THE EFFECT OF KILNING ON THE CAPABILITY OF MALT TO OXIDIZE LIPIDS

The influence of kilning on the ability of malt to oxidise lipids was studied. Barley was malted with a standard programme and subsequently dried with varying kilning procedures. The capability of samples taken during kilning to oxidise lipids was determined by the lipoxygenase ( LOX) reaction, i.e. by measuring O-2 consumption in an aqueous suspens ion of samples upon addition of excess amounts of exogenous linoleic a cid. Various kilning programmes from isothermal low-temperature kilnin gs to kilnings with varying temperature profiles induced a two- to thr eefold increase in the rate of the LOX reaction in the samples taken d uring the first two to six hours of kilning. However, when lipid chang es in the intact kernels were measured, oxidation of the endogenous ma lt lipids was very limited during the first half of kilning. Furthermo re, the rate of the LOX reaction decreased in samples taken during the latter part of kilning. the rate of decrease depending on the kilning programme and especially the final curing temperatures. These results indicate that a possible risk of a marked ability to oxidise lipids r emains at moderate kilning temperatures. In conclusion, kilning induce s a significant capability to oxidise lipids but does not affect the f atty acid composition of whole kernels. However, in aqueous suspension s of ground malt the oxidative instability created might lead to oxida tion of lipids.