Kurzfassung:
Human plasma tested in biochemical assays (ACC/HOCl, ABTS, Sin-1, X/XOD, diaphorase, peroxynitrite, Fenton) achieves different I-values in each assay, indicating different antioxidant properties. When examined closer in four out of these seven assays (ACC/HOCl, ABTS, Sin-1, Fenton), it became obvious that the plasma proteins are the main responsible antioxidants. Only in the Sin-1 and Fenton assay, is the influence of the low-molecular antioxidants visible. The comparison of 25 single-plasma samples with the plasma pool showed that they scatter closely around the pool. The means and standard deviations of these 25 samples fit well with the estimated I-values of the pool, except for the Fenton assay. In the Fenton assay, plasma of women with their menstruation at the time of the blood taking can be determined by the bad antioxidant value of their plasma. When the values of these volunteers are not considered for the means and standard deviations, there is no difference between the averaged samples and the pool. The investigations on the extracts of the buckwheat herb and kernels determined different contents of flavonoids in the sample, which is due to the extracting method. In general, the extract of the herb showed the best antioxidant properties in three of the used test assays (Sin-1, X/XOD, Rose Bengal). None of the extracts had any effect in the Fenton assay that was done with EDTA as iron chelator. The aqueous extract of the herb, which corresponds to the infusion of tea, achieved nearly as good a result as the ethanolic extract; whereas an alkalic-ethanolic extraction can not be recommended. The fractionation of the buckwheat herb resulted in the detection of a variety of peaks and compounds. Due to the lack of standards and problems with the HPLC, several peaks could not be identified. The identified peaks correspond with findings in the literature for buckwheat kernels. The herb contains mainly rutin, but it also contains catechin, epicatechin, the procyanidins B2, B5 and C1, quercitrin and different kinds of phenolic acids. When tested in the Fenton assay none of the fractions exhibits an effect. For the other assays (Sin-1, X/XOD, Rose Bengal), fractions containing high concentrations of flavans and procyanidins exerted the best properties. An in vivo supplementation study with either buckwheat tea or Pycnogenol enhanced the antioxidant properties of the plasma of one volunteer. This corresponded with the results of the flavan-rich fractions of the buckwheat herb. The flavan-rich mixture Pycnogenol has a better impact on enhancing the plasma than buckwheat tea, which also shows effects. The active compounds must be flavonoids, which exhibit even after absorption and metabolization antioxidant properties. Metabolites of quercetin, as they occur in human plasma after a quercetin-rich meal, protect LDL in the copper-induced LDL oxidation. The estimated best-fit lines of the lag times have exponential equations and they fit very well to the data points with their calculated r-squared values. The binding studies with the metabolites and two HSA preparations gave rise to the conclusion that there are no free metabolites circulating in human plasma. There were no significant differences between the two HSA preparations. The kq-values of quercetin, q7glca and q3s are not significantly different; the same is for q3glca and isoquercitrin. The degradation of quercetin and its metabolites in cell culture media is probably due to Fenton chemistry with copper ions. Ascorbic acid and HSA had a stabilizing effect on quercetin and q7glca, which degrades as quercetin. Q3glca is the most stable metabolite and neither addition of ascorbic acid or of HSA had any increasing effect. The recovery of q4glca is affected by the binding of the metabolite to the HSA. Only with q3s are no effects of stabilization found neither with ascorbic acid nor with HSA. Further studies have to be done on this subject to give more clarity.