Milk Lipase System. I. Chemical Analysis of Fat, Washed Fat, and the Alcohol Soluble Fraction of Fat Obtained from Homogenized Raw Milk

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Abstract
Studies were conducted to ascertain the possibility of determining the specific fatty acids involved in lipase action in milk by applying chemical analyses (a) to milk fat before and after removing the fatty acids by alkaline washing and (b) to an extracted product obtained by treating milk fat with hot alcohol. Acid degree, Reichert-Meissl number, Polenske number, iodine number, and refractive index were used. Other than in acid degree, the chemical analysis of milk fat before and after the alkali washing did not reveal any distinct difference between non-rancid and rancid fat. The alcohol extraction method resulted in a fraction in which the free fatty acids were highly concentrated and which also contained a greatly increased proportion of the lower fatty acids in comparison to the original fat. However, the Reichert-Meissl, Polenske, and iodine numbers and the refractive index of the alcohol-soluble fraction were not sufficiently different between the rancid and non-rancid series to reveal any appreciable specificity of the lipase action for particular fatty acids. In the non-rancid series, the alcoholic extract (when compared to the original fat) exhibited a 2-fold increase in Reichert-Meissl number, a 2.3-fold increase in Polenske number, and a 9.4 increase in acid degree. In the rancid series, the acid degree, Reichert-Meissl, and the Polenske were greater in the extract than in the fat by 6.1-fold, 1.6-fold, and 1.9-fold, respectively. The limitations and possible interpretation of the results are presented briefly.