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Modification of the Saturation Kinetics Model to Produce a More Versatile Protein Quality Assay^1,2,

Department of Food Science, University of Georgia Agricultural Experiment Station, Experiment, GA 30212

The saturation kinetics (SK) model relates response to nutrient (protein) intake in higher organisms by the equations: r = (bK_I + R_max Iⁿ)/(K_I + Iⁿ); where r is response and I is intake. Experimental data are fitted to this equation by iterative computer programs in which the intercept, b; a nutrition constant K_I; an asymptotic response value R_max; and an apparent kinetic order, n, are calculated. This model, unlike linear methods (PER, NPU) closely fits experimental data and predicts protein quality over a wide range of intake values. However, the SK model fails to converge to realistic values of R_max and K_I unless protein of a sufficient quality or concentration or both, to produce a distinct plateau is fed. Also, the model may fail to distinguish statistically between the qualities of proteins which are easily differentiated by linear methods. These problems are ameliorated by assigning predetermined values to b and R_max. When b was fixed as the mean response (body nitrogen) of rats fed protein-free diet, and R_max was assigned a value related to the maximum response of rats fed an excess of high quality protein (casein), reasonable and statistically different values of K_I and n were predicted for casein, peanut protein and wheat gluten.

KEY WORDS: • protein nutritional quality • modified saturation kinetics model

¹ This work was presented in part at the 66th Annual Meeting of the Federation of American Societies for Experimental Biology.

² Supported by State and Hatch funds allocated to the Georgia Agricultural Experiment Stations.

Manuscript received 4 September 1981.