Table 5.

Antifungal mechanisms of action proposed for citral.

Microorganism	Mechanism	Ref.
Saccharomyces cerevisiae BY4741	Loss of membrane and cell wall integrity results in a typical apoptotic/necrotic cell death. However, yeast cells that escape this first cell membrane disruption, particularly evident in sub-lethal concentration, die by metacaspase-mediated apoptosis induced by the accumulation of intracellular ROS.	[57]
B. dothidea	Changes in the morphological characteristics of fungal hyphae, resulting in loss of cell content and distortion of the mycelium. Increase in membrane permeability, with increases in extracellular electrical conductivity and a decrease in soluble protein content. A decrease in the range of ergosterol levels showed that citral altered the physiology of the cell membrane. Reduction in the level of enzymes associated with respiration, resulting in the disruption of energy metabolism.	[54]
Aspegillus ochraceus	Citral downregulated ochratoxin biosynthetic genes, including pks and nrps, but slightly upregulated global regulatory factors veA, velB, and laeA.	[54]
Aspegillus niger	Direct damage to the cell membranes of A. niger may explain the antimicrobial activity of citral combined with eugenol. Among the two components, eugenol is mainly responsible for the permeability of damaged cell membranes, whereas citral mainly causes membrane lipid peroxidation, which leads to a burst in ROS.	[16]
Penicillium roqueforti.	The combination of citral and eugenol destroyed the integrity of the cell membrane and internal structures and degraded the cell content. The combination induced membrane lipid peroxidation and promoted the ability to destroy the cell membrane. The combined agents eventually caused leakage of cell contents and, ultimately, cell death.	[16]
Penicillium digitatum	Citral can affect the mitochondrial morphology and function of P. digitatum, inhibiting the respiratory metabolism, decreasing the activities of TCA-related enzymes, and changing the TCA metabolic abilities.	[56]
Zigosachamomyces rouxii	The antifungal effect can be attributed to the alteration of the integrity and permeability of the cell membrane, which can cause irreversible damage to the cell wall and membrane. They can also destroy yeast proteins and inhibit their synthesis.	[58]