Cereals, such as wheat and barley which are ranking the most produced grains, are consumed as major staple food. However, because of the inseparable contact with soil, cereal crops are extremely prone to soil-borne toxigenic fungi infections such as Fusarium spp. that causing yield loss and grain quality reduction. In particular, F. graminearum, a causal agent of Fusarium head blight (FHB), causes millions of lost on wheat production in Northern and Central America every year. The current research studied the antifungal, mycotoxin inhibitory activity of emulsions formed with thyme oil and its four major components (thymol, p-cymene, γ-terpinene, and linalool) on two chemotype of F. graminearum isolates, and their corresponding mode of action (MOA). Among five essential oil (EO) compounds, thymol presented the strongest antifungal and mycotoxin inhibitory efficacy followed by thyme oil emulsion. The 50% inhibition of spore germination (EC₅₀) on two chemotype Fusarium graminearum isolates can be achieved by thymol emulsion at the concentration of 0.38 and 0.48 mg/ml, respectively. According to the SEM and CLSM images, spore morphology changes and cell membrane destruction were the main reasons attributed to the inhibition of spore germination. Significant (p ˂0.05) mycotoxin reduction was also observed when five EOs in emulsion based delivery systems were applied. Interestingly, linalool was shown to be a more effective spore germination inhibitor rather than mycotoxin production inhibitor, while p-cymene and γ-terpinene behaved the opposite way. We further investigated the MOA of thyme and thymol emulsions on suppression of mycotoxin production on genetic level. We observed that thyme oil significantly (p ˂0.05) up-regulated the expression of the genes studied (Tri3, Tri4, and Tri5), while thymol did not up-regulate any gene expression. This study established the potential application of thymol and thyme oil emulsion as a safe and more effective preservative in food. Future research will focus on discovering the potential synergistic effect of thymol with other compounds to reduce the essential oil usage level. 

This material is based upon work supported by the U.S. Wheat and Barley Scab Initiative under Agreement No. 59-0206-0-130 and USDA National Institute of Food and Agriculture (FAR0032822). 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.