Growth potential of Listeria monocytogenes in traditional Austrian cooked-cured meat products

European Union legislation limits for Listeria monocytogenes in ready-to-eat foods are based on whether or not foods favour the multiplication of this bacterium. The latter is defined by criteria for water activity (aw), pH and shelf-life. We studied a peculiar group of traditional Austrian meats implicated in foodborne listeriosis made from cured cooked comminuted meat with gelatin/aspic (Presswurst), blood (Blutwurst) or fat as a binder (Leberpaté, Streichwurst, Zwiebelstreichwurst). Average pH values were 5.74 ± 0.45; 6.62 ± 0.31; 6.18 ± 0.36; 6.19 ± 0.15; 6.28 ± 0.04 for Presswurst (n = 15), Blutwurst (n = 15), Leberpaté (n = 10), Streichwurst (n = 18) and Zwiebelstreichwurst (n = 3), respectively. Corresponding aw values were: 0.968 ± 0.004; 0.965 ± 0.004; 0.961 ± 0.005; 0.963 ± 0.003 and 0.957 ± 0.005. There were no statistically significant differences of pH among spreadable meat products. Presswurst had significantly lower pH values, but a significantly higher level of lactic acid bacteria. With the exception of one low pH Presswurst sample, all foods under study would favour the growth of L. monocytogenes. In a 9 days challenge test, Blutwurst showed a strong potential for supporting L. monocytogenes growth (2.4–4.6 log). In contrast, Presswurst was not able to support growth in all temperatures tested. A pH vs. aw chart was designed delineating the growth/no-growth border (defined as 0.43 log increase over 216 h) at 2, 4 and 8 °C. For a given sample (i.e. a pH/aw data pair), it could be easily assessed if the product would likely be “safe” for 9 days at temperatures of <2 °C, 2–4 °C etc. by simply plotting the data point in the chart. Agreement of predicted bacterial growth and multiplication in food samples was studied in one Presswurst and three Blutwurst products. In our conservative approach, additional anti-listerial effects of lactic acid bacteria and food additives were not considered, but could be integrated, if desired. The usefulness of such a pH vs. aw chart for small businesses, the competent authority and for didactic purposes is discussed.