Changes in the Cationic Isoenzymes of Peroxidase During the Malting of Barley. I: Tissue Location Studies

Sixteen cationic isoenzymes of peroxidase were detected in barley grain (variety: Chariot) and twenty in green malt, falling to fifteen after kilning. The distribution of these among the different seed tissues was examined with a view to determining which isoenzymes were likely to survive mashing and be active during brewing. In isolated barley tissues, the aleurone layer contained one major band (Rm 0.77), and the endosperm only the four fastest running bands (Rm values 0.84–0.97). In green malt the growing embryo tip contained fifteen isoenzyme bands (Rm values 0.04–0.70), with an absence of only the faster running bands. In kiln-dried malt, isoenzymes with Rm values 0.04–0.10 increased in activity, two extra light bands appeared (Rm 0.26 and 0.61) and three other bands present in barley were lost (Rm values 0.63, 0.70 and 1.0). Much of the activity in the aleurone layer was lost. Seven of the fifteen isoenzymes in finished malt accounted for over 75% of the cationic peroxidase activity. Variation in aleurone and endosperm isoforms between different cultivars was observed, whereas the embryo showed little variation. The endosperm isoforms seem to be the ones most likely to cause oxidation problems during brewing.