Seasonal and Regional Effects on the Yield and Bioactive Constituents of Torreya nucifera Essential Oils in South Korea

The essential oil of <i>Torreya nucifera</i>, a coniferous tree native to East Asia, has notable bioactive properties with potential industrial applications. This study examined the effects of seasonal and regional factors on the yield and bioactive constituents of <i>T. nucifera</i> oils in South Korea. Leaf samples were collected in spring (March), summer (June), and autumn (September) of 2023-2024 from three ecologically distinct regions: Jeju Island, Jinju, and Hwasun. Oil yield was stable across seasons (0.9-1.6%) but varied significantly by region (<i>p</i> < 0.05), with Hwasun showing the highest yield. This stability across seasons may reflect the perennial evergreen nature of <i>T. nucifera</i>. Gas Chromatography-Mass Spectrometry (GC-MS) identified 32 volatile components, predominantly monoterpenes (83.7-90.4%) and sesquiterpenes (5.4-11.7%), with <i>D</i>-limonene and 3-carene as key chemical markers. Notably, 3-carene levels were significantly affected by region (<i>p</i> < 0.0001), with higher concentrations in Jeju oils, while <i>D</i>-limonene was influenced by season, region, and their interaction (<i>p</i> < 0.001), reaching peak levels in Hwasun during summer and autumn (up to 70%). Therefore, <i>T. nucifera</i> oil from Hwasun harvested in autumn can be optimised for commercial production by maximising oil yield and enhancing chemical markers.