Lack of aberrant crypt promotion and of mutagenicity in extracts of cooked casein, a colon cancer-promoting food.

Dietary casein cooked at 180 degrees C promotes the growth of aberrant crypt foci and colon cancer in rats initiated with azoxymethane. We speculated that promotion was due to a product that could be extracted by a solvent, such as 5-hydroxymethyl-2-furaldehyde (HMF), with tumor- promoting activity or the carcinogenic heterocyclic aromatic amines (HAA). This hypothesis was tested by extracting cooked casein with solvents and water. The extracts were then 1) assayed by high-performance liquid chromatography for HMF and HAA, 2) measured for mutagenicity on a frame-shift-sensitive strain of Salmonella typhimurium, and 3) fed for 100 days to azoxymethane-initiated rats to test the promoting effect on aberrant crypt foci. Data show that 1) no HMF or HAA was detected in cooked casein, 2) no mutagenicity was detected on strain TA98, with or without metabolic activation, and 3) promotion was not associated with the extracts but with the cooked casein residue. Therefore the promotion by cooked casein would not appear to be associated with a product that can be extracted by solvents.