Cardboard odour

The most important precursors for lipid oxidation are unsaturated fats and fatty acids like oleic (18 1), linoleic (18 2), linolenic (18 3) and arachidonic acid (20 4). The more unsaturated ones are more prone to oxidation. Lipid peroxidation and the subsequent reactions generate a variety of volatile compounds, many of which are odour-active, especially the aldehydes. That is why lipid oxidation is also a major mechanism for thermal aroma generation and contributes in a great measure to the flavour of fat-containing food. Lipid oxidation also takes place under storage conditions and excessive peroxidation is responsible for negative aroma changes of food like rancidity, warmed-over flavour, cardboard odour and metallic off-notes. 

The cardboard like flavour that occurs in stale beer is thought to arise fi-om the fi ee radical mediated oxidation of various constituents in beer. The characteristic odour and taste are caused by decomposition products finm the free radical process. Similar processes occur in many foods, but in beer, these off-flavour products can be detected by the consumer even at very low concentrations. 

Descriptive terminologies for the odours of pyridines use terms such as green, bitter, astringent, roasted, burnt, pungent, solvent and fishy, none of which could be considered desirable. Their presence in some food commodities, such as beer and whisky, is disagreeable and associated with a cardboard, oxidised and harsh flavour. In roasted coffee, pyridines may contribute to a pleasant smell that is, however, less pleasant than the smell of pyrazines. 

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