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Study on factors (pH, water activity, salt content) affecting the growth of Listeria Monocytogenes in raw dried cured sausages

Keywords: L.monocytogenes , raw dried cured sausage , water activity , pH , salt

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Abstract:

Commission Regulation (EC) 2073:2005 considers the factors which can support or inhibit the growth of Listeria monocytogenesin ready-to-eat foods. The aim of the experiments was to examine the values of pH, water activity (aw), salt content and level of contamination with Listeria monocytogenes of some popular in Bulgaria raw dried cured vacuum packed sausages, produced from June 2006 till May 2008. 81 vacuum-packed samples were taken from 5 different meat producing plants during the period of study. Average water activity level of the tested sausages was 0,87 ± 0,035; pH level - 5,61 ± 0,59 and salt content - 4,12 ± 1,11%. Four specimens contained Listeria spp. (two samples L.monocytogenes, one L.welshimeri and one L.innocua). All contaminated raw dried cured sausages had aw bellow ≤ 0,92 and pH ≥ 4,4 or pH ≥ 5. After 3 months of storage of the same contaminated samples at 40C, in three of them Listeria spp. (two L.monocitogenes and L.welshimeri) survived and was detected. Salt content of the samples varied from 2,46 to 6,28% and was not able to affect the growth of L.monocytogenes.Data showed that the detected levels of aw could support the growth of L.monocytogenes in only 6 (7,4%) of the tested samples. pH values lower than 5 were presented in three samples and only the combination with low aw was able to inhibit the growth of L.monocytogenes. The detected levels of salt content did not affect the presence and growth of L.monocytogenes. ‘Microbiological criterion’ set in COMMISSION REGULATION (EC) No 2073/2005 for ready-to-eat foods unable to support the growth of L. monocytogenescan be applied to 75 (92,6%) of the tested sausages.

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