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

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 (Fagopyrum esculentum). 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 (T_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.