Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: November 28, 2007
Publication Date: June 2, 2008
Citation: Fish, W.W. 2008. Mother nature's packaging and organization of carotenoids in watermelon and cantaloupe [abstract]. HortScience. 43(3):614.
Carotenoids are one of the classes of compounds occupying an ever-increasing role as food supplements. Nutritional and physiological effects of carotenoids are, in general, limited by their bioavailability. As a means to better understand the factors that influence the bioavailability of carotenoids in their natural sources, the properties of plant-derived precipitates of watermelon lycopene and cantaloupe B-carotene were examined in water and in aqueous sodium dodecyl sulfate (SDS). Electron microscopy and chemical analyses revealed that the carotenoids were packaged inside a membrane to form a chromoplast. Watermelon chromoplasts ranged in apparent diameter from 0.1 to 6 um while cantaloupe chromoplasts ranged in apparent diameter between 0.1 to about 1 um. The chromoplasts could be made more water soluble by treating them with levels of SDS >0.2%; only SDS in its monomeric state appeared to bind to the membrane. Binding measurements indicated that about 120 molecules of SDS were bound to the watermelon chromoplast membrane per molecule of lycopene inside the chromoplast. Around 90% of the chromoplast-SDS complexes were retained on a 0.45 um membrane filter. Spectral peaks in the visible region of both sources of chromoplasts in SDS exhibited a bathochromic, or red, shift from their location in organic solvent. Carotenoid-containing chromoplasts dispersed in aqueous SDS obeyed Beer's law; thus, this system can be used for quantitation of lycopene in watermelon or B-carotene in cantaloupe. Watermelon chromoplasts in SDS exhibited a pronounced circular dichroic activity in the visible region. Taken together, these observations are consistent with the carotenoid monomers being assembled into a chiral aggregate inside a membrane to form the chromoplast. The binding of SDS molecules to the chromoplast membrane forms a complex that is extensively more water-soluble than the chromoplast alone.