Intra-Species Response Variability of Listeria monocytogenes and Salmonella enterica to Lemon Essential Oils in Cheese- and Fish-Based Spreadable Foods

This study examined the growth dynamics of Salmonella enterica and Listeria monocytogenes in two food matrices, cheddar cheese sauce (CCS) and salmon spreadable paste (SSP), and assessed the antimicrobial efficacy of freshly extracted essential oils (EOs) from Citrus limon cv. Femminello Santa Teresa (FST) compared with commercial (COM) EOs. Sensory sniffing tests indicated that lemon EOs were unsuitable for bio-preserving CCS. SSP supported rapid growth of both pathogens, whereas CCS caused an immediate and progressive population decline, highlighting strong matrix-dependent effects mainly related to pH. When applied to SSP, FST EOs significantly modified microbial behaviour, showing bacteriostatic activity against S. enterica and a rapid, irreversible bactericidal effect against L. monocytogenes, with complete inactivation within 24 h and no regrowth. In contrast, COM EOs showed weaker antimicrobial activity, producing limited growth reductions. SSP exhibited high growth potential (δ > 0.5) for both pathogens, with intra-species variability. FST EOs eliminated L. monocytogenes growth, yielding strongly negative δ values, while Salmonella δ values remained > 0.5, indicating reduced yet persistent growth. Throughout the experiments, pH and water activity (aw) remained nearly unchanged after EO addition, confirming that inhibition depended on EO bioactivity rather than matrix modification. Overall, FST lemon EOs represent a promising preservation strategy for fish spreads.