The Possibility of Copper-Induced Oxidation of Milk in Stainless Steel-White Metal Systems

Samples of the first 30 gallons of milk through a white metal-stainless steel system were examined organoleptically and for Cu, Fe, and Ni contents and thiobarbituric acid values.Two components of the oxidized flavor that developed are described --one which followed the skimmilk fraction and the other which followed the cream phase.Editor.During recent years, oxidized flavors have become prevalent in both creamline and homogenized milks, during both summer and winter, in Iowa.A number of factors have contributed to greater incidence of oxidation in milk in Iowa: Adoption of milk ordinances have resulted in the production of lowercount milks; the industry has changed to every other day or three times per week delivery, causing the milk to be held for longer periods before delivery; and in-place cleaning practices have been adopted.During the period embracing these changes, milk-handling systems have in the main become combinations of stainless steel sanitary tubing (SSST) and white metal (WM) fittings.These systems seem to have been accepted without question.Copper dissolved from WM fittings in SS-WM systems might be a contributory factor causing oxidation in Iowa milk, particularly since Krukovsky and Guthrie (28) have indicated that 0.1 p.p.m.Cu in milk can cause tallowy flavors to develop in 24 hours at 0 to 5 ° C. if the milk has not been depleted of ascorbie acid.This study is a preliminary investigation to attempt to determine whether or not the above hypothesis has any validity. EXPERIMENTAL PROCEDURESMilk samples were obtained from the market milk plant of the Dairy Industry Department on.the same day each week during a I0-week period (April 5 through June 7, 1955) ; this period included samples produced during dry feed and pasture feeding periods.The milk was received in milk cans and was transported from the intake to the raw milk storage tank through an all SS system about 50 ft.in length