title: [Nutritional quality of soybean proteins and casein, thermally damaged, and determined in vivo by an enzymatic method].
abstract: In this study, the potential of the hepatic activity of the enzyme nucleoside phosphorylase (E. C. 2.4.2.1) as an indicator of dietary protein quality was tested in chickens. For this purpose, a thermal damage of increasing severity was induced on the proteins of casein and soy by heating them in an autoclave (121 degrees C) for 10 to 40 minutes in the presence of glucose. These treatments resulted in variable losses of available lysine, measured chemically, and protein quality, measured by growth assays (PER and NPR) or assays based on nitrogen gained (NPU and nitrogen retained) with chickens. These measurements were then compared with the hepatic activity of the nucleoside phosphorylase measured in the same chicks. The data revealed that the NPU and nitrogen retained procedures were more sensitive than PER or NPR in detecting changes in the protein quality associated with a heat treatment. Moreover, NPU, nitrogen retained and the activity of nucleoside phosphorylase showed that a mild heat treatment of casein, improved the quality of this protein. More prolonged heat treatments, however, caused a reduction in the quality of soy or casein protein as determined by all the methods for measuring protein quality used here, including the enzymatic method. The high correlation coefficients found in this study between the enzymatic method and those based on nitrogen gain or growth, indicate that this method may have a potential as a predictor of the quality of dietary protein.
mesh_terms: D000818:Animals; D001835:Body Weight; D002364:Caseins; D002645:Chickens; D006358:Hot Temperature; D008099:Liver / Q000378:metabolism*; D009753:Nutritive Value; D010430:Pentosyltransferases / Q000378:metabolism*; D014674:Plant Proteins, Dietary; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*; D013025:Glycine max
chemical_list: D002364:Caseins; D014674:Plant Proteins, Dietary; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase
vernacular_title: Calidad nutricional de las proteínas de soya y caseina, dañadas térmicamente, y determinada in vivo por un método enzimático.