Aim of the study: The present study was conducted to investigate changes in the plasma concentration of carotenoids and carotenoid oxidation products, vitamin A, alpha- and gamma-tocopherol, and ubiquinone-10 during a dietary intervention trial with 23 male healthy volunteers.
Method: A two week carotenoid depletion period was followed by a daily consumption of 330 mL tomato juice (40 mg lycopene), then by 330 mL carrot juice (15.7 mg alpha-carotene and 22.3 mg beta-carotene), and then by a 10 g spinach powder preparation (11.3 mg lutein and 3.1 mg beta-carotene) served with main meals for two weeks, respectively. Blood samples were collected in the morning after an overnight fasting and carotenoids, vitamin A, tocopherols, and ubichinone were analyzed by reversed-phase HPLC.
Results: During the tomato juice intervention, plasma concentrations of trans- and cis-lycopene increased 3-fold compared to the depletion period. Lycopene oxidation products could be demonstrated in plasma and were significantly elevated compared to control (p < 0.001). After two weeks of carrot juice consumption, alpha-carotene and beta-carotene concentrations increased 8.6- and 3.2-fold, respectively. Finally, during the spinach consumption period the lutein concentration increased 2-fold, while the beta-carotene concentrations were still elevated 2-fold.
Conclusions: The moderate change in dietary habits, e.g., the consumption of 330 mL of carotenoid-rich vegetable juices caused significant changes in the plasma carotenoid concentrations, indicating a high bioavailability of carotenoids from these processed vegetable products. The changes in plasma carotenoid concentrations reflected the carotenoid composition of the consumed foods. However, particularly during the tomato juice intervention period the occurrence of lycopene oxidation products and cis-lycopene isomers in plasma was eminent. The formation may be due to antioxidant reactions of lycopene in the organism.