Inactivation of salmonella strains in acidified broth and raw egg yolk as a function of pH and acid type

Raw egg-based dishes present a safety risk when eggs of uncertain Salmonella status are used. Here, the inactivation of four Salmonella serovars at different combinations of acid, pH and temperature were investigated. Strains of egg or broiler-associated Salmonella serovars Enteritidis, Infantis, Typhimurium, and a heat resistant Senftenberg 775W were tested in broth and egg yolk. It was observed that although S. Senftenberg 775W survived better than its mutant lacking the loci of heat resistance, the wild type per se was not acid tolerant. For all strains, egg yolk acidification with vinegar to pH 3.9 and storage at 25 degrees C or 8 degrees C resulted in >4Log(cfu/mL) reductions within 2h or 24h, respectively. At pH 4.2, 2-3Log(cfu/mL) reductions were seen within 6h at 25 degrees C. In contrast, acidification with lemon juice to pH of 3.9 allowed for growth at 25 degrees C, while a pH of 2.9 ensured >4Log(cfu/mL) reductions within 24h. Egg yolk and acid form the basis for many recipes and with a ratio of 0.82 of vinegar (>= 5% acetic acid) to egg yolk or 1.23 of lemon juice to yolk and storage at 25 degrees C for 2h or 24h, respectively, a high degree of safety can be obtained, if properly chilled raw eggs are used.