154, 155). Yamamoto et al. (156) have summarized the chemistry and application aspects of green tea, especially in relation to using their catechins. 

UNIVERSAL CHEMILUMINESCENT ASSAY FOR OXIDATIVE AND ANTIOXIDATIVE PROCESSES IN CHEMICAL AND BIOLOGICAL MEDIA FUNDAMENTALS AND APPLICATION ASPECTS... 

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. 

The correlation between the TEARS assay and MDA dnring oxidation of edible oils may be complicated by the presence of tocopherols (e.g. Vitamin E, 21) . An evaluation was carried of MDA, determined by an independent method , and TEARS as indices for direct oxygen uptake of edible oils and unsatnrated fatty acids. The linear increase of MDA and TEARS with oxygen consumption of soybean oil, in a closed vessel at 170 °C, stops when the latter value reaches 500 p.molL, when both MDA and TEARS start to decrease on further O2 consumption. The same process carried out at 40 °C, using 2,2 -azobis(2,4-dimethylvaleronitrile) (171) as initiator, shows linearity up to 1500 p,molL O2 consumption . A similar behavior is observed for nnsatnrated fatty acids snch as oleic, linoleic and linolenic acids . On the other hand, depletion of Vitamin E (a-tocopherol, 21) and its analogs y- and 5-tocopherol (172, 173) present in the oil show a linear dependence on O2 consumption of the oil, np to 1800 p,molL . This points to the consumption of these antioxidants, and especially 21, as a good index for the O2 uptake in oils at high temperature. The determination of the tocopherols is carried ont by HPLC-FLD (Xex = 295 nm, Ah = 325 nm) . ... 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

Numerous methods are required to characterize drug substances and drug products (Chapter 10). Specifications may include description identification assay (of composite sample) tests for organic synthetic process impurities, inorganic impurities, degradation products, residual solvents, and container extractables tests of various physicochemical properties, chiral purity, water content, content uniformity, and antioxidant and antimicrobial preservative content microbial tests dissolution/disintegration tests hardness/friability tests and tests for particle size and polymorphic form. Some of these tests may be precluded, or additional tests may be added as dictated by the chemistry of the pharmaceutical or the dosage form. 

In conclusion, in this work we demonstrate the excellent capabilities of using ASE to extract compounds with antioxidant activity from natural sources as rosemary leaves and the microalga Spirulina platemis. ASE shows several advantages compared with traditional extraction processes such as 1) it is faster (IS min vs 2-24h in traditional extraction procedures) 2) it has less solvent volume consumption (13 ml vs 30>S00 mL/lOg) 3) it is more efficient (less dependant on matrix) and 4) it is automatic and allows sequential extraction of samples. The use of in-vitro assays and CE coupled to both, DAD and ESI-MS allows obtaining information about the biological and chemical properties of the ASE extracts. 

Electron Paramagnetic Resonance (EPR, ESR) spectroscopy is a unique tool to answer specific questions evolving radical processes in both research and development (R D) as well as quality control (QC). Key QC examples comprise the food irradiation control for customer care according to European Union (EU) norms and the flavour stability and shelf life assessment on fresh beer. For the first time, an automated DPPH-assay to measure the effectiveness of antioxidants by CW-EPR is reported. 

Robards, K., Prenzler, P.D., Tucker, G., Swatsitang, P. and Glover, W. Phenolic compounds and their role in oxidative processes in fruits. Food Chem. 66, 401-436 (1999). Roberts, W.G. and Gordon, M.H. Determination of the total antioxidant activity of fruits and vegetables by a liposome assay. J. Agric. Food Chem. 51, 1486-1493 (2003). Schlesier, K. Harwat, M. Bohm, V. and Bitsch, R. Assessment of antioxidant activity by using different in vitro methods. Free Rad. Res. 36, 177-187 (2002). 

To determine the real effects of natural antioxidants, it is important to obtain specific chemical information about which products of lipid peroxidation are inhibited. Several specific assays are needed to elucidate how lipid oxidation products act in the complex multi-step process of lipid peroxidation (Figure 13.6) and oxidative damage in biological tissues. The results of many complementary methods are required to determine oxidation products formed at... 

Helichrysum (strawflower, Asteraceae) species are traditionally used for the treatment of wounds, infections, and respiratory conditions (Lourens et al., 2004). In the inflammatory process free radicals adsorb on the phagocyte cells, so the antioxidative activity of the extract and the EOs of different Helichrysum species were examined. Therefore, the plant material of Helichrysum dasyanthum, Helichrysum excisum, and Helichrysum petiolare were collected and the EO obtained by hydrodistillation. The GC-MS analysis showed that 1,8-cineole (20-34%), p-cymene (6-10%), and a-pinene (3-17%) are principal components of the EO. The EOs of all three different species show an antioxidative activity in the DPPH assay, bnt it has to be noticed that the extract, which was obtained by a cold... 

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