Water accelerated transformation of d-limonene induced by ultraviolet irradiation and air exposure

- Isotope labelling, GC-MS and GC-PCI-Q-TOF analyses were used to investigate the transformation of d-limonene.
- The combination of UV irradiation, air exposure and water existence facilitated the transformation of d-limonene.
- Water molecules could significantly promote the transformation of d-limonene.
- Isotope labelling experiment showed that the hydrogen radicals released from water took part in the transformation.

d-Limonene is a fragrant chemical that widely exists in aromatic products. Isotopic labelling of water molecules plus GC-MS and GC-PCI-Q-TOF analyses were used to investigate the influence of water molecules on chemical transformation of d-limonene induced by UV irradiation and air exposure. The results showed that the synergistic effect of UV irradiation, air exposure and water presence could facilitate d-limonene transformation into the limonene oxides: p-mentha-2,8-dienols, hydroperoxides, carveols, l-carvone and carvone oxide. UV irradiation, air exposure, or water alone, however, caused negligible d-limonene transformation. With the aid of isotopic labelling of water and oxygen molecules, it was found that water molecules were split into hydrogen radicals and hydroxyl radicals, and the hydrogen radicals, in particular, promoted the transformation reactions. This study has elucidated the mechanism and factors that influence the transformation of d-limonene, which will benefit industries involved in production and storage of d-limonene-containing products.