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Certain Factors Affecting the Phosphatase Test When Applied to Ice Cream¹

Kansas Agricultural Experiment Station, Manhattan, Kansas

ABSTRACT

A study has been completed to determine whether or not the phosphatase test can be satisfactorily used to determine the pasteurization efficiency of ice cream. Factors studied were: (1) ingredients, (2) vanilla flavors, (3) variations in the time and temperature of treatment, (4) contamination of pasteurized mix with raw products, (5) homogenization and freezing, and (6) storage of the frozen ice cream.

The more important results of this study may be summarized as follows:

1. Sugar in the mix was found to protect phosphatase against inactivation by heat when pasteurization temperatures of 142, 143.5 and 145° F. for 30 minutes respectively were used. Portions of these same mixes, but pasteurized without sugar, gave negative phosphatase reactions at these same temperatures.
   
2. When the pasteurization temperature was increased to 150° F. for 30 minutes negative phosphatase results were observed in all cases irrespective of the presence of sugar in the mix.
   
3. Certain vanilla flavors if used in excess were found to cause a significant increase in the phenol value of an ice cream mix.
   
4. The data show that the usual 30 minute holding period may be materially shortened before it would be detected by either the Gilcreas and Davis, or New York field phosphatase tests when ice cream mixes are pasteurized at 150° F. or higher.
   
5. It was possible with the Gilcreas and Davis test to detect the admixture of as little as 0.2 per cent added raw milk and cream to a sample of pasteurized mix.
   Seventy-five hundredths of one per cent added raw milk and cream could be detected with the original New York field test and with a modified technic it was possible to detect the presence of 0.3 per cent added raw products.
   
6. No differences were observed in the results of the phosphatase tests as a result of homogenization or freezing.
   
7. Samples of ice cream stored for two weeks in an ice cream cabinet (at approximately + 10° F.) and in an ice cream hardening room (at approximately –10° F.) showed no significant change in their phenol values.
   

¹ Contribution No. 126, Department of Dairy Husbandry, Kansas State College.