Fusarium head blight: Effects on fungal protease activity and wheat gluten functionality

The breadmaking quality of wheat depends on the viscoelastic properties of the dough, largely determined by gluten quality. The latter is influenced by wheat genetics and environmental factors. To identify whether fungal infection can compromise gluten quality, greenhouse-grown spring wheat was inoculated with Fusarium graminearum or Fusarium avenaceum at flowering. Grain harvested at maturity was analysed for fungal infection (concentration of fungal DNA), thousand-grain weight (TGW), size distribution of glutenin polymers (proportion of un-extractable polymeric proteins, %UPP), gluten-degrading protease activity, and viscoelastic properties of gluten (maximum resistance towards stretching [R_MAX] and extensibility). Fusarium graminearum caused severe infections, and strong negative correlations were observed between F. graminearum-DNA and TGW, %UPP and R_MAX. Significant reductions in %UPP and R_MAX were observed even when only 10% of the flour-blend originated from infected grain. The degradation of gluten proteins was attributed to both enzymatic activity and disrupted grain maturation. In contrast, F. avenaceum infections were less severe, with only slight reductions in TGW, %UPP, and R_MAX, though signs of gluten-degrading enzyme activities were observed in the most infected samples. In summary, F. graminearum significantly compromised gluten quality through protein degradation and reduction in the proportion of large glutenin polymers. While F. avenaceum had a lesser impact on gluten quality, the risk of compromised grain entering the food chain may be greater than with F. graminearum, as neither F. avenaceum nor its associated mycotoxins are regulated. These findings highlight the importance of further research on how fungal infection influences the breadmaking quality of wheat.