PROTEIN QUALITY OF FOODS. I. Evaluation of Biological and Biochemical Parameters for Protein Quality Assessment

Abstract

Biological and biochemical parameters were evaluated to assess protein quality. Some of the parameters are already well-established such as true digestibility, biological value and net protein utilization; others are still being used tentatively such as total urine nitrogen (Nt), urine urea nitrogen (Nu), ratio of Nu to Nt (nu/Nt), serum urea, serum total protein and liveweight gain; one was devised in the study which is the ratio of retained nitrogen to absorbed nitrogen (Nu/nt). The efficiency of the parameters to evaluate protein quality was studied by using egg albumin, a good quality protein, and zein, a poor quality protein. Both protein sources were incorporated in the diet at different levels. The parameters used gave a clear indication of the quality of the protein studied, although they were much affected by the protein level in the diet and the total protein intake. Standard protein level and protein intake are then suggested as necessary so that the parameters can be more efficiently used as protein quality evaluators.