710. The determination of free fatty acids in milk

An extraction-titration method is described for the determination of free fatty acids in small samples of fresh milk.Recoveries of fatty acids added to milk ranged from 63% for butyric acid to 97% for stearic acid. For a composite sample approximating milk fat in fatty acid composition the recovery was 83%.Interference from citric and lactic acids was not significant for reasonably fresh samples.The method gives a higher recovery of the lower molecular weight fatty acids than is possible by earlier methods.For titrating very dilute solutions of fatty acids α-naphtholphthalein was shown to be a more accurate indicator than phenolphthalein; it also provides a better defined endpoint.