Free and bound volatile composition and characterization of some glucoconjugates as aroma precursors in melón de olor fruit pulp (Sicana odorifera).

Free and glycosidically bound volatiles obtained from the fruit pulp of Sicana odorifera by liquid-liquid extraction and by chromatography, followed by enzymatic hydrolysis with Rohapect D5L, respectively, were analyzed by capillary gas chromatography (HRGC), HRGC-mass spectrometry (HRGC-MS), and HRGC-Olfatometry (HRGC-O) analyses. A total of 37 free volatiles was detected, with the major components being 3-methyl-2-butanol, 3-hydroxy-2-butanone, ethyl 3-hydroxybutanoate, and (Z)-3-hexenol. Among the 22 detected glycosidically bound compounds, 4-hydroxybenzyl methyl ether, 4-hydroxybenzyl alcohol, and 2-phenylethanol were found to be the major constituents. Additionally, two glucoconjugates were isolated in pure form by multilayer coil countercurrent chromatography (MLCCC) of the glycosidic extrac and further purification. Their structures were elucidated by MS and NMR analyses to be the novel [4-(beta-D-glucopyranosyloxy)benzyl] 2,3-dihydroxy-3-methylbutanoate 2, and the known 4-(beta-D-glucopyranosyloxy)benzyl alcohol 1. Compounds 1 and 2 are precursors of 4-hydroxybenzyl alcohol, one of the major volatiles generated by enzymatic hydrolysis of the glycosidic fraction.