Use of ChemiluminescenceHPLC for Measurement of Positional Isomers of Hydroperoxy Fatty Acids in Malting and the Protein Rest Stage of Mashing

Abstract

Fatty acid hydroperoxides (9- and 13-hydroperoxides of linoleic acid and linolenic acid) were extracted from barley, malt and wort, and quantified by chemiluminescence HPLC. Although not detected in dried barley (<0.5 μmol kg -1 (dry wt)), the concentrations of hydroperoxides increased during germination (up to 156 μmol kg -1 (dry wt) in the case of 9-hydroperoxylinoleic acid). Lipoxygenase (LOX) activity increased more than two-fold during germination. LOX activity and hydroperoxide concentrations were reduced considerably on kilning of malt. During mashing on a laboratory scale, malts with higher total LOX activities produced higher concentrations of hydroperoxides. The concentrations of 9-hydroperoxides were double those of the 13-hydroperoxides during malting and up to 10-fold greater during mashing, indicating a greater activity of LOX-1 in both processes.