Roles of the volatile and non-volatile fractions of thyme (Thymus vulgaris L.) essential oil in inhibiting Fusarium graminearum growth and trichothecene mycotoxin production

Abstract

This study investigated the antifungal activity, mycotoxin inhibitory effects, and mechanisms of action of whole thyme oil, along with its volatile and non-volatile fractions. Thyme oil was fractionated into relatively volatile and non-volatile components using solvent-assisted flavor evaporation (SAFE) at 50 °C. The compositions of the two fractions were profoundly different. Afterwards, physically stable emulsions were prepared from the two fractions and whole thyme oil, and their effects were evaluated against two chemotypes of Fusarium graminearum including spore germination and mycotoxin production. All emulsions inhibited fungal growth and reduced mycotoxin accumulation to varying degrees. The non-volatile fraction of thyme oil exhibited the strongest suppression of spore germination, validated by the lowest EC₅₀ values (0.54 and 0.74 µg mL⁻¹, respectively) and demonstrated the greatest disruption of cytoplasmic membrane integrity, confirmed by advanced microscopic technologies, and total lipid content analyses. In terms of mycotoxin inhibitory effect, all emulsions significantly reduced deoxynivalenol (DON) levels to values compliant with FDA regulations and suppressed acetylated derivatives to as low as undetectable amounts. A non-detectable level of the acetylated derivatives was achieved by the non-volatile fraction at the EC₅₀ concentration. Tri gene expression analysis in the DON biosynthesis pathway revealed that thyme oil and the non-volatile fraction up-regulated all Tri genes in both isolates, while the volatile fraction down-regulated Tri3 and Tri5 in strain isolate 10-124-1. In summary, the findings highlighted the potential of SAFE fractionation to selectively enrich the non-volatile fraction of Thymus vulgaris L., offering an effective and sustainable strategy for fungal control and mycotoxin reduction in food systems.