USE OF CHEMILUMINESCENCE HPLC FOR MEASUREMENT OF POSITIONAL ISOMERS OF HYDROPEROXY FATTY-ACIDS IN MALTING AND THE PROTEIN REST STAGE OF MASHING

Fatty acid hydroperoxides (9- and 13-hydroperoxides of linoleic acid a nd linolenic acid) were extracted from barley, malt and wort, and quan tified by chemiluminescence HPLC. Although not detected in dried barle y (< 0.5 mu mol kg(-1) (dry wt)), the concentrations of hydroperoxides increased during germination (up to 156 mu mol kg(-1) (dry wt) in the case of 9-hydroperoxylinoleic acid). Lipoxygenase (LOX) activity incr eased more than two-fold during germination. LOX activity and hydroper oxide concentrations were reduced considerably on kilning of malt. Dur ing mashing on a laboratory scale, malts with higher total LOX activit ies produced higher concentrations of hydroperoxides. The concentratio ns of 9-hydroperoxides were double those of the 13-hydroperoxides duri ng malting and up to 10-fold greater during mashing, indicating a grea ter activity of LOX-1 in both processes.