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.