Monitoring of Aflatoxins in Peanuts

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Turkish Journal of Agricultural and Natural Sciences
Special Issue: 1, 2014
1310
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Monitoring of Aflatoxins in Peanuts
a,b
Okşan UÇKUN*,
b
Işıl VAR
a
Oilseeds Research Station, Osmaniye, Turkey
b
Department of Food Engineering, Faculty of Agriculture, University of Cukurova, Adana, Turkey
*Corresponding author: uckun_oksan@hotmail.com
Abstract
Peanuts (Arachis hypogaea L.) are one of the most important oilseed crops and snack foods in the world
Agro-food trade market. The major producers/exporters of peanuts are the United States, China, Argentina,
Sudan, Senegal, and Brazil. Peanuts are a perishable commodity, easily spoiled by fungi. Aflatoxins are a group
of natural compounds mainly produced by Aspergillus flavus and Aspergillus parasiticus. They have been found
to be carcinogenic, teratogenic, and mutagenic to humans and animals. Aflatoxin contamination of peanuts is
one of the most important factors determining the quality of peanuts and has caused significant financial losses
for producing and exporting countries. Therefore, monitoring of aflatoxins in peanuts and peanut-contained
products is very important for protecting consumers. Various methods have been tried to decontaminate
aflatoxin contaminated commodities (e.g. peanuts). These include physical methods (sorting, irradiation
techniques, heating), chemical methods (acids, bases, oxidising agents), biological methods (microbiological).
All EU member states have set tolerance limits for certain mycotoxin food combinations but at present no
country has covered all important mycotoxins and all relevant commodities. The data varies greatly from
country to country. The overall competent authority for carrying out a monitoring for aflatoxin levels in
foodstuffs lies within the Ministry of Food, Agriculture and Livestock in order to estimate the actual dietary
exposure of aflatoxin contaminants in the foodstuffs (eg. peanuts) concerned.
Keywords: Peanut, Mycotoxin, Aflatoxin, Decontamination
Introduction
Peanut (Arachis hypogaea L.) can produce
energy due to their high oil, protein and fibre
content. These characteristics led the nut to
become sensitive to fungal contamination, both
pre- and post-harvest (Canavar and Kaynak, 2013).
Numerous moulds may be involved in peanut
spoilage, such as species of Aspergillus, Penicillium,
Fusarium and of Alternaria in low percentage
(Passone et al., 2008).
Aflatoxins are secondary metabolites
produced by species of Aspergillus, specifically
Aspergillus flavus and Aspergillus parasiticus
(Rustom, 1997). The name ‘‘aflatoxin” is derived
from the first letter in Aspergillus, and the first
three letters in flavus (Rawal et al., 2010). The
most important types of aflatoxins are AFB
1
, AFB
2
,
AFG
1
, AFG
2
, AFM
1
, and AFM
2
. They are highly toxic
and carcinogenic compounds that cause disease in
livestock and humans. Aflatoxin B
1
is most
frequently found in plant substrates and shows the
greatest toxigenic potential. Aflatoxins are stable
small molecules and cannot be destroyed by heat
treatment or during processing (Chen et al., 2013).
Though aflatoxins are very stable and do not
degrade up to 270 °C (their melting temperature)
in dry conditions, biologically they can be
converted into further toxic derivatives, such as
epoxide, M
1
, or M
2
, by metabolism in humans and
animals or less toxic derivatives, such as B
2
a, by
microorganisms (Samuel et al., 2014). Thus,
monitoring and prevention of aflatoxins in foods
and feeds are important issues worldwide (Chen et
al., 2013).
The worldwide accepted levels for AFB
1
and
total AFT (the sum of AFB
1
, B
2
, G
1
, and G
2
) range
from 1 to 20 mg/kg and from 0 to 35 mg/kg (FAO,
2004). The Codex Alimentarius Commisssion (CAC)
Joint Food and Agricultural Organization of the
United Nations and the World Health Organization
food standards program adopted a level of 15
mg/kg for AFT for unprocessed peanuts and 10
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Turkish Journal of Agricultural and Natural Sciences
Special Issue: 1, 2014
1311
mg/kg for ready-to-eat tree nuts (Ding et al.,
2012). For peanuts, nuts, dried fruits and cereals,
the maximum level of 2 ng/g for B
1
and 4 ng/g for
total aflatoxins have been set by the European
Commission (Afsah-Hejri et al., 2011).
Prevention of Aflatoxin in Peanut
Aflatoxin contamination may occur in the
field before harvest, during harvesting, or during
storage and processing, thus methods for the
prevention of contamination can be divided into
preharvest, harvesting and post-harvest strategies.
Whereas certain treatments have been found to
reduce aflatoxin formation in peanuts, the
complete elimination of aflatoxin is currently not
realistically achievable (Torres et al., 2014). The
best way to control mycotoxin contamination of
peanuts is to prevent it in the first place. This is not
always possible, but technologies exist which, if
available and affordable, can prevent much of the
contamination that would otherwise occur
(Dorner, 2008).
Pre-harvest control: Preharvest aflatoxin
contamination of peanuts is associated with
drought stress that occurs late in the growing
season while the crop is maturing (Dorner and
Cole, 1997). Pre-harvest contamination can be
reduced by introduction of good crop husbandry
and appropriate cultural practices that limit the
growth of aflatoxigenic fungi (Rustom, 1997).
-Resistance Varieties: The theoretically
soundest approach of prevention is doubtless the
breeding of cereals and other feed plants for
resistance to mould infection and, consequently,
mycotoxin production. Particularly in breeding
wheat and corn, significant improvement of
resistance has been achieved (Bata and Lasztity,
1999). However, resistance in peanuts to aflatoxin
contamination under all conditions has still not
been achieved and breeding efforts continue
(Torres et al., 2014).
-Kernel moisture control: Pre-harvest
aflatoxin contamination of peanuts essentially can
be eliminated with proper and adequate irrigation.
Developing and maturing peanuts are not
susceptible to colonization by A. flavus and A.
parasiticus until kernel moisture (water activity)
begins to decrease in response to late season
drought conditions with increased soil
temperature (Dorner, 2008). For this reason, late
season irrigation is recommended to help combat
heat and drought stress, but this cultural practice
seems to be impractical in some areas, especially in
semi-arid and arid areas where water supplies are
limited (Torres et al., 2014).
-Chemical and biological control: Several
chemical control agents have been reported to
inhibit aflatoxigenic mold growth and subsequent
aflatoxin biosynthesis. While some studies
suggested that pesticides and fungicides may be
useful in controlling mycotoxin production under
field conditions, other results have found that
pesticides were ineffective in controlling
mycotoxin production by Aspergillus species
(Torres et al., 2014).
One strategy that has been developed for
reducing preharvest aflatoxin contamination of
crops is biological control, which is achieved by
applying competitive non-toxigenic strains of A.
flavus and/or A. parasiticus to the soil of
developing crops (Dorner and Cole, 2002). This
approach is based on the premise that when high
number of spores of the nontoxigenic strains is
added to soil, they will compete with naturally
occurring toxigenic strains for infection sites for
growth on peanut and for essential nutrients
(Alaniz-Zanon et al., 2013).
Harvest control: It is very important to harvest the
crop at optimum maturity, as excessive numbers of
overmature or very immature pods at harvest can
be reflected in high levels of aflatoxin in the final
product. Also delays in harvesting will result in
poor quality seed due to mold infections and
subsequent aflatoxin contamination of the
seeds/pods (Torres et al., 2014). During the
harvesting process it is important that every effort
is made to avoid physical damage to the
agricultural commodities with crops which have
been physically damaged being more susceptible
to fungal growth (Kabak et al., 2006). The
temperature, soil humidity and climate conditions
of target peanut production areas are very useful
in determining the best harvest time (Canavar and
Kaynak, 2013).
Post-harvest control: Post-harvest contamination
can be minimized by application of proper curing,
drying, sorting and storage procedures (Rustom,
1997). According to the guide of Codex, to prevent
an increase in aflatoxin contamination occurring
during storage and transportation, it is important
to control the moisture content, the temperature
in the environment, and the hygienic conditions.
The minimum moisture content for A. flavus
growth on peanut is 8–10% at around 82% relative
humidity, and aflatoxin production is generally
correlated with kernel moisture contents of 10% or
higher (Torres et al., 2014). Both the main
aflatoxin producing Aspergillus strains A.flavus and
A.parasiticus can grow in the temperature range
from 10-12 °C to 42-43 °C, with an optimum in the
32 to 33 °C range. Aflatoxins are produced at

Turkish Journal of Agricultural and Natural Sciences
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1312
temperatures ranging from 12 to 40 °C
(Sweeney and Dobson, 1998).
One strategy to reduce the entry of
aflatoxin into the peanut chain is the use of
chemical treatments such as acetosyringone,
syringaldehyde and sinapinic acid and ammonia
applications during post-harvest to reduce both
fungal growth and toxin production (Canavar
and Kaynak, 2013). From a human health
perspective, the antioxidants such as butylated
hydroxyanisole (BHA), propyl paraben (PP) and
butylated hydroxytoluene (BHT) are allowed for
use as antimicrobial agents by the US Food and
Drug Administration (FDA) and are regarded as
safe (GRAS) chemicals (Passone et al., 2008).
Detoxification Methods Of Aflatoxin in Peanut
Various methods have been tried to
decontaminate aflatoxin contaminated
commodities (e.g. peanut). These include
physical methods (sorting, irradiation
techniques, heating), chemical methods (acids,
bases, oxidising agents), biological methods
(microbiological) (Jewers, 1990).
According to the FAO any
decontamination process to reduce the toxic
and economic impact of mycotoxins needs the
following requisites (Kabak et al., 2006;
Rustom, 1997; Piva et al., 1995):
-It must destroy, inactivate, or remove
aflatoxins;
-It must not produce or leave toxic
and/or carcinogenic/mutagenic residues in the
final products or in food products obtained
from animals fed decontaminated feed;
-It should not adversely affect desirable
physical and sensory properties of the product;
-It must be capable of destroying fungal
spores and mycelium in order to avoiding
mycotoxin formation under favorable
conditions;
-It has to be economically feasible, and
technically applicable.
Physical methods
Physical methods of aflatoxin
contaminated peanut have been include:
sorting, heating, irradiation.
-Sorting: Physical removal or separation
of aflatoxin-contaminated crops is an important
strategy for reducing aflatoxin levels and can be
achieved based on differing physical properties
such as size, shape, color and visible fungal
growth on the affected commodity (Womack et
al., 2014). The most effective technique for
managing aflatoxin contamination in
commercial shelling plants is electronic colour
sorting (ECS). Peanuts that have been
colonized by aflatoxigenic fungi are often
discoloured, and ECS very efficiently removes a
high percentage of the contaminated,
discoloured kernels (Dorner, 2008).
-Irradiation: Radiation is typically
categorized as either ionizing (IR) or non-
ionizing (NIR), with IR involving X-rays and
gamma (γ) rays and NIR involving UV rays,
microwaves, infrared rays and radio waves
(Kabak et al., 2006). The use of gamma
radiation to inactivate aflatoxins was
investigated. The toxicity of a peanut meal
contaminated with AFB
l
was reduced by 75%
and 100% after irradiation with gamma rays at
a dose of 1 and 10 kGy, respectively. However,
doses higher than 10 kGy inhibited the seed
germination, and increased the peroxide value
of the oil in gamma-irradiated peanuts
(Rustom, 1997).
-Heating: Aflatoxins have high
decomposition temperatures ranging from
237°C to 306°C. Solid AFB
l
is quite stable to dry
heating at temperatures below its thermal
decomposition temperature of 267°C (Rustom,
1997). Özkarslı and Var (2003) reported that
microwave roasting of peanuts in a 2450 MHz
for 90 seconds caused a 35.4% reduction in
aflatoxin levels. In another study, Mobeen et al.
(2011) achieved 50 to 60 % reduction in
aflatoxin levels in peanut and peanut products
by microwave roasting at 92 ̊C for 5 min.
Chemical methods
A wide range of chemicals have been
shown to reduce, destroy or inactivate
mycotoxins (Piva et al., 1995). These chemicals
include sodium hyroxide, hydrogen peroxide,
ozone, sodium hypochlorite (Zhang et al.,
2012). Although such treatment reduces nearly
completely the mycotoxin concentration, these
chemicals cause losses of some nutrients (Bata
and Lasztity, 1999).
Ozone due to its safety, environment-
friendly, low cost, high efficiency in
decomposing aflatoxin B
1
, has been widely
studied and used in the food industry (Diao et
al., 2013). Ozone eliminates the handling,
storage, and disposal problems of
conventionally used post-harvest pesticides
(Zorlugenç et al., 2008). Proctor et al. (2004)
achieved the highest level of degradation for
aflatoksin B
1
(77±2%) after ozonation of peanut
kernels for 10 min at 75°C. However, it is
important to note that, as a chemical

Turkish Journal of Agricultural and Natural Sciences
Special Issue: 1, 2014
1313
detoxification method, ozonation with low
ozone concentration and short treatment time
is required to mitigate the damage to peanut
nutrition (Chen et al., 2014).
Biological methods
Biological detoxification is the method of
choice to deactivate mycotoxins. This
comprises binding by adsorptive materials as
well as microbial inactivation by specific
microorganisms or enzymes (Schatzmayr et al.,
2006).
Many microorganisms including
bacteria, lactic acid bacteria and acid producing
molds can metabolize and inactivate aflatoxins,
with Flavobacterium aurantiacum as the most
active organism (Rustom, 1997). Özkaya (2001)
showed that F.aurantiacum strain NRRL B-184
reduced the amount of aflatoxin B
1
at 79-98.9
%, 92.6-99.8 % and 88.7-100.0 % in 48 hours in
phosphate buffer, peanuts and dried red
pepper, respectively. In another study,
Zorlugenç (2009) reported that using
F.aurantiacum strain NRRL B-184 the reduction
of aflatoxin B
1
content in the rate of 84.28 %
and 98.84 % in 72 hours at whole soy bean
(1000 ng/g AFB
1
) and milled hazelnut (500 ng/g
AFB
1
), respectively.
The importance of biological methods of
aflatoxin degradation will likely increase if
consumer resistance to chemical treatments
continue to grow. However, the bright orange
pigmentation associated with this bacterium
would likely limit its applicability for food and
feed fermentations (Bata and Lasztity, 1999).
Conclusion
Aflatoxin contamination of peanuts is
one of the most important factors determining
the quality of peanuts and has caused
significant financial losses for producing and
exporting countries. Thus, monitoring of
aflatoxins in peanuts and peanut-contained
products is very important for protecting
consumers. Although the different methods
used at present are to some extent successful,
they have big disadvantages with, limited
efficacy and possible losses of important
nutrients and normally with high costs.
Therefore, new methods of detoxification are
necessary to prevent health risks and economic
losses that result from aflatoxin contamination.
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