Location: Vegetable Crops ResearchTitle: Formation of norisoprenoid flavor compounds in carrot (Daucus carota L.) roots: characterization of a cyclic-specific carotenoid cleavage dioxygenase 1 gene Author
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2013
Publication Date: 11/30/2013
Publication URL: http://handle.nal.usda.gov/10113/58545
Citation: Yahyaa, M., Bar, E., Dubey, N.K., Meir, A., Davidovich-Rikanati, J., Hirschberg, J., Ali, R., Tholl, D., Simon, P.W., Tadmor, Y., Lewinsohn, E., Ibdah, M. 2013. Formation of norisoprenoid flavor compounds in carrot (Daucus carota L.) roots: characterization of a cyclic-specific carotenoid cleavage dioxygenase 1 gene. Journal of Agricultural and Food Chemistry. 61(50):12244-12252. Interpretive Summary: Typical carrots are orange because they accumulate orange carotenoid pigments called carotenes. Novel colored yellow carrots accumulate xanthophylls, another class of carotenoid pigment. Novel colored white carrots accumulate no pigments. Norisoprenoids are breakdown products of carotenoids in some vegetables and fruits and in this study, several flavorful norisoprenoids were found in orange carrots, but not yellow or white carrots. The generation of these flavorful isoprenoids was found to be attributable to the action of an enzyme, DcCCD1. This research is of interest to plant molecular biologists, geneticists, breeders, food scientists and carrot processors studying plant metabolism, and developing carrots and carrot products with desirable and predictable flavor.
Technical Abstract: Carotenoids are isoprenoid pigments that upon oxidative cleavage lead to the production of norisoprenoids that have profound effect on flavor and aromas of agricultural produce. The biosynthetic pathway to norisoprenoids in carrots (Daucus carota L.) is still widely unknown. We found that geranial is the major norisoprenoid volatile in freshly cut carrots of different colored cultivars. The volatile norisoprenoids farnesylacetone, a-ionone and ß-ionone accumulated in Nairobi, Rothild and Purple Haze cultivars, but not in Yellowstone and Creme de Lite, in a pattern reflecting their carotenoid content. A cDNA encoding a protein with carotenoid cleavage dioxygenase activity, DcCCD1, was identified in carrot, and was overexpressed in E. coli strains previously engineered to produce different carotenoids. The recombinant DcCCD1 enzyme cleaves cyclic carotenes to generate a- and ß-ionone. No cleavage products were found when DcCCD1 was co-expressed in E. coli strains accumulating noncyclic carotenoids such as phytoene or lycopene. Our results suggest a role for DcCCD1 in carrot flavor biosynthesis.