Aspergillus flavus and the closely related subspecies parasiticus have long been recognized as major contaminants of organic and nonorganic items. A. flavus, a common soil fungus, can infest a wide range of agricultural products. Some A. flavus varieties produce aflatoxins, which are carcinogenic toxins that induce liver cancer in laboratory animals. A. flavus var. flavus, A. flavus subsp. parasiticus, and A. nomius share the ability to produce aflatoxins. Identification of the A. flavus species group is mainly based on the color and macroscopic and microscopic characteristics of the fungus. A. flavus growth and aflatoxin biosynthesis depend on substrate, moisture, temperature, pH, aeration, and competing microflora. The growth of A. flavus and aflatoxin production are sometimes unavoidable. Aflatoxins are considered natural contaminants; the ideal control approach is prevention of mold growth and aflatoxin production. The detection of members of the A. flavus species group in foods and feed is generally carried out by using plate techniques such as surface spread or direct plating. Research on alternative fungal detection methods is still in its infancy. Few immunoassay techniques have been investigated in this regard. Aflatoxins are generally analyzed by chemical methods, although immunochemical methods which use antibodies are becoming common analytical tools for aflatoxins.

A mixture of Lactobacillus species from a commercial silage inoculum reduced mold growth and inhibited aflatoxin production by Aspergillus flavus subsp. parasiticus. Actively growing Lactobacillus spp. cells totally inhibited germination of mold spores. Culture supernatant broth from the mixture of strains inhibited mold growth but did not destroy mold spore viability. Some mold spores were observed microscopically to have germinated and produced short nonbranching germ tubes; then growth ceased. While the pH of the culture broth and supernatant were about 4.0, acidification of nonfermented broth to pH 4.0 with HCl and lactic acid did not cause a similar inhibition of spore germination. The mixture of Lactobacillus species growing in a dialysis sack inhibited aflatoxin production by the A. flavus culture growing outside of the sack in broth, whereas mold growth was not affected. The pH values outside of the dialysis sack in the control and the treatments were similar (6 to 7) throughout the incubation period. When a dialysis sack with a molecular weight cutoff (MWCO) of 1,000 was used, there was little inhibition of aflatoxin B1 production, but with MWCOs of 6,000 to 8,000 and 12,000 to 14,000 aflatoxin production was greatly inhibited. In mixed culture experiments, levels of aflatoxin B1 and G1 were depressed compared to the control (monoculture). Mold growth in this case was also reduced compared to the monoculture system. Purified isolates of Lactobacillus from the commercial mixture had a slight effect on mold growth and aflatoxin production, but supernatant liquid of one isolate was quite inhibitory to production of aflatoxins B1 and G1, without affecting mold growth.

Lactic acid bacteria are extensively used in the fermentation of a wide variety of food products and are known for their preservative and therapeutic effects. Many lactic acid bacteria species have been reported to inactivate bacterial pathogens, and numerous antibacterial substances have been isolated. However, the antimycotic and antimycotoxigenic potential of lactic acid bacteria has still not been fully investigated. Fermented foods such as cheese can be contaminated by molds and mycotoxins. Mold causes spoilage and renders the product unusable for consumption, and the presence of mycotoxins presents a potential health hazard. A limited number of reports have shown that lactic acid bacteria affect mold growth and aflatoxin production. Although numerous lactic acid bacteria such as Lactobacillus spp. were found to inhibit aflatoxin biosynthesis, other lactic bacteria such as Lactococcus lactis were found to stimulate aflatoxin production. The morphology of lactic acid bacteria cells has also been found to be affected by the presence of fungal mycelia and aflatoxin. Lactococcus lactis cells became larger and formed long chains in the presence of Aspergillus flavus and aflatoxins. Numerous investigations reported that low pH, depletion of nutrients, and microbial competition do not explain the reason for aflatoxin inhibition. Some investigators suggested that the inhibition of aflatoxin is due to lactic acid and/or lactic acid bacteria metabolites. These metabolites have been reported to be heat-stable low-molecular-weight compounds.

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