• L. monocytogenes survival was determined on brine-free green olives under refrigeration. • Long-term survival of the pathogen was observed in brine-free refrigerated green table olives. • Weilbull modelling revealed non-linear survival with increased resistance of adapted cells. • Survival was affected by olive cultivar, salt level, strain type, and stress adaptation. • Post-processing contamination of reduced-salt olives poses safety risks. The present study investigated the survival dynamics of Listeria monocytogenes after post-processing contamination of Spanish-style pitted green table olives packaged without brine and stored under aerobic refrigerated conditions (4 °C) to simulate a commercial scenario. Industrially fermented green olives of two commercially important Greek cultivars (Conservolea and Halkidiki), produced under high and low salt concentrations, were inoculated with two L. monocytogenes strains, namely a reference strain (NCTC 10527) and a food-derived strain (B133). In addition, the effect of prior bacterial adaptation to mild acidic (pH 5.5) and saline (1.5% NaCl) conditions was assessed. The population of the pathogen was monitored by direct enumeration and selective enrichment for up to 33 days, and survival kinetics were described using the Weibull primary inactivation model. The results demonstrated that the pathogen survived for extended periods on olives under all tested conditions, with persistence influenced by olive cultivar, salt concentration, strain origin, and stress adaptation. For instance, the strain B133 exhibited longer survival periods than the reference strain NCTC 10527, especially on high-salt cv. Conservolea pitted green table olives. Reduced salt content favored pathogen persistence in several treatments, while prior adaptation to mild acidic and saline stress enhanced survival, extending detection by selective enrichment up to 792 h ( ca. 33 days). Weibull modelling revealed non-linear survival patterns, with significantly higher scale and shape parameters for adapted cells, indicating increased survival of the pathogen. Overall, the findings demonstrate that Spanish-style pitted green table olives packaged without brine and stored under refrigerated conditions, may support long-term survival of the pathogen after post-processing contamination, especially in low-salt formulations and when stress-adapted strains are involved. These results underline the importance of strict hygienic control after fermentation and highlight potential food-safety risks with reduced-salt, ready-to-eat table olives.
Charmantzi et al. (Wed,) studied this question.