Background: Evaluating the protein quality of food is of high importance for biological and economical reasons. To determine quality of proteins different biological, microbiological, chemical and combined methods have been presented and used. Among them NPR, RNPR, and PER are considered the most appropriate methods. Using these methods, this study was conducted on Soya products to evaluate the protein quality of Soya in 2003.

Materials and Methods: In an experimental study, 32 male Wistar rats, aged 21-23 days, were assigned to 4 groups (8 in each). Each group underwent a diet: Soya, wheat flour+Soya (10% protein), Casein+Methionine (10% protein), and no protein diet (as control). Period of study for NPR was 14 days. Protein intake and weight increased were determined for calculating NPR. Period of study for PER was 28 days. Protein intake and weight gains of animals were determined. NPR, RNPR, and PER were evaluated by t test.

Results: NPR for Soya and Casein+methionine groups were 3.65 ± 0.35 and 4.37 ± 0.48 respectively (p< 0.01). RNPR was 83. In wheat flour+soya group NPR was 2.7 ± 0.3 (P<0.001) and RNPR was 62.7. PER were 2.28 ± 0.35 and 3.04 ± 0.24 for soya and Casein+Methionine respectively (P<0.001) and Soya PER/Casein PER was 75. PER was 1.1 ± 0.1 for Wheat flour+soya (P<0.001).

Conclusion: Protein quality of Soya is lower than Casein+Methionine.