食品安全监管食品安全 (7).pdf

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1、Mycotoxins(Aflatoxins)Mycotoxins(Aflatoxins)Professor William Riley,PhD,Cornell U.Professor William Riley,PhD,Cornell U.Chemical HazardsDioxins,dibenzofurans,and dioxin-like PCBs Heavy Metals(Cadmium,Lead,Mercury,Arsenic)Veterinary DrugsOrganochlorine and other banned pesticidesMelamineBiotoxins(Cig

2、uatoxin,Scrombrotoxin)MycotoxinsMycotoxins:non-volatile,relatively low-molecular weight,secondary metabolic products;may affect exposed animals or persons in a variety of ways.Secondary metabolites:not necessary for fungal growth;simply a product of primary metabolic processes.MycotoxinsMost common

3、mycotoxins-6 major categories:aflatoxins,zearalenone（玉米赤霉烯酮，F-2毒素,Fusariumgraminearum）trichothecenes（单端孢霉烯族)ochratoxins赭曲霉毒素,fumonisins伏马毒素,ergot alkaloids麦角生物碱.Found in every variety of grain and forage produced for food and animal feed.Accumulate in crops:1.in field,2.during transportation or 3.im

4、proper storage.Diverse structural,chemical,biological and toxicological properties of mycotoxins.Toxicity levels extremely variable;depend on:Intake level,exposure duration,animal species,sex,age,breed,physiological status,nutritional standing,environment(i.e-hygiene,temperature,air conditioning,hum

5、idity,production density);synergismsamong mycotoxins simultaneously present in feeds or foods.MycotoxinToxic effects:carcinogenicity,geno-toxicity,teratogenicity,nephrotoxicity,hepatotoxicity,reproductive disorders,immunosuppression.Extensive preventive actions taken during growing,harvesting and st

6、orage periods,but mycotoxin contamination still probable.Therefore,successful detoxification procedures post-harvestare important.MycotoxinsMycotoxinsFungi that produce mycotoxins:toxigenic fungi.Most frequently studied mycotoxins produced by:Aspergillus,Fusarium,Penicillium,Stachybotrys,Myrothecium

7、.However,toxins have been detected from many other fungi under certain growth conditions.AspergillusAspergillus flavusFusariumFusarium solaniPenicilliumPenicillium chrysogenumStachybotrys“Toxic Black Mold”MyrotheciumMyrothecium verrucariaMycotoxinsFunctions:not clearly established;may role in elimin

8、ating other micro-organisms that compete in same environment.Believed to help parasitic fungi invade host tissues.Amount of toxin needed to produce adverse health effects varies widely among toxins,as well as each hosts immune system.MycotoxinsKinds and amounts of toxin produced depend on fungal str

9、ain,growing conditions,presence or absence of other organisms.Mycotoxins accumulate on fungal spores,cell fragments,substrates(nutrient sources).Typical Entry Routes of Fusarium graminearumInfection in CerealsMycotoxinsFungi that produce potent mycotoxins seldom abundant in outdoor ambient air.Most

10、toxic exposure occurs from indoor growth of fungi,related to excessive moisture.Some mycotoxins are carcinogenic,some are vasoactive,some cause central nervous system damage.Often,single mycotoxin can cause more than one type of toxic effect.AflatoxinsAflatoxicosis:poisoning that results from ingest

11、ion of aflatoxins in contaminated food or feed.Aflatoxins:group of structurally related toxic compounds produced by certain strains of the fungi Aspergillus flavus,Aspergillus parasiticus.Under favourable conditions of temperature and humidity,these fungi grow on certain foods and feeds,resulting in

12、 the production of aflatoxins.AflatoxinsAflatoxins B1 and M1Toxins produced by certain strains of the fungi A.flavus,A.parasiticusAflatoxinsAflatoxin G1Toxin produced by certain strains of the fungi A.flavus,A.parasiticusAflatoxinsMost pronounced contamination encountered in tree nuts,peanuts,other

13、oilseeds,including corn and cottonseed.Major aflatoxins of concern designated B1,B2,G1,G2.These toxins usually found together in various foods and feeds in various proportions;however,Aflatoxin B1usually predominant and most toxic.AflatoxinsWhen commodity analyzed by thin-layer chromatography,aflato

14、xins separate into individual components in order:B1,B2,G1,G2;however,first two fluoresce blue when viewed under ultraviolet light,second two fluoresce green.Aflatoxin Mis major metabolic product of Aflatoxin B1 in animals;usually excreted in milk and urine of dairy cattle and other mammalian specie

15、s that have consumed aflatoxin-contaminated food or feed.AflatoxinsFactors Favouring Aflatoxin ProductionFungal growth and aflatoxin contamination consequence of interactions among fungi,host,environment.Appropriate combination of factors determines infestation and colonization of substrate;type and

16、 amount of aflatoxin produced.Suitable substratealso required for fungal growth and toxin production;precise factors that initiate toxin formation not well understood.AflatoxinsWater and high-temperature stress,insect damage of host plant:major determining factors in mould infestation and toxin prod

17、uction.Similarly,specific crop growth stages,poor fertility,high crop densities,weed competitionassociated with increased mould growth and toxin production.Aflatoxin formation also affected by associated growth of other moulds or microbes.AflatoxinsFor example,pre-harvest aflatoxin contamination of

18、peanuts and corn favoured by:high temperatures,prolonged drought conditions,high insect activity.Post-harvest production of aflatoxins on corn and peanuts is favoured by:warm temperatures,high humidity.AflatoxinsAflatoxins produce acute necrosis坏死,cirrhosis肝硬化,carcinoma癌of liver in a number of anima

19、l species.No animal species is resistant to acute toxic effects of aflatoxins;hence,it is logical to assume that humansmay be similarly affected.Wide variation in LD50values obtained in animal species tested with single doses of aflatoxins.AflatoxinsFor most species,LD50value ranges from 0.5-10 mg/k

20、g btw.Animal species respond differently to chronic and acute toxicityof aflatoxins.Toxicity influenced by environment,exposure level,duration of exposure,age,health,nutritional status of diet.Aflatoxin B1:very potent carcinogenin many species,including non-human primates,birds,fish,and rodents.Afla

21、toxinsIn each species,liveris primary target organ of acute injury.Metabolism plays major role in determining toxicity of aflatoxin B1.Studies show that this aflatoxin requires metabolic activationto exert its carcinogenic effect;these effects can be modified by induction or inhibition of the mixed

22、function oxidase system(oxidase enzymes that catalyze reaction in which each of 2 atoms of oxygen in O2used for different function in reaction).AflatoxinsAdverse effects of aflatoxins in animals categorized in two general forms:(Primary)Acute Aflatoxicosis:produced when moderate to high levels of af

23、latoxins are consumed.Specific,acute episodes of disease may include hemorrhage出血,acute liver damage,edema浮肿,alteration in digestion,absorption and/or metabolism of nutrients,and possibly death.Aflatoxins(Primary)Chronic Aflatoxicosis:results from ingestion of low to moderate levels of aflatoxins.Ef

24、fects usually sub-clinical,difficult to recognize.Some common symptoms are impaired food conversion and slower rates of growth with or without the production of an overt aflatoxin syndrome.AflatoxinsIn developed countries,aflatoxin contamination rarely occurs in foods at levels that cause acute afla

25、toxicosisin humans.Therefore,studies on human toxicity from aflatoxin ingestion have focused on their carcinogenic potential.Relative susceptibility of humans to aflatoxins unknown,even though epidemiological studies in Africa/SE Asiahave revealed association between cancer incidence and dietary afl

26、atoxin content.AflatoxinsStudies have not proven cause-effect relationship,but evidence suggests association.One of the most important accounts of aflatoxicosis in humans occurred in more than 150 villages in adjacent districts of two neighbouring states in NW India in fall of 1974.According to one

27、report of this outbreak,397 persons were affected and 108 people died.AflatoxinsContaminated cornwas the major dietary constituent;aflatoxin levels of 0.25-15 mg/kg were found.Daily aflatoxin B1 intake estimated to have been at least 55 micrograms/kg bwtfor an undetermined number of days.Patients ex

28、perienced:high fever,rapid progressive jaundice黄疸;,edema of limbs,pain,vomiting,swollen livers.AflatoxinsOne investigator reported peculiar,notable feature of outbreak-appearance of signs of disease in one village population preceded by similar disease in domestic dogs(usually fatal).Histopathologic

29、al examination of humans showed:extensive bile duct proliferation and peri-portal fibrosis of the liver together with GI hemorrhages.10-Year Follow-up of Outbreak:found survivors fully recovered with no ill effects from experience.AflatoxinsEconomic Impact of Aflatoxins Derives directly from crop an

30、d livestock losses;indirectly from cost of regulatory programsdesigned to reduce risks to animal and human health.FAO estimates that 25%of worlds food crops are affected by mycotoxins;most notorious are aflatoxins.Aflatoxin lossesto livestock and poultry producers from aflatoxin-contaminated feeds i

31、nclude:death and immune system suppression,reduced growth rates,losses in feed efficiency.AflatoxinsOther adverse economic effects of aflatoxins include:lower yields for food and fibre crops.In addition,ability of aflatoxins to cause cancerand related diseases in humans given their seemingly unavoid

32、able occurrence in foods and feeds make prevention and detoxification of mycotoxins one of the most challenging toxicology issues of present time.Prevalence of Mycotoxins in Different Geographic RegionsOccurrence of Mycotoxins within Analyzed Finished Feed SamplesMycotoxinsAddition of adsorbent mate

33、rialsto animal feeds often used to prevent mycotoxicosis(esp.aflatoxicosis).Compounds bind toxin during digestive process in GI tract;reduces toxin available to be absorbed into blood stream.Efficacious adsorption of mycotoxins requires that polar groups of adsorbentand mycotoxins are in suitable po

34、sitions to bind together.Due to this,only a few mycotoxins can be adsorbed efficiently(e.g.-aflatoxins).MycotoxinsBiological detoxification of mycotoxins by microorganisms and/or enzymes has been researched for 30 years.Method based on deactivation of mycotoxins directly in GI tract;offers very spec

35、ific,irreversible and efficient way of detoxification.Consequently,less or non-adsorbable mycotoxins must be treated by enzymatic deactivation.Only combination of different strategies has proven successful.MycotoxinsCombined,two modes of actionprovide most effective way to deactivate toxic effects o

36、f mycotoxins.Mycotoxin Deactivators:can be mixed into animal feed to bind(in case of adsorbents)and/or break down(in case of microorganisms,enzymes)respective mycotoxins.Adsorbents:effective against aflatoxins,but do not appear useful in protecting against other mycotoxins(i.e.-fumonisins,deoxynival

37、enol脱氧雪腐镰刀菌烯醇,T-2 toxin,zearalenone玉米赤霉烯酮,ochratoxin赭曲霉毒素A).MycotoxinsAlternative way of mycotoxin detoxification is microbial or enzymatic detoxification(or“Biotransformation”).Method defined as degradation or transformationthat leads to less or nontoxic products.Live bacteria and yeast strainsexpr

38、essing specific mycotoxin-degrading enzymes offer a unique natural way of providing Biotransformationin digestive tract of animals.References1.Anon.1989.Mycotoxins,Economic and Health Risks.Council for Agricultural Science and Technology,Report No.116,pp.91.2.Eaton,D.L.and Groopman,J.D.1994.The Toxi

39、cology of Aflatoxins.Academic Press,New York,pp.383-426.3.Finley,J.W.,Robinson,S.F.,and Armstrong,D.J.1992.Food Safety Assessment.American Chemical Society,Washington,D.C.,pp.261-275.4.Goldbatt,L.A.1969.Aflatoxin.Academic Press,New York,pp.1-40.5.Heathcote,J.G.and Hibbert,J.R.1978.Aflatoxins:Chemica

40、l and Biological Aspect.Elsevier,New York,pp.173-186.6.Liener,I.E.1969.Toxin Constituents of Plant Foodstuffs.Academic Press,New York,pp.392-394.7.Wyllie,T.D.and Morchause,L.G.1978.Mycotoxin Fungi,Mycotoxins,Mycotoxicoses-An Encyclopedic Handbook,Vols.1,2,and 3.Marcel Dekker,Inc.,New York.References