Unsaturated aliphatic aldehydes are known to play a major role in odors of plants, foods and insects. They are believed to originate from unsaturated fatty acids in several nonenzymatic and enzymatic processes, such as autoxidation, photosensitized oxidation, lipoxygenaze, peroxydaze, and microsomal enzymes, which have been suggested as initiators of lipid oxidation.
Many papers have shown the potency and significance of C9-aldehydes for the aroma of numerous volatiles. They are able to contribute to the flavor by themselves, but in addition, used in concentrations below the flavor threshold value, they can mask an undesirable odor or enhance a desirable one.
(E,Z)-2,6-Nonadienal, called sometimes violet leaf aldehyde, has a green, fresh cucumber-like odor. Its structure has been well established on the basis of physiochemical studies and confirmed by syntheses and spectral data. The physiochemical and spectral data of the aldehyde are given in Table 1.