Prevention of Mold Growth and Toxin Production through Control of Environmental Conditions

Environmental conditions influence mold growth and mycotoxin production. Such things as water activity (a_w), temperature, pH and atmosphere can strongly affect and profoundly alter patterns of growth and mycotoxin production. Generally, maintenance of low temperatures will prevent aflatoxin production in stored products, whereas other toxins such as penicillic acid, patulin, zearolenone and T-2 toxin may be produced at low temperatures. Toxic Penicillium and Fusarium species are generally more capable of growth at low temperatures than are toxic species of Aspergillus . Temperature interacts with a_w to influence mold growth and mycotoxin production. Aflatoxin B₁ can be produced at conditions of a_w and temperature which are close to the minimum a_w and temperature for growth. On the other hand, patulin, penicillic acid and ochratoxin A are produced within a narrower range of a_w and temperature, compared with those for growth. In fact, production of patulin and penicillic acid by Penicillium species appears to be confined to high a_w values only. In optimal substrates, the minima of a_w and temperature for growth and toxin production may be lower than in other substrates. It appears that pH and substrate composition have no great effect on growth of toxic molds, but may have a great influence on toxin production. Presence of CO₂ and O₂ influences mold growth and mycotoxin production. A 20% level of CO₂ in air depresses aflatoxin production and markedly depresses mold growth. Decreasing the O₂ concentration of air to 10% depresses aflatoxin production, but only at O₂ levels of less than 1% are growth and aflatoxin production completely inhibited. With patulin- and sterigmatocystin-producing molds, concentrations of 40% CO₂ depress growth and toxin production, but a level of 90% CO₂ is needed to completely inhibit production of these toxins. Decreasing O₂ concentration to 2% depresses production of patulin and sterigmatocystin but does not affect fungal growth. Only at levels down to 0.2% are growth and toxin production completely inhibited. Controlled atmospheres with increased CO₂ (above 10%) and decreased O₂ (2%) can be used to retard mold growth. Exclusion of O₂ by vacuum packaging in materials with low O₂ permeability will depress or even prevent aflatoxin production. Presence of other microorganisms may also restrict fungal growth and mycotoxin production. Aflatoxin production by Aspergillus flavus in mixed cultures with Aspergillus niger is less than in pure culture. Mixtures of fungi growing in grains and nuts in competition with A. flavus seem to prevent aflatoxin production. Other organisms including Rhizopus nigricans , Saccharomyces cerevisiae , Brevibacterium linens and some lactic acid bacteria have been shown to reduce growth and aflatoxin production by Aspergillus parasiticus . In general, mold growth and mycotoxin production can be prevented by employing various measures based on knowledge of the factors involved. Choice of the measures depends upon the type of product, storage period and available techniques.