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DIONNE FLETT EMMA GILL FUNGAL TOXINS IN FOOD APRIL 2002. Introduction Fungal toxins, also referred to as mycotoxins, are secondary metabolites produced by moulds. The most important mycotoxins include: 1. Aflatoxins 5. Fumonisins

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APRIL 2002


Fungal toxins, also referred to as mycotoxins, are secondary metabolites produced by moulds. The most important mycotoxins include:

1. Aflatoxins 5. Fumonisins

2. Tricothecenes 6. Tremorgenic

3. Ochratoxins Toxins

4. Zearelenone 7. Ergot Alkaloids

Mycotoxin Overview
  • 1. Aflatoxins
  • Produced by Aspergillus spp. and can grow on most foods/crops
  • Aflatoxins B1 & B2, (B1 is most toxic and is discussed in more detail later), are produced by A. flavus, A. parasiticus & A. nomius
  • Aflatoxins G1 & G2 are produced by A. parasiticus & A. nomius
  • Aflatoxins M1 & M2 are produced from the B1 & B2 aflatoxins & found in the milk of lactating animals
  • The letters denoted by the aflatoxins indicate the colours in which they are seen under UV light. (B=blue & G=green)2
Mycotoxin Overview
  • 2. Tricothecenes
  • Produced by Fusarium sporotrichioides, F. graminearum, F. poae & F. culmorum
  • These toxins may also be produced by Myrothecium, Trichothecium, Cephalosporium & Stachybotrys spp.4
  • Found in corn, barley, wheat & rice
  • Included in tricothecenes are:
  • * T-2 Toxin * Diacetoxyscirpenol (DAS)
  • * Nivalenol * Deoxynivalenol (DON)1
  • T-2 toxin is most toxic (discussed in more detail later)
Mycotoxin Overview
  • 3. Ochratoxins
  • Group of 7 mycotoxins
  • Ochratoxin A, (OTA), most toxic & is associated with kidney disease
  • OTA produced by Penicillium verrucosum & Aspergillus ochraceus1
  • Contaminates barley, corn, peanuts & coffeebeans4
  • 4. Zearelenone
  • Produced by Fusarium culmorum
  • Recently has been linked with stimulation of cancer cells in breast tissue
  • Contaminates cereal grains2

Fig.1. Fig.2. Structure of

Structure of Zearelenone3


Mycotoxin Overview
  • 5. Fumonisins
  • Produced by Fusarium verticillioides, F. moniliforme & F. proliferatum
  • Fumonisins B1 & B2 are both possible human carcinogens but Fumonisin B1 is most toxic
  • Fumonisins have been found to contaminate asparagus, beer & rice1

Fig.3. Structure of Fumonisins B1 & B23

Mycotoxin Overview
  • 6. Tremorgenic Toxins
  • Example of such toxins include, lolitrem B toxin3
  • Produced by Acremonium ,Claviceps & Penicillium spp.
  • Affects the CNS and causes tremors2
  • 7. Ergot Alkaloids

Fig.4. Structure of lolitrem B toxin3

  • Examples of theses toxins include ergotamine & ergostine
  • Produced by Claviceps purpurea & Acremonium spp.3
  • Found in grasses & cereal grains in which they replace the developing ovary
  • If exposed to humans can result in convulsions & gangrene
  • Outbreak in Middle Ages termed ‘St Anthonys Fire’4

Fig.5. Structure of ergotamine3

Aflatoxin B1
  • Produced by Aspergillus flavus, A. parasiticus & A. nomius6
  • Found in nuts & oilseeds, especially corn, peanuts & cottonseeds6
  • Preharvest contamination of above crops occurs via temperatures greater than 70oC, insect damage & severe, prolonged drought5
  • Health Effects2,4,5,6,7
  • Aflatoxin B1 causes:
  • * acute liver damage
  • * cirrhosis
  • * liver carcinogen
  • * immunosuppresive effects
  • * epidemics of acute toxic hepatitis
Mechanism of Action2
  • Aflatoxin B1 is metabolised by the microsomal mixed function oxidase system in liver, leading to formation of highly reactive intermediates, one of which is 2,3-epoxy-aflatoxin B1. These reactive intermediates bind to DNA & disrupt transcription, resulting in abnormal cell proliferation. This leads to mutagenesis or carcinogenesis.
  • This toxin also inhibits O2 uptake in tissues by acting on electron transport chain & inhibiting various enzymes, resulting in a decreased production of ATP.
  • Hepatitis B virus can be an additional factor but evidence concerning this is contradicting.
  • Aflatoxin B1 is biotransformed by microsomal cytochrome monooxygenase.
Incidence of Disease2,5,6,7
  • India 1974 - 100 out 400 people who contracted hepatitis died
  • because of aflatoxins
  • - corn contaminated with A. flavus (~15mg/kg)
  • - died mainly from gastrointestinal haemorrhage
  • In the North Western Malaysian state of Perak, 13 children died due to aflatoxin poisoning
  • Aflatoxin related deaths reported in Africa due to high cosumption of mouldy grain & brewery products
  • Death rates due to aflatoxins in China & Africa range from 10-60%
  • ~ 25,000 deaths in China & Sub Saharan Africa caused by human hepatocellular carcinomas attributed to risk factors such as high daily intake of aflatoxins & high incidence of hepatitis B
T-2 Toxin
  • Produced by a number of Fusarium spp. including, F. aqcuminatum, F. crookwellense, F. graminearum, F. poae, F. sambucinum & F. tricinctum3
  • Contaminates cereal grains, wheat, rye, barley, corn & bread2
  • Health Effects
  • Initial clinical symptoms include; vomiting, diaorrhea, haemorrhaging, breathing difficulty, chest pain, blisters, headaches, fatigue & dizziness2
  • Conditions caused by this toxin:2,5,7
  • * Alimentary Toxic Aleutia (ATA)
  • * neurotoxicity
  • * inflammations
Alimentary Toxic Aleutia (ATA)5
  • Disease caused by ingestion of T-2 toxin and resembles radiation poisoning.
  • Divided into four stages:
  • * stage 1: 3-9 days after exposure. Symptoms; skin
  • inflammation, sore throat, abdominal pain,
  • salivation, headaches, weakness & rapid heart
  • rate
  • * stage 2: bone marrow depression, anaemia, decreased platelet & white
  • blood counts
  • * stage 3: bleeding from gums, GI tract & nose. Increased susceptibility
  • to infectious agents (possible death)
  • * stage 4: improvement in bone marrow function. Patient usually recovers
  • if this stage is reached
Mechanism of Action2,3
  • T-2 toxin inhibits the synthesis of protein, RNA & DNA synthesis. The toxin binds to polysomes & ribosomes & peptide linkages are interrupted. The initiation & termination sequences are diminished & the ribosomal cycle is disrupted.
  • T-2 toxin disrupts the transport of amino acids, nucleotides & glucose, along with the activity of Ca - K channels on cell membranes.
  • Succinate Dehydrogenase activity is suppressed by the T-2 toxin, & mitochondrial electron transport is inhibited.
Incidence of Disease
  • 1944 in Russia during World War II, food shortages meant people ate overwintered Mouldy grain cereals5,7
    • This lead to an outbreak of alimentary toxic aleukia.
    • Symptoms were severe haemorrhaging, anaemia and death
  • Sick houses
    • immunosuppressive diseases like leukaemia develop
    • every member of the household is effected
    • caused by Fusarium in dust2,7
  • Aflatoxins3,4
  • Determine levels that are unlikely to be of a health concern
  • European Union set aflatoxin B1 levels at 2ppb with a maximum upper limit of 4ppb in agricultural commodities
  • US Federal Food Drug & Cosmetic Act section 402a set levels at 20ppb in foods & feeds. Grains & nuts were limited at 1µg/kg
  • By 1994, 177 countries had regulations for aflatoxins in foods & feeds
  • T-2 Toxin3,4
  • As yet there is no legislation regarding Fusarium spp. & T-2 toxin

1. Creppy, Edmond E. (2001) Update of Survey ,Regulation & Toxic Effects of Mycotoxins in Europe, Toxicology Letters, In Press, Uncorrected Proof

2. Doyle, Michael P., Beuchat, Larry B. & Montville, Thomas J. (1997) Food Microbiology Fundamentals & Frontiers, ASM Press, Washington D.C. Pp393-431

3. Hussein, S. Hussein & Brasel, Jeffrey M. (2001) Toxicity, Metabolism & Impact of Mycotoxins on Humans & Animals, Toxicology, 167 pp101-134

4. Kuiper-Goodman, T. (1995) Mycotoxins: risk assessment and legislation, Toxicology letters, 82/83, pp853-859

5. Lederberg Joshua., (2000) Encyclopedia of Microbiology, 2nd Edition, Vol 3 L-P, Academic Press, pp338-347

6. Mossel,D.A.A., et al,(1995) Essentials of the Microbiology of Foods: A textbook for advanced studies, J.Wiley & sons, pp154-158

7. Robinson, Richard K. (2000) Encyclopedia of Food Microbiology, Academic Press, London, pp339-342, pp1518-1523