2‐<i>trans</i>,4‐<i>cis</i>,7‐<i>cis</i>‐Decatrienal, the fishy off‐flavor occurring in strongly autoxidized oils containing linolenic acid or ω 3,6,9, etc., fatty acids

Abstract

Abstract A possible decomposition product of oils containing unsaturated fatty acids with the double bond pattern ω3,6,9 or ω3,6,9, etc., is 2‐ trans ,4‐ cis ,7‐ cis ‐decatrienal. It has therefore been investigated whether this trienal is present in strongly autoxidized linolenic acid, soybean, linseed and fish oils. Via a degassing technique the carbonyls from the samples of oils heated in a closed system under nitrogen were collected and separated as their 2,4‐dinitrophenylhydrazones (DNPHs) by thin layer chromatography (TLC). The presence of 2‐ trans ,4‐ cis ,7‐ cis ‐decatrienal in the samples was positively established by TLC, UV absorption and mass spectroscopy of its DNPH. All analytical data established the complete identity of the isolated DNPH with a synthesized 2,4,7‐decatrienal‐DNPH. The free aldehyde obtained on hydrolysis of the alkatrienal‐DNPH in question had the same flavor as authentic 2‐ trans ,4‐ cis ,7‐ cis ‐decatrienal, having a fish or rather a whale oil flavor.