Identification and quantification of apo-lycopenals in fruits, vegetables, and human plasma

Research has suggested that lycopene may be metabolized by eccentric cleavage, catalyzed by beta-carotene oxygenase 2, resulting in the generation of apo-lycopenals. Apo-6'-lycopenal and apo-8'-lycopenal have been reported previously in raw tomato. We now show that several other apo-lycopenals are also present in raw and processed foods, as well as in human plasma. Apo-lycopenal standards were prepared by in vitro oxidation of lycopene, and a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method using atmospheric pressure chemical ionization in negative mode was developed to separate and detect the apo-6'-, apo-8'-, apo-10'-, apo-12'-, apo-14'-, and apo-15'-lycopenal products formed in the reaction. Hexane/acetone extracts of raw tomato, red grapefruit, watermelon, and processed tomato products were analyzed, as well as plasma of individuals who had consumed tomato juice for 8 weeks. Apo-6'-, apo-8'-, apo-10'-, apo-12'-, and apo-14'-lycopenals were detected and quantified in all food products tested, as well as plasma. The sum of apo-lycopenals was 6.5 microg/100 g Roma tomato, 73.4 microg/100 g tomato paste, and 1.9 nmol/L plasma. We conclude that several apo-lycopenals, in addition to apo-6'- and -8'-lycopenal, are present in lycopene-containing foods. In addition, the presence of apo-lycopenals in plasma may derive from the absorption of apo-lycopenals directly from food and/or human metabolism.