Oxidized Flavor in Milk: I. Effect of the Development of Oxidized Flavor on the Iodine Number of the Phospholipid Fraction of Milk

Oxidized flavor in milk and milk products is generally accepted to be the result of oxidation of one or more of the lipids present in milk.The oxidation of the unsaturated fatty acids present in butterfat was originally thought to be the source of oxidized flavor, but the evidence presented by certain workers shows that the phospholipids present in milk may play an important rSle.The work reported herein was undertaken to determine which of the lipid constituents in milk had undergone a change on the development of oxidized flavor.The oxidized flavored milk used in these experiments was obtained by the addition of copper in the form of copper sulfate solution.Unfortunately there was no milk available which would develop the off flavor spontaneously. REVIEW OF LIT~P~TUREThurston (13) states that three classes of milk must be recognized when oxidized flavor is studied.He suggests that the following names and classifications be used: 1, spontaneous milk--milk which will develop oxidized flavor without any added metallic catalyst; 2, susceptible milk--milk which requires the addition of copper or iron to cause the development of oxidized flavor; and 3, non-susceptible milk--milk in which oxidized flavor cannot be produced by the addition of a metallic catalyst.The above classifications will be used in this paper when referring to the different classes of milk.Evidence was presented by Thurston, Brown and Dustman (14) to indicate that the phospholipid fraction of milk rather than the butterfat was the substance which had undergone oxidation on the development of oxidized flavor.These workers found that the intensity of the oxidized flavor in cream, skimmilk, buttermilk and butter obtained from oxidized milk was in direct relation to their phospholipid content.Remade milk, in which washed cream from oxidized milk was incorporated into normal skimmilk, did not have an oxidized flavor.The addition of copper to remade milk in which butterfat from normal milk was used did not develop an oxidized flavor.Tallowy butterfat incorporated into skimmilk produced a milk having a flavor differing from the typical oxidized flavor.These findings would indicate that the phospholipids which are removed by washing the butterfat play an important rSle in the development of oxidized flavor.