Four batches of stirred-curd Cheddar cheese were prepared, using milk which was naturally contaminated with aflatoxin M1. This cheese was analyzed for aflatoxin M1 content at intervals while the cheese ripened for about 1 year. Levels of aflatoxin M1 detected in cheese started low, increased and then leveled off for the remainder of the ripening period. This cheese was used to make process cheese spread. The spread appeared to contain as much or more aflatoxin M1 as the cheese from which it was made. The aflatoxin M1 content of cheese spread appeared to increase, and then return to near original levels during storage at 7°C. Contaminated Cheddar cheese was treated with heat (90°C for 20 min), emulsifying salt (5% Na2HPO4) or both to determine the influence of processing conditions on aflatoxin M1. Samples treated with emulsifying salt or heat showed an increase in aflatoxin M1 content but not as much as when samples were treated with both. The apparent increased in aflatoxin M1 content in natural cheese and in process cheese spread may be associated with greater recovery of toxin by the analytical method as cheese ripens or is treated to make the process cheese spread.

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