Bioavailability of lysine in selected foods by rat growth assay

Lysine bioavailabilities in reference protein and 16 test protein diets were estimated using 10 day rat growth assays. A standard growth curve was obtained by feeding 5 diets containing casein, zein and synthetic amino acids ranging in total lysine concentration from 0.3 to 0.7%. Experimental foods were added to the basal diet at the expense of zein and/or synthetic amino acids to provide 2 specific lysine concentrations, i.e., 0.4 and 0.6%. Availabilities were established by comparing growth responses from the test food diets to the regression line of the standard growth data. Availabilities were over 88% for 13 of 16 products. Utilization was poor in pinto beans (73%), rice-wheat gluten cereal (70%), and skim milk powder heated to 100 degrees C for 12 h (66%). Addition of excess lysine (700 mg/100 g diet) to the pinto bean diet did not improve growth response; thus poor digestibility or some unidentified growth inhibitor is indicated.