The aflatoxins are a group of chemically similar poisonous, carcinogenic fungal secondary metabolites produced by Aspergillus flavus, A. parasiticus, and A. nomius, which are abundant in warm and humid regions of the world. They are probably the most intensively researched toxins in the world due to their carcinogenic and mutagenic effects. Aflatoxins have also been identified as a potential biological weapon for food and water contamination. The four major aflatoxins commonly isolated from different foods and feed stuffs are AFB1, AF B2, AFG1, and AFG2. Aflatoxin contamination of food and feed has gained global significance as a result of its deleterious effects on human as well as livestock health including gastrointestinal dysfunction, reduced feed utilization, anemia, jaundice, liver damage and immunity suppression. The profitability and marketing of various agricultural products are adversely affected by either contamination of aflatoxins or aflatoxin‐producing fungi. The foods at highest risk of aflatoxin contamination are maize, chilies, peanuts, and cotton seeds. There are various physical, chemical, and natural methods investigated to prevent aflatoxin production and the growth of aflatoxin‐producing fungus in various agricultural products. Here, we describe various natural plant extracts that would be potential source of controlling aflatoxin production in agricultural products.
- Aspergillus flavus
- Aspergillus parasiticus
- plant extract
- agricultural products
Aflatoxins are poisonous, carcinogenic, mutagenic, immunosuppressive, and teratogenic secondary metabolites formed by
The aflatoxin was a combination of three words: first letter “A” from genus
The International Agency for Research on Cancer (IARC) classified AFB1 as class I human carcinogens  and have a positive association between dietary aflatoxins and liver cell cancer (LCC). This was the third leading reason of cancer death around the world . The cytochrome p450 metabolized AFB1 in their epoxide form. Depurination occurs, when epoxide reacts with DNA or RNA. That will obstruct DNA and protein synthesis in active tissues of bone marrow, intestine, and liver. The order of toxicity of aflatoxins is AFB1 > AFB2 > AFG1 > AFG2 , and the critical point, which determined the biological activity of this group of mycotoxins, is terminal furan moiety of aflatoxin . In cereal and their derivatives, maximum residual limits (MRLs) of aflatoxins are 2 μg kg1 for AFB1 and 4 μg kg⁻1 for the sum of four aflatoxins. In processed cereal‐based foods and baby foods for infants and young children, the level of AFB1 is 0.1 μg kg‐1. These values were recommended by the European Union Commission Regulation (EC) . According to the Food and Drug Administration (FDA), the safe limit of aflatoxins is 20 ppb (Figure 1) .
In developing countries, about 4.5 billion people are chronically exposed to uncontrolled amounts of aflatoxins . Consumption of contaminated products causes aflatoxicosis in humans and animals. Aflatoxicosis may be acute and chronic. Acute condition caused death, while chronic condition results in immune suppression and cancer. In human, it is characterized by vomiting, abdominal pain, pulmonary edema, convulsions, coma, and death with cerebral edema and fatty involvement of the liver, kidneys, and heart . Due to aflatoxicosis, in Kenya about 215 people died in 2004 [26–28]. In animal, aflatoxicosis is characterized by gastrointestinal dysfunction, reduced feed utilization, anemia, jaundice, liver damage, decreased milk and egg production, and immunity suppression . In plants, AFs retarded seed germination, seedling growth, and root elongation. It also inhibits chlorophyll, carotenoid, and some enzymes synthesis .
Contamination rate of aflatoxin depends upon humidity, temperature, storage, and soil conditions . Optimum condition for fungal growth in cereal is moisture content about 18% (equal to 85% relative humidity) and temperature about 12–42°C with an optimum at 27–30°C in tropical and sub‐tropical areas . An important point to be considered was the time of incubation that effects the production of toxin by
The infectious cycle of
Aflatoxin contamination is inescapable due to health hazards in human and animal, crops deterioration, and economical loses. In the past, many strategies (physical, chemical, and biological) are used to avoid aflatoxin contamination. Physical strategies usually used are rodent‐proof room, cold storage of feeds with less than 100‐g/kg moisture level, use rapid drying and gamma radiation, and so on. In chemical strategies, propionic acid, acetic acid, benzoic acid, citric acid, hydrogen peroxide, copper sulfate, and ammonium hydroxide are used to inhibit the growth of fungi and aflatoxin production. But the formation of toxic residue by chemical treatment was the main concern that causes potent health problems. As compared to chemical, physical practice is a healthier option but it is slow processes. Other strategies used were the biological control in which different microorganisms such as bacteria, yeast, and non‐toxic stain of
2. Effect of active ingredients of medicinal plants on aflatoxins producing fungus
Modern research found that phytophenols as plant secondary metabolite existed above 8000 structures. These structures resemble with tannin and phenolic acid . Phytophenols showed antiallergenic, antioxidant, anti‐inflammatory, antimicrobial, antiorthrogenic, and antithrombotic activity . These plant compounds exhibited key biological activity in the degradation of many microorganisms . Plants, herbs, essential oils, and spices in powder or extracts form are used to detoxify microbes due to the presence of flavonoids, betalain, phenolics, phytoalexins, and thiosulfonates. But mostly antimicrobial and antioxidant activities of plant extracts were due to their phenolic alignments .
A recent study exposed the antifungal and antiaflatoxigenic nature of phenolic components of plant extracts [54–56]. The syringaldehyde, sinapic acid, and acetosyringone were the plant phenolic compounds that inhibited the production of aflatoxin B1 . However, salicylic acid, thymol, vanillyl acetone, cinnamic acid, and vanillin were phenolic compounds that ceased
Medicinal plants have been used from centuries for the treatment of various diseases. There are about 53,000 medicinal plants around the world . In developing countries, according to World Health Organization, about 70–95% people used medicinal plants as primary health care for the treatment of diseases . In current scenario, 70% of synthetic medicines are derived from plants . Medicinal plants have antifungal, antimicrobial, anthelmintic, antibiotic, antiviral, anti‐inflammatory, antiarthritic, antirheumatic, and antihemorrhoidal properties.
The various medicinal plants native to Southeast Asia including bitter cucumber (
The highest activity was showed by betel vine, a traditional Thai medicine, followed by false coriander, Indian mulberry, Chaa Phluu, Chinese radish, and clove. The leaf of betel vine is used topically for urticaria, contains eugenol and chavicol, and mostly chewed by mouth as antiflatulent, antimicrobial, and antipruritic .
Crude ethanolic extract of olive callus in different ratios was used to inhibit the aflatoxins synthesis  by the addition of appropriate amounts of extracts onto potato dextrose agar (PDA) to obtain the final concentration of 0.5 and 1%, and
Various concentrations (0, 2, 4, 6, 8, and 10% (w/v)) of clove, garlic, and carrot’s crude aqueous extracts were tested for their possible inhibitory effect on
The aqueous and phenolic extracts of several other natural and medicinal plants have been tested against
3. Role of essential oils on the inhibition of aflatoxins producing fungus and its production
The search for naturally occurring compounds or metabolites having bioactivity against aflatoxins producing fungi has been the target of interest in the search for ecologically friendly products . There are many essential oils produced by medicinal plants that have been tested for their inhibiting ability of aflatoxin production [69, 70].
Essential oils were extracted from 16 aromatic plants, that is, safflower (
Different ratios (50, 25, 12.5, 6.25%) of each essential oil were placed onto a cylinder cup (6 mm dia) on agar plate streaked with
Despite all efforts, it has been very difficult to control the exposure of man and animals to aflatoxins, because of their natural occurrence in the environment. Although the prevention of aflatoxin contamination by inhibiting the fungal growth in food and feeds is the best practice, other measures are also necessary. The advantage of using active compound based on natural plant is that they are safer, ecologically friendly than any chemical compounds, and synthetically produced antimicrobial agents. Other procedures such as the removal or decomposition of aflatoxins are also necessary as the prevention of contamination alone may not always be successful.