Influence of Fusarium avenaceum infections on barley malt: Monitoring changes in the albumin fraction of barley during the malting process

Abstract

Fusarium spp. are ubiquitous field pathogens, which are known to affect quality characteristics of cereals. Infections with Fusarium pathogens in brewing cereals are problematic and augur for a poor malt quality. The negative effects of Fusarium infections are various. Besides causing agronomic losses, kernel discoloration, and the production of several mycotoxins, Fusarium spp. are known to enhance the proteolytic activity of infected barley malt. Enhanced proteolysis can be observed in higher values in free amino nitrogen (FAN) as well as in soluble nitrogen. Previous studies showed that, in recent crop years, the predominant Fusarium spp. detected in European malt was F. avenaceum. This study focuses on the changes in the albumin fraction during the malting process of barley samples artificially infected with F. avenaceum in comparison to uninfected control samples. The barley samples were grown under controlled conditions in a greenhouse, and two different sample types were studied: One was not infected with Fusarium spores whereas the other sample was inoculated during anthesis with a spore suspension of F. avenaceum. Malting trials were carried out in a micromalting facility under defined conditions. To monitor the changes in protein profiles due to Fusarium infection, samples were analyzed at different stages of the malting process: barley (raw grain), poststeeping, postgermination, and postkilning. To evaluate the changes in the protein composition, different fractionation techniques (Osborne fractionation, isoelectric focusing, and capillary gel electrophoresis) were utilized. The albumins of the Osborne fractionation were further analyzed as they represent the main metabolically active proteins. Protein maps of the different malting steps were plotted with a custom-programmed visualization tool for comparing the infected and uninfected samples at each malting step. The results elucidate the changes in the albumin fraction during the malting process and reveal the influence of Fusarium infection on the albumin composition of barley, barley malt, and the intermediate products of malting.