An early development of the nonenal potential in the malting process

Abstract  The scarce knowledge of the significance of enzymatic oxidation of polyunsaturated fatty acids throughout the malting process led the authors to conduct studies on the monitoring of a set of selected parameters involved in the reaction. Lipoxygenase (LOX) activity, the nonenal potential, the temperature and the moisture content were assessed for the top and bottom malt layers in various stages of an industrial kilning process. Significant differences were obtained between the lower and upper malt bed, suggesting that the moisture content and temperature gradient play a key role on the production of E-2-nonenal during the early stages of kilning. The residual nonenal potential already present in the finished malt (malt-RNP) may account for approximately 25% of the total nonenal potential in the mash, depending on the residual LOX activity. LOX showed a good degree of relationship with the nonenal potential for micro-malts (r=0.79, p<0.05), whereas for commercial malts no correlation was found. These results suggest that the malt-RNP plays a prominent role for commercial malts, probably owing to the great heterogeneity observed for the malt bed in the industrial kiln. On the other hand, a major role of LOX during mashing was observed for micro-malts, emphasizing that the intrinsic properties of the barley and malt may be overwhelmed by technological factors. Therefore, kilning programmes should be adopted in order to minimize formation of malt-RNP during the drying phase of the malting process.