Viability of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in butter, yellow fat spreads, and margarine as affected by temperature and physical abuse

Survival and growth characteristics of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in six commercial butter, yellow fat spread, and margarine products that had been subjected to temperature and physical abuse were determined. Sweet cream whipped salted butter, sweet cream whipped unsalted butter, salted light butter, two yellow fat spreads, and light margarine were surface inoculated with pathogens to simulate incidental post-processing contamination. Products (31–78% fat, pH 4.05–6.40) at 4.4°C were then held at 37°C under high relative humidity (85%) for 1 h to induce condensation of water on the surface before storing at 4.4°C or 21°C for up to 21 days. All three pathogens grew between 1 and 2 days in sweet cream whipped salted butter (pH 6.40) stored at 21°C. L. monocytogenes began to grow between 7 and 14 days on the same product stored at 4.4°C. None of the pathogens grew on sweet cream whipped unsalted butter (pH 4.51), salted light butter (pH 4.58), yellow fat spreads (pH 4.05 and 5.37), or light margarine (pH 5.34) stored at 4.4 or 21°C for 21 days. Rates of inactivation of the three pathogens were more rapid in products stored at 21°C, compared to 4.4°C, and in products containing preservatives and acidulants. The adverse affects of acidic pH and preservatives presumably were amplified at 21°C compared to 4.4°C. In a second study, products at 37°C were physically abused by pummeling for 3 min in a stomacher before inoculating with pathogens and storing at 4.4°C or 21°C for up to 21 days. Salmonella, but not E. coli O157:H7 or L. monocytogenes, grew in sweet cream whipped salted butter at 21°C. None of the pathogens grew in the other five products stored at 21°C or in any of the six products stored at 4.4°C.