Ultrastructural deposition forms and bioaccessibility of carotenoids and carotenoid esters from goji berries (Lycium barbarum L.)

Abstract

Goji berries (Lycium barbarum L.) have been known to contain strikingly high levels of zeaxanthin, while the physical deposition form and bioaccessibility of the latter was yet unknown. In the present study, we associated ripening-induced modifications in the profile of carotenoids with fundamental changes of the deposition state of carotenoids in goji berries. Unripe fruit contained common chloroplast-specific carotenoids being protein-bound within chloroplastidal thylakoids. The subsequent ripening-induced transformation of chloroplasts to tubular chromoplasts was accompanied by an accumulation of up to 36mg/100g FW zeaxanthin dipalmitate and further minor xanthophyll esters, prevailing in a presumably liquid-crystalline state within the nano-scaled chromoplast tubules. The in vitro digestion unraveled the enhanced liberation and bioaccessibility of zeaxanthin from these tubular aggregates in goji berries as compared to protein-complexed lutein from spinach. Goji berries therefore might represent a more potent source of macular pigments than green leafy vegetables like spinach.

Keywords: Bioavailability; Chloroplast; Chromoplast ultrastructure; Lutein; Macular pigments; Simulated digestion; Tubular chromoplasts; Zeaxanthin.