The aim of this work was to determine antioxidant capacity of beverages containing black, white, and green tea extracts using the photochemiluminescence method, and to monitor its changes based on the storage temperature and time. Samples were stored at two different temperatures (refrigerated at 4°C and laboratory temperature 22°C), analyzed after opening of the original package, and consequently after 4 and 7 days. Results of the antioxidant capacity are expressed as the standard equivalents, that is, ascorbic acid in mmol/L. The highest mean value of the antioxidant capacity was found after opening of the original package in fruit-juice-enriched samples and totaled 9.793 mmol/L. This group revealed significant dependence (P < 0.05) not only on the storage time, but also temperature. In samples without added fruit juices containing preservatives the value was 0.428 mmol/L. This group showed significant dependence (P < 0.05) on the decrease of antioxidant capacity only when based on the storage time. Samples without fruit juices or preservatives showed significant decrease in the antioxidant capacity (P < 0.05) after 4 days of storage based on the storage time. The dependence on temperature was revealed only after 7 days of storage.
Estrogens are chemical compounds considered to be endocrine disruptors. They are thought to affect the endocrine system even at low concentrations found in water (ng·l -1 ). The aim of this work was to determine estrogenic compound levels in the rivers in the Brno area. The concentration of 17β-estradiol, ethynylestradiol, estrone and diethylstilbestrol was estimated in the water samples collected in the Svratka and Svitava rivers.Estrogens were isolated from the samples using solid-phase extraction with Oasis HLB cartridges and determined by means of reversed phase HPLC with UV detection. The detection limit of the method used was 6 ng·l -1 , repeatability expressed as RSD was 11%, and recovery was 87 -103%. Estrogen values detected ranged in the interval of 6-209 ng·l -1 , depending on the sampling site. After treatment in the sewage water treatment plant, the water displayed markedly lower levels of estrogenic compounds.The results of the experiment demonstrate that HPLC-UV is a suitable method for determination of low concentrations of estrogens in water. The sewage water treatment plant reduces concentrations of estrogens but not sufficiently to prevent their estrogenic effect on fish.
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