Improved Method for Measuring Lipoxygenase Activity in Barley and Malt

ABSTRACT

For 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 LOX_Soybean 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 LOX_Soybean standard curve into absolute amounts of LOX (LOX_eq), 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 LOX_eq content and the protein amount, the data were expressed in µg LOX_eq/mg protein. The values of the barley samples ranged from 10.7 to 18.2 µg LOX_eq/mg protein and the malt samples from 1.1 to 2.5 µg LOX_eq/mg protein. As expected, the amount of LOX in malt was over 80% less, than the amount in barley.

KEYWORDS:

• Analysis
• extraction
• lipoxygenase
• solvent

Acknowledgments

We thank S. Glaser and R. Marx, Department of Chemistry (Organic Chemistry), Technical University of Munich, for providing lab space and for their continuing support. Without their help, our research would not have been possible. Also, we thank Dieter and Jörg Gewalt, Mälzerei Steinbach, Zirndorf (Germany) for the donation of the barley and malt samples.