Aflatoxins are the most prominent mycotoxins in accordance with their abundance and toxicity.
Mycotoxins are fungal metabolites which are among the most important food contaminants threatening human health. Food and Agricultural Organization reported 25% of agricultural products are contaminated with mycotoxins worldwide. Mycotoxins, which are mostly heat stable small molecules, can not be destroyed by usual cooking procedures and hence cause severe health implications including hepatotoxicity, genotoxicity, oncogenicity, nephrotoxicity, immunomodulation, fertility and reproduction perturbation, central nervous system damage or skin toxicity. Although nearly 300 types are known, Aflatoxins are the most prominent mycotoxins in accordance with their abundance and toxicity.
Aflatoxins are secondary metabolites of fungi from Aspergillus spp. which can cause acute and chronic toxicity in both humans and animals when ingested. High level exposure to AFs results in acute toxicity which may lead to death, and chronic exposure often leads to liver diseases including liver cancer, chronic hepatitis, jaundice, hepatomegaly and cirrhosis in humans.
Among 20 different types of identified AFs, major members are AF B1, B2, G1, G2 and M1. AFB1 is grouped as class 1 human carcinogen by IARC. AF B1, B2, G1 and G2 are the four common naturally occurring analogs of AF and AFM1 is a water-soluble AF analog found in milk produced by animal metabolism . They are metabolized by cytP450 enzymes in liver. Their metabolites cause immune suppression, change in cell morphology and form DNA and protein adducts. The primary metabolite which causes hepatotoxic effects is Aflatoxin-8,9- epoxide is produced by the metabolization of AFB1 by CYP1A2 and CYP3A4. This metabolite induces selective mutation in p53 oncogene, which leads to hepatocellular carcinoma.
AF levels are controlled in food and feed products. Different maximum allowable AF levels for different feed products established by FDA are as follows; 20 ng/g for feed of immature animals, 100 ng/g for feed of breeding cattle, swine or poultry, 300 ng/g for the feed of finishing cattle, swine and poultry. For food products, 20 ng/g limit is accepted, however, AFM1 level in milk and milk products is limited by 0.5 ng/g. These levels show differences in the regulations of different countries and organizations.
Aflatoxins are freely soluble in moderately polar organic solvents such as methanol, ethanol and dimethyl formamide and have limited solubility (10-20 mg/L) in water. They show spectral activity at UV range, where their maximal absorbance is between 360-363 nm and show a secondary absorption peak at 265 nm.
Their stability and reactivity was extensively studied in order to elucidate detoxification strategies. They are extremely stable to heat up to 100°C but unstable at extreme pH ranges (<3, >10). They are degraded by reacting with hypochloride and ammonia. Structure of common AFs are presented at Table
Aflatoxins Detection and Quantification
AFs are amongst the most abundant food and feed contaminants, and due to their high toxicity and carcinogenicity, they are of major concern for food producers, the food processing industry, traders and consumers. National and international directives are employed in order to prevent the associated health risks. Corresponding methods have been developed for accurate and reliable analysis in various food products.
Internationally accepted precise AF quantification is conducted with laboratory based methods such as thin layer chromatography (TLC), HPLC, LC-MS/MS or immunological test methods including ELISA. Most commonly used method is instrumental analysis with HPLC which requires a series of steps including sampling, homogenization, extraction, extract cleanup with IAC and detection.
Conventional AF quantification methods require expensive, sophisticated equipment and trained staff. The availability of rapid and on-site systems for the analysis of AF will both provide better control of AF contamination in food and feedstuff and also decrease the analytical costs. Biosensors are powerful tools which can meet this requirement.
AF specific antibodies are indispensible components of these methods. They are utilized in IACs for sample cleanup prior to instrumental methods and they are the core components of ELISA and biosensor systems.