Assessment of Bacillus licheniformis α-amylase as a candidate enzyme for genetic engineering of malting barley

Abstract

Bacillus licheniformis α-amylase, a thermostable starch-degrading enzyme, has been assessed as a candidate enzyme for the genetic transformation of malting barley. The temperature optimum, pH optimum and thermostability of B. licheniformis α-amylase were compared with those of barley α-amylase. The bacterial enzyme has a higher pH optimum (−9), a higher temperature optimum (−90°C) and much higher thermostability at elevated temperatures than the barley enzyme. The specific activity of the bacterial enzyme under conditions of pH and temperature relevant to the brewing process (pH 5.5, 65°C) is −1.5-fold higher than that of the barley enzyme. Measurements of α-amylase activity during a micro-mash showed that the bacterial enzyme is at least as stable as the barley enzyme under these conditions, and that a level of expression for the bacterial enzyme corresponding to −0.5% of total malt protein would approximately double the α-amylase activity in the mash. B. licheniformis α-amylase activity was rapidly eliminated by boiling following mashing as would occur during brewing. The combined results suggest that barley expressing the bacterial enzyme may be useful in the brewing process.