No abstract

Commonly used medicinal plant extracts with standardized content of polyphenols were investigated for their total antioxidant activity (TAA). Green tea, oligomeric procyanidins (from grape seed and pine bark), bilberry, and ginkgo exhibited TAA in the range of 5.12−2.57 mM Trolox, thereby indicating a valuable antioxidant capacity. Witch hazel, propolis EPID, artichoke, and hawthorn afforded lower TAA (1.54−0.44 mM Trolox), whereas echinacea, ginseng, passionflower, sweet clover, and eleuthero were rather uneffective (TAA < 0.32 mM Trolox). Excipients normally used to prepare the extracts did not interfere with the assay, and a good correlation between the content of polyphenols and the TAA was assessed. The measured TAA was higher than those calculated from the content and antioxidant potential of specific components, as exemplified for green tea and ginkgo extracts. This may be attributed to the presence in these extracts of other substances with antioxidant capacity. On the other hand, some components (such as ginkgolides in ginkgo extract) insensitive to the TAA assay played an important antioxidant role in vivo. These results suggest that TAA determination is of interest for a comparative evaluation of in vitro antioxidant potential, but it needs to be combined with in vivo data for adequate assessment of the antioxidant capacity of medicinal plant extracts. Keywords: Medicinal plants; polyphenols; total antioxidant activity; total radical-trapping antioxidant parameter

Stevia rebaudiana standardized extracts (SSEs) are used as natural sweeteners or dietary supplements in different countries for their content of stevioside or rebaudioside A. These compounds possess up to 250 times the sweetness intensity of sucrose, and they are noncaloric and noncariogenic sweeteners. The aim of this study was to investigate the in vitro transformation of stevioside and rebaudioside A after incubation with human microflora, the influence of these sweeteners on human microbial fecal community and which specific groups metabolize preferentially stevioside and rebaudioside A. The experiments were carried out under strict anaerobic conditions in batch cultures inoculated with mixed fecal bacteria from volunteers. The hydrolysis was monitored by HPLC coupled to photodiode array and mass spectrometric detectors. Isolated bacterial strains from fecal materials incubated in selective broths were added to stevioside and rebaudioside A. These sweeteners were completely hydrolyzed to their aglycon steviol in 10 and 24 h, respectively. Interestingly, the human intestinal microflora was not able to degrade steviol. Furthermore, stevioside and rebaudioside A did not significantly influence the composition of fecal cultures; among the selected intestinal groups, bacteroides were the most efficient in hydrolyzing Stevia sweeteners to steviol.

The total antioxidant activity (TAA) of 13 typical Italian wines was determined (average 12.3 and 1.6 mM Trolox equivalents for red and white wines, respectively), and the resulting values were correlated with total phenols (1365−3326 and 96−146 mg/L for red and white wines, respectively), flavanols (203−805 and 11−49 mg/L, for red and white wines, respectively), and flavonols. Only the red wines contained appreciable amounts of flavonols (average 15.3 mg/L), with quercetin and rutin being the most abundant, followed by myricetin, kaempferol, and isorhamnetin accounting for only 0.7−3% of TAA. The TAA of investigated wines are well correlated with phenol (r = 0.9902) and flavanol (r = 0.9270) content. These results confirm that red wine polyphenols are in vitro significant antioxidants and may explain the beneficial effects of a moderate daily intake of red wines, probably through a sparing action of highly bioavailable vitamins C, E, and β-carotene. Keywords: Wine; antioxidant; phenols; flavanols; flavonols