A novel carotenoid cleavage activity involved in the biosynthesis of Citrus fruit-specific apocarotenoid pigments

Citrus is the first tree crop in terms of fruit production. The colour of Citrus fruit is one of the main quality attributes, caused by the accumulation of carotenoids and their derivative C30 apocarotenoids, mainly β-citraurin (3-hydroxy-β-apo-8'-carotenal), which provide an attractive orange-reddish tint to the peel of oranges and Mandarins. Though carotenoid biosynthesis and its regulation have been extensively studied in Citrus fruits, little is known about the formation of C30 apocarotenoids. The aim of this study was to the identify carotenoid cleavage enzyme(s) [CCD(s)] involved in the peel-specific C30 apocarotenoids. In silico data mining revealed a new family of five CCD4-type genes in Citrus. One gene of this family, CCD4b1, was expressed in reproductive and vegetative tissues of different Citrus species in a pattern correlating with the accumulation of C30 apocarotenoids. Moreover, developmental processes and treatments which alter Citrus fruit peel pigmentation led to changes of β-citraurin content and CCD4b1 transcript levels. These results point to the involvement of CCD4b1 in β-citraurin formation and indicate that the accumulation of this compound is determined by the availability of the presumed precursors zeaxanthin and β-cryptoxanthin. Functional analysis of CCD4b1 by in vitro assays unequivocally demonstrated the asymmetric cleavage activity at the 7',8' double bond in zeaxanthin and β-cryptoxanthin, confirming its role in C30 apocarotenoid biosynthesis. Thus, a novel plant carotenoid cleavage activity targeting the 7',8' double bond of cyclic C40 carotenoids has been identified. These results suggest that the presented enzyme is responsible for the biosynthesis of C30 apocarotenoids in Citrus which are key pigments in fruit coloration.

Key to xenobiotic carotenoids

A listing of carotenoids with heteroatoms (X = F, Cl, Br, I, Si, N, S, Se, Fe) directly attached to the carotenoid carbon skeleton has been compiled. The 178 listed carotenoids with C, H, X atoms demonstrate that the classical division of carotenoids into hydrocarbon carotenoids (C, H) and xanthophylls (C, H, O) has become obsolete.

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.

An update on the health effects of tomato lycopene

Lycopene is a non-provitamin A carotenoid that is responsible for the red to pink colors seen in tomatoes, pink grapefruit, and other foods. Processed tomato products are the primary dietary lycopene source in the United States. Unlike many other natural compounds, lycopene is generally stable to processing when present in the plant tissue matrix. Recently, lycopene has also been studied in relation to its potential health effects. Although promising data from epidemiological, as well as cell culture and animal, studies suggest that lycopene and the consumption of lycopene containing foods may affect cancer or cardiovascular disease risk, more clinical trial data is needed to support this hypothesis. In addition, future studies are required to understand the mechanism(s) whereby lycopene or its metabolites are proven to possess biological activity in humans.