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Title: Mycotoxins


1
  • Mycotoxins
  • Introduction

2
  • Mycotoxins are secondary metabolites (secondary
    metabolite  A compound that is not necessary for
    growth or maintenance of cellular functions but
    is synthesized, generally, for the protection of
    a cell or micro-organism, during the stationary
    phase of the growth cycle. Many are used in
    foods, pharmaceuticals, and other industrial
    applications.) of fungi that are recognized as
    toxic to other life forms.
  • 1.Fungal growth
  • a. Field fungi fungi that attack plants that
    grow in the field (occurring prior to harvest)
    grow under special conditions. (Fusarium)
  • b. Storage fungi Storage fungi usually invade
    grain or seed during storage and are generally
    not present in large quantities before harvest in
    the field. The most common storage fungi are
    species of Aspergillus and Penicillium.
    Contamination occurs through spores contaminating
    the grain as it is going into storage from the
    harvest. The development of fungi is influenced
    by the
  • Moisture content of the stored grain
  • Temperature
  • Condition of the grain going into storage
  • Length of time the is grain stored and
  • Amount of insect and mite activity in the grain

3
  • 2. Characteristics of mycotoxin induced disease
  • a. not transmitted among animals
  • b. Pharmaceutical treatment does not alter the
    course of disease
  • c. Mycotoxicosis most often presents as a
    uncertain, sub-acute or chronic condition

4
3.Treatment of mycotoxin-induced disease
  • a. For most mycotoxins, there is no specific
    treatment or antidote
  • b. Supplement with vitamins selenium may be
    helpful, and provision of adequate high-quality
    protein

5
4.Prevention of mycotoxin-induced disease
  • a. Avoiding
  • b. Diluting
  • c. Cleaning
  • d. Testing
  • e. Drying
  • f. Adding (organic acids will prevent mold growth)

6
A- Aflatoxin
  • 1. Sources
  • Aspergillus flavus A.paraciticus
  • Corn, peanuts
  • 2. Factor favoring production of aflatoxins
  • a. Temperature 25-30 ?c
  • b. Grain moisture

7
3. Chemical characteristics
  • Exhibit intense blue or green fluorescence under
    UV.
  • aflatoxins B1, B2, G1 and G2
  • also
  • aflatoxin M1 is a metabolites of AFB1 found
    in animal urine, milk or tissues.

8
5.Mechanism of toxicologic damage
Also called steatosis, fatty liver can be a
temporary or long-term condition, which is not
harmful itself, but may indicate some other type
of problem. Left untreated, it can contribute to
other illnesses. It is usually reversible once
the cause of the problem is diagnosed and
corrected. The liver is the organ responsible for
changing fats eaten in the diet to types of fat
that can be stored and used by the body.
Triglycerides are one of the forms of fat stored
by the body and used for energy and new cell
formation. The break down of fats in the liver
can be disrupted by alcoholism, malnutrition,
pregnancy, or poisoning. In fatty liver, large
droplets of fat, containing mostly triglycerides,
collect within cells of the liver. The condition
is generally not painful and may go unnoticed for
a long period of time. In severe cases, the liver
can increase to over three times its normal size
and may be painful and tender
9
  • a. Loss of enzyme
  • b. Lack of formation of lipid acceptor protein in
    liver
  • c. Decreased cellulose digestion, volatile fatty
    acid formation proteolysis (breakdown of
    proteins )
  • d. Necrosis

10
6.Toxicity
  • a. Young animals are more susceptible than adult.
  • b. Nutrition deficiency increase susceptibility

11
7. Diagnosis
  • Clinical sign decreased growth rate, reduced
    feed efficiency,,, mild anemia, and increased
    susceptibility to infectious disease.

12
8.Treatment Prevention
  • a. Detoxification Hydrated sodium calcium
    aluminosilicate (HSCAS) can absorb aflatoxins
  • b. Supportive Vitamin .E selenium
  • c. Prevention
  • - Mold inhibitor
  • - Treatment of grain with anhydrous ammonia for
    10-14 days.

13
B- Zearalenone
  • 1. Sources Fusarium roseum
  • ( F.graminearum )
  • corn, wheat, barley, oats
  • 2. Factor favoring production
  • a. High moisture 22 - 25
  • b. Alternating high and low temp. (7-21 ?c)

14
3. Mechanism of toxicological damage
  • a. initiating specific RNA synthesis
  • b. Function as a weak estrogen.

4.Toxicity
a. Swine are most susceptible b. low for all
effects except reproductive function.
15
C-Ergot
  • 1.Source
  • Claviceps purpurea
  • barley, wheat oats
  • 2. Factor favoring
  • Warm humid

16
3.Mechanism of toxic
  • a. potent initiators of contraction in smooth
    muscle
  • b. mimic the action of dopamine.

4.Clinical sign
a. necrosis of the feet, ears and tail b.
increased temperature., pulse respiration rate
c. lactation does not occur d.
hyper-excitability tremors e. heat intolerance
in cattle
17
E.Treatment
  • a. animals should be provided with a warm,
    clean, stress-free environment
  • b. Control secondary bacterial infection
  • c. milk supplement

18
D- Ochratoxin Citrinin
  • 1.Sources Aspergillus orchraceus
  • Penicillium viridicatum
  • 2. Mechanism of toxic
  • target the renal proximal tubule
  • - Disrupt protein synthesis
  • -Bind strongly to protein (albumin)
  • -Interfere with synthesis of tRNA mRNA
  • -Disrupt carbohydrate metabolism
  • -Increase the generation of free radical

19
4.Clinical sign
  • a. Acute vomiting, diarrhea, dehydration
    depression
  • b. Subacute to chronic weight loss, feed
    efficiency, dehydration. Immunosupression,
    teratogenicity, carcinogenesis hemorrhage

20
  • Mycotoxins

21
Mycotoxin
  • Mycotoxin is a convenient generic term describing
    the toxic
  • secondary metabolites produced by fungi. Myco
    means
  • fungal (mold) and toxin represents poison.
  • They encompass a considerable variety of low
    molecular weight compounds with diverse chemical
    structures and biological activities.
  • Some mycotoxins could also be toxic to plants or
    other
  • microorganisms but these compounds are not
    classified as
  • antibiotics of fungal origin.
  • Like most microbial secondary metabolites, the
    benefit of mycotoxins for the fungi themselves is
    still not clearly defined.

22
  • In considering the effects of mycotoxins on
    animals, it is important to distinguish between
    mycotoxicosis and mycosis.
  • Mycotoxicosis is used to describe the action of
    mycotoxin(s) and is frequently mediated through a
    number of organs, notably the liver, kidney,
    lungs, and the nervous, endocrine, and immune
    systems.
  • Mycosis refers to a generalized invasion of
    living tissue(s) by growing fungi.

23
  • Due to their diverse chemical structures,
    mycotoxins may exhibit a number of biological
    effects, including both acute and chronic toxic
    effects as well as carcinogenic, mutagenic,
    genotoxic, and immunotoxic effects.
  • The interaction of mycotoxins with cellular
    macromolecules plays a dominant role in their
    toxic actions. Recent studies on the effect of
    mycotoxins on apoptosis have further revealed
    their mode of action at the cellular level.

24
  • Historical
  • Modern mycotoxicology was not developed until the
    discovery of aflatoxins in the early 1960s as the
    causative agent in the
  • peanut meal causing the Turkey X disease that
    killed more than 10,000 turkeys fed with the
    contaminated meal.
  • Because aflatoxins are a series of highly potent
    carcinogens produced by commonly occurring
    Aspergillus flavus and A. parasiticus, research
    has focused new attention on mycotoxins.
  • In the last 40 years, many new mycotoxins have
    been identified and characterized, and their
    biosynthetic origin in various fungi elucidated.
    It has been estimated that at least 25 of the
    worlds agricultural product is contaminated with
    mycotoxins and certain diseases have been linked
    to ingestion of food and feed contaminated with
    mycotoxins.

25
Economic Impact of Mycotoxin Contamination
  • The most obvious negative economic impact of
    mycotoxins is an outright loss of crops and
    affected animals.
  • Also, humans may encounter severe health hazard
    or high mortality rates in countries with less
    regulation or monitoring programs.
  • Thus, the negative economic impact resulting
    from mycotoxin contamination is certainly very
    significant and estimated to be 932 million
    annually.

26
PRODUCTION OF MYCOTOXINS BY TOXICOGENIC FUNGI
Invasion by fungi and production of mycotoxins in
commodities can occur under favorable conditions
in the field, at harvest, and during
processing, transportation and storage
Fungi that are frequently found in the field
include A. flavus, Alternaria longipes, A.
alternata, Claviceps purpura, Fusarium
verticillioides (previously called moniliforme),
F. graminearum, and a number of other Fusarium
spp. Species most likely introduced at harvest
include F. sporotrichioides, Stachybotrys atra,
Cladosporium sp., Myrothecium verrucaria,
Trichothecium roseum, as well as A. alternata.
Most penicillia are storage fungi. These
include Penicillium citrinum, P. cyclopium, P.
citreoviride, P. islandicum, P. rubrum, P.
viridicatum, P. urticae, P. verruculosum, P.
palitans, P. puberulum, P. expansum, and P.
roqueforti. All of which are capable of
producing mycotoxins in grains and foods.
27
  • Other toxicogenic storage fungi are Aspergillus.
    parasiticus, A. flavus, A. versicolor, A.
    ochraceus, A. clavatus, A. fumigatus, A. rubrum,
    A. chevallieri, Fusarium verticillioides, F.
    tricinctum, F. nivale, and several other Fusarium
    spp.
  • It is apparent, most of the mycotoxin producing
    fungi belong to three genera Aspergillus,
    Fusarium, and Penicillium. However, not all
    species in these genera are toxicogenic

28
Factors Affecting Mycotoxin Production
  • Genetics and environmental and nutritional
    factors greatly affect the formation of
    mycotoxins.
  • Depending on the susceptibility of the crop,
    geographic and seasonal factors, as well as
    cultivation, harvesting, storage, and
    transportation practices, mycotoxins are found
    worldwide.
  • In the field, weather conditions, plant stress,
    invertebrate vectors, species and spore load of
    infective fungi, variations within plant and
    fungal species, and microbial competition all
    significantly affect mycotoxin production.

29
Continue Factors Affecting.
  • Physical factors such as time of exposure,
    temperature during exposure, humidity, and extent
    of insect or other damage to the commodity prior
    to exposure determine mycotoxin contamination in
    the field or during storage.
  • Chemical factors including the nutritional status
    of the crops or chemicals (such as fungicides)
    used in crop management could affect fungal
    populations, and consequently toxin production

30
Continue Factors Affecting.
  • In general, mycotoxins are optimally produced at
    2428C, but some toxins such as T-2 toxin is
    maximally produced at 15C.
  • Contamination during crop storage may be affected
    by changes in temperature and water activity,
    that allow ecological succession of different
    fungi as water activity and temperature of stored
    grain changes.

Water activity It is defined as the vapor
pressure of water above a sample divided by that
of pure water at the same temperature
31
Continue Factors Affecting.
  • During storage and transportation, water activity
    (aw), temperature, crop damage, and a number of
    physical and chemical factors, such as aeration
    (O2, CO2 levels), types of grains, pH, and
    presence or absence of specific nutrients and
    inhibitors are important.

32
Aflatoxins
Chemical structure of flatoxins
  • The B-type aflatoxins are characterized by a
    cyclopentane E-ring. These compounds have a blue
    fluorescence under long-wavelength ultraviolet
    light.
  • (B) The G-type aflatoxins, with a green
    fluorescence, have a xanthone ring in place of
    the cyclopentane.
  • (C) Aflatoxins of the B2 and G2 type have a
    saturated bis-furanyl ring. Only the bis-furan is
    shown.
  • (D) Aflatoxin of the B1a and G1a type have a
    hydrated bis-furanyl structure.

33
  • At least 16 structurally related toxins in this
    group are produced by Asparagillus flavus and A.
    parasiticus and infrequently by A. pseudotamarii
    and A. nominus
  • A. ochraceoroseus has also been found to produce
    aflatoxins
  • The optimal temperatures and water activity (aw)
    for the growth of A. flavus and A. parasiticus
    are around 3537C (range from 654C) and 0.95
    (range from 0.781.0), respectively whereas for
    aflatoxin production, they are 2833C and
    0.900.95 (range from 0.830.97), respectively.

34
  • Aflatoxin B1 is most toxic in this group and is
    one of the most potent naturally occurring
    carcinogens).
  • Other significant members of the aflatoxin
    family, such as M1 and M2, are metabolites of
    AFB1 and AFB2, respectively, and originally
    isolated from bovine milk.

35
Natural Occurrence
  • Aflatoxins have been found in corn, peanuts ???
    ??????? and peanut products, cotton seeds,
    peppers, rice, pistachios, ???? tree nuts,
    pumpkin ??? seeds, sunflower seeds and other oil
    seeds, copra, ??? ??? spices, and dried fruits
    (figs, raisins).
  • Among these products, frequent contamination with
    high levels of AF in peanuts, corn, and
    cottonseed, mostly due to infestation with fungi
    in the field, are of most concern.
  • Soybeans ??????, beans ??????????, pulses
    (Pea)????????, cassava ??????, sorghum ????? ,
    millet ?????, wheat ?????, oats ?????, barley
    ??????, and rice?? are resistant or only
    moderately susceptible to AF contamination in the
    field.
  • It should be reiterated that resistance to AF
    contamination in the field does not guarantee
    that the commodities are free of AF contamination
    during storage. Inadequate storage conditions,
    such as high moisture and warm temperatures
    (25308C), can create conditions favorable for
    the growth of fungus and production of AF.

36
Toxic Effects
  • Aflatoxins are mutagenic, teratogenic, and
    hepatocarcinogenic.
  • Aflatoxin B1 is one of the most potent naturally
    occurring carcinogen, extensive research was
    primarily done on this toxin. The main target
    organ of AF is the liver.
  • AFB1 also affects other organs and tissues
    including the lungs and the entire respiratory
    system.
  • For the carcinogenic effects, rats, rainbow
    trout, monkeys, and ducks are most susceptible
    and mice are relatively resistant.
  • Consumption of AFB1-contaminated feed by dairy
    cows results in the excretion of AFM1 in milk.
    AFM1, a hydroxylated metabolite of AFB1, is about
    10 times less toxic than AFB1 but its presence
    in milk is of concern for human health.

37
Impact on Human Health
  • Whereas AFB1 has been found to be a potent
    carcinogen in many animal species, the role of AF
    in carcinogenesis in humans is complicated by
    hepatitis B virus (HBV) infections in humans).
  • Epidemiological studies have shown a strong
    positive correlation between AF levels in the
    diet and primary hepatocellular carcinoma.
  • Since multiple factors are important in
    carcinogenesis and environmental contaminants
    such as AFs and other mycotoxins may, either in
    combination with HBV or independently.

38
Ochratoxins
  • Ochratoxins, are produced by a number of fungi in
    the genera Aspergillus and Penicillium. The
    largest amounts ochratoxins are made by A.
    ochraceus and P. cyclopium.
  • A. ochraceus and P. viridicatum (reclassified as
    P. verrucosum), two species that were first
    reported as ochratoxin A (OA) producers, occur
    most frequently in nature.
  • Other fungi, such as Petromyces alliceus, A.
    citricus, and A. fonsecaeus (both in A. niger
    group), have also been found to produce OA. Most
    of the OA producers are storage fungi and
    preharvest fungal infection.

39
  • Although most OA producers can grow in a range
    from 48C to 37C and at aw as low as 0.78, optimal
    conditions for toxin production are narrower with
    temperature at 2425C and aw values .0.97.
  • Ochratoxins are produced primarily in cereal
    grains (barley, oats, corn, wheat) and mixed feed
    during storage in temperate climatic conditions,
    with levels higher than 1 ppm being reported.
  • OA has been found in other commodities, including
    beans, coffee, nuts, olives, raisin, cheese,
    fish, pork, milk powder, fruit juices wine beer,
    peppers.
  • OA can be carried through the food chain because
    of the presence of OA residues in animal products
    as result of its binding with serum albumin.
    Natural occurrence of OA in kidneys, blood serum,
    blood sausage.

40
Structure of the ochratoxins. These metabolites
form different classes depending on the nature of
the amide group (ac), and the presence or
absence of a chlorine moiety at R2 in the phenyl
group.
41
  • Ochratoxin A, the most toxic member of this
    group of mycotoxins, has been found to be a
    potent nephrotoxin causing kidney damage as well
    as liver necrosis and enteritis in many animal
    species

The OA inhibits carboxypeptidase A, renal
phosphoenolpyruvate carboxykinase,
phenylalaninetRNA synthetase, and phenylalanine
hydroxylase activity.
Formation of free radicals has been considered as
one of the mechanisms for the carcinogenic/toxic
effects of OA.
42
Fumonisins Fumonisins (Fm) are a group of toxic
metabolites produced primarily by F.
verticillioides, F. proliferatum and other
related species readily colonize corn all over
the world. Although F. anthophilum, F. nupiforme,
and F. nygamai are capable of producing Fms.
More than 11 structurally related Fms (B1, B2,
B3, B4, C1, C4, A1, A2, etc.), have been found
since the discovery of FmB1. Fumonisins are
most frequently found in corn, corn-based foods,
and other grains (such as sorghum and rice). The
level of contamination varies considerably with
different regions and year, ranging from
negligible to more than 100 ppm but is generally
reported to be between 1 and 2 ppm.
FmB1 is the most common Fm in naturally
contaminated samples FmB2 generally accounts for
1/3 or less of the total. Although production of
the toxin generally occurs in the field,
continued production of toxin during postharvest
storage also contributes to the overall levels.
43
Toxicologic Effects Fumonisin B1 is primarily a
hepatotoxin and carcinogen in rats. Feeding
culture material from F. verticillioides or pure
FmB1 to rats resulted in cirrhosis and hepatic
nodules, carcinoma. Kidney is also a target
organ. Mechanistically, Fms are inhibitors of
ceramide synthase (sphinganine/sphingosine
N-acyltransferase), a key enzyme involved in the
biosynthesis of sphingolipids, which are heavily
involved in cellular regulation, including cell
differentiation, mitogenesis and apoptosis
????? ?????
The ability of FmB1 to alter gene expression and
signal transduction pathways are considered
necessary for its carcinogenic and toxic effects.
FmB1 is a good example of an apparently
non-genotoxic (non-DNA reactive) agent producing
tumors through the regulation of apoptosis
44
Trichothecenes (TCTCs)
Several species of Fusaria infect corn, wheat,
barley, and rice. Under favorable conditions,
they elaborate a number of different types of
mycotoxins (look figure). (TCTCs) are generally
classified as macrocyclic (Type C) or
nonmacrocyclic (Types A and B). Although more
than 100 TCTCs have been identified, only a few
frequently found in foods and feeds are
potentially hazardous to human and animal health.
Trichothecenes
Other fungal genera elaborate TCTCs are
Myrothecium, Trichoderma, Trichothecium,
Cephalosporium, Verticimonosporium, and
Stachybotrys. In addition to fungi, extracts from
a Brazilian shrub, Baccharis megapotamica, also
contain macrocyclic TCTCs. The term TCTCs is
derived from trichothecin, the first compound
isolated in this group.
45
The TCTC mycotoxicoses affect many organs,
including the gastrointestinal tract,
hematopoietic, nervous, immune, hepatobiliary,
and cardiovascular systems. Mechanistically,
inhibition of protein synthesis is one of the
earlier events in manifestation of TCTC toxic
effects and they act at different steps in the
translation process. Inhibitory effects of these
mycotoxins vary considerably with the chemical
structure of the side chain.
a) T-2 toxin,
T-2 toxin, a highly toxic type A TCTC, is
produced by F. tricinctum, F. sporotrichioides
(major), F. poae, F. sulphureum, F. acuminatum,
and F. sambucinum. Unlike most mycotoxins, which
are usually synthesized near 25C, the optimal
temperature for T-2 toxin production is around
15C.
46
Almost all the major TCTCs, including T-2 toxin,
are cytotoxic and cause hemorrhage, edema, and
necrosis of skin tissues.
b) Deoxynivalenol (DON)
The DON is a major type B TCTC mycotoxin produced
by F. graminearum (major) and other related fungi
such as F. culmorum and F. crookwellense. Because
DON causes feed refusal and emesis in swine, the
name vomitoxin is also used for this mycotoxin.
47
  • Worldwide frequent natural occurrence of DON in
    cereal grains has been reported. Contamination of
    this toxin in corn and wheat is generally high.
  • Also, contamination of barley, oats, sorghum,
    rye, safflower seeds, and mixed feeds has also
    been reported.
  • Although inadequate storage may lead to the
    production of some TCTC mycotoxins, infestation
    of fusaria in wheat and corn in the field is of
    most concern for the DON problem.
  • With wet and cold weather during
    maturation,grains are especially susceptible to
    F. graminearum infection, which causes so-called
    scabby wheat and simultaneously produces the
    toxin. The optimal temperature for DON production
    is about 248C.

48
  • Toxicologically, DON induces anorexia and emesis
    both in humans and animals. Swine are most
    sensitive to feed contaminated with DON. Whereas
    most TCTCs are immunosuppressors, DON is a
    hyperinducer of cytokines.

49
  • Other Selected Mycotoxins
  • In addition to the mycotoxins discussed above, a
    number of other mycotoxins occur naturally.
  • Other Mycotoxins Produced by Aspergillus
  • Sterigmatocystin (ST) is a naturally occurring
    hepatotoxic and carcinogenic mycotoxin produced
    by fungi in the genera Aspergillus, Bipolaris,
    and Chaetomium as well as P. luteum.
  • Structurally related to AFB1 ST is known to be a
    precursor of AFB1.
  • ST is a mutagen and genotoxin and has been found
    in cereal grains (barley, rice, and corn), coffee
    beans, and cheese.

Structure of sterigmatocystin. The bis-furanyl
structure is similar to that of the aflatoxins
except that the E-ring is a substituted phenol.
50
  • A. terreus and several other fungi (e.g., A.
    flavus and A. fumigatus) have been found to
    produce the tremorgenic toxins, territrems,
    aflatrem, and fumitremorgin.
  • A. terreus, A. fumigatus, and Trichoderma viride
    also produce gliotoxin, In addition, A. flavus,
    A. wentii, and A. oryzae, are capable of
    producing nitropropionic acid (NPA), a mycotoxin
    causing apnea, convulsions, congestion in lungs
    and liver.
  • Production of NPA in sugarcanes by Arthrinium
    sacchari, Arth. saccharicola, and Arth.
    Phaeospermum has been found to be involved in
    fatal food poisoning in humans

51
  • Other Mycotoxins Produced by Penicillium

Penicillia produce many mycotoxins with diverse
toxic effects. Cyclochlorotine, luteoskyrin (LS),
and rugulosin (RS) have long been considered to
be possibly involved in the yellow rice disease
during the Second World War. They are
hepatotoxins. Several other mycotoxins, including
patulin (PT) penicillic acid (PA) citrinin (CT),
cyclopiazonic acid (CPA, citreoviridin, and
xanthomegnin, which are produced primarily by
several species of Penicillia. PT and PA are
produced by many species in the genera
Aspergillus and Penicillium. Byssochlamys nivea
also produces PT
penicillic acid
Patulin
52
Chemical structure of cyclopiazonic acid
Structure of alternariol
Stucture of zearalenone
53
  • Other Mycotoxins Produced by Fusarium
  • Some fusaria are capable of producing mycotoxins
    other than TCTCs and Fm. Zearalenone (ZE) a
    mycotoxin produced by the scabby wheat fungus, F.
    graminearum (roseum), is of most concern. Also
    called F-2, ZE is a phytoestrogen causing
    hyperestrogenic effects and reproductive problems
    such as premature onset of puberty in female
    animals,especially swine.
  • ZE has been shown to bind with the estrogen and
    steroid receptors, and stimulates protein
    synthesis by mimicking hormonal action.
  • Zearalenone can be toxic to plants it can
    inhibit seed germination and embryo growth at low
    concentrations.
  • Natural contamination with ZE primarily occurs in
    cereal grains such as corn and wheat

54
  • Fusarium verticillioides and related species,
    also produce several other mycotoxins, including
    fusarins A-F, moniliformin, fusarioic, and
    fusaric acid, fusaproliferin and beauvericin.
  • Although the impact of these mycotoxins on human
    health is still not known, fusarin C (FC) has
    been identified as a potent mutagen and is also
    produced by F. subglutinans, F. graminearium and
    several other Fusaria.
  • Moniliformin, which causes cardiomyopathy in test
    animals, may be involved in the Keshan disease in
    humans in regions where dietary selenium
    deficiency is also a problem.
  • Among many fungi, F. verticilioides is also most
    capable of reducing nitrates to form potent
    carcinogenic nitrosamines. These observations
    further suggest that the contamination of foods
    with this fungus could be one of the etiological
    factors involved in human carcinogenesis in
    certain regions of the world.

55
Zearalenone
Alternariol
Mycotoxins Produced by Alternaria
Species Alternaria has been known for centuries
to cause various plant diseases. Species of this
fungus are widely distributed in soil and on
aerial plant parts. More than 20 species of
Alternaria are known to produce about 70
secondary metabolites belonging to a diverse
chemical group. However, only alternariol
tenuazonic acid, altertoxin-I, alternariol
monomethyl ether (AME), altenuene are common
contaminants in consumable items like fruits
(apples), vegetables (tomato), cereals (sorghum,
barely, oat), and other plant parts (such as
leaves) The most common species of Alternaria,
A. alternata (formerly known as A. kikuchiana)
produces all important Alternaria toxins
including the five mentioned above and tentoxin,
alteniusol, alternaric acid, altenusin,
dehydroaltenusin
56
  • Mycotoxins Produced by Other Fungi
  • Sporidesmines, a group of hepatotoxins discovered
    in the 1960s. These mycotoxins, causing facial
    eczema in animals, are produced by Pithomyces
    chartarum and Sporidesmium chartarum and are very
    important economically to the sheep industry.
  • Slaframine, a significant mycotoxin produced by
    Rhizoctonia leguminicola (in infested legume
    forage crops).

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PREVENTIVE MEASURES
  • Management of Mycotoxin Contamination
  • The economic implications of the mycotoxin
    problem and its potential health threat to humans
    have clearly created a need to eliminate or at
    least minimize mycotoxin contamination of food
    and feed.
  • While an association between mycotoxin
    contamination and inadequate storage conditions
    has long been recognized, studies have revealed
    that seeds are contaminated with mycotoxins prior
    to harvest . Therefore, management of mycotoxin
    contamination in commodities must include both
    pre- and postharvest control measures

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  • Preharvest Control
  • Mycotoxin contamination can be reduced somewhat
    by using of resistant varieties (most effective,
    but not all are successful) and earlier harvest
    varieties
  • crop rotation,
  • adequate irrigation,
  • control of insect pests.
  • Significant control of toxin contamination is
    expected to be dependent on a detailed
    understanding of the
  • physiological and environmental factors that
    affect the biosynthesis of the toxin,
  • the biology and ecology of the fungus,
  • the parameters of the host plantfungal
    interactions.
  • Efforts are underway to study these parameters
    primarily for the most agriculturally significant
    toxins, namely AFs, Fms, and TCTCs

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  • Use of atoxigenic biocompetitive, native A.
    flavus strains to out-compete the toxigenic
    isolates has been effective in significantly
    reducing preharvest contamination with aflatoxin
    in cotton and peanuts.
  • However, the aflatoxin contamination process is
    so complex that a combination of approaches will
    be required to eliminate or even control the
    preharvest toxin contamination problem.

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Mycotoxins and food chain
61
  • Postharvest Control
  • After harvest, crop should not be allowed to
    over-winter in the field as well as subjected to
    birds and insects damage or mechanical damage.
    Grains should be cleaned and dried quickly to
    less than 1013 moisture and stored in a clean
    area to avoid insect and rodent infestation.
  • Postharvest mycotoxin contamination is prevalent
    in most tropical countries due to
  • a hot, wet climate coupled with
  • subadequate methods of harvesting,
  • (handling, and storage practices),
  • which often lead to severe fungal growth and
    mycotoxin contamination of food and feed.

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  • Sometimes contaminated food has been diverted to
    animal feed to prevent economic losses and health
    concerns. However, this is not a solution to the
    contamination problem.
  • Irradiation has been suggested as a possible
    means of controlling insect and microbial
    populations in stored food, and consequently,
    reducing the hazard of mycotoxin production under
    these conditions .
  • Significant emphasis has been placed on
    detoxification methods to eliminate the toxins
    from the contaminated lots or at least reduce the
    toxin hazards by bringing down the mycotoxin
    levels under the acceptable limits.

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  • I. Removal or Elimination of Mycotoxins.
  • Since most of the mycotoxin burden in
    contaminated commodities is localized to a
    relatively small number or seeds or kernels
    removal of these contaminated seeds/kernels is
    effective in detoxifying the commodity.
  • Methods currently used include
  • (a) physical separation by
  • identification and removal of damaged seed
  • mechanical or electronic sorting
  • flotation and density separation of damaged or
    contaminated seed
  • physical screening and subsequent removal of
    damaged kernels by air blowing
  • washing with water
  • use of specific gravity methods
  • All these methods have shown some effect for some
    mycotoxins, including DON, FmB, and AFB1
  • (b) removal by filtration and adsorption onto
    filter pads, clays, activated charcoal, etc.,
  • (c) removal of the mycotoxin by solvent
    extraction

64
  • II. Inactivation of Mycotoxins.
  • When removal or elimination of mycotoxins is not
    possible, mycotoxins can be inactivated by
  • (a) physical methods such as thermal
    inactivation, photochemical or gamma irradiation,
  • (b) chemical methods such a treatment of
    commodities with acids, alkalies, aldehydes,
    oxidizing agents, and gases like chlorine, sulfur
    dioxide, NaNO2, ozone and ammonia,
  • (c) biological methods such as fermentations and
    enzymatic digestion that cause the breakdown of
    mycotoxins. The commercial application of some of
    these detoxifying mechanisms is not feasible
    because, in a number of cases, the methods will
    be limited by factors such as the toxicity of the
    detoxifying agent, nutritional or aesthetic
    losses of commodities during treatment, and the
    cost of the sophisticated treatment.
  • Although several detoxification methods have
    been established for aflatoxins, only the
    ammoniation process is an effective and practical
    method. Other chemicals such as ozone, chlorine,
    and bisulfite have been tested and some effect
    for some mycotoxins was shown in it. Solvent
    extractions have been shown to be effective but
    are not economically feasible.

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  • III. Removal of Mycotoxins During Food
    Processing.
  • While cooking generally does not destroy
    mycotoxins, some mycotoxins can be detoxified or
    removed by certain kinds of food processing.
  • For example, extrusion cooking appears to be
    effective for detoxifying DON but not AFB. FmB1
    can form Schiffs bases with reducing sugars such
    as fructose under certain conditions and lose its
    hepato-carcinogenicity but the hydrolyzed FmB1
    was found to be still toxic.

66
  • Avoiding Human Exposure
  • Role of Rigorous Monitoring Programs
  • While it is impossible to remove mycotoxins
    completely from foods and feeds, effective
    measures to decrease the risk of exposure depend
    on a rigorous program of monitoring mycotoxins in
    foods and feeds. Consequently, governments in
    many countries have set limits for permissible
    levels or tolerance levels for a number of
    mycotoxins in foods and feeds.
  • Over 50 countries of the world have developed
    such guidelines. For example, levels varying from
    zero tolerance to 50 ppb have been set for total
    AFs.
  • A tolerance level of 1 ppm for DON in grains for
    human consumption has been set by a number of
    countries, including the United States. The FmB1
    levels established by FDA in 2000 are limited to
    5, 20, 60 100, 30, and 10 ppm, in corn and corn
    by-products to be used for horse and rabbit,
    catfish and swine, and mink, poultry,

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  • Among 77 countries which have regulations for
    different mycotoxins, eight have specific
    regulations for OA, with limits ranging from 1 to
    20 mg/kg in different foods.
  • Regulatory guidelines to limit the presence of PT
    to 50mg/kg in various foods and juices have been
    established by at least ten countries worldwide.
    Details on worldwide regulatory issues and
    permissive levels of mycotoxins in foods and
    feeds have appeared in a number of recent
    reviews.

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  • Detection and Screening of Mycotoxins
  • Because of the diverse chemical structures of
    mycotoxins, the presence of trace amounts of
    toxins in very complicated matrices that
    interfere with analysis, and the uneven
    distribution of the toxins in the sample,
    analysis of mycotoxins is a difficult task.
  • Because many steps are involved in the analysis,
    it is not uncommon that the
  • analytical error can amount to 2030
  • To obtain reliable analytical data, an adequate
    sampling program and an accurate analytical
    method are both important.
  • To minimize the errors, studies have led to many
    improved and innovative analytical methods for
    mycotoxin analysis over the years.
  • New, more sensitive TLC, HPLC, and GC techniques
    are now available.
  • The MS methods have also been incorporated into
    HPLC systems.
  • New chemical methods, including capillary
    electrophoresis and biosensors are emerging and
    have gained application for mycotoxin analysis.

69
  • After a number of years of research,
    immunoassays have
  • gained wide acceptance as analytical tools for
    mycotoxins in the last decade. Antibodies against
    almost all the mycotoxins are now available. Some
    quantitative and qualitative immunoassays have
    been approved. Many immunoscreening kits, which
    require less than 15 min. per test, are
    commercially available.



  • Rather than analysis of toxin, PCR methods,
    based on the primers of key enzymes involved in
    the biosynthesis of mycotoxins, have been
    introduced for the determination of toxicogenic
    fungi present in foods.
  • Detailed protocols for mycotoxin analysis can be
    seen in several of the most recent reviews and
    books and the most recent edition of AOAC .

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  • Dietary Modifications
  • Dietary modification greatly affects the
    absorption, distribution, and metabolism of
    mycotoxin and subsequently affect its toxicity.
    For example, the carcinogenic effect of AFB1 is
    affected by nutritional factors, dietary
    additives, and anticarcinogenic substances. Diet
    containing chemoprotective agents and
    antioxidants such as ascorbic acid, and even
    green tea, have also been found to inhibit
    carcinogenesis caused by AFB1 in test animals.
  • The toxic effect of OA and FmB to test animals
    was minimized when antioxidants such as vitamins
    C and E are added to the diet. Ascorbic acid also
    provided protective effect against AFs.
  • Most mycotoxins have a high affinity for hydrated
    sodium calcium aluminasilicate (HSCAS) and other
    related products.

71
CONCLUSIONS
  • Mycotoxins are low molecular weight secondary
    metabolites of fungi that are contaminants of
    agricultural commodities, foods, and feeds.
  • Fungi that produce these toxins do so both prior
    to harvest and during storage. Although
    contamination of commodities by toxigenic fungi
    occurs frequently in areas with a hot and humid
    climate, they can also be found in temperate
    conditions.
  • Production of mycotoxins is dependent upon the
    type of producing fungus and environmental
    conditions such as the substrate, water activity
    (moisture and relative humidity), duration of
    exposure to stress conditions, and microbial,
    insect, or other animal interactions.

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  • Although outbreaks of mycotoxicoses in humans
    have been documented, several of these have not
    been well characterized, neither has a direct
    correlation between the mycotoxin and resulting
    toxic effect been well established in vivo.
  • Even though the specific modes of action of most
    of the toxins are not well established, acute and
    chronic effects in prokaryotic and eukaryotic
    systems, including humans have been reported.
  • The toxicity of the mycotoxins varies
    considerably with the toxin, the animal species
    exposed to it, and the extent of exposure, age,
    and nutritional status.

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  • Most of the toxic effects of mycotoxins are
    limited to specific organs, but several
    mycotoxins affect many organs. Induction of
    cancer by some mycotoxins is a major concern as a
    chronic effect of these toxins.
  • It is nearly impossible to eliminate mycotoxins
    from food and feed in spite of the regulatory
    efforts at the national and international levels
    to remove the contaminated commodities.
  • This is because mycotoxins are highly stable
    compounds, the producing fungi are ubiquitous,
    and food contamination can occur both before and
    after harvest. Nevertheless, good farm management
    practices and adequate storage facilities
    minimize the toxin contamination problems.

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  • A combination of natural biocontrol competition
    fungi and enhancement of host-resistance against
    fungal growth or toxin production could prevent
    toxin formation to a very significant extent.
  • Rigorous programs for reducing the risk of human
    and animal exposure to contaminated food and feed
    also include
  • economically feasible
  • safe detoxification processes
  • dietary modifications.

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  • Additional, systematic epidemiological data for
    human exposure is needed for establishing
    toxicological parameters for mycotoxins and the
    safe dose for humans.
  • It is unreasonable to expect complete elimination
    of the mycotoxin problem. But multiple approaches
    will be needed to minimize the negative economic
    impact of the toxins on the entire agriculture
    industry as well as their harmful effects on
    human and animal health.
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