Evaluation of the molecular and biochemical mechanisms associated with the accumulation of zeaxanthin and β-carotene in pepper (Capsicum annuum) and β-carotene in tomato (Solanum lycopersicum) fruit.

Zeaxanthin and β-carotene are key bioactive carotenoids, with zeaxanthin being a vital bioactive compound in the maintenance of central macular and for the prevention of age-related macular degeneration, while β-carotene is the primary source of provitamin A. Provitamin A is fundamental in prevention of childhood blindness and mortality. These carotenoids are also responsible for the orange pigmentation which can be observed in pepper and tomato fruits, making them ideal candidates for enhancement.
In this study, the carotenoid content was characterised across a pepper diversity panel consisting of 365 distinct lines which focused on the accumulation of zeaxanthin and β-carotene. In addition, a tomato diversity panel consisting of 50 distinct lines, was analysed for β-carotene accumulation. Lines were selected based on carotenoid content in the fruit, and a ripening series of the fruit were analysed, to understand the accumulation of carotenoids in the fruit tissues over ripening. In orange pepper, sequencing of the enzyme zeaxanthin epoxidase highlighted mutations which result in the increased levels of accumulation of β-carotene and zeaxanthin, while a decrease in the accumulation of other downstream carotenoid products in the fruit tissue occurred, when compared to red pepper. In the tomato lines which accumulate β-carotene, the presence of S. galapagense lycopene β-cyclase, promotes the increased accumulation of β-carotene in tomato.
Sub-chromoplastic and sub-chloroplastic fractionation of ripe pepper fruit and leaf tissue was used to evaluate the method of sequestration of carotenoids in the pepper fruit and leaf from red and orange phenotypes. In vitro bioaccessibility assays of pepper and tomato under different pre-digestive processing were carried out, highlighting the stability and the accessibility of β-carotene and zeaxanthin during digestion. This data shows the potential use of these lines as a sustainable source of these carotenoids, for prevention of vitamin A deficiency and reduction of age-related macular degeneration.