Inhibition of Aspergillus flavus Growth by 1-Nonanol

1-Nonanol is a straight chain fatty alcohol with nine carbon atoms and the molecular formula CH3(CH2)8OH. It is a colorless oily liquid with a citrus odor similar to citronella oil. 1-Nonanol occurs naturally in orange oil. The primary use of 1-Nonanol is in the manufacture of artificial lemon oil. Various esters of nonanol, such as nonyl acetate, are used in perfumery and flavors.

Figure1: Picture of 1-Nonanol

Physicochemical Properties

1-Nonanol is a chemical substance with the molecular formula C9H20O. It appears as a colorless to yellowish oily liquid with a boiling point of 213-215°C. 1-Nonanol is soluble in 3 volumes of 60% ethanol as well as in oils and fats, and has an acid value of <1.0. The compound exhibits a potent, sweet, and green waxy rosy aroma with fruity waxy notes, accompanied by subtle hints reminiscent of orange and sweet orange.

Inhibition of Aspergillus flavus growth

Chemical control of fungal spoilage of postharvest cereal grains is an important strategy for the management of grain storage. Here, the potential antifungal activity of 1-nonanol, a main component of cereal volatiles, against Aspergillus flavus was studied. The growth of A. flavus was completely inhibited by 0.11 and 0.20 μL/mL 1-nonanol at vapor and liquid contact phases, respectively. Metabolomic analysis identified 135 metabolites whose expression was significantly different between 1-nonanol-treated and untreated A. flavus. These metabolites were involved in the tricarboxylic acid cycle, amino acid biosynthesis, protein degradation and absorption, aminoacyl-tRNA biosynthesis, mineral absorption, and in interactions with ABC transporters. Biochemical validation confirmed the disruptive effect of 1-nonanol on A. flavus growth, as indicated by the leakage of intracellular electrolytes, decreased succinate dehydrogenase, mitochondrial dehydrogenase, and ATPase activity, and the accumulation of reactive oxygen species. We speculated that 1-nonanol could disrupt cell membrane integrity and mitochondrial function and might induce apoptosis of A. flavus mycelia. Simulated grain storage experiments showed that 1-nonanol vapor, at a concentration of 264 μL/L, completely inhibited A. flavus growth in wheat, corn, and paddy grain with an 18% moisture content. This study provides new insights into the antifungal mechanism of 1-nonanol against A. flavus, indicating that it has a promising potential as a bio-preservative to prevent fungal spoilage of postharvest grains. KEY POINTS: 1-Nonanol showed higher antifungal activity against A. flavus. The antifungal mechanisms of 1-nonanol against A. flavus were revealed. 1-Nonanol could damage cell membrane integrity and mitochondrial function. [1]

Bioactivity

1-Nonanol is one of the main components of wheat volatiles, which was found to have considerable antimicrobial activity. It has been reported that 1-nonanol showed the highest inhibitory activity against the growth of the postharvest fungal pathogen Geotrichum candidum citrus race among the straight-chain (C6-C12) alcohols. 1-Nonanol can inhibit Mycobacterium smegmatis and Mycobacterium tuberculosis by damaging their cell envelope and has bactericidal and membrane-damaging activity against Staphylococcus aureus. Additionally, 1-nonanol inhibits the growth of Saccharomyces cerevisiae and Zygosaccharomyces bailii by disrupting the membrane-associated function of integral proteins. As a cereal-derived volatile and an authorized food additive by the National Health and Family Planning Commission of China (Chinese Standards for Food Additives GB2760-2014), 1-nonanol shows great potential as a preservative in preventing fungal spoilage of cereal grains. However, there are few reports about the fungicidal activity of 1-nonanol against spoilage fungi in cereal grains. [1]

Biological Research

The growth of A. flavus was completely inhibited by exposure to 0.11 μL/mL 1-nonanol vapor or to 0.20 μL/mL liquid contact. Metabolomic analyses identified 135 significantly differential metabolites between the 1-nonanol-treated and untreated A. flavus. 1-Nonanol disrupts the permeability and integrity of the cytoplasmic membrane, the TCA cycle, and fatty acid and amino acid metabolism, and may induce apoptosis. This results in cell membrane leakage, mitochondrial dysfunction, increased oxidative stress, and metabolic disorders in A. flavus. These effects were validated biochemically. We speculate that the antifungal mechanism of 1-nonanol is mediated through the disruption of cell membrane integrity and mitochondrial function, as well as the induction of apoptosis in A. flavus cells. The remarkable effectiveness of 1-nonanol in controlling the growth of A. flavus in cereal grains suggests that it is a promising bio-preservative for preventing fungal spoilage in postharvest grains, although other factors beyond its antifungal capability must be considered. The apoptotic phenotype of A. flavus induced by 1-nonanol remains to be characterized in more detail. [1]

Reference

[1] Shuai-Bing Z, ,et al. Antifungal mechanism of 1-nonanol against Aspergillus flavus growth revealed by metabolomic analyses[J]. Applied microbiology and biotechnology, 2021, 105:7871-7888.