3‐Methylnonane‐2,4‐dione – An Intense Odour Compound Formed during Flavour Reversion of Soya‐Bean Oil

Nonane‐2,4‐dione and 3‐mehthylnonane‐2,4‐dione were identified in reverted soya‐bean oil. The odour threshold of the latter compound, which smelled “lard‐like, strawy, fruity”, was very low (0.01 ng/1 air) in comparison to that of the nonane‐2,4‐dione (3.9ng/1 air). Based on its odour properties and the result of an aroma extract dilution analysis, which have been recently reported (Fat Sci. Technol. 90, 332 [1988]), it was concluded that 3‐methylnonane‐2,4‐dione contributed very strongly to the reversion odour of soya‐bean oil. 3‐Methylnonane‐2,4‐dione, 3,7‐dimethyloctane‐2,4‐dione, decane‐2,5‐, ‐3,5‐and‐ ‐4,5‐dione, 3‐oxo‐ and 5‐oxodecanal were prepared as reference for the identification experiments. The spectroscopic (1H‐NMR, MS) and odour threshold data are reported.