Estimation of the Relative Nutritive Value of Vegetable Proteins by Two Chemical Methods

A comparison was made between gain in weight per unit of supplementary protein as determined by Draper and Evans (’44) on ten samples of commercial soybean oil meal, two of cottonseed meal, and two of cull peas, and the chemical protein quality index (Almquist, Stokstad, and Halbrook, ’35). A comparison between the gain in weight of chicks per unit of protein and the per cent protein present as albumin, globulin, prolamine, glutelin, and residual protein was also made. The chemical protein quality index appeared to give good indication of the relative protein nutritive value of the vegetable protein concentrates studied with the exception of the overcooked soybean oil meals. A coefficient of correlation between the gain per unit of supplementary protein and the chemical protein quality index of + 0.946 was obtained for all of the concentrates studied except the three expeller process soybean oil meals. A high coefficient of correlation of + 0.928 between the gain per unit of supplementary protein and the per cent glutelin was obtained for the heat treated concentrates. A determination of the per cent glutelin may offer a chemical means of estimating differences in the protein nutritive value of soybean oil meals and, in combination with the per cent residual protein, the extent of heat denaturation of the soybean proteins.