Effect of Water of Hydration on the Measurement of the Protein Efficiency Ratio of Casein and Soybean Protein with Rats

Abstract
The hydration of soybean protein or casein prior to mixing of the diet improves the apparent protein efficiency ratio (PER). The PER of soybean protein was improved more than that of casein, so that an increase in adjusted PER of soybean protein was observed also. The improvement did not appear to be associated with digestibility. It is theorized that some diets with dry protein isolates may be less acceptable to the rat due to the dusty nature of the isolate. Consequently, diets with such isolates may have a lower PER. The effect can be overcome by hydrating the protein isolates prior to mixing the diet.