Formation and Control of Mycotoxins in Food

Mycotoxin production is favored by high humidity and high water activity (a_w). To control mycotoxin formation on the basis of moisture, the moisture content must be maintained below a certain critical level for each commodity. Aflatoxin production is favored by temperatures of 25 to 30°C, whereas below 8 to 10°C, aflatoxin production can occur, but the amounts produced are less and the time required for production is longer. Cycling or changing temperature may or may not increase aflatoxin production, depending on the temperatures, mold species and substrates involved. Other mycotoxic molds respond to temperature differently than the aspergilli. Species of Penicillium , Fusarium and Cladosporium are capable of growing at temperatures below 5°C, and some even just below freezing. Penicillium spp. can produce patulin, penicillic acid and ochratoxin at temperatures from 0 to 31°C, whereas Aspergillus ochraceus does not produce ochratoxin or penicillic acid below 12°C. Penitrem production by Penicillium crustosum can occur at refrigeration temperature. Fusarium spp. can produce zearalenone and the trichothecenes at temperatures below 10°C and even below freezing. Maintaining storage temperatures of stored commodities at 5°C or lower will prevent the production of aflatoxins and ochratoxin by aspergilli but will not prevent the production of mycotoxins by Penicillium spp. and Fusarium spp. Mycotoxic molds may grow on a vast array of substrates, but some substrates support little or no mycotoxin production while supporting extensive mold growth. Most substrates that support aflatoxin production are plant products, such as peanuts, Brazil nuts, pecans, walnuts, almonds, filberts, pistachio nuts, cottonseed, copra, corn sorghum, millet and figs. Animal products are less likely substrates for aflatoxin production. The main source of aflatoxins in animal products are residues in milk and animal tissues as a result of consumption of toxic feed by the animal. Some herbs and spices have antifungal properties and do not support mycotoxin production. However, aside from this, most food substrates are susceptible to mold growth and mycotoxin production. Some substrates, such as cheese, cured meats and soybeans, might be less favorable for mycotoxin production, but may still support mycotoxin formation. Drought stress, insect damage and mechanical damage may increase the ability of Aspergillus flavus and other fungi to invade peanuts, cottonseed and grain. Some measure of control can be gained by minimizing drought stress through irrigation and minimizing insect and mechanical damage. Development of peanut varieties and corn hybrids that are resistant to preharvest invasion by A. flavus may also offer some measure control. Competing microorganisms tend to restrict fungal growth and mycotoxin production. Low oxygen concentration (<1%) and/or increased concentrations of other gases (i.e., >90% CO₂) may depress mold growth and mycotoxin formation. Antimycotic agents can be used to control mold growth and mycotoxin production. Sorbic acid, potassium sorbate, propionic acid and propionates appear to be more effective antimycotics over a greater range of conditions than benzoates. Other substances, such as sodium diacetate and BHA, also have antifungal activity. Certain herbs and spices, particularly cinnamon, cloves and mustard, may contain enough antifungal activity to exert a protective effect at normal usage levels.