Studies on Milk Proteins. II. Colorimetric Determination of the Partial Hydrolysis of the Proteins in Milk

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Abstract
A method for measuring partial hydrolysis of milk proteins through colorimetric detn. of tyrosine and tryptophane is described. 5 ml. of milk are precipitated with 10 ml. of 0.72 N CC13COOH and filtered after standing 10 min. 5 ml. of the filtrate are made alkaline by addition of 10 ml. of a reagent containing 15% Na2CO3 and 2% Na polyphosphate (Quadrafos) after which 3 ml. of Folin and Ciocalteau''s diluted phenol reagent (diluted with 2 parts dist. water) is added. 5 min. is allowed for color development. The amt. of color is measured photoelectrically by determining transmission at 650 mu and the free tyrosine detd. by interpolation from a previously prepd. standard tyrosine curve. The degree of protein hydrolysis is proportional to the amt. of tyrosine liberated. The method is capable of detecting smaller amts. of hydrolysis than is possible by the classic N detn. techniques.

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