Difference between revisions of "Summary - Aflatoxins"
m (Protected "Summary - Aflatoxins" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)))
Latest revision as of 12:44, 8 January 2018
Aflatoxins (B1, B2, G1, G2)
Aflatoxins were first isolated and characterized after the death of more than 100.000 Turkey poults in the United Kingdom from acute liver necrosis (Turkey-X-disease) in the 1960s. Toxicity was traced to the consumption of a mold contaminated peanut meal. Analysis of the feed led to the discovery of Aspergillus flavus, a major aflatoxin producing fungus (Bradburn et al., 1994) 1-Link.
Aflatoxins consist of a group of approximately 20 related secondary fungal metabolites although only major aflatoxins B1, B2, G1 and G2 are normally found in foods. These four main types were named based on their fluorescence under UV light (blue or green) on thin-layer chromatography (Richard 2007) 2-Link. Aspergillus species that produce aflatoxins belongs to section Flavi. The species of this section include A. flavus, A. parasiticus, A. nomius, A. oryzae, A. sojae and A. tamarii. However, they are mainly produced by three species, A. flavus, A. parasiticus and A. nomius and can occur in a wide range of important raw food commodities including cereals, tree nuts, spices, figs, dried fruits, oilseeds, cottonseed and tobacco (Bayman and Cotty, 1993) 3-Link. Aflatoxins are found in food as a result of fungal contamination pre and postharvest, with the rate and degree of contamination depend on temperature, humidity, soil and storage conditions but temperature and relative humidity are considered to be the most critical. The optimal temperature and water activity for fungal growth and aflatoxin production by the two high-temperature species, A. flavus and A. parasiticus, is 35°C with 0.95 aw and 33°C with 0.99 aw, respectively. Neither species produces aflatoxins when grown below 7.5°C or above 40°C. The composition of the atmospheric gases around the toxigenic fungus is another factor affecting toxin production. Controlled or modified atmospheres packaging were found capable of preventing aflatoxin production by A. flavus. Additional factors such as water activity, moisture, substrate composition, storage time, insect damage and presence of a shell also influence fungal growth and aflatoxin production (Jackson and Al-Taher, 2008) 4-Link. Although aflatoxins are greater problem in the tropics than in temperate zones of the world, no region of the world is free of aflatoxins due to worldwide commercial activities.
Aflatoxins (AFs) are considered the most toxigenic fungal metabolites with carcinogenic, mutagenic, teratogenic and immunosuppresive effects on humans as well as on animals. Of the four major aflatoxins, aflatoxin B1 has the greatest acute toxicity to animals followed by G1, B2 and G2 (Coppock and Christian, 2007) 5-Link. The diseases caused by aflatoxin consumption are called aflatoxicoses. Acute aflatoxicosis is produced when moderate to high levels of aflatoxins are consumed. Chronic aflatoxicosis results from prolonged ingestion of low to moderate levels of aflatoxins (Varga et al., 2009) 6-Link. Aflatoxin B1 (AFB1) is known to be potent hepatocarcinogen and hepatotoxic for humans and classified as carcinogenic to humans (Group I) by The International Agency of Research on Cancer (IARC, 1993) 7-Link. Epidemiological studies have shown associations between aflatoxin exposure and incidence of hepatocellular carcinoma in areas with high prevalence of chronic hepatitis B, a risk factor for liver cancer (EFSA, 2007) 8-Link.
Based on toxicological studies, all mycotoxins have the specific HBGV (TDI, PTWI or PMTDI) except AFs. Because of carcinogenic effects of AFs (including AFM1) there is no tolerable daily intake (TDI) level estimated. Although there is no HBGV for AFs, MOE value is defined by EFSA (EFSA, 2005) 9-Link. Based on epidemiological data in human, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) calculated a risk per unit dose of 0.013x10-5 (ng AFs/kg bw/day)-1 which means a potential effect increasing in the incidence of hepatic cancer in the general population, i.e. an increase in the incidence of cancer in the general population of 0.013 cancers per year per 100,000 subjects per ng AFs per kg body weight per day during life-years, or 13 cancers per 100 million people (JECFA, 1998) 10-Link. The European Union Scientific Committee for Food also concluded like JECFA that even very low levels of exposure to aflatoxins, as little as 1 ng/kg bw day_1 or even less, could contribute to a risk of liver cancer (SCF, 1994) 11-Link. Therefore the EU applied the ALARA principle in 1998 by adopting strict maximum levels at concentrations as low as reasonably achievable. Harmonised maximum levels for aflatoxins have been in place in the EU since 1 January 1999 and are laid down in the Annex, Section 2 of Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs (EFSA, 2007) 8-Link.
Aflatoxins exposure has been assessed in several countries and also EU level and no risk identified. In the first French TDS, dietary exposure of mycotoxins was evaluated and the estimated average intake of total aflatoxins in the French population was found to be 0.12 ng/kg bw for adults and 0.32 ng/kg bw for children per day. The proportion of individuals whose estimated intake >1 ng/kg bw per day total aflatoxins is estimated to be 0.01% for adults, 3.4% for children, and between 2.6 and 23% for vegetarians, who are the highest consumers of cereal products and dried fruits in the French population (Leblanc et al., 2005) 12-Link.
In the opinion of the EFSA Panel on Contaminants in the Food Chain (CONTAM) on a request from Comission related to the potential increase of consumer health risk by a possible increase of the existing maximum levels for aflatoxins in almonds, hazelnuts, pistachios and derived products, a total of 49,748 analytical results on occurrence of aflatoxins in various food commodities (almonds, Brazil nuts, baby food, pistachio, maize, other cereals, spices, figs, hazelnuts, peanuts, cashews, other nuts, other dried fruits, other foodstuffs) collected from 2000 to 2006 were examined. About %75 of the samples tested were free of the AFs or they were below the limit of detection or quantification. The mean AFB1 levels varied between 0.07 μg/kg for baby foods to 22.2 μg/kg for Brazil nuts. The CONTAM Panel concluded that, although a rare occurrence, the heterogeneous distribution of aflatoxins with occasionally very high values is a concern (EFSA, 2007) 8-Link.