Fusarium mycotoxin contamination of malting barley has been a persistent food safety issue for malting company. Our previous studies indicated that a number of essential oils have the antifungal and mycotoxin inhibitory activities in vitro such as thyme, clove and hop oils by disrupting of cell wall composition formation and cytoplasm membrane permeability. As hop is one of four essential beer brewing ingredients, it would be interest to understand the potential application of hop essential oil (HEO) as a dual-functional ingredient during malting process.

In our study, the effect of hop essential oil (HEO) nanoemulsion to control of fungal biomass and mycotoxin production during malting process was evaluated. In addition, fluorescent dye coupled with advanced microscopy techniques including confocal laser-scanning microscopy (CLSM) and scanning electron microscopy (SEM) were applied to study the localization of fungal hyphae on original barley kernels and the development of fungal hyphae within malted barley tissue as affected by HEO nanoemulsion. Lastly, the impact of HEO nanoemulsion on the final malt flavors was measured. The application of HEO nanoemulsion was able to reduce fungal biomass marker (Tri 5 DNA) and deoxynivalenol (DON) content at each stage of malting process when compared with control malts. With the aid of CLSM and SEM, majority of fungal hyphae were observed in furrow crease (transverse section), distal end (longitudinal section), the surface of husk, followed by between husk and pericarp, testa layers. Steeping process greatly decreased the large amount of fungal hyphae in furrow crease, distal end and on the surface of husk as compared to malt samples. However, an increased fungal colonization between husk and pericarp, testa layers was identified in the final malts because of the ideal environmental conditions during germination stage. Regarding the impact of HEO nanoemulsion on the final malt flavor, the flavor profile of both malts shared similarity. In addition, HEO nanoemulsion could prevent the formation of free aldehydes in final malts. As a result, it might act as antioxidant to prevent beer staling. 

ACKNOWLEDGEMENT AND DISCLAIMER

This material is based upon work supported by the U.S. Wheat and Barley Scab Initiative (FAR0031915) and United States Department of Agriculture National Institute of Food and Agriculture (FAR0032822). We thank Mr. Pawel Borowicz from NDSU for his assistance with CLSM image. We also thank Dr. Xiang S Yin from RAHR corporation company for his support on the arrangement of naturally FHB- infected barley samples. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture.