Background: E valuation of foods protein quality is of great importance for their biological and economical impacts. Different biological, microbiological, chemical and combined methods have been introduced and used to determine this item. Among these True Protein Digestibility ( TPD ) has been suggested as an appropriate method for the determination of protein quality. Considering the importance of protein quality in foods, especially in low income families, this study was designed to evaluate TPD of wheat flour and wheat flour mixture plus soy protein in comparison with casein standard protein in Kashan in 2003.

Materials and Methods: This e xperimental study was carried out on 32 male Wistar rats, aged 21 days under 4 regimens including wheat flour, and wheat flour plus soy protein as case group, casein+methionine (standard) and protein free (basal) diets in order to determine TPD. The period of study for TPD was 9 days. To calculate TPD, nitrogen intake and fecal nitrogen were determined and TPD of the group casein+methionine with wheat flour and wheat flour mixture plus soy protein were analyzed using t-test.

Results: TPD was 93.4 ± 2.3, 93.9 ± 3.6 and 80.3 ± 5.9 for casein+methionin, wheat flour and wheat flour mixture with soy (P<.0001) respectively. The values means of food intake were 19, 48.7, 28.3 and 45.4 for Protein free, casein+methionin, wheat flour and wheat flour mixture with soy respectively.

Conclusions: Wheat flour has an equal protein quality and wheat flour mixture with soy a lower quality in comparison with casein. In fact TPD of wheat flour mixed with soy can be improved by increasing soy protein values, arranging appropriate strategies in soy production technology and using better kinds of flour especially Semolina.