Propylparaben Sensitizes Heat-Resistant Salmonella Enteritidis and Salmonella Oranienburg to Thermal Inactivation in Liquid Egg Albumen

Propyl p-hydroxybenzoic acid (propylparaben [PRPA]) is a phenolic antioxidant, known to occur in nature and used as a microbiostat in foods, feeds, pharmaceuticals, cosmetics, and medications. The U.S. Department of Agriculture, Food Safety and Inspection Service (FSIS) requires that liquid egg white (LEW) be pasteurized at 56.7°C for 3.5 min. This study evaluated the effects of PRPA on the pasteurization sensitivity of Salmonella in LEW. When LEW (pH 7.8) was pasteurized under FSIS conditions, salmonellae declined by 0.5, 4.6, 4.5, > 7.0, and > 7.0 log CFU/ml, with 0, 125, 250, 500, or 1,000 ppm of PRPA, respectively, and D(56.7°C)-values were 2.99, 1.05, 0.68, 0.26 and ≤0.16 min. Albumen (pH 8.9) pasteurized under FSIS standards incurred salmonellae reductions of 3.3, 2.8, 5.2, > 7.0, and > 7.0 log CFU/ml, with 0, 125, 250, 500, or 1,000 ppm of PRPA, respectively, while D(56.7°C)-values were 0.87, 0.99, 0.66, 0.22, and 0.09 min. Adding 500 ppm of PRPA to albumen (pH 7.8) reduced D(56.7°C)-values more than 11-fold, and reduced the time to achieve a 5-log reduction from 15.0 to only 1.3 min. A 7-log reduction in plain LEW (pH 7.8) at 56.7°C required 20.9 min, versus only 1.8 and 1.1 min with 500 and 1,000 ppm of PRPA, respectively. Furthermore, a 7-log reduction in plain LEW (pH 8.9) required 6.1 min, versus only 1.5 and 0.6 min with 500 and 1,000 ppm of PRPA, respectively. This study is the first to report the efficacy of PRPA (pK(a) = 8.4) in sensitizing Salmonella in LEW to thermal pasteurization, while documenting that PRPA retains its antibacterial efficacy at pH levels as high as 8.9.