A Rapid Method for estimating Total Protein in Milk

Abstract

IN 1944, Fraenkel-Conrat and Cooper¹ determined the acid-binding capacities of several proteins by treating the protein with an excess of an anionic dye, orange G, at a pH of 2.2. The dye and protein react quantitatively to form an insoluble complex which can easily be separated either by centrifuging or filtering. (Ordinary filter paper binds a small amount of dye which must be accounted for to obtain accurate results.) From the concentration of unbound dye (measured colorimetrically), the binding capacity can be calculated. Using this method in principle in an investigation designed to determine the acid-binding capacities of several protein fractions derived from wheat flour, I² noted an unexpected uniformity in the binding capacity of mixtures of the two major fractions as obtained from each of several varieties of wheat. These two individual protein fractions have binding capacities differing by a factor of nearly two.