A Colorimetric Method for Estimating the Quality of Butter.—A Preliminary Report

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Abstract
In presenting a test for the quality of butter, the authors realize that the quality of butter is a resultant of a number of characteristics some of which are not measurable by physical or chemical means. Therefore, the definitive evaluation of the quality of butter must perforce remain a matter of art and judgment. However, dealing with a system consisting prin- cipally of fat, it is to be expected that many of the changes that take place in butter would involve the fat component, and the present test is a quick and simple way of measuring the degree of hydrolysis of the fat of the butter. In a recent paper, Knaysi (2) has shown that the free bases of basic dyes are usually soluble in neutral fat, and that the color of certain dye bases is different from that of their soaps. Therefore, if the proper dye base be dis- solved in neutral fat, hydrolysis is immediately indicated by a shift in the color of the fat solution toward that of the soap, and the extent of the shift is a measure of the degree of hydrolysis. The reaction is that of simple neutralization : Dye base + Free fatty acid = Dye soap + water It is, therefore, to be expected, and it can be readily demonstrated, that a direct, simple proportion exists between the shift in the color of the fat solu- tion and the degree of hydrolysis. TECHNIQUE In this work, we made use of the base of neutral red which has been shown by I(naysi (3) to be quite stable and easy to prepare. It can be prepared from the aqueous solution of the dye salt by precipitation with sodium hydroxide. About 0.5 ml. of N Na0H are sufficient for complete precipita- tion from 50 ml. of solution containing 0.2 gin. of neutral red. The precipi- tate is filtered and washed with slightly alkaline distilled water of pH 7.5- 8.0. It is then dried and kept for use. It is only slightly soluble in water but dissolves readily in xylol and in neutral fat. Its xylol solution is orange yellow with a green fluorescence. In order to test the degree of hydrolysis of milkfat, a few grams of butter are placed in a clean test tube and melted at 60 ° to 70 ° C. The tubes are allowed to stand in the water bath until most of the coarse particles of casein and other non-fatty material have settled to the bottom of the tube. That

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