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During the cultivation of the edible mushroom Fomitopsis betulina on agro-industrial side streams, a pleasant flavor strongly reminiscent of pineapple was perceived. Aroma extract dilution analyses identified two flavor components with a distinct pineapple odor. On the basis of mass spectrometric data, a Wittig reaction of ( E )-penta-2,4-dien-1-yltriphosphonium bromide with ethyl levulinate was conducted. The resulting (5 E / Z ,7 E ,9)-decatrien-2-ones were identical to the compounds isolated from the fungal culture. Some structurally related methyl ketones were synthesized, confirmed by nuclear magnetic resonance and mass spectrometry, and their odor was characterized. The lowest odor threshold and most characteristic pineapple-like odor was found for (5 Z ,7 E ,9)-decatrien-2-one. Global minimum energy calculation of the methyl ketones and the comparison to (1,3 E ,5 Z) -undecatriene, a character impact compound of fresh pineapple, showed that a chain length of at least 10 carbon atoms and a terminal double bond embedded in a "L"-shaped conformation were common to compounds imparting an intense pineapple-like odor. Both (5 E / Z ,7 E ,9)-decatrien-2-ones have not been described as natural flavor compounds.