In vivo rat assay for true protein digestibility and protein quality of beef and meat products extended with soy protein.

The protein quality of ten food products in including beef, bovine rumen and four meat products extended with soy proteins had been evaluated by rat feeding experiment; defatted freeze-dried whole egg served as a reference protein. Mean endogenous fecal and metabolic urinary nitrogen amounted to 1.01 and 1.11 mg/g food consumed, respectively. True protein digestibility and biological value of beef averaged 90.3% and 82.6%, respectively. The protein qualities of bovine rumen are quite similar to that of beef. Beef products extended with soy protein are quite inferior in their true protein digestibilities (81.4-84.6%) and biological value (68.8-76.0%) as compared to beef. The utilizable protein of extended meat fluctuated between 22.6-29.3% compared with a mean level of 70% in beef.