Carvacrol and caprylic acid nanoemulsions as natural sanitizers for controlling Salmonella Enteritidis biofilms on stainless steel surfaces

Salmonella Enteritidis is a major foodborne pathogen that can form sanitizer tolerant biofilms in food processing environments leading to food contamination and subsequent human infections. Therefore, reducing pathogen biofilms in processing environments is critical for enhancing food safety. This study investigated the efficacy of two Generally Recognized as Safe status phytochemicals, Carvacrol (CR) and Caprylic acid (CA), in their nanoemulsion form, in inhibiting biofilm formation and inactivating mature S . Enteritidis biofilms on stainless-steel surface. Moreover, the effect of CR and CA on S . Enteritidis genes critical for biofilm formation was studied. CR nanoemulsion (CRNE) and CA nanoemulsion (CANE) were prepared with gum arabic and lecithin as emulsifiers. In biofilm inhibition assays, sub-inhibitory concentrations of CRNE (0.008 %) and CANE (0.01 %) reduced biofilm formation by 80 % and 70 %, respectively, when biofilms were developed at 25 °C for 24 and 48 h. The biofilm inhibition efficacy of CANE was greater than CA. In biofilm inactivation assays, bactericidal concentrations of CRNE (0.125 %) and CANE (0.2 %) reduced S. Enteritidis counts in mature biofilm (developed at 25 °C for 48 h) by 5.5 and 3.5 log CFU, respectively, within 1 min of treatment ( P < 0.05). Both CRNE and CANE were more effective than corresponding CR and CA treatments. Furthermore, CR and CA downregulated the expression of S . Enteritidis genes ( sipA, sipB, sipC, sopB, flhD, sdiA, csgA, csgD, sdiA ) critical for biofilm formation ( P < 0.05). Results suggest that CRNE and CANE could potentially be used as natural disinfectants for controlling S . Enteritidis biofilms on steel surfaces in food processing environments. • CRNE and CANE inhibited S. Enteritidis biofilm formation by 80 % and 70 %. • CRNE and CANE inactivated mature S. Enteritidis biofilms by more than 3.5 log CFU. • CR and CA reduced biofilm-associated gene expression in S. Enteritidis. • CRNE and CANE were more effective than their non-nanoemulsion counterparts. • CRNE and CANE showed potential as natural disinfectants in processing environments.