Thermally Stable Oleosin Is a Major, Cross-Reactive Allergen in Common Buckwheat ( <i>Fagopyrum esculentum</i> )

To address the underdiagnosis of buckwheat allergy caused by the loss of hydrophobic allergens during standard aqueous extraction, we aimed to isolate and characterize a novel lipid-associated allergen from common buckwheat (<i>Fagopyrum esculentum</i>). An ∼18 kDa common buckwheat oleosin was enriched by lipid-soluble extraction, identified by mass spectrometry, and tested for IgE reactivity in sera from 18 buckwheat-sensitized patients; its structure was analyzed by circular dichroism. The oleosin-bound IgE in 9 of these 18 individuals, with OD₄₅₀ values ranging from 0.13 to 0.52. It displayed an α-helical structure with a melting temperature (<i>T</i>_m) of 53.2 °C. Competitive ELISA showed 2.5-75.0% inhibition of IgE binding by peanut, sesame, almond, and pistachio extracts, depending on the serum and allergen source. This work identifies oleosin as a clinically relevant, thermally stable buckwheat allergen with broad cross-reactivity, providing a molecular basis for improved diagnosis and food safety.