The carbonyl contents of benzene extracts of aqueous cucumber homogenates were estimated spectrophotometrically as the 2, 4-dinitrophenylhydrazones. A large increase in the formation of carbonyl compounds occurred when cucumbers were blended with water in the presence of oxygen. This formation of carbonyl compounds was prevented by three methods: blending the cucumbers at pH 1.0; blending in an oxygen-free atmosphere; and heating whole cucumbers to an internal temperature of 77°C before blending.
Chromatographic assays indicated that negligible amounts of the 2-enals, 2, 6-nonadienal, 2-nonenal, and P-hexenal are present in intact cucumbers; but a rapid synthesis of this class of carbonyl compounds occurred when fresh cucumbers were blended in the presence of oxygen. The most significant increase occurred in the formation of 2, 6-nonadienal, the aldehyde largely responsible for the flavor of fresh cucumbers. There were indications that ethanal and propanal were present in appreciable levels in intact cucumbers.
These observations suggest that the characteristic flavor components of fresh cucumbers are generated enzymatically as a consequence of cutting or mechanically rupturing the fruit.