Analysis of Aromatic Volatile Compounds in 'Miyabi' Melon (Cucumis melo L.) using the Porapak Q Column.

Abstract

To evaluate the effectiveness of the Porapak Q column concentration method (PQM) of analyzing the volatile aromatic compounds in 'Miyabi' melon, we compared it with the direct headspace sampling method (DHSM) and simultaneous distillation extraction method (SDEM) in regard to quantitative value, recovery rate, and reproducibility of the compounds. A total of 103 volatile compounds were quantified by PQM, 66 by SDEM, and 8 by DHSM, respectively. The widest range of volatile compounds, ranging from low-boiling-point to high-boiling-point, were quantified by using the PQM rather than by the other two methods. A total of 76 compounds were identified by the GC-MS analysis and the Kovats Index. Among the alcohols, 2-methyl-1-propanol, 2-methyl-1-butanol, 1-hexanol, 1-nonanol, (Z)-3-nonen-1-ol, (Z)-6-nonen-1-ol, (Z, Z)-3, 6-nonadien-1-ol, benzyl alcohol, and 2-phenethyl alcohol also occurred in relatively large quantities. Among the aldehydes, 3-methylbutanal, nonanal, and (E, Z)-2, 6-nonadienal were identified in large quantities by PQM. Among the esters, propyl acetate, 2-methypropyl acetate, butyl acetate, 2-methylbutyl acetate, and benzyl acetate were detectable in relatively large quantities by PQM and SDEM. The recovery rates of most low boiling-point compounds, such as methyl butyrate and ethyl propionate, were same in both methods, whereas the recovery rates of medium and high boiling-point compounds were higher with the PQM. Among sulfur-containing compounds, ethyl (methylthio) acetate and 2-(methylthio) ethyl acetate were identified by the PQM and SDEM, while ethyl 3-(methylthio) propionate and 3-(methylthio) propyl acetate were only detected by PQM. The average coefficient of variation of the compounds was 11.90% using the PQM, with stable reproducibility compared with that of SDEM (37.13%). With respect to flavor, the odor concentrates from the PQM were similar to the natural aroma of muskmelon, but the odor concentrates from the SDEM were degraded to a thick, off-flavor odor. Therefore, we concluded that PQM is an excellent method to extract volatile aromatic compounds of melon because it is quick, easy to operate, and capable of recovering a wide range of boiling-point volatile compounds without degrading their flavor. Furthermore, the results are highly reproducible.