COLONIC PROTEIN FERMENTATION AND PROMOTION OF COLON CARCINOGENESIS BYTHERMOLYZED CASEIN

Thermolyzed casein is known to promote the growth of aberrant crypt fo ci (ACF) and colon cancer when it is fed to rats that have been initia ted with azoxymethane. We speculated that the promotion was a conseque nce of increased colonic protein fermentation (i.e., that the thermoly sis of the casein decreases its digestibility, increases the amount of protein reaching the colon, and increases colonic protein fermentatio n and that the potentially toxic products of this fermentation promote colon carcinogenesis). We found that the thermolysis of casein reduce s its digestibility and increases colonic protein fermentation, as ass essed by fecal ammonium and urinary phenol, cresol, and indol-3-ol. Th ermolysis of two other proteins, soy and egg white protein, also incre ases colonic protein fermentation with increased fecal ammonia and uri nary phenols, and thermolysis of all three proteins increases the leve ls of ammonia and butyric, valeric, and i-valeric acids in the cecal c ontents. We found, however, that the increased protein fermentation ob served with thermolysis is not associated with promotion of colon carc inogenesis. With casein, the kinetics of protein fermentation with inc reasing thermolysis time are clearly different from the kinetics of pr omotion of ACF growth. The formation of the fermentation products was highest when the protein was thermolyzed for one hour, whereas promoti on was highest for protein that had been thermolyzed for two or more h ours. With soy and egg white, thermolysis increased colonic protein fe rmentation but did nor promote colon carcinogenesis. Thus, although th ermolysis of dietary casein increases colonic protein fermentation, pr oducts of this fermentation do not appear to be responsible for the pr omotion of colon carcinogenesis. Indeed, the results suggest that prot ein fermentation products do not play an important role in colon cance r promotion.