Fusarium
graminearum is
a fungal plant pathogen, most known for causing Fusarium head blight (FHB) in wheat
and barley. Globally, FHB is responsible for significant economic impacts on the
grain industry arising through lowering of grain quality related to mycotoxin
contamination and yield loss. In malting, the environmental conditions set to stimulate
barley germination are also conducive to new fungal growth and can lead to production
of mycotoxins such as deoxynivalenol (DON). One important aspect of Fusarium
growth on barley in malting is the presence of defensive plant compounds such
as phenolic acids. Functional and structural modifications to the grain that
occur in malting, including modifications associated with the activities of Fusarium, may influence the composition and/or
availability of the phenolic acids in barley, and may have implications for Fusarium growth and toxin production. In
this study, we investigated the effects of Fusarium infection during
steeping on the availability of phenolic acids. The concentrations of four phenolic acids (caffeic,
p-coumaric, ferulic, and sinapic) in the soluble free and insoluble bound extracts from barley, green
malt, and malt were determined using high performance liquid chromatography. The
dominant phenolic acids that were detected were ferulic and p-coumaric acid. During the course of malting,
the quantity of each phenolic acid decreased (barley > green malt >
malt). However, the rate of decline in the quantity of extractable p-coumaric acid was slowed by the
presence of Fusarium; in other words,
more p-coumaric acid was extracted from green malt that was infested
with Fusarium, compared to
non-infested green malt. The antifungal activities of ferulic and p-coumaric
acid were examined in-vitro. Ferulic acid demonstrated the most significant
fungal inhibition, at over 70% growth reduction at the highest concentration
(1.0 mM) tested 7 days post-inoculation. A dose-effect relationship was found,
where higher concentrations of the phenolic acids resulted in greater growth
reduction of fungal mycelia. Current work is focused on clarifying the influence
of Fusarium degradative enzymes on the release of phenolic compounds
during malting of barley. Outcomes from this study could provide a better
understanding of the
interactions between barley and Fusarium which may form the basis for
practical approaches to improve malt quality.