Antioxidant activity individual compounds

Glavind and Holmer proposed a method of determination of antioxidants by TLC using the DPPH radical. They sprinkled a plate with separated substances with methanol solutionofthe radical and observed discoloration where substances able to quench radicals were present [57]. The TLC-DPPH assay allows a researcher to access the analysed substances and to assess the biological activity of individual compounds. Another advantage of the method is the possibili-... 

Fig. 1. pH dependence of total antioxidant capacity of blood plasma and antioxidant activities of individual antioxidants. After Tubaro el al. (T7). TAC was estimated by crocin bleaching the value at pH 7.4 for each was assumed as 1 for each compound and blood plasma. 

Synergism is the cooperative effect of antioxidants or an antioxidant with other compounds to produce enhanced activity than the sum of activities of the individual... 

In nature, flavonoids usually occur as mixtures of several compounds rather than as pure solutions of one single polyphenol. To simulate this, attempts have been made to deduce the antioxidant capacity in fruits and berries and their products from the antioxidant capacity of their individual polyphenols. Frankel et al. (1995) calculated the antioxidant capacity of 14 red and 6 white wines from the antioxidant activity of the individual polyphenols determined in the wines. The calculated antioxidant activity accounted for only 25% of the measured value. The difference was partly ascribed to unidentified polyphenols and polyphenolic acids and their polymers. Thus, there apparently is still no complete understanding of the factors contributing to the antioxidative capacity of a product. The best strategy at present seems to be to measure the products of interest directly. 

In products with complex combinations of various types of flavonoids and other phenolic compounds, effort has been made to ascribe the antioxidant activity of the product to different classes of polyphenols. Frankel et al. (1995) studied 20 selected California wines and related the antioxidant activity to the polyphenolic components of the wines, rather than to resveratrol. Antioxidant activity was measured by the ability of the wines to inhibit copper-catalyzed oxidation of human LDL. The correlation coefficient between antioxidant activity and total phenolic components of the wines was r = 0.94. Individual phenolic compounds (gallic acid, catechin, myricetin, quercetin, caffeic acid, rutin, epicatechin, cyanidin, malvidin-3-glucoside) contributed to the antioxidant activity. The correlation coefficient for the compounds ranged from r = 0.92 to r = 0.38 in descending order. 

Recent studies " " have shown that some natural antioxidants, such as vitamin E, vitamin C, and carotenoids can exhibit synergistic interactions, with the consequence that a combination of these compounds has a better antioxidant activity than the sum of the individual components. 

In the same oxidation system, an enhanced antioxidant activity of carotenoid mixtures (lutein, lycopene, paprika, bixin, etc.) have been reported as compared to each separate compound. Moreover, Kiokias and Gordon found that mixtures of olive oil phenolics with various carotenoids exhibited a strong activity against the autoxidation of bulk and emulsified olive oil, whereas individual carotenoids presented no inhibitory effect. 

Isolation of individual compounds described above produced insufficient amounts for an in vivo evaluation of their antioxidant activities [32], Instead, in vivo testing was carried out using a WPF,... 

Spranger, I.M., C. M. Climaco, B. Sun, N. Eiriz, C. Fortunato, A. Nunes, C. M. Leandro, M. L. Avelar, P. A. Belchior. (2004). Total polyphenolic compounds contents (TPC), total antioxidant activities (TAA) and HPLC determination of individual polyphenolic compounds in selected Moravian and Austrian wines. Anal. Chim. Acta. 513,151-161. 

Just as in the case of individual compounds, in mixtures of two antioxidants replacement of the active hydrogen in the functional group by an alkyl radical leads to a reduction of the effectiveness of the mixtures. 

The EO of Elionurus elegans Kunth. (African pasture grass, Poaceae) was investigated for its biological activities. GC/MS analyses showed that the oil contains a-bisabolol (1.6% in the roots and 1.2% in the aerial parts). None of the other compounds exhibited in individual test systems antioxidative activities with the exception of limonene and, which were available only in low amounts. The antioxidant activity of the EO was tested with the chemiluminescence method using a luminometer, where the chemilnminescence intensity of the reaction mixture containing the EO or a standard (a-tocopherol), AAPH, and luminol was measured. The IC50 value for the EO obtained from the aerial parts amonnted to 30% and the 50% inhibition rate of the roots EO to 46%. 

The antioxidant capacity of anthocyanins has been demonstrated by radical scavenging of reactive oxygen species, reducing capacity, inhibition, or delaying of lipoprotein oxidation and platelet aggregation. Anthocyanins as individual compounds or present in a more complex extract have been found to play a role in the prevention of cardiovascular diseases and to be involved in several different events like the prevention of DNA damage, estrogenic activity, enzymatic inhibition, anti-inflammation response, lipid peroxidation inhibition, etc. [3-7]. 

Further studies on the dynamic interactions of polyphenols with physiological compoimds endowed with antioxidant activity showed that the polyphenols may be more intricately involved with physiologically relevant antioxidant mechanisms. Using continuous-flow EPR measurement, Laranjinha and Cadenas (1999) have demonstrated that the caffeic acid-derived o-semiquinone radical formed upon regeneration of a-TOH ifom a-tocopheroxyl radical may be reduced back to caffeic by ascorbate. Therefore, a sequence of redox-coupled reactions can be envisage whereby the radical character is sequentially transferred from lipid phases to the aqueous medium through the one-electron reduction of tocopheroxyl radical by caffeic acid and, in turn, of the caffeic acid radical by ascorbate. This sequence amplifies the antioxidant effects of individual compounds in lipid structures such as LDL (Laranjinha Cadenas, 1999). 

These results suggest that the antioxidant activity of some tested extracts might be attributed to the presence of non-phenohc compounds. Nevertheless, it should be taken into consideration that individual phenohcs may have distinct antioxidant activities there may be antagonistic or synergistic interactions between phenolics and other compounds like carbohydrates, proteins, etc. (Odabasoglu et al. 2005). 

Edris AE (2007) Pharmaceutical and therapeutic potentials of essential oils and their individual constituents a review. Phytother Res 21 308-323 El-Baroty GS, El-Baky HH, Earag RS et al (2010) Characterization of antioxidant and antimicrobial compounds of cinnamon and ginger essential oils. African J Biochem Res 4 167-174 Espina L, Somolinos M, Loran S et al (2011) Chemical composition of commercial citrus fruit essential oils and evaluation of their antimicrobial activity acting alone or in combined processes. Food Control 22 896-902... 

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