Enzymatic oxidation of linoleic acid in barley suspensions.

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