Hydrolytic Rancidity in Milk. I. Surface Tension and Fat Acidity as Measures of Rancidity

Abstract

Summary On the basis of acid degree determinations applied to fat obtained from cream samples, it is concluded that fat acidity determinations are helpful in classifying cream as not or rancid, but they are of little value as a measure of the intensity of rancidity when compared with organoleptic evaluations as the standard. Rancidity in milk was estimated more conveniently by changes in surface tension than by fat acidity determinations. There was less overlapping of the surface tension ranges for the not and rancid classes of milk than of the acid degree ranges for the same classes of cream. Rancidity seldom was detected in samples with surface tensions above 46 dynes, but was evident in most samples with values below 45 dynes per centimeter. The results reported confirm that the fat percentage influences both the surface tension of milk and the surface tension at which rancidity can be detected organoleptically. Variations in procedures for sampling and treatment of samples may cause differences in surface tension and/or lipolysis.