Characterization of Essential Oil Composition, Polymethoxyflavones, Total Carotenoids, and Sensory Properties of Japanese and Taiwanese Hirami Lemon (<i>Citrus depressa</i> Hayata)

Abstract: Hirami lemon (Citrus depressa Hayata) is a small citrus plant native to southern Japan and Taiwan. This study distinguishes the essential oil composition, polymethoxyflavones (PMFs), total carotenoids, and sensory characteristics of Hirami lemons from Japan (Kagoshima and Okinawa) and Taiwan. The mature fruit essential oils of 23 evaluated strains (5 from Kagoshima, 16 from Okinawa, and 2 from Taiwan) primarily contained volatile organic compounds (VOCs), with limonene and γ-terpinene being predominant (40.4-76.2 % and 9.7-29.3 %, respectively). Distinct geographical signatures were also observed–piperitone and octanal in Kagoshima strains, ethyl dodecanoate and ethyl decanoate in Okinawan strains, and 2-hexenal and phenylacetaldehyde in Taiwanese strains–implying a potent aroma distinctiveness of each cultivation region. Nantou (Taiwan), Shikunin spicy (Kagoshima), and Izumi kugani (Okinawa) had higher PMF concentrations, including nobiletin and tangeretin, whereas Shikunin sweet from Kagoshima exhibited notably higher total carotenoid content than the other strains. Furthermore, variations in total soluble solids and titratable acidity were correlated with perceived differences in sweetness and sourness, while VOCs influenced aroma traits, including citrus, fruity, herbal, and green notes, refining overall flavor perception. These findings offer important implications for breeding strategies and product diversification of Japanese and Taiwanese Hirami lemons.