In this study, the in vitro low-density lipoprotein oxidation model was used to assess the relative antioxidant activity of the polyphenolic beverages tea, coffee, and cocoa on a cup-serving basis. The beverages were prepared as 0.7-2.5% soluble coffee and 1.5-3.5% cocoa; teas (green, black, or herbal) were prepared as one tea bag infused over 5 min in 220 mL of hot water. Under these standard cup serving conditions, the antioxidant activity as determined by the lag time was in the range of 292-948 min for coffee, 217-444 min for cocoa, 186-338 min for green tea, 67-277 min for black tea, and 6-78 min for herbal tea. Addition of milk did not alter the antioxidant activity. The influence of coffee bean source and degree of roasting was further investigated. Green coffee beans of Robusta coffee exhibited a 2-fold higher antioxidant activity than Arabica coffee, but after roasting this difference was no longer significant. In conclusion, these commonly consumed beverages have a significant antioxidant activity, the highest being soluble coffee on a cup-serving basis.

The following study investigates the preparation of human blood plasma for metabolomic profiling analysis by ultrahigh performance liquid chromatography coupled to time-of-flight mass spectrometry (UPLC/TOFMS) in a novel two-step design study. Four different organic solvents (acetonitrile, acetone, methanol, and ethanol) were used to assess human blood plasma preparation via protein precipitation. The optimal conditions for sample preparation were investigated, with consideration to the number of extracted markers, data quality/reproducibility, and column lifetime prolongation. Isotopically labeled internal standards were used to monitor data quality/reproducibility. Gel electrophoresis was also used to measure the protein content in the supernatant of the "first design step" allowing assessment of the amount of protein that would be injected/accumulate onto the column after many injections that would be apparent in a global metabolic profiling study. The second design step followed on from the results obtained in step one, with four of the best conditions selected and further investigated, looking at the effects of vortex time and temperature on precipitation/extraction. Two choices of solvent compositions were found to be "optimal" for preparation of plasma for global metabolic profiling analysis; these were "methanol/ethanol" (1:1, v/v) and "methanol/acetonitrile/acetone" (1:1:1, v/v/v) added to plasma (4:1 ratio, 400 microL total volume).

Objective: To evaluate the plasma kinetics in man of epicatechin from black chocolate. Design: An intervention study with 8 volunteers. Each served as his own control. Theobromine was used as control marker of the chocolate intake. Setting: Metabolic Unit, Nestle  Research Center, Vers-chez-les-Blanc, Switzerland. Subjects: Eight healthy male volunteers (4 smokers and 4 non-smokers) were enrolled in this study. They abstained from foods rich in polyphenols (coffee, tea, wine, fruit juice, cocoa products) for 24 h prior to the test until its completion. Intervention: Volunteers ate 40 g and 80 g of black chocolate (Nestle  Noir) together with bread with a one-week interval. Blood samples were drawn every hour during the ®rst 4 h and a last one at 8 h after chocolate consumption. Plasma samples were analysed for epicatechin and theobromine content by HPLC. Results: Plasma concentrations of epicatechin and theobromine increased markedly after chocolate consumption (P 0.002 and P 0.001, respectively), reaching a maximum between 2 and 3 h. The maximal concentration and area under the curve of plasma kinetics of both substrates correlated very well with the dose of chocolate. Conclusions: Epicatechin is absorbed from chocolate and is rapidly eliminated from plasma. Attainable plasma values are 0.7 mmolal from 80 g of black chocolate.

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This study aims to determine if isoprostanes accurately reflect in vivo lipid peroxidation or whether they are influenced by the lipid content of the diet. Isoprostanes were measured in urine of healthy subjects under different conditions of lipid intake and under conditions of oxidative stress (fasting). We found that isoprostanes were not influenced by the lipid content of the diet: the urinary level remained constant over 24 h as well as over 4 consecutive days when switching from high to low lipid intake. Urinary isoprostane excretion was increased by 40% following a 24 h fast. We concluded that urinary isoprostane excretion reflects endogenous lipid peroxidation in vivo.z 1999 Federation of European Biochemical Societies.