Evaluation of recovery of fatty acids in milk by copper soap method

Measurement of copper soaps of free fatty acids is one of the most commonly used methods to estimate the extent of lipolysis in milk. Since short chain fatty acids have a strong flavor and odor, it is very important that any method for estimating hydrolytic lipolysis be sensitive to short chain fatty acids. To evaluate the efficiency of the copper soap method for measuring short chain fatty acids, known quantities of even chain length, saturated fatty acids from butyric through stearic and unsaturated oleic acid were added to milk.

The method of Shipe et al. (1980) was used to estimate the recovery of each fatty acid from the milk. A standard curve was developed using known quantities of each of the added fatty acids. Recovery was calculated using a regression equation for each standard curve to estimate the fatty acid concentration. The concentration of the control was accounted for. Recoveries of butyric and caproic acids were minimal regardless of the fatty acid used in the standard curve. The highest recoveries were for capric and lauric acids. Although this method was developed for long chain fatty acids, the highest recoveries were not for these. The copper soap method had the ability to measure long chain fatty acids in water, which meant that something in milk interfered with the recovery of long chain fatty acid. When palmitic acid was used as a standard, the total recoveries were slightly higher than when oleic acid was used as a standard.

The copper soap method could not be improved by changing the pH conditions or by changing the components of the solvents. The copper soap method does not precisely estimate all of the fatty acids resulting from hydrolysis of milk fat. However, it could be used to estimate some of the fatty acids responsible for lipolyzed flavor, but not all and should be used with caution as a routine quality control procedure.