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Digestion and fermentation of proteins in rats fed keratin, albumin, cooked casein and antibiotics.

Dietary cooked casein promotes colon cancer in rats. We speculated and tested the hypothesis that cooking reduces the digestibility of casein, and increases the yield of bacterial metabolites, which are potential promoters of cancer. We investigated dietary means to manipulate nitrogen transfer and fermentation in the caecum. The caecal digestion of casein (cooked or not), keratin (hydrolysed or not) and bovine serum albumin (oxidized or not) was measured in rats. Protein fermentation was estimated by assaying caecal ammonia and branched-chain fatty acids. Keratin and cooked casein were digested to a very low extent, and were poorly fermented. Rats given cooked casein had 2-3 times more ammonia in their caecum than animals given the other proteins. Antibiotics (bacitracin, chlortetracycline, neomycin and spiramycin, at either 20 and 80 micrograms/ml water) decreased caecal ammonia in rats eating cooked casein, with spiramycin being most efficient. These data support the hypothesis given above, and provide ways to manipulate caecal ammonia.