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 casei n, and increases the yield of bacterial metabolites, which are potenti al promoters of cancer. We investigated dietary means to manipulate ni trogen transfer and fermentation in the caecum. The caecal digestion o f 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 acid s. Keratin and cooked casein were digested to a very low extent, and w ere poorly fermented. Rats given cooked casein had 2-3 times more ammo nia in their caecum than animals given the other proteins. Antibiotics (bacitracin, chlortetracycline, neomycin and spiramycin, at either 20 and 80 mu g/ml water) decreased caecal ammonia in rats eating cooked casein, with spiramycin being most efficient. These data support the h ypothesis given above, and provide ways to manipulate caecal ammonia.