Effect of Acute Consumption of Blackcurrant Juice on Plasma and Urine Concentrations of Phenolic Acids and Flavonoids and on Antioxidant Status in Human Subjects

Epidemiological evidence suggests that consumption of fruits and vegetables rich in flavonoids is inversely linked to the risk of CVD, but the exact mechanisms are unclear. The present study investigated the effects of acute consumption of a 20% blackcurrant juice drink on plasma and urine concentrations of anthocyanin metabolites and plasma antioxidant status in humans. In a randomized, double-blind, placebo-controlled cross-over design, 20 healthy human subjects (ages 30-70 y, 11 females 9 males) consumed 250 mL of the 20% blackcurrant juice drink or a placebo drink on two intervention visits with one-month washout. Blood and urine samples were collected at baseline and periodically after juice intake for 8 hours, in addition to a 24-hour urine sample. Plasma vitamin C concentrations increased significantly from baseline after blackcurrant juice consumption compared to those of the control group throughout the study day (P = 0.001), particularly at 60 – 90 minutes after consumption. The plasma concentrations of phenolic acids that are known metabolites of flavonoids, namely benzoic acid, hippuric acid, salicylic acid and phenylacetic acid tended to increase at 30 and 180 minutes after blackcurrant juice intake, and a weak interaction was observed between juice treatment and time (P = 0.099). The urinary hippuric acid and total phenolics also tended to show non-significant increases after juice consumption. Delphinidin and cyanidin derivatives were not detected in urine samples at quantifiable concentrations, although there was some evidence of traces present in some samples. There were no significant treatment effects on the oxidative stability of plasma assessed by the Oxygen Radical Absorbance Capacity (ORAC) and Ferric Reducing Antioxidant Power (FRAP) values. Plasma uric acid concentration was significantly correlated with the FRAP value of plasma at 0 - 480 minutes after drink consumption (P = 0.000), which is consistent with the important contribution of uric acid to antioxidant capacity. Overall, the effects of the 20% blackcurrant juice drink on plasma concentrations of flavonoid metabolites and plasma antioxidant status did not reach statistical significance