Aflatoxin B2 is a naturally occurring toxin produced by specific molds, primarily Aspergillus flavus and Aspergillus parasiticus. These molds are common in agricultural environments and can contaminate various crops. Its presence in food and animal feed poses health and economic concerns. While less potent than some other aflatoxins, it still contributes to overall toxicity in both humans and animals.
Sources and Contamination Pathways
Aflatoxin B2 is produced by Aspergillus flavus and Aspergillus parasiticus, molds widespread in soil and decaying vegetation. These molds can infest a variety of crops, including corn, peanuts, cottonseed, tree nuts like almonds and pistachios, spices, rice, and sorghum.
Contamination can occur at different stages of crop production. During pre-harvest, factors like drought stress, insect damage, and inadequate irrigation create favorable conditions for fungal growth and toxin production. Post-harvest contamination often results from improper drying, storage in warm and humid conditions, and insufficient aeration. Aflatoxin B2 can then enter the human food chain directly through consumption of contaminated crops or indirectly via products from animals that have consumed contaminated feed, such as milk, meat, and eggs.
Health Effects
Exposure to aflatoxin B2 can lead to various health issues in both humans and animals. Acute exposure, from consuming high levels of the toxin over a short period, can manifest as severe liver damage, hemorrhage, abdominal pain, and in some cases, be fatal. Symptoms in humans may include nausea, vomiting, lethargy, and jaundice.
Chronic exposure to lower levels of aflatoxin B2 can lead to more subtle but serious long-term effects. These include immunosuppression, which increases susceptibility to infections, and growth impairment, particularly in children. Aflatoxin B2 is classified by the International Agency for Research on Cancer (IARC) as a Group 2B carcinogen, meaning it is possibly carcinogenic to humans. While less potent in its carcinogenic effects than aflatoxin B1, it still contributes to the overall risk of liver cancer (hepatocellular carcinoma) by binding to DNA and proteins, potentially causing cellular damage and mutations. Animals like poultry and livestock can experience reduced productivity, liver dysfunction, and decreased feed efficiency from contaminated feed, which can then lead to aflatoxin residues in their products, posing an indirect risk to human consumers.
Minimizing Exposure and Management
Reducing exposure to aflatoxin B2 involves implementing strategies across various stages of food and feed production. In agriculture, proper irrigation, effective pest control, and timely harvesting help prevent fungal growth in the field. Selecting crop varieties with natural resistance to Aspergillus species also contributes to minimizing contamination.
After harvest, rapid and thorough drying of crops to a safe moisture content, typically below 13-15%, inhibits fungal proliferation. Proper storage conditions, including low humidity, cool temperatures, and adequate ventilation, are also important. Food processing methods like sorting, cleaning, and sometimes specific detoxification techniques can further reduce aflatoxin levels. Regulatory bodies establish maximum limits for aflatoxins in food and feed to safeguard public health.
Understanding Aflatoxin Variants
Aflatoxins exist in several forms, with Aflatoxin B2 being one of the four major naturally occurring types, alongside Aflatoxin B1, G1, and G2. These variants are distinguished by their chemical structures and the color of their fluorescence under ultraviolet light; B1 and B2 emit a blue fluorescence, while G1 and G2 fluoresce yellow-green.
Aflatoxin B1 is the most prevalent and potent in toxicity and carcinogenicity among the group. Aflatoxin B2 is a dihydro-derivative of B1, structurally similar but exhibiting less carcinogenic potency. Metabolites like Aflatoxin M1 and M2 are formed when animals consume feed contaminated with B1 and B2, respectively, and these metabolites are found in milk. The relative order of toxicity for the main aflatoxins is B1 > G1 > G2 > B2.