ROLE OF FUNGI, IT’S TOLERANCE LIMITS & MEASURES TO CHECK THEM IN STORED PRODUCTS
- Geeta Choudhary*, 1 •Monika Karnani1• Sheela Choudhary 1 •Manju1
1Department of Animal Nutrition, PGIVER, Jaipur, Rajasthan, INDIA 302031
Introduction:
Fungi are a subdivision of the subkingdom thallophyta. Fungi impair feed quality in at least 2 ways
- They may alter the nutritional quality of feeds by destroying important nutrients such as vitamins.
- They may produce mycotoxin that is harmful to animals
Toxin producing fungi may invade at pre harvesting period, harvest time, during post harvesting handling & in storage. Toxigenic fungi in crops have been historically divided into 2 distinct groups-
The first category includes those which invade and produce their toxins before harvest, is known as ‘field fungi’.
The second group, which becomes a problem after harvest, generally Aspergillus, Fusarium, and Penicillium are known as ‘storage fungi
Damages caused by storage fungus:
- Loss of nutrients
- Discoloration of grains
- Reduction in germination ability
- Caking of grains
- Moldy smell & taste
- Production of mycotoxins
- Creation of environment for the development of special insect species
https://www.pashudhanpraharee.com/mycotoxins-mycotoxicosis-a-health-hazard/
Table-1.Major fungi species & commodities they affected
| Fungus species | Commodities affected |
| Alternaria alternate | rice, sorghum, soyabean |
| A. longissima | rice, sorghum |
| A. padwickii | Rice |
| Aspergillus flavus | Cashews,maize,groundnut, soyabean, sorghum |
| Fusarium moniliforme | Maize, soyabean, sorghum |
| F. semitectum | Maize |
| Penicillium citrinum | Sorghum, soyabean |
Mycotoxins & Mycotoxicoses
Mycotoxins are a diverse group of chemicals that are harmful to animals & humans and have the greatest impact on human & animal health. They are secreted by the fungi growing under favorable conditions in the field even before harvesting the crop, during transport and in the storage place.
The severity of mycotoxins contamination is determined by major environmental factors such as excessive moisture in the field and storage places, temperature extremes, humidity, variation in harvesting practices & insect infestations. Global climate change has also contributed to an increased frequency of mycotoxin contamination of grains. Drought, excessive rainfall and excessive flooding can also promote mould grains.
Mycotoxicoses are diseases caused by the ingestion of foods or feeds contaminated with mycotoxins.
Table-2: Mycotoxins & causative fungi
| Mycotoxin | Fungal species |
| Aflatoxin (B1,B2,M1,M2) | Aspergillus flavus, A. parasiticus &A. nomius |
| Zearalenone | Fusarium culmorum, F.graminearum, F.sporotrichioides |
| Trichothecenes (Deoxynivalenol (DON) or vomitoxin) | Fusarium culmorum, F.graminearum |
| Fumonisins | Fusarium verticillioides, F. priliferatum |
| Ochratoxins ( nephrotoxins) | A. ochraceus, Penicillium viridicatum, P. verrucosum, P.cyclopium |
| Tremorgens & rubratoxin | Penicillium sp, Aspergillus sp |
| Patulin | Penicillium expansum |
| Phomopsins | Phomopsis |
| Sporidesmins | Leptostromiformis |
| Ergopeptine alkaloids | Acremonium coenophialum |
| Lolitrem alkaloids | Acremonium lolii |
Consequences of consumption of mouldy feed in farm animals:
In farm animals, consumption of mycotoxin feed reduces growth efficiency, lowers feed consumption & reproductive rates, impairs resistance to infectious diseases, reduce efficacy of vaccination, induces pathologic change to the liver and other organs, etc
Aflatoxins (hepatotoxins)–
Aflatoxin is produced primarily by fungus, Aspergillus. Ideal condition for Aspergillus growth includes moisture content above 14%, temperature above 25℃ &the presence of oxygen. It is known to affect many feed ingredients including corn, rye, oat, wheat, barley, soyabean meal, sunflower meal rapeseed and alfalfa.
Aflatoxins are highly toxic, mutagenic & carcinogenic compounds. They are known to cause liver damage and liver failure in animals, lower disease resistance power, interfere with vaccination & acquired immunity in livestock may also cause rectal prolapsed.
Zearalenone-
It is often associated with corn but may can infect other crops including wheat. It is an estrogenic compound, mainly cause estrogenic syndrome in swine. In the prepubertal gilt, the vulva become swollen, may progress to vaginal or rectal prolapse, abortion and still birth in pregnant animals. Young male pigs undergo symptoms of “feminization”, such as enlarged nipples & testes atrophy.
Dairy cows have decreased fertility& prolonged estrus. Turkey develops enlarged vents within four days.
Trichothecenes-
Main sources are contaminated cereal grains. Trichothecenes includes Deoxynivalenol (DON), HT-2 vaccine, diacetoxyscirpenol (DAS)and T-2 toxin that inhibit eukaryotic protein synthesis causing human & animal health impairment. The toxic effects in animal include gastrointestinal disturbances, potent immunosuppressive agents that affect immune cells and modify immune responses as a consequence of other tissue damage.
Feed containing more than 1ppm of DON may reduce feed intake, weight gain and vomition (so termed as vomitoxin) in swine.
Chickens suffered no detectable ill effects from rations containing upto 18 ppm of DON & then toxin was not detected in the flesh or eggs.
Unthriftyness, decreased feed consumption, slow growth, lowered milk production, sterility, gastrointestinal hemorrhages and death can occur when cattle consumes rations containing T-2 & DAS.
Effects of T2 on swine include infertility with some lesions in uterus &ovaries.
Fumonisins-
Associated with occasional outbreaks of blind staggers (equine leucoencephalomalacia) in horses, pulmonary edema in swine and esophageal cancer in humans. Fumonisins reduced feed intake and weight gain in chickens. Cattle seem to be less susceptible than either swine or horses.
Fumonisins increased the free sphingosine levels which mean that the sphingolipid biosynthesis is inhibited.
Ochratoxin A–
Infects many crops including barley, oat, wheat, corn & soyabean meal & causative fungi are generally restricted to areas to temperate climate.
Ochratoxin cause kidney damage & can cause birth defects. Immunosuppression has also been associated with ochratoxin A.
Ergot alkaloids –
Ergot alkaloids are very potent toxins produced by fungi ergot (claviceps purpurea).
Triticale & rye are most susceptible grains, but wheat, barley, oats and corn can also become infected. They impair blood flow to the extremities, affecting tissues such as kidney and uterus. Reduced blood flow to the reproductive tissues can result in spontaneous abortion.
Some moulds &bacteria can destroy nutrients in feeds, like Pseudomonas species & Aspergillus species can separate glutamic acid from pteroic acid in the vitamin, folic acid. Thus they can destroy the vitamin and &cause folic acid deficiency.
Regulatory limit for various mycotoxins:
- Aflatoxins-
| Commodity (animal feeds) | Concentration(ppb) |
| Corn &peanut products intended for finishing (i.e. feedlot)beef cattle | 300 |
| Corn &peanut products intended for breeding beef cattle, breeding swine or mature poultry | 100 |
| Cottonseed meal intended for beef cattle, swine or poultry(regardless of age or breeding status) | 300 |
| Corn &peanut products and other animal feeds and feed ingredients but excluding cottonseed meal, intended for immature animals | 20 |
| Corn, peanut products, cottonseed meals and other animal feed ingredients intended for dairy animals, for animal species or uses not specified above ,or when intended use is not known | 20 |
| Milk | 0.5(aflatoxinM1) |
- Advisory levels for DON:
(a).Total ration (includes grains ,all grain by products including distillers &brewers grains, hay, silage and roughage) for ruminating beef & feedlot cattle older than 4 months not exceed 10ppm DON and the total ration for ruminating dairy cattle older than 4 months not exceed 5ppm DON.
(b). For chickens, 10ppm DON on grain & grain byproducts (not exceed 50% of the diet of chickens).
(c). 5 ppm of DON on grain &grain by products designed for swine (not exceed 20% of their diet).
(d). 5ppm DON on grain &grain byproducts destined for all other animals (not exceeding 40% of their diet)
- Fumonisins:
| Corn &corn byproducts intended for | Total Fumonisins(FB1+FB2+FB3) |
| Equids & rabbits | 5ppm(not>20%of diet on dry weight basis) |
| Swine | 20ppm(not>50% of diet on dry weight basis) |
| Breeding ruminants( including lactating dairy cattle) &breeding poultry(laying hens) | 30ppm(not>50% of diet on dry weight basis) |
| Ruminants>3 months old being raised for slaughter | 60ppm(not>50% of diet on dry weight basis) |
| Poultry being raised for slaughter | 100ppm(not> 50 of diet on dry weight basis) |
| All other species or classes of livestock & pet animals | 10ppm(not>50% of diet on dry weight basis) |
- Zearalenone: hyperestrogenism occur when contamination of ZEA is as low as 0.1ppm. Broiler chicks &laying hens are less susceptible even at very high dietary concentration.
Strategies for prevention & control of mycotoxins:
(A). Primary prevention: The step of prevention should be initially carried out before the fungal infestation &mycotoxin contamination &making the conditions unfavorable for fungal growth like
- Development of fungal resistant varieties of growing plants.
- Making schedule for pre harvest, harvest & post harvest.
- Lowering moisture content of plant seeds, after post harvesting &during storage.
- Store commodities at low temperature whenever possible.
- Using fungicide &preservatives against fungal growth.
(B).Secondary prevention: If the invasion of some fungi begins in commodities at early phase, this level of prevention will then be required. It includes elimination of existing toxigenic fungi or stopping its growth to prevent further deterioration &mycotoxin contamination. Several measures under this prevention includes-
- Stop growth of infested fungi by re-drying the products;
- Removal of contaminated seeds;
- Inactivation or detoxification of mycotoxins contaminated;
- Protect stored product from any conditions which favour continuing fungal growth.
(C).Tertiary prevention: Once the products are heavily infested by toxic fungi, the primary &secondary preventions would not be then feasible. Some measures should be done to prevent the transfer of fungi & their health hazardous toxins highly contaminated in products into daily feeds &environment. It includes
- Complete destruction of contaminated products;
- Detoxification or destruction of mycotoxins to minimal level .
Managing the mycotoxins
- Increase the content of methionine: Absorbed mycotoxins are detoxified by the liver & liver uses biological reduction oxidation reactions based upon glutathione, a tripeptide comprising glutamic acid, cysteine &glycine.
Methionine supplementation, 30-40% over NRC levels, helps to detoxify the aflatoxins faster and to overcome the depression in the performance of broilers, layers etc.
- Follow the decontamination techniques:
(A). Chemical treatment: liquid extraction of mycotoxin using organic solvents or water based solutions of calcium chloride or sodium bicarbonate or heated salt water.
Ammonia (aqueous or gaseous) treatment is a promising method for commercial detoxification of mycotoxins to destroy aflatoxin.
(B).Physical treatments: Heat treatment can destroy unstable agents such as ergot alkaloids & citrinin (in wheat on a range of other mycotoxins including Zearalenone, vomitoxin, &ochratoxin A
Sunlight can destroy about 50% of aflatoxin in groundnut cake.
Autoclaving at 120℃ with a pressure of 15lb psi resulted in progressive detoxification of toxic groundnut meal & cottonseed.
(C). Ultraviolet &ionizing radiation: may be effective in destroying aflatoxins.
- Addition of mould inhibitors, mycotoxin binding/ inactivating agents &antioxidants: Formic acid & Propionic acid have been found to be effective grain preservatives against fungal growth & toxin production.
Mycotoxin binding agents includes activated charcoal, yeast cell wall products, synthetic zeolites and mined mineral clays like aluminosilicates, sodium bentonites &sepiolites.
Vitamin E &vitamin C appear to be effective in lessening the adverse effects of ochratoxin contamination. The binding agents are capable of adsorbing or trapping mycotoxin molecules.
Examples:
- Alfalfa fiber can have protective effects against Zearalenone &T-2 toxin.
- Hydrated sodium calcium aluminosilicate (HSCAS) has been shown to have potential to reduce aflatoxicosis.
- Bentonites – effective against T-2 toxin.
- Glucomannan mycotoxin adsorbents (GMA): Mycosorb (mannan oligosaccharides) can specifically adsorb certain toxins such as aflatoxin, ochratoxin, Zearalenone, T-2 toxin.
- Enzymes: One of the recent techniques for mycotoxin decontamination.
Enzymes are available to inactivate Zearalenone, all trichothecenes (T-2, HT-2, DON, DAS, etc.). The enzymes degrade the toxin by breaking the molecule apart to form harmless metabolites e.g. esterase & epoxidase.
The enzyme esterase breaks the lactone ring of Zearalenone, while the enzyme epoxidase degrades the 12, 13 epoxy group in the trichothecenes. Removal of the 12, 13 epoxide ring using de epoxidase entails a significant reduction in its toxicity.
The challenge to this approach is to identify non specific enough to detoxify combinations of mycotoxins that might produce toxicological synergies, but also specific enough not to cause structural damage to the digestive tract or to interfere with digestive function.
(5).Microbial detoxification: Eubacterium strain, known as BBSH 797, exhibits de-epoxidation, ester hydrolysation and deacetylation activity, all of which are useful in detoxifying common feed mycotoxins. The bacterium was to be effective against DON in piglet feeding trials.
Clostridium sporogenes & Lactobacillus vitulinus are able to cleave ochratoxin A into non toxic metabolites.
Trichosporan yeast appears to destroy Zearalenone estrogenic effects.
Flavobacterium multivorum and Aspergillus repens are potential aflatoxin (B1 and G1) degrading organisms.
Conclusion:
The presence of mycotoxins in food products has serious implications for human & animal health. Prevention of fungal invasion of commodities is far the most effective method of avoiding mycotoxin problems. Selection of fungal resistant hybrids of crops are recommended and further experimented.
Research is needed on inexpensive and appropriate sampling and testing protocols. Research on identification and application of appropriate technologies for obtaining low grain moisture at harvest & maintaining low grain moisture during storage are needed. Research to reduce mycotoxins vulnerability of crops is as important today as ever.
http://www.fao.org/3/x5036e/x5036e0q.htm
