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Influence of Barley and Malt Storage on Lipoxygenase Reaction

¹Helsinki University of Technology, P.O. Box 6100, FIN-02015 HUT, Finland. ²Corresponding author. Phone: 358-9-451 2555. Fax: 358-9-462 373. E-mail: Anu.Kaukovirta-Norja@hut.fi ³Oy Lahden Polttimo Ab, P.O. Box 22, FIN-15141 Lahti, Finland

The dioxygenation of linoleic acid (LA) by aqueous flour suspensions of barley and malting samples was studied. The rate of this lipoxygenase (LOX) reaction varied as the malting process proceeded, giving a characteristic LOX reaction profile for a malting. The differences in the profiles from one malting to another were dramatic. It also appeared that during storage of dry, intact kernel samples from a single malting, a reduction in the rate of LOX reaction always occurred, and the rates of reduction with time were dependent on the stage of malting at the time of sampling. The kinetics of this aging could roughly be divided into four categories representing different stages of malting. Consequently, greatly varying LOX reaction profiles can be obtained from a single malting depending on the time of storage of kernels before assays. The results indicate that steeping, germination and the subsequent drying render the state of kernels unstable with respect to the LOX reaction for at least two to three weeks. Homogeneity of malt quality is important in the further applications of malt, especially in the brewing industry. Therefore, the rate of LOX reaction should be considered as a quality factor of malt.