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Slaven Zjalić,
Department of ecology, agronomy and aquaculture,
University of Zadar, Croatia
Mycotoxins are secondary metabolites produced by some moulds
Most of mycoxtoxins have no odor and no taste
Through whole human history mycotoxinswere present in food and feed
Mycotoxins were discovered only in the last century after the outbreak of Turkey X desease in UK in 1960
In different farms more than 100.000 turkeys and ducklings died
The only thing in common was peanut based feed contaminated by Aspergillus flavus
The discovered toxin was named aflatoxin
Few years later the definition “mycotoxins” was assigned to the toxins produced by fungi
Up to day about 400 fungal metabolites are considered mycotoxins
Only a dozen of them of constant interest of scientist and authorities
Aflatoxins are among the most studied and controled mycotoxins
WHY?
Aflatoxins has genotoxic and cytotoxic effects on human and animal cells
They are teratogenic, cancerogenic and immnosuppressors
Aflatoxins can be transmitted allong the food chain, unchanged or modified in more or less toxic compounds
Moulds produce 4 aflatoxins B1, B2, G1, G2
Aspergillus flavus
Aspergillus parasiticus
More than 70% of produced aflatoxins
When iradiated with UV light aflatoxins have fluorescence blue (B) or green (G)
In the same organism different tissues are differently affected by aflatoxins
Detoxifications of animal cells from aflatoxins is operated by cytochrome P450 family
In mammalians part of AFB1 is transformed in less toxic M1 secreted in milk. The carryover is up to 6%
In 70´s different authors have hypothesized possible influences of aflatoxins, and mycotoxins, on human history:
- short life expectans of medieval man
- pest epidemies
- collective hysteria
Due to their toxicity the legislations of almost all the countries have limited the concentration of aflatoxins in food and feed commodities
EU
g kg-1
USA
g kg-1
China
g kg-1
Almonds 8 (B1)
12 (tot)
20 (tot) 30 (tot)
Animal feed 2 (B1) 20 (B1) 20 (B1)
Milk 0.05 (M1) 0.5 (M1) 0.5
Infant formulae 0.025 (M1) - -
Spices 5 (B1)
10 (tot)
20 (tot) -
Contamination with aflatoxins is a worldwide problem
Different commodities can be contaminated: cereal seeds, spices, dry fruits, meat products, cheese
Aflatoxigenic moulds requires relatively low aw (>0.7)
Contamination can occur in preharvest, in field, and postharvest period during any phase of transformation process or stocking
Producer
(farmer)
storage
transformation
Feed storage
Dairy cows milk
Aflatoxin control
Official control
Oxidative stress is considered a prerequisite for aflatoxin biosynthesis
Oily seeds, at same humidity, have higher aw and lipid oxidation triggers aflatoxin biosynthesis
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
afl
ato
xin
s (
g/k
g)
15 30 45
days
wheat
mais
peanuts
sunflower
For contamination in field high temperatures and drought or insect attack are needed
In Europe contamination with aflatoxins were considered more a problem of import or bad conservation
Due to global climatic changes in some years aflatoxin contamination in field is a serious problem in some European countries
Aflatoxin control is needed worldwide
Zone with perennial contamination risk
35°S
35°N
Mehl H.L., CORN UTILIZATION & TECHNOLOGY CONFERENCE (CUTC), INDIANAPOLIS, 2012
2003 and 2012 were “black” years for aflatoxin contamination in Europe
In 2013 Gafta (Grain and Feed Trade Association) has signalized reported high levels of aflatoxins in maize grains from:
Spain, Italy, Serbia, Bulgaria, Romania, Croatia
0
5
10
15
20
25
2009 2010 2011 2012 2013
%
wheat
maize
maize products
other cereals
Aflatoxin B1 concentration over EU limits in Croatia
Average temperatures, humidity and rain (1961-1990 and 1971-2000) compared to year 2012
Role of aflatoxins still not clarified
Gens are clustered, part of the signaling network that regulates expression of the cluster described
Incompleate aflatoxin cluster has been found in non producing strains
No method for total prevention of their presence in food and feed has been achieved
Control can be divided in:
prevention
detoxification
adsorption
Prevention
good agriculture practice (avoiding stress, quick postharvest drying)
aflatoxigenix fungi need relatively low aw, in corn dried to 14% of moisture aw could be on the limit for fungal growth
use of fungicides
Environmental problem
Aflatoxins are response to a stress, especially oxidative stress
Major growth of mould doesn’t mean higher production of aflatoxins
0
50
100
150
200
250
300
growth (erg) ATOX
g k
g-1
control
treated
use of antioxidants and organic acids
use of natural products (plant and fungal extracts) cont BHA 1 ppm
0
20
40
60
80
100
120
140
5 days
10 days
15 days
control BHA
15 30 45 15 30 45
Aflatoxins produced on maize seeds treated and non with BHA
Effect of extracts of different strains of Trametes
versicolor, an edible mushroom, on aflatoxin synthesis
by A. flavus
18S
hsf2-like
yap1-like
skn7-like
24h 36h 48h 60h 72h 4d 7d
SOD
0
2
4
6
8
10
24 h 36 h 48 h 60 h 72 h 96 h 7d
U m
g p
rote
in-1
Cont-pH
7,8
LF-pH
7,8
Cont-pH
10 ,0
LF-pH
10 ,0
CAT
0
2
4
6
8
10
12
24 h 36 h 48 h 60 h 72 h 96 h 7d
U m
g p
rote
in-1
Cont
LF
GPX
0
400
800
1200
24 h 36 h 48 h 60 h 72 h 96 h 7d
U m
g p
rote
in -1
Cont
LF
24h 36h 48h 60h 72h 96h 7d
18S
hsf2-like yap1-like
skn7-like
Cont LF
Inhibition seems to be related to the stimulation of
Aspergillus antioxidant system
Biocontrol
Use of non toxigenic strains as competitors
Use of resistant maize cultivars
Use of maize cultivars that stimulates less aflatoxin production (Burow et. al, 1997)
Comparison of constitutive and inducibile maize kernel proteins of genotype resistant or susceptible to aflatoxin production.
Chen ZY, Brown RL, Cleveland TE, Damann KF, Russin JS. J Food
Prot. 2001 Nov;64(11):1785-92.
A USA-Africa collaborative strategy for identifying, characterizing, and developing maize germplasm with resistance to aflatoxin contamination.
Menkir A.., Brown RL, Bandyopadhyvay R, Chen ZY, Cleveland
TE. Mycopathologia 2006, Sept; 162(3): 225-32
Molecular Plant-Microbe Interactions
MPMI Vol. 10, No. 3, 1997, pp. 380-387. Publication no. M-1997-0122-02R. © 1997
Seed Lipoxygenase Products Modulate Aspergillus Mycotoxin Biosynthesis
G. B. Burow, T. C. Nesbitt, J. Dunlap and N. P. Keller
Decontamination
removal of husks can significantly lowers the quantity of aflatoxins
chemical treatments
use of microbial enzymes
Most cultural filtrates (xylidine stimulated) degrade more than
90% of AFB1 on maize seeds after 72 hpi
A. flavus
inoculation on
maize seeds (1 kg) At 10 dpi, 1 ppm of
AFB1 is produced
Toxin residual/ g maize kernels
Isola
tes
Adsorption
different hydrated sodium calcium aluminosilicates (HSCAS) used to adsorb aflatoxins in animals
possible negative effects on adsorption of some nutrients
new generation of adsorbants based on cell walls
Estimated food contamination in Europe
Leblanc et al., 2005. and 2013. has estimated exposure to mycotoxins in French population
Results were encouraging, aflatoxin exposure was lower than 1ng kg-1 day-1
The most important sources were cereals followed by eggs, milk,
Aflatoxins represent high health hazard for humans and animals
No method for total prevention of their presence in food and feed has been achieved
Nevertheless the presence of aflatoxins in food and feed in EU countries is under control
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