Inhibition effect of some EOs on the growth of
Aspergillus flavus has been reported to be one of the most common fungal species in foods. Under conditions of high humidity and moderate temperature, this fungus may synthetize the mycotoxin Aflatoxin B1 (AFB1), which is reported to be hepatotoxic, teratogenic, mutagenic and immunosuppressive to human beings and livestock and it is classified as carcinogenic to humans (Group 1 by IARC). AFB1 affects cereals, oilseeds, nuts, spices, legumes, and dried fruits, while Aflatoxin M1 is a metabolite of AFB1 that can occur in milk and milk products. Current control is aimed at controlling fungal growth and AFB1 production in food by eco-friendly, biodegradable and safer alternatives, in contrast to synthetic chemicals that can be toxic to humans and cause adverse environmental effects. Recently, considerable attention has been directed towards natural compounds, such as essential oils (EOs) as a promising approach for controlling AFB1 production in food. The main reason for supporting the application of natural products is the consumer’s preference for natural methods to preserve foods. The aim of the present review is to summarize knowledge of EOs and AFB1 production from the literature.
- Aspergillus flavus
- aflatoxin B1 (AFB1)
- essential oils
- food system
Molds are ubiquitous micro-organisms with a high capacity to colonize different types of substrates and to proliferate under extreme environmental conditions . They alter various types of foods namely cereals, nuts, oil seeds, legumes, spices, vegetables, fruits, etc. and some species produce mycotoxins. Of all mycotoxins, Aflatoxin B1 (AFB1) produced primarily by
Pesticides and fungicides have been widely used to prevent the development of fungal agents. However, because of their own toxicity, their use is subjected to certain restrictions. Biological control is also a possible option. Thus, antiaflatoxigenic bacterial and fungal strains were found effective in reducing the development of toxic strains of
Aflatoxins are produced primarily by the common fungus
3. Methods of aflatoxin decontamination
Foodstuffs should not be hazardous to consumer health; as consequence, elimination of mycotoxin from products is a challenge for the food industry. Concerns have been directed towards aflatoxins because of their global threat and toxicity. Most of the factors obtained from studies on aflatoxins can be applied to other mycotoxins. Although prevention is the most effective intervention, chemical, physical and biological methods have been investigated to eliminate aflatoxins or reduce them ( Figure 2 ). However, these techniques are not completely safe, are expensive and not well preferred by consumers.
4. Essential oils: an alternative strategy for control against aflatoxin contamination
The frequency of contamination of world crops by aflatoxins shows that the strategies currently used are insufficient to guarantee the security of the foods and that it is necessary to develop others, as a complement or substitution of those already existing. In this context, strategies based on the use of compounds naturally recognized as not harmful to the environment and to health, seem interesting. Indeed, plants produce different secondary metabolites (terpenoids, phenolic compounds, etc.) for their protection against external agents (mechanical, biological or climatic). These compounds could possibly be used as a means of combating fungal contamination and/or mycotoxins .
4.1 Essential oils
EOs are a mixture of volatile compounds (secondary metabolites) isolated from plants mainly by hydro-distillation. They are mostly consisting of mono- and sesquiterpenes but may also contain non-terpenoid hydrocarbons, phenylpropanoids, esters, lactones, phthalides, nitrogen or sulfurized structures and isothiocyanates. They are lipophilic compounds which are distinguished by their aromatic properties, hence their use as flavorings or perfumes . In addition, certain compounds are also used for their many biological activities: bactericide, fungicide and antioxidant .
4.1.2 Mechanism of cellular action of essential oils
The mode of action of EOs has not been completely understood yet [20, 21]. In general, EOs actions are described in three phases. Firstly, EOs spreading on the cell wall of fungi changes the membrane permeability resulting in the loss of cellular components. Secondly, an acidification inside the cell that blocks the production of cellular energy (ATP) due to ion loss, the collapse of proton pumps, the reduction of membrane potential, and destruction of genetic materials that leads to the death of fungus. Furthermore, some reports have indicated that EOs can also coagulate the cytoplasm and damage lipids, proteins, cell walls and membranes that can lead to the leakage of macromolecules and the lysis [22, 23, 24, 25, 26, 27].
Phenolic compounds are known to affect microbial cell permeability, allowing the loss of macromolecules from the interior. They could also interact with membrane proteins, causing a deformation in their structure and functionality .
4.1.3 Use of essential oils as antifungal and antiaflatoxigenic agents
In view of their different biological properties, EOs have been tested as alternative strategy for combating mycotoxins, especially aflatoxins [29, 30, 31, 32, 33, 34] ( Table 1 ). EOs are molecules of natural origin, biodegradable, and are therefore considered as a possible alternative to synthetic pesticides . Their use as food additives or flavorings has recently been authorized in the USA . As their active components are highly volatile, they are mainly used as fumigants for products after harvest. A number of commercially available EOs can be used in crops produced according to the specifications such as E-Rase™ (jojoba EO,
|Plant scientific name||Plant common name||Applied concentrations in culture medium||Inhibition of ||Inhibition of AFB1 production||Reference|
0.04 μg/ mL
|Holy basil||0.10 μg/ mL|
0.20 μg/ mL
|Holy basil||0.10 μL/ mL|
0.40 μL/ mL
|Betel||0.40 μL/ mL|
0.60 μL/ mL
|Callistemon||0.546 mg/ mL|
0.819 mg/ mL
|Cinnamon||4.00 μL/ mL|
6.00 μL/ mL
|Cardamom||0.25 mg/ mL|
0.50 mg/ mL
|Water hemlock||1.00 μL/ mL|
4.00 μL/ mL
|Lemongrass||0.20 mg/ mL||3.00%||100.00%|||
|Coriander||0.75 μL/ mL||66.50%||25.00%|||
|Cumin||0.40 μL/ mL|
0.50 μL/ mL
|Fennel||0.75 μL/ mL||54.40%||23.00%|||
|Mint||0.60 μL/ mL|
0.90 μl/ mL
|Palmarosa-Indian geranium||0.30 μL/ mL|
0.40 μL/ mL
|Thyme||0.30 μL/ mL|
0.70 μL/ mL
The antifungal activity of EOs of
The EO of
The effects of EOs of
Similar types of results were also found in the case of
The EO of
The inhibition of AFB1 production by
On the other hand, cinnamaldehyde was assessed on AFB1 production of
Ben Miri et al.  reported that
In vivoassays of essential oils
The effect of hemlock (
6. Limitations of the use of EOs in food systems
In spite of the great potential of EOs against fungal growth and mycotoxin production, their large scale utilization is limited because of volatile nature, organoleptic effect in food systems and susceptibility to oxidation under light, heat, oxygen and moisture. To develop stability, control the release and enhance the efficacy of EOs in food systems, it is necessary for the current research to develop some structural barriers to enclose these bioactive compounds. In this regards, encapsulation of EOs by different physical, physico-chemical and mechanical methods with the assistance of carrier matrices is a trending area of research.
Thus, although the use of EOs can be an interesting strategy, it faces several constraints:
The present review has focused on the antifungal and antiaflatoxigenic activity of essential oils. Additionally, other plant extracts possess potential antifungal activities against
In view of the potential of EOs as inhibitory of
Thanks to the Government of Aragón and FEDER 2014-2020 (Grant Grupo de Investigación A06_17R) and the Ministry of Higher Education and Scientific Research of Algeria (Project number: PRFU/D00L01UN150120180002) for financial support.
Conflict of interest
The authors declare that there are no conflicts of interest.