Behavior of Aflatoxin M₁ in Yogurt, Buttermilk and Kefir

Yogurt, buttermilk and kefir were made from milk that was naturally contaminated with aflatoxin M₁ (AFM₁). Yogurt was made from skim milk alone or skim milk supplemented with 4% nonfat dry milk. The AFM₁ content of yogurt, regardless of formulation, appeared to vary during storage, but after 6 weeks at 7°C it was essentially at the same levels as in the initial milk. Buttermilk was made from skim milk and stored up to 2 weeks at 7°C. In the first 3 trials, the AFM₁ content appeared to increase after fermentation. This apparent increase remained through 4 d when these studies were stopped. In the second 3 trials, the apparent increase in AFM₁ did not occur after fermentation. In these trials, AFM₁ in buttermilk behaved as in yogurt; the apparent content was variable during holding, but AFM₁ remained stable through 2 weeks of refrigerated storage. Kefir was made from skim milk subjected to low-heat (64°C for 30 min) or high-heat pasteurization (84°C for 30 min). After fermentation, the apparent AFM₁ content of kefir decreased. During storage the AFM₁ content of kefir in 3 of 4 trials appeared to increase slightly, but in no instance did it return to original levels during or at the end of storage at 7°C.