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Separation and Recombination as a Means of Deferring an Oxidized or Cardboard Flavor in Milk during Frozen Storage¹

Bureau of Dairy Industry, Agricultural Research Administration, U. S. D. A., Washington, D. C.

ABSTRACT

The development of an oxidized (cardboard) flavor in milk during frozen storage was deferred by separating the milk, pasteurizing and homogenizing the cream and mixing this cream with the pasteurized skimmilk. Best results were obtained when the temperature of the cream during homogenization was well above the melting point of the fat, the homogenizing pressure exceeded 1,500 lb. per square inch and the fat content of the cream was 25 to 30 per cent.

The increased flavor stability of this recombined milk was not sufficient to counteract the catalytic effect of 0.5 ppm. of added Cu.

Recombined milk prepared by mixing raw cream and raw skimmilk and then pasteurizing and homogenizing the mixture was more susceptible to the development of an oxidized flavor during frozen storage than the unseparated milk that was similarly pasteurized and homogenized.

The difference in susceptibility to the development of an oxidized flavor of the recombined milks prepared by these two methods was not due to a difference in content of lecithin and related substances because the milk was subjected to the same centrifugal forces during separation.

Low pressure homogenization of recombined milk made by mixing pasteurized and homogenized 25 to 30 per cent cream and pasteurized skimmilk, increased the susceptibility of the milk to the development of an oxidized flavor. As the pressure was increased the flavor stability of the milk increased until at 2,000 to 2,500 1b. it was no more likely to develop an oxidized flavor than was the same recombined milk before it was homogenized. At the same time, the body stability decreased and there was less tendency to form a cream plug.

¹ This work was done with funds from the Research and Marketing Act of 1946.