Quantification of apo-lycopenals in food products and human blood plasma

Abstract

Consumption of tomato and tomato products is correlated with a reduced incidence of a number of diseases. Research has suggested that lycopene, the most predominant carotenoid in tomatoes, may be responsible for this effect. However, researchers have also suggested that lycopene may be metabolized in mammals by eccentric cleavage to biologically active aldehydes, in an analogous fashion to cleavage of ß-carotene, catalyzed by ß-carotene oxygenase. Since apo-6’- and apo-8’-lycopenal have been reported earlier in raw tomato, we hypothesized that several other apo-lycopenals may be present in raw and processed foods, as well as blood plasma. Apo-lycopenal standards were prepared by in vitro oxidation of lycopene, and an HPLC-MSMS method using atmospheric pressure chemical ionization in negative mode was developed to separate and detect the apo-6’-, 8’-, 10’-, 12’-, 14’-, and 15’-lycopenal products formed in the reaction. Hexane/acetone extracts of raw tomato, grapefruit, watermelon, and processed tomato products were analyzed, as well as blood plasma of individuals who had consumed tomato juice for 8 weeks. Apo-6’-, 8’-, 10’-, 12’-, and 14’-lycopenals were detected and quantified in all food products tested, as well as blood plasma. The sum of apo-lycopenals was 6.5µg/100g roma tomato, 73.4 µg/100g tomato paste, and 1.88nmol/L of blood plasma. We conclude that several apo-lycopenals, in addition to apo-6’- and 8’-, are present in lycopene containing foods. In addition, the presence of apo-lycopenals in plasma may partly derive from the absorption of apo-lycopenals directly from food.