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The Alpha-Naptholphthalein (ANP) Method for Measuring Fat Hydrolysis. I. Application to Butter¹

Department of Dairy Technology, The Ohio State University, Columbus

ABSTRACT

A rapid colorimetric method using -naphtholphthalein originally developed by Roberts et al. (6) has been modified to eliminate certain inherent weaknesses. For convenience, the modified procedure is designated as the ANP test.

The method may be applied to butter to give a roughly quantitative measure within an accuracy of 100 mg. per 100 g. fat of water-insoluble fatty acids below a concentration of 400 mg. acid per 100 g. of fat. With extra precautions greater accuracy may be achieved, since color changes may be detected with variations of 25 mg. water-insoluble acids at concentrations of less than 400 mg. per 100 g. fat.

The ANP method is not affected by the presence of butyric and lactic acids, but does measure caproic and higher fatty acids. The results indicate a close agreement between the ANP method and the WIA method of Hillig (4).

¹ Scientific article 7–51, Department of Dairy Technology, The Ohio State Univ. Financed in part by the Ohio Dairy Products Research Fund.