Thymol and carvacrol in nanoliposomes: Characterization and a comparison with free counterparts against planktonic and glass-adhered Salmonella

Abstract

Nanoliposome-encapsulated and free thymol, carvacrol, and thymol/carvacrol (1:1) were assessed as antimicrobials against a Salmonella pool. Liposome-encapsulated thymol (TL), carvacrol (CL) and thymol/carvacrol (TCL) presented 230–270 nm diameter, satisfactory polydispersity (0.24–0.31), zeta potential of approximately −30 mV and high encapsulation efficiencies (~99%), remaining stable during 28 days at 4 °C. Minimum inhibitory concentrations (MIC) of free antimicrobials were 331 μg/mL. Encapsulation increased MIC to 663 (TL, CL) and 1325 μg/mL (TCL). Time-kill curves with antimicrobial preparations (265.0 μg/mL) demonstrated superior activities for free antimicrobials; among nanoliposomes, TCL exhibited higher activity. At MIC, antimicrobials impeded bacterial adhesion to glass. Without antimicrobials, Salmonella (~8 log Colony Forming Units (CFU)/mL) adhered to glass reaching 5.89 log CFU/cm2 after 15 min. Inactivation of glass-attached Salmonella was complete following 1-min treatments with free (MIC, 2 × MIC) or encapsulated (2 × MIC) antimicrobials. At MIC, antimicrobial-loaded nanoliposomes decreased adhered populations by ~3.9 log CFU/cm2; at 0.5 × MIC, reductions of 1.93 (CL) and 1.58 log CFU/cm2 (TCL) were observed. Free antimicrobials were more effective against planktonic and sessile Salmonella at contact times employed in food processing environments. Nanoliposome-encapsulated natural antimicrobials warrant investigations on surface disinfection schemes and incorporation into foods.