Effect of Polyphosphate and Sodium Chloride on the Growth of Listeria monocytogenes and Staphylococcus aureus in Ultra-High Temperature Milk

¹ Microbial Food Safely Research Unit, ARS, USDA, Eastern Regional Research Center, 600 East Mermaid Lane, Philadelphia, PA 19118

With UHT-sterilized milk as a model system, combinations of polyphosphate (.5 and 1.0%) and NaCl (.5 and 4.5%) were studied to determine their effects on the growth kinetics of Listeria monocytogenes Scott A and Staphylococcus aureus 196E. The milk was inoculated with 10³ to 10⁴ cfu/ml of either L. monocytogenes or S. aureus and incubated under aerobic conditions at 12, 19, 28, or 37°C. The addition of polyphosphate did not significantly inhibit the growth of either microbe at the temperatures studied, but the addition of NaCl or a combination of salts significantly inhibited growth. The addition of .5 or 1.0% polyphosphate alone to dairy products is not likely to affect substantially the growth of S. aureus or L. monocytogenes.

Key Words: sodium hexametaphosphate • ultra-high temperature milk • Listeria monocytogenes • Staphylococcus aureus

Submitted on April 19, 1993
Accepted on February 14, 1994