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A New Protein Quality Evaluation Index Based on Growth Responses of Rats

Department of Biochemistry, Schools of Medicine and Dentistry, Oral Roberts University, Tulsa, OK 74171

The protein efficiency ratio (PER) is the official method for protein quality evaluation in the United States and Canada. Two other widely used indices of evaluation are the slope ratio and net protein ratio (NPR) methods. Each of these methods has problems associated with its calculation and interpretation. In this paper, a new index, actual protein utilization (APU) is discussed, and its relationship to the other indices is examined. Each of the indices is given a theoretical basis by relating it to the four parameter mathematical model for physiological responses. To compare the indices, growth bioassays were carried out using male rats (40, 60, 115 g) consuming three different proteins (casein, lactalbumin and soy) and an amino acid mixture (Rogers and Harper). Dose-response curves were generated for each diet, and the indices PER, NPR, Slope and APU were calculated. APU was shown to have certain characteristics that make it superior to the other methods of protein quality evaluation, i.e., it closely approximates the growth response curve and it incorporates a term for the protein intake required for maintenance.

KEY WORDS: • protein • bioassay • biological value

Manuscript received 26 September 1983.