Changes of Lemon Flavor Components in an Aqueous Solution during UV Irradiation

A lemon flavor composed of lemon oil, water (pH 6 phosphate buffer), and ethanol, and the lemon-flavored drink were irradiated with UV light. Citral ( 1 and 2 ), which is one of the most important components expressing the typical lemon-like odor, significantly decreased with Z − E isomerization and there appeared 2-(3-methyl-2-cyclopenten-1-yl)-2-methylpropionaldehyde ( 6 ), trans -1,3,3-trimethylbicyclo[3.1.0]hexane-1-carboxaldehyde ( 7 ), cis -1,3,3-trimethylbicyclo[3.1.0]hexane-1-carboxaldehyde ( 8 ), (1,2,2-trimethyl-3-cyclopenten-1-yl)acetaldehyde ( 9 ), α-campholenealdehyde ( 10 ), photocitral A ( 3 ), epiphotocitral A ( 4 ), and photocitral B ( 5 ). New compounds of aldehyde 9, 6 and 10, were newly identified as photoreaction products of citral. Limonene, terpinolene, and nonanal decreased, while p -cymene increased after UV irradiation. Other components, such as sesquiterpene hydrocarbons, citronellal, linalool, and terpineols, were only slightly changed. These results suggested that citral is a more UV-unstable component in lemon flavor and the photolysis of citral could affect other components in lemon flavor during UV irradiation.