RANCIDITY IN HAZELNUTS DUE TO VOLATILE ALIPHATIC-ALDEHYDES

Hazelnut kernels became rancid on storage under ambient conditions in the presence of air. The kernels have a high oil content. The oil contains approximately 75 g per 100 g oleic acid (18:1) and 9 g per 100 g linoleic acid (18:2). Rancidity was detected organoleptically, by gas chromatography/mass spectrometry of the volatile off-flavour compounds and by reduction in both the total fatty acid content (g per 100 g oil) and the iodine value (g per 100 g oil). There was an accumulation of volatile alkanals, 2-alkenals and alkanoic acids on storage of the kernels at ambient temperature in the presence of oxygen. Hexanal (derived from oxidation of linoleic acid) and octanal (derived from oxidation of oleic acid) increased over tenfold on storage, whilst there was concomitant decrease in fatty acid content (83 g per 100 g oil) and iodine value (79) during the same period. It is suggested that analysis of volatile aldehydes such as hexanal and octanal could be used to assess rancidity in foods or oils rather than relatively nonspecific tests such as iodine or peroxide value. There was no evidence in this work that the rancidity was due to microbial spoilage.