Photometric Milk Fat Determination

Abstract

The theoretical consideration and practical application of a photometric procedure for milk fat determination are presented. The interfering turbidity due to casein micelles is eliminated chemically by use of a calcium chelating agent. Coherent scattering is eliminated by a fivefold dilution of milk samples. Using a favorable wave length of light, in the visible range, turbidity is measured as a function of average globule size for the size range of fat in homogenized milk. The two characteristics of the milk fat emulsion which then remain unalterably to influence the total scattering are fat content and average globule size. Two independent photometric measurements are required to solve for the two variables simultaneously. The parallel transmitted and the total transmitted light through a thin layer of the prepared sample constitute two independently variable intensities. Mathematical development of the problem led to two linear equations from which a nomogram can be constructed to read both fat content and average particle size. From photometric readings on known samples, a nomogram was drawn and the two characteristics read for a number of commercial milk samples. The results agree well with the Babcock comparative values. Applicability of the present method to other dairy products is discussed. © 1959, American Dairy Science Association. All rights reserved.