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A Spectrophotometric Study of the Changes inPeroxide Value of Spray-Dried Whole Milk Powder during Storage

Department of Dairy Husbandry, University of Illinois, Urbana, Illinois

ABSTRACT

One-hundred gram samples of four different lots of powdered whole milk were stored at 35° and 100° F. for a period of one year. Half the samples were air-packed and the remainder were nitrogen-packed. Determinations were made periodically of the oxygen and carbon dioxide present in the headspace gas. Peroxide values were also measured and the reconstituted milk was judged for flavor. Summarized results follow:

1. The amount of carbon dioxide evolved during storage was not uniform, suggesting that this gas is reabsorbed to some extent by certain constituents of the milk. Higher carbon dioxide values were obtained on the samples stored at 100° F.
   
2. After twelve months storage there was approximately 2.7 times as much oxygen absorbed at 100° F. as at 35° F. in the air-packed samples. In the nitrogen-packed samples there was approximately 3.3 times as much oxygen absorbed at the higher storage temperature.
   
3. Most of the freshly packed samples showed some peroxide value though a number of these samples did not develop an oxidized flavor until after nine months of storage.
   
4. Although fluctuating peroxide values were obtained on the same lot of powder during storage, in general, maximum values were reached in 6 to 9 months, after which the trend was downward.
   
5. There was no correlation between peroxide value and either the temperature of storage or the method of packing the powder.
   
6. The flavor score of all samples decreased during storage but at a more rapid rate in the case of the air-packed samples and those samples held at 100° F.
   
7. Although peroxide formation in all samples was higher after 12 months of storage, the values were not sufficiently correlated with flavor scores to justify the use of the peroxide test as a means of measuring or predicting the keeping quality of whole milk powder.
   
8. Organoleptic tests remain the most accurate method of measuring changes that occur in flavor and odor of powdered whole milk during storage at either 35° F. or 100° F.