Salmonella Survival During Spray Drying and Subsequent Handling of Skimmilk Powder. II. Effects of Drying Conditions

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Abstract
The survival of Halmonella typhimur- ium, SalmoneUa thompson, Salmonella ten- nessee, and Salmonella kentucky inocu- lated into concentrated skimmilk and spray dried with various operating conditions was studied. While spray drying at com- mercial temperatures killed substantial numbers of Salmor~eUa in sk~mmilk, in no case did it yield salmonella-free powder with the levels of contamination used. Survival of Salmonella decreased as spray- drying temperature was increased. With outlet air at 121.1 C, log reductions were from 1.994 to 4.915 depending upon Sal- monella strain. Milk droplet and dried particle size, controlled by varying feed- atomizing pressure, had no significant effects ou Salmonella survival. Similarly, level of contamination in milk before dry- ing did not influence rate of Salmonella destruction during drying. Under all oper- ating conditions, ~Y. tennessee was much more resistant to spray drying than the three other strains and, in most instances, this amounted to population decreases of 2 to 3 log cycles less than with the other strains. Contaminated milk powders also were agglomerated and redried by simu- lating commercial instantizing. Salmonella contamination was introduced before and after spray drying. Significant reductions in Salmonella were not achieved by the heat of redrying.