Abstract
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 C13- and C15-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 C13-norisoprenoid glucoside, (5R,6S,7E,9R)-5,6,9-trihydroxy-7-megastigmene 9-O-β-d-glucoside (1); one new C15-norisoprenoid, (6S,7E,10S)-Δ9,15-10-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 C15-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) C13-norisoprenoid glucosides from the genus Averrhoa for the first time enriches the knowledge of carotenoid-derived flavor precursors in star fruit.
Highlights
Averrhoa carambola L., belonging to the family Oxalidaceae, is widely cultivated in SoutheastAsia, China, and India
Β-ionone and β-ionol were detected as the only two C13 -norisoprenoids from star fruit until MacLeod and Ames [4] reported 14 C13 - and C15 -aroma compounds by using the simultaneous distillation/extraction (SDE) method
Star fruit extract was subjected to SDE treatment and almond glucosidase hydrolysis by Herderich et al [5], which liberated 29 C13 -aroma compounds, Molecules 2019, 24, 256; doi:10.3390/molecules24020256
Summary
Averrhoa carambola L., belonging to the family Oxalidaceae, is widely cultivated in Southeast. Β-ionone and β-ionol were detected as the only two C13 -norisoprenoids from star fruit until MacLeod and Ames [4] reported 14 C13 - and C15 -aroma compounds by using the simultaneous distillation/extraction (SDE) method. SDE have a high probability of liberating well studied for their attractive sensory qualities and low flavor thresholds. The C13-norisoprenoid aroma components of star fruit have been well structural studied information about their glycosidically bound precursors is deficient, andthe hitherto onlyinformation three ionone for their attractive sensory qualities and low flavor thresholds. There is a need to study the accurate structural information glycosides have been isolated from star fruit and structurally identified by mass and of measurements the precursors[6,7]. 1), and structures were flavor elucidated by spectroscopic methods These findings enrich the the(Figure knowledge oftheir carotenoid-derived precursors in star fruit.
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