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 compon...