Enzymes Associated with Fusarium Infection of Barley

Abstract

Infection of barley with species of Fusarium has been reported to decrease malt yield, wort β-glucan, and viscosity and to increase wort soluble nitrogen, free amino nitrogen, and color. These changes are suggestive of the presence of active fungal enzymes, and the objective of this research was to determine whether proteolytic or cell wall degrading enzymes were associated with Fusarium-infected barley. Barley was inoculated with Fusarium graminearum and F. poae in the greenhouse to reduce contamination with other microorganisms. Control samples were inoculated with distilled water only. Mature harvested grain was screened for the presence of endoproteinase, endoxylanase, and β-glucanase. Inoculated barley was found to contain considerable amounts of proteinase and β-glucanase, whereas only a trace of these activities were detected on the control samples. Malts prepared from these samples showed correspondingly elevated free amino nitrogen levels and reduced levels of wort β-glucans. Inoculated barley also displayed significant amounts of endoxylanase, wih no activity being detected in the controls. The results strongly suggest that fungi associated with the Fusarium head blight infection of barley contribute β-glucanase, xylanase, and proteinase activities to the grain. Further, the enzyme levels appear to be such that they may affect the quality of the malt and its consequent wort.