Salmonella survival during spray drying and subsequent handling of skimmilk powder. II. Effects of drying conditions.

Abstract The survival of Salmonella typhimurium, Salmonella thompson, Salmonella tennessee, and Salmonella kentucky inoculated into concentrated skimmilk and spray dried with various operating conditions was studied. While spray drying at commercial temperatures killed substantial numbers of Salmonella in skimmilk, in no case did it yield salmonella-free powder with the levels of contamination used. Survival of Salmonella decreased as spraydrying temperature was increased. With outlet air at 121.1C, log reductions were from 1.994 to 4.915 depending upon Salmonella strain. Milk droplet and dried particle size, controlled by varying feedatomizing pressure, had no significant effects on Salmonella survival. Similarly, level of contamination in milk before drying did not influence rate of Salmonella destruction during drying. Under all operating conditions, S. 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 simulating commercial instantizing. Salmonella contamination was introduced before and after spray drying. Significant reductions in Salmonella were not achieved by the heat of redrying.