Fate of Salmonella and Listeria monocytogenes in Commercial, Reduced-Calorie Mayonnaise

Two new varieties of commercial low-calorie mayonnaise, i.e., cholesterol-free, reduced-calorie (CFM) and reduced-calorie (RCM), made with different levels of acetic acid, were evaluated to determine the survival characteristics of Salmonella or Listeria monocytogenes . Two formulations of CFM, made with 0.3 or 0.7% acetic acid in the aqueous phase, and four formulations of RCM, made with 0.1, 0.3, 0.5, or 0.7% acetic acid in the aqueous phase, were evaluated. The initial pH of the products after equilibration ranged from 3.9 to 4.3, which was adjusted by addition of HCl. Products were inoculated with an eight- or six-strain mixture of Salmonella sp. or L. monocytogenes , respectively, at ca. 106 CFU per gram and held at 23.9°C for up to 2 weeks. L. monocytogenes survived longer than Salmonella in equivalent preparations of mayonnaise. No Salmonella (per 100 g) was detected at 48 h in either variety of mayonnaise made with 0.7% acetic acid in the aqueous phase. Salmonella levels in mayonnaise made with lower levels of acetic acid decreased during storage, and at 2 weeks the organism was not detectable in samples containing 0.3% acetic acid in the aqueous phase. No L. monocytogenes (per 100 g) was detected at 14 or 10 d postinoculation in CFM or RCM, respectively, made with 0.7% acetic acid in the aqueous phase. Results indicate these new varieties of mayonnaise, when formulated with 0.7% acetic acid in the aqueous phase, will inactivate >107 Salmonella and >104 L. monocytogenes per gram within the 72-h holding time required for regular mayonnaise made with unpasteurized eggs. Hence, properly acidified (pH