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Effect of Level of Protein Feeding upon Nutritional Value of Lysinefortified Bread Flour¹

Department of Food Technology, Massachusetts Institute of Technology, Cambridge

Four diets containing 8% wheat protein (70% extraction wheat flour) were supplemented with zero, 0.31, 0.62 and 2.48 gm of L-lysine·HCl per 100 gm. Four diets containing 15% wheat protein (8% wheat flour plus 7% wheat gluten) were supplemented with zero, 0.59, 1.18 and 4.72 gm of L-lysine·HCl per 100 gm. These 8 diets, plus two diets containing 8 and 15% egg albumin protein, were fed to weanling rats for 14 and 28 days. The carcasses and livers were then analyzed for content of water, fat, ash and nitrogen.

The lysine deficiency of the bread flour protein was overcome by including 0.31 and 1.18 gm of L-lysine·HCl per 100 gm of diets containing 8 and 15% wheat protein, respectively. The total lysine content of the protein in these diets was 5 and 7.8%, respectively.

When fed at the 8% level, lysine-fortified wheat protein was nutritionally inferior to egg albumin as measured by body weight increase, protein efficiency and carcass protein synthesis.

When fed at the 15% level, lysine-fortified wheat protein was nutritionally equal to egg albumin as measured by body weight increase and protein efficiency, but inferior in its ability to promote the synthesis of body protein. It is important to measure carcass protein synthesis when the nutritional values of proteins are evaluated.

The amount of carcass protein synthesized per gram of essential amino acids fed, whether as egg albumin or lysine-supplemented bread flour, was essentially the same. Thus the lysine-fortified bread flour protein was inferior in the rat because of dilution by glutamic acid and because of a poorer balance of essential amino acids.

Manuscript received 3 April 1958.