Modified Copper Soap Solvent Extraction Method for Measuring Free Fatty Acids in Milk

Abstract

A modified Cu soap method was developed to provide a sensitive, rapid method for determining the free fatty acids in milk and estimating the intensity of lipolyzed flavor. The modification is simpler and more rapid than the original copper soap method. Only a small sample (.5 ml) of milk is needed for this colorimetric test, so it would be feasible to take aliquots from a universal sample. The method can be semiautomatic with an automatic sampler and spectrophotometer with a flow-through cell to test up to 200 samples/h. It would take approximately 2 days to run the equivalent number by the Bureau of Dairy Industry method. The coefficients of correlation between Cu soap measures and flavor for nonhomogenized and homogenized milk were 0.83 and 0.82. The corresponding coefficients between Bureau of Dairy Industry measures and flavor were 0.67 and 0.78. Correlation between Cu soap and Bureau of Dairy Industry meq/l for 124 nonhomogenized milk samples was 0.90. The corresponding correlation for 109 homogenized samples was 0.88. A comparison of nonhomogenzied and homogenized milk revealed that the availability of free fatty acids is less in homogenized milk. Fewer free fatty acids are recovered from homogenized milk by solvent extraction, and they have a lower sensory impact. Presumably some of the free fatty acids in homogenized milk are bound or entrapped.