Antigenicity and nutritional value of selected milk proteins and their hydrolysate in growing rats

Two liquid diets containing selected milk proteins (SMP) or its small peptide hydrolysate (SPH) were fed to growing rats for 2 wk and the effects on growth, nitrogen balance, and small intestine adaptation were determined. Residual antigenicity of the SPH diet as measured by immunodot was reduced by 98.8%. Nitrogen intakes were not different. Weight gain was significantly higher in rats fed the SMP diet. In contrast, the absolute nitrogen balance was similar, suggesting that protein storage was identical with the two diets. A better nitrogen digestion-absorption rate with the SPH diet was observed as evidenced by the significantly increased fecal excretion with the SMP diet. Small intestine adaptation showed no difference between the two diets for mucosal weight, protein content/10 cm as well as for sucrase, glucoamylase, and N-aminopeptidase total activity/10 cm or specific activity (mU/mg protein). The DNA content of the mucosa/10 cm was significantly higher suggesting a mucosal hyperplasia in the SPH diet. The data suggest that in rats the SPH diet leads to nitrogen retention and small intestine adaptation similar to that of the SMP diet, despite better body weight gain by the latter.