| Summary: | The effect of UV-C irradiation on antifungal properties of orange essential oil (EO) against <i>Penicillium digitatum</i> in inoculated Navel oranges was examined. The UV-C irradiation of orange EO resulted in a 20% loss of the major constituent, limonene, and the generation of three hydroperoxide oxidation products, (2S,4R)-p-mentha-6,8-diene-2-hydroperoxide,(1S,4R)-p-mentha-2,8-diene-1-hydroperoxide, and (1R,4R)-p-mentha-2,8-diene-1-hydroperoxide. The <i>P. digitatum</i> growth in oranges dipped in non-irradiated orange EO at 1000–4000 µL L<sup>−1</sup> was not significantly different to control the fruit. Dipping in UV-C treated orange EO inhibited the growth of <i>P. digitatum</i> with 4000 µL L<sup>−1</sup> having the greatest effect. No phytotoxic injury to the rind was observed at any concentration. Citral, as a known antifungal chemical, was included for comparison. The non-irradiated citral (1000 µL L<sup>−1</sup>) was more effective than irradiated orange EO, but elicited rind phytotoxicity. The irradiated citral was less effective in inhibiting <i>P. digitatum</i> growth with the loss of citral, but not hydroperoxide formation. These results suggest UV-C irradiated orange EO as a potential alternative to synthetic fungicides to inhibit <i>P. digitatum</i> decay. The source of orange EO could be waste flavedo generated by the orange juice processing industry.
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