AND SUMMARYIn the last few decades, flavor research has developed along different main routes. The first step was the discovery of the complex mixtures of volatile components that together build the particular flavors. Apart from this, interest became focused on the taste substances which, through interaction with the flavor carriers, impart aroma to a food. The third main route was the investigation of the deterioration in odor and taste due to oxidative or microbial spoilage. As these investigations progressed, it became clear that these flavor areas show considerable interaction and that, in addition, other sensory impressions of a product as regards shape, texture, color, etc., play a role in the ultimate subjective perception by the consumer. In this way, flavor research has widened into a complex branch of science, and it is becoming more and more apparent that consumer testing that encompasses all the elements mentioned above will have to indicate the real preferences of the public.

The characteristic hardening flavor which develops in hardened linseed and soybean oils during storage has been coned from hardened linseed oil by stripping with nitrogen. After separating the volatile substances by adsorption chromatography on silica, the fraction containing the hardening flavor has been converted into 2,4-dinitropheny]hydrazones (DNPHs) and separated by means of partition chromatography. On regeneration of the fractions of DNPSs obtained, the characteristic hardening flavor was observed in one specific band. Both by hydrogenation and by oxidation of the free carbonyl the carrier of the flavor was found to be an unsaturated aldehyde; however, not of the a-fl unsaturated type. Further separation of the regenerated carbonyls by means of gas-liquid chromatography (GLC) points to a Cg-aldehyde. After synthesis of the 4-,5-and 6cisand trans-nonenals, comparison made it probable that the carrier of the hardening flavor is a mixture of 6-cis and 6-trans-nonenal, the latter of which has the greatest share in the hardening flavor.In order to confirm the location of the double bond in the carrier of the hardening flavor a recent isolation technique was applied. The volatile substances from hardened linseed oil were first separated via GLC. After conversion of the carbonyls in question into their DNPHs, the latter have been separated by means of thin-layer chromatography (TLC). By means of IR-analysis and oxidation with osmium tctroxide of the pure derivative, the principal carrier of the hardening flavor has been identified as 6-trans-nonenal.

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The hardening flavor that develops in hydrogenated linseed oil and soybean oils during storage was recently identified as 6-nonenal. According to the theory of Farmer, certain iso-linoleic acids must be the precursors of this unsaturated aldehyde. By means of oxidation experiments on 9,15-, 8,15-, and 7,lS-iso-linoleie acids, it was established that only the first two iso-acids are the precursors of this typical flavor.

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