Stability of Aflatoxin M in Milk

Abstract

This three-part study was designed to determine aflatoxin M recovery from pasteurized and/or stored cow's milk. (a) Aflatoxin M was added to samples of raw Holstein milk at a concentration of 2.0μg/liter. Half of each sample then was pasteurized at 63C for 30min, and both raw and pasteurized portions were stored at 4C up to 17 days. (b) Samples of raw milk, pasteurized (77C, 16s) skim milk, dry cottage cheese curd, and cottage cheese whey were taken from a commercial operation in an area in which natural contamination had been encountered. (c) Milk from a cow dosed with aflatoxin B1 was stored frozen (−18C) in bulk and in assay-size sample containers for 120 days. Aflatoxin M was recovered completely after either storage or pasteurization in (a) and (b). In (c), a recovery deficiency was detectable after 68 days of storage, which increased to 45% of the original value by 120 days. These observations differ from those of others in that loss of aflatoxin M was significant after pasteurization or storage of raw milk, totaling 87% loss after 120 days of frozen storage. Aflatoxin M partitioning between curd and whey in the preparation of cottage cheese agrees with more recent studies, but differs from previous reports. Three possible explanations for the differences are offered.