Carotenoid-Derived Flavor Precursors from Averrhoa carambola Fresh Fruit

The fruit of Averrhoa carambola L. (Oxalidaceae), commonly known as star fruit or carambola, is popular in tropical and subtropical regions. Carotenoid-derived components, mainly C(13)- and C(15)-norisoprenoids, contribute greatly to the flavor of star fruit. Previously reported norisoprenoids were tentatively identified by GC-MS analysis after enzymatic hydrolysis. To gain accurate information about glycosidically bound flavor precursors in star fruit, a phytochemical study was conducted, which led to the isolation of 16 carotenoid derivatives—One new C(13)-norisoprenoid glucoside, (5R,6S,7E,9R)-5,6,9-trihydroxy-7-megastigmene 9-O-β-d-glucoside (1); one new C(15)-norisoprenoid, (6S,7E,10S)-Δ(9,15)-10-hydroxyabscisic alcohol (11); and 14 known ones, of which 12 were in glucoside form. The structures of the two new compounds were elucidated on the basis of extensive spectroscopic data analysis and chemical reaction. Compound 11 was a rare C(15)-norisoprenoid with a double bond between C-9 and C-15, and its possible biogenetic pathway was proposed. The known compounds were identified by comparison of their mass and nuclear magnetic resonance (NMR) data with those reported in the literature. The structure identification of one new (1) and seven known (3–7, 9, and 10) C(13)-norisoprenoid glucosides from the genus Averrhoa for the first time enriches the knowledge of carotenoid-derived flavor precursors in star fruit.