Blood urea content for evaluating dietary protein quality

The protein quality of broad beans was evaluated by using three different methods: the net protein ratio (NPR), the net protein utilization (NPU) and the relative protein value (RPV). Casein was used as a reference protein. The relationship between the values obtained on rats by each method and serum urea concentrations were examined. Serum urea concentration increased by increasing the dietary protein content. It showed a positive correlation of 0.70 and 0.60 for broad beans and casein respectively. NPR values increased by decreasing the level of dietary protein. There was no relationship between the NPR and the serum urea contents in animals fed the casein and broad bean diets. The NPU values indicated that protein utilization was greatest at low dietary protein levels and decreases by increasing the protein content of diet. Serum urea concentration showed an inverse proportion with the NPU values. This was demonstrated by correlations of -0.67 and -0.75 for broad beans and casein respectively. The highest RPV for broad beans was obtained by using the change in body water and the lowest by using the change in body nitrogen as a response parameter. An inverse relationship exists between serum urea concentration and the RPV for broad beans.