Aflatoxins are naturally occurring poisonous carcinogens as well as mutagens which grow in soil, decaying matter, hay and grains. They are a group of secondary metabolites produced by three species of Aspergillus, i.e. A. flavus, A. parasiticus and A. nomius. They can easily occur in staple commodities which lack proper storage like wheat, rice, millets, sorghum, sweetcorn, cottonseed and peanuts.
How Do Aflatoxins Occur in Milk?
The physical and biochemical conditions of Aspergillus highly affect the production of toxins. Aflatoxin B1 remains the most toxic as well as the predominant form of toxin present in crops, hay or silage. When ruminants like cattle, buffaloes, goats, etc consume aflatoxin B1 contaminated fodder, as a result of the metabolic process occurring in their liver, the aflatoxin M1 (AFM1) will be found in milk. Likewise, this leads to human exposure to such dangerous toxins.
Occurrence in Developed and Developing Countries
National estimates of dietary exposure to aflatoxins indicate that there remains a huge difference in dietary aflatoxin exposure in developing and developed countries. For instance, in developing countries average aflatoxin dietary exposures exceed 100 ng/kg body weight (BW)/day and in developed countries, the average value is less than 1ng/kg BW/day.
Estimates of dietary exposure to aflatoxin M1 (AFM1) have rarely exceeded 1ng/kg BW/day in any country however up to 6.5-8.8 ng/kg BW/day has also been reported for young children and breastfed infants. In India, as per the FSSAI study, the exposure to AFM1 from milk is 46 ng/day on average, but children bear higher exposure of 3.5 ng/kg BW/day as compared to adults which are 0.8 ng/kg BW/day. Since milk consumption is more in infants and children therefore they are at more risk. Exposure to contaminated milk can cause immune suppression, delayed development and stunted growth in them.
Dangers of Aflatoxins in Milk
Consumption of food containing aflatoxin concentrations of 1 mg/kg or higher has been suspected to cause aflatoxicosis, the prognosis of which consists of acute liver failure, liver cirrhosis, liver cancer, jaundice, lethargy and nausea, eventually leading to death, as per a World Health Organization (WHO) study in February 2018.
As per FSSAI standards, the permissible limit of aflatoxins in milk is 0.5 µg/kg. As per the survey report given by FSSAI October 18 2019, out of the 6,432 total milk samples, 368 (5.7 per cent) were found to have aflatoxins beyond permissible limits. The highest rates of aflatoxin contamination were found in Tamil Nadu (88 out of 551 samples), Delhi (38 out of 262 samples) and Kerala (37 out of 187 samples). The quite surprising fact that carcinogen contamination was more predominant in processed milk as compared to raw milk.
How to Detect Presence of Aflatoxins in Milk?
There are many methods commercially available to detect AFM1 in milk. However, solid-phase correction and immuno-affinity chromatography cartridges remain efficient techniques. Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) are adequate techniques to separate and determine AFM1 in milk. However, due to ease of usage and rapid screening. Enzyme-linked immune sorbent assay (ELISA) remains a more popular method. These methods are costly and employ unfriendly procedures to our environment. Therefore, there exists a huge scope in the development of eco-friendly techniques to determine aflatoxins.
Prevention and Control
In general, it can be understood that the prevention and control of fungal growth are very important to reduce the growth of AFM1 in milk.
There is a direct linear correlation between AFB1 in animals feed and quantity of AFM1 in their milk. Thus, to prevent aflatoxin contamination in milk dairy animals should be vaccinated against aflatoxins specially AFB1 regularly. Another method is to reduce the initial contamination of feed consumed by dairy animals. To ensure this, you should avoid the portions of crops which have damage. Temperature and moisture of storages should be controlled in such a way that they are not favourable for fungal growth.
The thermal treatment during the processing of milk is completely insufficient to reduce AFM1 in milk. The important fact is that thermal processing treatments like pasteurisation and sterilisation may be lethal to microorganisms but fail to eliminate aflatoxins.
Student, Maharana Pratap University of Agriculture and Technology
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