Studies on the metallic off-flavour in buttermilk: Identification of potent aroma compounds

The odour-active volatiles in fresh fermented sweet cream buttermilk, exhibiting a mild, sweet-buttery odour, and sour cream buttermilk in which a metallic odour note had been formed after a storage period of 4 d at 8°C, were compared on the basis of aroma extract dilution analyses. Among the 13 odorants detected in the sweet cream buttermilk sample, the coconut-like smelling γ-and δ-decalactone and δ-octalactone showed the highest flavour dilution (FD) factors. Nine of the 13 odorants present in the sweet cream buttermilk sample appeared with significantly higher FD factors in the sour cream buttermilk. Among them, 4,5-epoxy(E)-2-decenal, 3-methyl indol and (E)-2-undecenal showed the most significance increase. Ten additional odorants were detected in the sour cream buttermilk sample, among which the metallic smelling (E,Z)-2,6-nonadienol predominated with the highest FD factor. Sensory experiments suggest that the dienol, showing the low odour threshold of 0.07 ng/L in air and 1.3/ μg/L in buttermilk, is the key flavour compound causing the metallic off-odour in stored sour cream buttermilk.