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Antioxidant status of South African beverages and its role on the chemical parameters in human blood
In recent years antioxidants present in various beverages have attracted a great deal of research interest due to their potential benefits to human health. Epidemiological evidence shows an indirect relationship between the intake of beverages rich in antioxidants and the reduced incidences of some chronic diseases, certain cancers and coronary heart disease mortality. The study was divided into two phases. The aim of the first phase was to compile a database of antioxidant capacities (Oxygen radical absorbance capacity, Ferric reducing antioxidant potential and Trolox equivalent antioxidant capacity) and contents (polyphenols, flavonols, flavanols, anthocyanins and vitamin C) of selected South African beverages. The second phase of the project included an intervention study to investigate the short term in vivo effects of consumption of an antioxidant-rich beverage, rooibos, on the antioxidant and oxidative stress status of human participants. The parameters that were investigated in human plasma included the total antioxidant capacity (ORAC and FRAP) and content (total polyphenols) as well as the reduced-oxidised glutathione ratios (GSH/GSSG) in erythrocytes. Results from this study were used to compile a database for antioxidant capacities and contents of selected South African beverages. The results showed that, in the case of fruit juices their antioxidant capacity and content covered a wide range. This could be attributed to the juice's differences in fruit composition, e.g. either as a single fruit or as a combination of two or more fruits. In the case of wines, red wines had the highest antioxidant capacity for all the beverages tested and had 22 times higher polyphenols compared to that of white wines. Results also indicated that black tea and coffee had a higher antioxidant capacity and polyphenol content than the local herbal tea, rooibos. The duration of extraction (brewing) of the teas also influenced the antioxidant capacity. Correlations between the three antioxidant capacity assays were very high in the case of wines and teas, but lower in the case of fruit juices. This antioxidant database for South African beverages is useful not only to consumers, but also nutritionist, researchers, dieticians and functional food formulators.