Graveland, A., Pesman, L. and van Eerde, P.

Abstract
The development of an oxidised flavour in beer during storage is generally believed to be due to the formation of 2-trans-nonenal and 2-methyl furfural. Presumably, the main precursors of 2-trans-nonenal are long chain unsaturated fatty acids. Evidence is given that 2 isomeric hydroperoxides are formed from linoleic acid in barley flour/phosphate buffer suspensions. These hydroperoxides are either reduced to the corresponding monohydroxy acids or transformed by the isomerases present in barley into 2 isomeric alpha-hydroxy-keto acids, 2 isomeric alpha-hydroxyketo acids, and 2 isomeric dihydroxy acids. Moreover, the lipoxygenase associated with the glutein protein forms 2 isomeric trihydroxy acids. In addition, another 2 keto-dihydroxy acids are formed. It could not yet be established whether these compounds are formed directly from linoleic acid or from hydroperoxides.
Keywords: barley beer cardboard flavour fatty acid oxidation storage