The Importance of Aflatoxin Discrimination in Food Testing
Mycotoxins have been on the news during the last couple of years, but it was the aflatoxins’ case (a sub-group of mycotoxins) which drew the public’s attention. Highly toxic chemical compounds, excreted by specific fungi under specific circumstances, mycotoxins are considered to be a fluctuating phenomenon depending on each year’s climatic conditions and the matrix in which they are excreted. Aflatoxins have been an issue in food and feed since the 1970’s, but the first global effort to regulate them took place in 2003, when more than 100 countries began enforcing legislation on aflatoxins and some of the most potent mycotoxins. In 2006, the EU took a step forward by imposing the lowest limits the world had ever seen for all major mycotoxins, for all member countries.
There are four different chemical compounds characterized as aflatoxins, B1, B2, G1 and G2, known currently to man. Among these four compounds, one is more potent and most prevalent: aflatoxin B1. Whilst aflatoxins G1 and G2 are not metabolized, aflatoxins B1 and B2 are metabolized in the mammalian liver, into aflatoxins M1 and M2 respectively and can then be excreted into milk. According to the vast majority of research focused on aflatoxins worldwide, B1 naturally accounts for 70-95% of the aflatoxin total sum, depending on the matrices. Aflatoxin B1 is also considered to be far more toxic than the rest of the aflatoxins, even permeating through human skin. Aflatoxin B2 is far less abundant, representing 15% of aflatoxin total sum at most. Aflatoxin B1 therefore presents three important features which render it a primary target over the rest of the aflatoxins: potency, prevalence in nature and presence in milk, which justifies the regulation of only aflatoxin M1 in milk and not M2.
Taking these facts into account, it is important to therefore highlight that in instances where aflatoxin total sum is within the regulated limits, aflatoxin B1 may still easily be above legal limits. For example, a total sum reading of 3.8 ppb is below the limit, but aflatoxin B1 (naturally 70-95% of the total sum) would therefore be around 2.9 ppb which is above the 2 ppb limit. This is often the case in cereals and dried fruit and nuts.
In terms of aflatoxins more specifically, the EU brought forward complex legislation discriminating aflatoxin B1 from aflatoxin total sum. For infant food and animal feed, only aflatoxin B1 was regulated, whereas in all other categories both B1 and total were limited up to specific concentrations.
There is on-going global debate regarding the transfer of M1 in milk, in correlation to the B1 ingested. Most legislations consider 2-3% as a scientifically acceptable hydroxylation ratio, thus placing their limit for M1 at 500 ppt. On the other hand, the EU, Turkey and Iran, to be on the safe side, have placed the hydroxylation ratio at 10% while the B1 limit on feed for lactating animals is 5 ppb. By taking these two facts into account, they set the limit for milk at 50ppt (1% hydroxylation) in order to maximize food safety.
Concluding, it is arbitrary to check only for aflatoxin total, expecting that if results are below the limit, then the sample is safe for consumers. The more toxic and naturally abundant, aflatoxin B1 will probably be above the regulated limit. Therefore, it is necessary to test both aflatoxin B1 and aflatoxin total, regardless of whether the legislation obligates you to do so, or not.
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