| Abstract
| - Accumulation of β-carotene and trans−cis isomerization of ripening mango mesocarp wereinvestigated as to concomitant ultrastructural changes. Proceeding postharvest ripening was shownby relevant starch degradation, tissue softening, and a rising sugar/acid ratio, resulting in a lineardecrease (R 2 = 0.89) of a ripening index (RPIKS) with increasing ripening time. A modest accumulationof all-trans-β-carotene and its cis isomers resulted in a slight pigmentation of the mango chromoplasts,because ambient temperatures of 18.2−19.5 °C provided suboptimal ripening conditions, affectingcolor development and β-carotene biosynthesis. The ultrastructures of chromoplasts from mangomesocarp and carrot roots were comparatively studied by means of light and transmission electronmicroscopy. Irrespective of the ripening stage, mango chromoplasts showed numerous plastoglobulivarying in size and electron density. They comprised the main part of carotenoids, thus supportingthe partial solubilization of the pigments in lipid droplets. However, because different pigment-carryingtubular membrane structures were also observed, mango chromoplasts were assigned to the globularand reticulotubular types, whereas the crystalline type was confirmed for carrot chromoplasts. Thelarge portions of naturally occurring cis-β-carotene in mango fruits contrasted with the predominanceof the all-trans isomer characteristic of carrots, indicating that the nature of the structure wherecarotenoids are deposited and the physical state of the pigments are crucial for the stability of theall-trans configuration. Keywords: β-Carotene stereoisomers; chromoplast ultrastructure; electron microscopy; Mangiferaindica L.; postharvest ripening
|
