Absorption and Bioavailability of Antioxidant Phytochemicals and Increase of Serum Oxidation Resistance in Healthy Subjects Following Supplementation with Raisins

The aim of this study was to examine the postprandial impact of raisin supplementation in serum resistance to oxidation of healthy subjects, to quantify the bioavailable phenolic compounds and oleanolic acid. The content of phytochemicals in raisins was determined by GC-MS. Fifteen healthy volunteers who consumed 144 g of raisins were subjected to blood collection at time 0 and 1, 2, 3 and 4 h after consumption. Blood samples were used for the quantification of (a) serum oxidizability (b) plasma total polyphenol content and (c) phenolic compounds and oleanolic acid by applying GC-MS analysis. A total of 25 phytochemicals were identified and quantified in raisins, while the triterpenoid oleanolic acid was present at the highest concentration. The peak of plasma total phenolics and serum oxidation resistance appeared 1 h after raisin supplementation (p < 0.05) and correlated strongly with each other. Seventeen phytochemicals (16 phenolics and oleanolic acid) were clearly identified and quantified in volunteers' plasma. Each compound followed different kinetics, however 13 out of 17 peaked in plasma also 1 h after supplementation. The results indicate that raisins influence antioxidant potential in vivo, while the contained phytochemicals are bioavailable.