Improved Method for Measuring Lipoxygenase Activity in Barley and Malt

Abstract

ABSTRACTFor the lipoxygenase (LOX) activity assay, we dissolved the substrate linoleic acid in dimethyl sulfoxide (DMSO) rather than the usual 1% Tween 20. Activity curves with LOXSoybean were established and nine measurements within more than a month showed a standard deviation of the linear slopes of 4.8%. LOX activities in barley and the corresponding malt samples were followed at 10 min time-points for one hour. The activities during the time-course had the tendency to decrease at the end of the extraction time. LOX activity was then converted with the use of a LOXSoybean standard curve into absolute amounts of LOX (LOXeq), assuming the same specific activities for LOX from soybean and the ones from barley and malt, respectively. Furthermore, the protein amounts of all the extracts were determined and, finally, with the LOXeq content and the protein amount, the data were expressed in µg LOXeq/mg protein. The values of the barley samples ranged from 10.7 to 18.2 µg LOXeq/mg protein and the malt samples from 1.1 to 2.5 µg LOXeq/mg protein. As expected, the amount of LOX in malt was over 80% less, than the amount in barley.