Invited review : remediation strategies for Mycotoxin control in feed
Mycotoxins are secondary metabolites of various fungal species that can cause acute or chronic toxicity in animals. More than 500 mycotoxins have been identified, but the major ones of importance in feed are produced by five fungal genera: Aspergillus, Fusarium, Penicillium, Clavimyps, and Alternaria. Aflatoxin B1, deoxynivalenol, zearalenone, and fumonisin B1 are the major mycotoxins in feed contamination, including corn, barley, wheat, peanuts, peas, nuts, millet, forages, and their by-products. The toxicity of a mycotoxin depends on its chemical structure. The most toxic known aflatoxin is aflatoxin B1, which is produced by the fungus Aspergillus and is a class of carcinogens that exhibit mutagenic, carcinogenic, autoimmune, and liver-inducing properties in many animal species. Zearalenone, deoxynivalenol and fumonisin B1 are mainly produced by the fungus Fusodium. Deoxynivalenol is a type B trichotoxin that can inhibit the synthesis of nucleic acids and proteins, induce anorexia and vomiting, and compromise intestinal function and immunity in animals. Zearalenone has a similar structure to estrogen, thus competing with beta-estradiol for receptor sites, resulting in reproductive disorders in livestock. Mycotoxins have significant negative effects on animal health, performance, product quality and product safety, and this has prompted much research in this field. In general, physical, chemical, biological and nutritional approaches have been developed as the main strategies for detoxification of mycotoxins in the feed industry.
Strategies for reducing mycotoxins
Physical methods:
Physical methods for reducing mycotoxin contamination include separation (sorting), washing, solvent extraction, heating, irradiation and adsorption.
Separation and Separation:
Mycotoxins are not uniformly distributed in the grains and are mainly found in the moldy and broken parts. Meanwhile, the specific gravity of mycotoxin-contaminated grains is relatively lower than that of normal grains. This feature allows the separation of mycotoxin-contaminated feed using sieving, gravity separation, photoelectric separation and image processing techniques. Researchers have reported that water flotation and dehulling alone can remove 51 and 53% of the toxin and fumanzins from white-hulled corn. However, it was shown that these techniques are expensive and time-consuming and can only be applied on a small scale.
Water washing or solvent extraction:
Since mycotoxins have water- or fat-soluble properties, they can be disinfected by washing with water or another solvent. Floating in water can remove 69-64%, 62-61%, 73-74% of trichothecenes, zearalenone and fumonisin from grains, respectively. Floating in water and 10-30% salt, 60% sucrose or 0.1 mol/L sodium carbonate can increase the removal rate of fumonisin from corn and wheat. The most commonly used solvents for mycotoxin extraction are methanol, ethanol, hexane, acetonitrile, isopropanol and aqueous acetone. Although a large amount of mycotoxins is removed by this method, its disadvantages include loss of nutrients and disposal of extracts and re-drying of grains.
Heat:
Heat has been used for many years to remove mycotoxins. The effectiveness of this method depends on the chemical structure, concentration of mycotoxins, temperature, duration, humidity, pH and ionic concentration during heat treatment. The decomposition temperatures of zearalenone, deoxynivalenol, aflatoxin B1, fumonisin B1 are 220, 175, 237 and 150, respectively, which is one of the problems for their removal. Cooking at a pressure of 0.1 MPa at a temperature of 160 degrees for 20 minutes can remove 77 to 88% of aflatoxin B1 in rice. Also, heating peanuts at a pressure of 0.1 MPa for 20 minutes and at a temperature of 120 degrees can destroy 95% of aflatoxin B1. Considering the high amount of energy required by this method and the possibility of Maillard reaction caused by high temperature in this method, there are limitations in the use of this method.
Irradiation:
Irradiation may be a scientific method for removing mycotoxins on an industrial scale. The effect of irradiation on food can induce physical, chemical and biological effects that reduce or eliminate mycotoxins. In general, aflatoxin B1 can be reduced by 43-87.3%, 65.7-71.5%, 22-100% and 90.7% by gamma ray, electron beam, ultraviolet and microwave methods, respectively. Although the irradiation method can be considered as a potential and promising approach for mycotoxin disinfection, issues such as mutagenesis that produces harmful microorganisms and reduces the nutritional value of the food should also be considered.
Adsorbents:
Binders form a complex with mycotoxins that allows mycotoxins to pass through the digestive tract and prevent them from entering the blood and other organs. In the past decades, various adsorbents with different origins have been used. Each adsorbent must have the following conditions: 1- High adsorption capacity 2- Not bound to nutrients 3- High stability and 4- Good taste. Aluminosilicate minerals are known as the largest class of mycotoxin adsorbents and are the most widely used in the removal of mycotoxins in livestock and poultry farming. These adsorbents include: bentonite, montmorillonite, zeolite, hydrated sodium calcium aluminum silicate, kaolin, illite, etc. The application of each adsorbent depends on their chemical structure and the type of mycotoxin. Also, the efficiency of each adsorbent depends on the surface area, charge distribution, pore size, polarity and shape of the mycotoxins. Several studies have been conducted on the effects of zeolite, sodium bentonite, which has been shown to reduce aflatoxin B1 residues in the liver by 41-87% and to reduce aflatoxin B1 numerically in meat and eggs. In another study in pigs fed 1.11 mg/kg zearalenone, the use of 1% modified myfanite reduced zearalenone in the liver by 55%. Bentonites are very promising as adsorbents because they have high efficiency in absorbing mycotoxins, are environmentally friendly and are cost-effective.
Adsorbents:
Binders form a complex with mycotoxins that prevents mycotoxins from passing through the digestive tract and preventing them from entering the blood and other organs. In the past decades, various adsorbents with different origins have been used. Each adsorbent must meet the following conditions: 1- High adsorption capacity 2- Not binding to nutrients 3- High stability and 4- Tasty. Aluminosilicate minerals are known as the largest class of mycotoxin adsorbents and are the most widely used in the removal of mycotoxins in livestock and poultry farming. These adsorbents include: bentonite, montmorillonite, zeolite, hydrated sodium calcium aluminum silicate, kaolin, illite, etc. The use of each adsorbent depends on their chemical structure and the type of mycotoxin. The efficiency of each adsorbent also depends on the surface area, charge distribution, pore size, polarity and shape of the mycotoxins. Several studies have been conducted on the effects of zeolite, sodium bentonite, which has shown that it reduces the residual aflatoxin B1 in the liver by 41-87% and also reduces aflatoxin B1 numerically in meat and eggs. In another study in pigs fed 1.11 mg/kg zearalenone, the use of 1% modified myfanite reduced zearalenone in the liver by 55%. Bentonites are very promising as adsorbents because they have high efficiency in absorbing mycotoxins, are environmentally friendly and are cost-effective.
Second-generation adsorbents derived from the cell walls of microorganisms have been developed extensively. Glucomannan is a common adsorbent that is not absorbed by intestinal microbes and absorbs and removes pathogenic bacteria, and mycotoxins can be removed and absorbed by esterified glucomannan. Studies have shown that esterified glucomannan prevents the adverse effects of mycotoxins on performance, immunity, hematological and chemical indices of chickens.
Activated charcoal is a general adsorbent with a large surface area and ability to adsorb in humid environments. Activated charcoal has shown the ability to reduce deoxynivalenol, zearalenone and aflatoxin due to its porous structure in many studies. In a study, adding 0.1% activated carbon to a feed containing 10 mg/kg AFB1 was able to reduce its harmful effects on broiler chickens. Avantagiato showed that adding 0.2% activated carbon to the diet reduced zearalenone in the small intestine by 5 to 32%.
In fact, the precise efficiency of microbial adsorbents is such that bacteria adsorb mycotoxins and form a complex. Then they are excreted together with the toxins, thereby reducing the risk. Lactic acid bacteria and yeast are the most common microbial adsorbents. Lactobacillus casei significantly binds to mycotoxins and prevents their absorption by the intestine. Zeng et al. reported that Lactobacillus plantarum has a strong adsorption capacity on aflatoxin B1, and its adsorption rate is 56.8%. Lactobacillus platanorum B7 and Lactobacillus pentulosus 8X can remove 52.9 and 58% of fumincin B1, respectively. In a study conducted by Haltonen et al., the adsorption effect of several lactic acid bacteria on aflatoxin was compared, and the results showed that the combination of several lactic acid-producing bacteria was more effective than a single strain and had synergistic effects.
Chemical methods:
Chemical methods can destroy the mycotoxin structure. Chemical destruction of mycotoxins is usually done using alkaline and ozone methods.
Alkaline methods:
Alkaline methods include ammonium, sodium hydroxide, potassium hydroxide, sodium carbonate, etc., which are used to destroy various mycotoxins in feed. The lactone ring structure of aflatoxin B1 can be opened by basic hydrolysis to produce sodium coumarin salt, which is then removed by washing with water. The use of ammonia and hydroxide salts are common methods used to remove aflatoxin B1 from feed, and the removal rate is more than 95%. Sodium carbonate and hydroxide salts can remove deoxynivalenol by 83.9 and 100%, respectively, in feed. Although the methods mentioned above can remove 100% of mycotoxins, there is also a possibility that the mycotoxins will be converted into other forms by breaking down or becoming coated, which will have adverse effects on the environment.
Use of Ozone:
The use of ozone is a highly effective method of detoxification that changes the molecular structure of mycotoxins. The oxidants used in this method include hydrogen peroxide, sodium and calcium hypochlorite, chlorine and other oxidants. Studies have shown that zearalenone, deoxynivalenone, aflatoxin B1 and fumonisin B1 are effectively destroyed by ozone. Researchers reported that ozone concentration, form and exposure time can have a significant effect on the reduction of aflatoxin S and deoxynivalenol. Aflatoxin can be reduced by 92-95% in corn, 78-91% in cottonseed meal or peanuts using ozone. Deoxynivalenol can also be reduced by 70-90% in corn and 20-80% in wheat by ozone. Zearalenone levels can be reduced by 90.7% using 1000 mg/L ozone for 180 min. Although ozone can reduce the concentration of mycotoxins, it can cause changes in the chemical and physical structure of the feed, such as changes in starch structure, lipid oxidation, protein denaturation, color and texture. Ozone may also have adverse effects on animal health.
Biological methods
Although many antimicrobial strategies have been proposed to reduce mycotoxins in feed, there are very few methods that meet all the requirements of biosafety, cost-effectiveness, industrial applicability, and scientific application. Therefore, as a promising strategy, the biodegradation of mycotoxins by microorganisms or enzymes has attracted the attention of researchers.
Microorganisms with detoxification ability:
Microorganisms with detoxification activity are known to be efficient and environmentally friendly. Screening and isolation of microorganisms that are capable of binding to and removing mycotoxins is a popular strategy. Various fungi have been discovered that have the ability to detoxify AFB1. Fungal strains such as Saccharomyces cerevisiae can reduce aflatoxin B1 by up to 69%. Similarly, some studies have shown that various Aspergillus strains including A. neger FSLO and A. neger RAFLO6 showed the ability to degrade aflatoxin B1 by 88.6 and 98.7, respectively. Bacillus is a very important group of bacteria that have the ability to degrade aflatoxin B1. In a study conducted by Farzaneh et al., it was shown that Bacillus subtilis was able to reduce 78.4 to 95% of aflatoxin B1 in pistachio kernels. In addition, Bacillus subtilis isolated from fish intestine was able to degrade 81.5% of aflatoxin within 72 hours. Some microorganisms have been identified that have the ability to degrade fumonisins. Styriak et al. screened two strains of preserved yeast from the laboratory that had a high ability to degrade fumonisin in culture. Saccharomyces cerevisiae IS1 can degrade fumonisin by 45%. On the other hand, Saccharomyces cerevisiae SC82 can degrade a mixture of B1 and B2.
In another study, it was reported that the degradation rate of fumonisin B1 by the SAA579 bacterial consortium is 100%.
Use of catabolic enzymes:
Although some microbial microorganisms are very active in the biological degradation of mycotoxins, some of them may produce harmful metabolites that are harmful to the digestive tract and remain there. Therefore, screening enzymes from these microorganisms may be a promising solution to solve this problem. Recently, much research has been done on the isolation of enzymes for the degradation of aflatoxin B1, deoxynivalenol, zearalenol and fumancin B1. The fungal enzymes known to be capable of degrading aflatoxin B1 include laccase oxidases. In a study conducted, it was shown that the newly synthesized aflatoxin deoxyenzyme was able to detoxify aflatoxin B1 and significantly reduce its mutagenic effects. 1.5 U/ml manganese peroxidase could degrade up to 90% of aflatoxin B1 after 48 hours of reaction. Peroxides such as manganese peroxidase and lignin peroxidase have significant potential in the degradation of deoxynivalenol. Lactases are copper-containing oxidases that have high potential in the degradation of heat-stable zearalenols. A novel recombinant enzyme with two single genes, namely zearalenol-specific lactohydrolase and carboxypeptidase, was able to completely degrade zearalenone to a non-toxic product within 2 hours at the optimum pH (7) and at 35°C. Fumonisin carboxyesterase can degrade fumonisin B1.
Nutritional strategies:
It is well accepted that no physical, chemical or biological strategy can completely eliminate mycotoxins in feed, given that mycotoxins are chronically toxic and can cause performance and immune suppression in animals, therefore, it is important to develop nutritional strategies to help reduce mycotoxicoses. Any nutrient that can improve the normal function of one of the detoxification enzyme systems can be considered as a nutritional strategy. Glucamate, maxitin and glycine can be used as substrates for glucagon synthesis and participate in detoxification by forming glucagon peroxidase. On the other hand, mycotoxins can reduce nutrient absorption, so adding essential nutrients is one way to reduce the harmful effects of mycotoxins. Selenium, some vitamins including E, C, A, their primary markers have antioxidant properties that act as superoxide anion scavengers. For this reason, these substances can act as protective factors against the toxic effects of mycotoxins. Selenium is an essential trace element for humans and animals because it plays an important role in antioxidant defense, anticancer and immune and detoxification. Vitamins E.A.C can be used as antioxidants to protect the spleen and brain cell membranes against deoxynivalenol toxicity and against DNA damage in the liver caused by deoxynivalenol. Researchers reported that the use of vitamin B1 reduced the toxic effects of fumonisin in broiler chickens. Gross et al. reported that retinol, ascorbic acid, and alpha-tocopherol reduced the harmful compounds that cause mutations in DNA in the kidney and liver of mice exposed to ochratoxin A and zearalenol by 90%. Carotenoids are excellent antioxidants with anti-mutagenic and anti-cancer properties that can inhibit liver DNA damage caused by aflatoxin B1 in mice. Silymarin is an anti-hepatotoxic agent that protects against the negative effects of aflatoxin B1 on broiler chickens. Curcumin reduces the toxicity of aflatoxin B1 through the CYP450 enzyme and enhances ATPase activity in chickens. Curcumin significantly reduces apoptosis in cells exposed to deoxynivalenol. Studies have shown that butylated hydroxytoluene, a dietary antioxidant in mammals, reduces the toxic effects of aflatoxin B1 by inducing glutathione sulfotransferase activity and inhibiting cytochrome p45 activity. Supplementation of glutamic acid, arginine, aspartate and lysine in the diet had positive effects on improving deoxynivalenol-induced visceral disease and increasing antioxidant capacity and improving physiological and biochemical indices of blood in fattening pigs.
Conclusion:
The presence of mycotoxins in feed is a major concern and an unavoidable problem in the feed industry worldwide. Mycotoxins also pose a threat to human health through the food chain cycle. This study aims to review various strategies for reducing mycotoxins through physical (separation, washing, heating, irradiation and adsorption), chemical treatments (bases and oxidizing agents), biological detoxification methods (microorganisms and enzymes) and nutritional strategies. Each of these methods can be practically implemented, which have their own advantages and disadvantages. However, with the increasing awareness about environmental protection as well as feed and food safety, there is a growing expectation for green and innovative technologies to control mycotoxin contamination.
Mycotoxins have significant negative effects on animal health, performance, product quality and product safety, therefore, using the best method for detoxification can greatly contribute to economy and productivity. Also, considering that the nature and chemical structure of each mycotoxin is different from each other, using a set of different adsorbents in the diet can be much more effective. Bentomax Chitica product contains yeast cell wall (beta-glucan and mannan oligosaccharide), live yeast Saccharomyces cerevisiae, acid-washed bentonite, eight powerful probiotic strains and vitamin E.
