Clay minerals as adsorbents of aflatoxin M1 from contaminated milk and effects on milk quality

The capacity of clays to remove or attenuate the contamination of aflatoxin M1 in bovine milk was studied, while considering the effects of these clays on the nutritional properties of the milk (in terms of protein, fat and lactose). To make the experimental results transferable to practical use, only clays available from the market were tested, and a very simple clay-milk interaction procedure was used. A preliminary test was developed to compare the adsorption behaviour of two clays, a kaolin and a bentonite, at variable clay-milk ratios and to trace the variations in the protein, fat and lactose contents. Then, only bentonites were selected for additional study.The detoxification capacity of the bentonites used was variable but still very efficient: contaminated bovine milk (up to approximately 80ng/L) was purified to safe levels (50ng/L for adults and 25ng/L for lactants) with moderate alteration of the nutritional properties of the milk. Moreover, the amount of bentonite residue in the purified milk was very low (0.4%). The kaolin was less adsorptive than the bentonite but still able to decrease the aflatoxin M1 within legal limits and was better at maintaining the nutritional properties of the milk. The protein is more sensitive to clay adsorption than are fat and lactose, and there was a decrease in protein in the treated milk with increases in the ratio of clay to milk.Among the studied samples, a saponite-rich bentonite showed the highest adsorbent capacity, in agreement with theoretical considerations regarding higher cell surface areas (available for AFM1) and higher surface hydrophobicity of saponite. Analyses of isothermal adsorption in water using the two more effective bentonites were also performed.The data collected indicate an effective and safe use of clays in the detoxification of milk (and dairy products) contaminated with aflatoxin M1.