In order to elucidate the deterioration mechanism of lemon flavor, we investigated the time course changes of the flavor components in lemon-shu or lemon oil in the aqueous citric acid solution by GC, GC-MS and mass chromatography. Further, we examined whether off-odor substances were formed in the aqueous citric acid solution from d-limonene, β-pinene or γ-terpinene which were the major components in lemon oil. p-Mentha-1, 5-dien-8-ol and p-mentha-1 (7), 2-dien-8-ol, which are significant intermediates, were formed from citral in lemon oil under the acidic condition and subsequently converted to p-cymen-8-ol. After that, the more stable p-cymene and α, p-dimethylstyrene, which are responsible for the off-odor of deteriorated lemons, were produced. The deterioration rate of citral was much slower in lemon-shu than in lemon oil. β-Pinene was unstable compound under the acidic condtion, resulting in transformation to a-terpineol, fenchyl alcohol and others. d-Limonene and γ-terpinene were relatively stable compounds under the same condition, but incubation of them for a long time gives rise to formation of α-terpineol and p-cymene, respectively.
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