The Variation Of Lipoxygenase Activity During Malting

This paper studied lipoxygenase of three kinds of malt which were Metcalf、Schooner and Barley Kenpi NO.7 including the activities of lipoxygenase thermal inactivation and activities change of lipoxygenase during malting as well as discussed the impact of the kilning on lipoxygenase activity.For more in-depth understanding of lipoxygenase thermostability, first of all, the thermal inactivation kinetics of lipoxygenase was analyzed. The two-step inactivation model and Origin 8.0 were used to fit by formula, after lipoxygenase of three kinds of malt were heated in the range of 40-100 ℃. Due to good fitting, it was showed that lipoxygenase thermal inactivation curve of three kinds of malt accorded with the two-step inactivation model. Studies showed that the rate constants of thermal inactivation increased and the half-life decreased by heating in the range of 40-100 ℃ and inactivation rate expedited with the addition of temperature, but the lipoxygenase activity declined fastest and deactivation rate ascended fastest by heating this three kinds of malt at 70℃ with jumpy inactivation. Obviously,70 ℃ was a important critical temperature for lipoxygenase. Lipoxygenase half-lives of three kinds of malt dropped to 3.2min,1.5min and 2.4min by heating and the thermal inactivation was remarkable.Lipoxygenase activities and moisture content of three kinds of malt were detected in each stage by using conventional malting. The results showed that lipoxygenase activity declined after steeping. Lipoxygenase activity became more and more higher with sprouting and highest at the end of sprouting, whereafter, lipoxygenase activity became more and more lower with the temperature of drying dropping. After that, the residual activities of lipoxygenase in three kinds of malt were 9.27U/g,7.80U/g and 6.18U/g.Within the range of kilning temperatures and time, Schooner was kilned by choosing different temperatures and time. Design-Expert 7.0.0 had shown that lipoxygenase activity was decreased with the addition of temperature and time, and they showed a good linear relation. After testing the change of lipoxygenase activity in mashing and later fermentation, the result showed that wort still had residue activity at the end. The activity of lipoxygenase continued to rise and reached the maximum after 72h fermenting. Then activity of lipoxygenase declined and lipoxygenase residue maximum activity was zero after 168h fermenting. On the precondition of making no influence on quality of malt, the lipoxygenase activity could be abated reducing temperatures of steeping and sprouting and decreasing suitably moisture content in prospective malting.