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12.9.6 Major Factors Influencing Biosynthesis of AFB1
The biosynthesis of the AFB1 requires several steps, and it is perhaps affected by
the intervention of several environmental factors (stress, quorum sensing, and protein signaling pathway) without forgetting the factors regulating the transcription
unit. Amino acids such as tryptophan inhibit the synthesis of aflatoxin, whereas
tyrosine encourages it. The presence of the lipids induces the aflatoxinogenesis.
Among the organic factors affecting biosynthesis, carbon and nitrogen are the major
ones. In addition, simple sugars such as glucose and fructose support this biosynthesis, whereas in the cases of sorbose and lactose, no action has been recorded.
Concerning the physical factors, the optimal temperature of biosynthesis is located
between 28 °C and 35 °C. Above this temperature range, biosynthesis is inhibited
due to the attack of transcription genes aflR and aflS, whereas under the conditions
of dryness, the production of the aflatoxins is high. Synthesis is also influenced by
subcultures and changes in the morphology of producing cells. For pH, biosynthesis
is high in acidic media, while it is inhibited in basic conditions, for A. parasiticus,
the growth in water is faster with a pH ranging from 5.5 to 6.5. The secondary plant
metabolites play a key role in the synthesis of aflatoxins. For example, the presence
of the octanal causes a reduction of 60% of the fungic growth with a rate of increase
in the production of aflatoxins of 500%. However, hydrolysable tannins considerably inhibit the biosynthesis of aflatoxins. Some antioxidants such as the phenolic
compounds, ascorbic acid and caffeic acid decrease, in an important way, the aflatoxinogenesis, without any effect on the growth of the fungi (Bueno et al. 2007).
12.9.7 Degradation of Aflatoxins
12.9.7.1 Detoxification Using Lactic Acid Bacteria
Several lactic acid bacteria are able to bind AFB1 in vitro and in vivo on the surface
of the organism, and two aspects were taken into consideration: binding and release
of toxin. Turbic and his collaborators showed that 77–95% of AFB1 were removed
by strains of Lactobacillus rhamnosus GG and LC-705. El Khoury and his collaborators also noted that Lactobacillus bulgaricus and Streptococcus thermophilus
were effective in the reduction of aflatoxins M1. Lactobacillus pentosus and
Lactobacillus brevis have the capacity to absorb and release AFB1 (Joubrane et al.
2011; Hamidi et al. 2013). In binding of AFM1 from PBS Lb. acidophilus, LA1
showed a binding ability of 18.3% in viable and 25.5% in heat-killed cells (Pierides
et al. 2000). El Khoury et al. (2011) studied the ability of Lb. bulgaricus to reduce
AFM1 from PBS and yogurt. Binding was 40% after 2 h PBS incubation and
increased up to 87.6% after 14 h. In yogurt the AFM1 binding reached up to 60%
after a 6-h yogurt incubation. Sarimehmetoğlu and Küplülü (2004) analyzed commonly used yogurt bacteria, Lb. delbrueckii subsp. bulgaricus for its binding ability
12 Fungal Mycotoxins
12.9.6 Major Factors Influencing Biosynthesis of AFB1
The biosynthesis of the AFB1 requires several steps, and it is perhaps affected by
the intervention of several environmental factors (stress, quorum sensing, and protein signaling pathway) without forgetting the factors regulating the transcription
unit. Amino acids such as tryptophan inhibit the synthesis of aflatoxin, whereas
tyrosine encourages it. The presence of the lipids induces the aflatoxinogenesis.
Among the organic factors affecting biosynthesis, carbon and nitrogen are the major
ones. In addition, simple sugars such as glucose and fructose support this biosynthesis, whereas in the cases of sorbose and lactose, no action has been recorded.
Concerning the physical factors, the optimal temperature of biosynthesis is located
between 28 °C and 35 °C. Above this temperature range, biosynthesis is inhibited
due to the attack of transcription genes aflR and aflS, whereas under the conditions
of dryness, the production of the aflatoxins is high. Synthesis is also influenced by
subcultures and changes in the morphology of producing cells. For pH, biosynthesis
is high in acidic media, while it is inhibited in basic conditions, for A. parasiticus,
the growth in water is faster with a pH ranging from 5.5 to 6.5. The secondary plant
metabolites play a key role in the synthesis of aflatoxins. For example, the presence
of the octanal causes a reduction of 60% of the fungic growth with a rate of increase
in the production of aflatoxins of 500%. However, hydrolysable tannins considerably inhibit the biosynthesis of aflatoxins. Some antioxidants such as the phenolic
compounds, ascorbic acid and caffeic acid decrease, in an important way, the aflatoxinogenesis, without any effect on the growth of the fungi (Bueno et al. 2007).
12.9.7 Degradation of Aflatoxins
12.9.7.1 Detoxification Using Lactic Acid Bacteria
Several lactic acid bacteria are able to bind AFB1 in vitro and in vivo on the surface
of the organism, and two aspects were taken into consideration: binding and release
of toxin. Turbic and his collaborators showed that 77–95% of AFB1 were removed
by strains of Lactobacillus rhamnosus GG and LC-705. El Khoury and his collaborators also noted that Lactobacillus bulgaricus and Streptococcus thermophilus
were effective in the reduction of aflatoxins M1. Lactobacillus pentosus and
Lactobacillus brevis have the capacity to absorb and release AFB1 (Joubrane et al.
2011; Hamidi et al. 2013). In binding of AFM1 from PBS Lb. acidophilus, LA1
showed a binding ability of 18.3% in viable and 25.5% in heat-killed cells (Pierides
et al. 2000). El Khoury et al. (2011) studied the ability of Lb. bulgaricus to reduce
AFM1 from PBS and yogurt. Binding was 40% after 2 h PBS incubation and
increased up to 87.6% after 14 h. In yogurt the AFM1 binding reached up to 60%
after a 6-h yogurt incubation. Sarimehmetoğlu and Küplülü (2004) analyzed commonly used yogurt bacteria, Lb. delbrueckii subsp. bulgaricus for its binding ability
12 Fungal Mycotoxins