Carotenoid retention during post-harvest storage of Capsicum annuum: the role of the fruit surface structure

In this study, a chilli pepper (Capsicum annuum) panel for post-harvest carotenoid retention was studied to elucidate underlying mechanisms associated with this commercial trait of interest. Following drying and storage some lines within the panel had an increase in carotenoids approaching 50% compared to the initial content at the fresh fruit stage. Other lines displayed a 25% loss in carotenoids. The quantitative determination of carotenoid pigments with concurrent cellular analysis indicated that in most cases pepper fruit with thicker (up to four -fold) lipid exocarp layers and smooth surfaces, exhibit improved carotenoid retention properties. Total cutin monomer content increased in medium/high carotenoid retention fruits and sub-epidermal cutin deposits were responsible for the difference in exocarp thickness. Cutin biosynthesis and cuticle precursor transport genes were differentially expressed between medium/high and low carotenoid retention genotypes, and this supports the hypothesis that the fruit cuticle can contribute to carotenoid retention. Enzymatic degradation of the cuticle and cell wall suggests that in Capsicum the carotenoids (capsanthin and its esters) are embedded in the lipidic exocarp layer. This was not the case in tomato. Collectively, the data suggest the fruit cuticle could provide an exploitable resource for the enhancement of fruit quality.