Aspergillus flavus is a ubiquitous fungus that contaminates food and medicinal materials during production, transportation, and storage. This contamination results in the production of aflatoxins (AFT), posing a significant threat to global food safety and leading to diseases in humans and animals. AFT contamination in food, even at levels as low as 1 mg per kg, has been linked to liver cancer. Among various AFTs, aflatoxins B1 (AFB1) exhibits the strongest carcinogenic. In fact, AFB1 toxicity is 10 times that of KCN and 68 times that of As2O3. AFB1 is a potent liver toxin that causes mutations, immune suppression, and cancer, classified as a Group 1 carcinogen by World Health Organization (WHO).

Due to the high toxicity and pathogenicity of AFT, over 100 countries, including China, have established strict limits for AFT in food and feed. In China, the “GB 2761-2017 National Food Safety Standard Maximum Levels of Mycotoxins in Foods” standard regulates AFT levels in food, and the 2020 edition of the “Chinese Pharmacopoeia (CP)” limits aflatoxin B1 in 24 medicinal herbs to 5 μg/kg. This has led to an urgent need for developing safe, green, and effective antifungal essential oils for preventing and controlling A. flavus. Essential oils, composed of small polar compounds, penetrate A. flavus cell membranes easily, providing a rapid fungicidal effect. They rapidly volatilize, preventing contamination and preserving the original flavor and nutritional value of foods and medicinal materials. Extracting antifungal essential oils from plants used in both medicine and food presents a promising approach to enhancing public health and drug innovation.

Professor H. A. Aisa's team at the State Key Laboratory of Xinjiang Indigenous Medicinal Plants, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, discovered that Ajwain (Trachyspermum ammi L.) essential oil (AEO) fumigation significantly inhibits A. flavus growth and reduces aflatoxin B1 and ergosterol production. The study demonstrated the antifungal properties of AEO against A. flavus, revealing its potential for controlling aflatoxin contamination. GC-MS analysis revealed a diverse chemical composition of AEO in which thymol (59.9%) is dominant compound. After screening the application method and optimizing fumigation conditions, AEO significantly inhibited the growth and AFB1 production of A. flavus (MFC = 30 μL/L). Moreover, AEO treatment of A. flavus at different developmental stages resulted in inhibited spore germination, hypobranching, impaired condition, structural disruption, and reduced AFB1 and ergosterol levels (p<0.01). Metabolomics analysis revealed that AEO significantly affected 11 metabolic pathways in A. flavus, including inhibition of ergosterol biosynthesis and growth signaling molecules. Molecular biology research indicated that AEO downregulated the expression of multiple key genes in A. flavus, including global regulators, growth and development regulators, AFB1 biosynthesis pathway-specific activator aflR and coordinator aflS, and key genes in the ergosterol biosynthesis pathway. In conclusion, AEO effectively inhibits A. flavus growth and aflatoxin production by modulating key pathways, involving downregulation of the Velvet complex, aflatoxin and ergosterol biosynthesis pathway. This research provides a theoretical basis for the development of novel natural antifungal agents and offers a new strategy for controlling aflatoxin contamination in food.

The findings of this study, entitled “Ajwain essential oil inhibits aflatoxin B1 and ergosterol production in Aspergillus flavus: mechanisms and developmental stages-specific effects”, have been published in the Chinese Academy of Sciences' first-quartile journal, Food Bioscience. The corresponding author is Professor Maitinuer Maiwulanjiang from the Xinjiang Technical Institute of Physics and Chemistry, and the first author is his PhD student, Lu Xiuxiang. 

The article can be accessed at: https://doi.org/10.1016/j.fbio.2024.105561.

A schematic illustration of the mechanism by which Ajwain essential oil fumigation inhibits A. flavus