Survival and growth of Listeria monocytogenes and Staphylococcus aureus in ready-to-eat Mediterranean vegetable salads: Impact of storage temperature and food matrix

Abstract

This study aimed to evaluate the survival or growth behavior of L. monocytogenes and S. aureus in ready-to-eat vegetable salads including Arabic salad (tomato-cucumber salad) with or without 0.5% (w/w) salt and 1% (v/w) lemon juice, tahini salad, coleslaw salad, toum sauce salad (aioli) stored at 4, 10, and 24 °C for 5 d. L. monocytogenes showed greater growth or survival in all types of salads at all temperatures tested. L. monocytogenes grew in Arabic salad without additives at 10 °C and tahini salad at 4 and 10 °C. L. monocytogenes survived all preparation and storage conditions used in the current study and its numbers were detectable in all types of salads tested, and with a maximum reduction of 3.0 log CFU/g, except for toum sauce salad at 24 °C, the cells were not detected using enrichment broth. In addition, S. aureus survived in Arabic salad with or without additives and in tahini salad with a maximum reduction of 2.3 log CFU/g. However, S. aureus numbers sharply decreased in coleslaw and toum sauce salad and at 5 d they reached undetectable levels (≥2 log CFU/g) in coleslaw at 24 °C and in toum sauce at 10 and 24 °C. Addition of lemon juice and salt to Arabic salad significantly reduced the numbers of both pathogens.

Keywords: Foodborne pathogens; Fresh cut vegetables; Fresh produce; Lemon juice; NaCl; Ready-to-eat food.