Combined effects of heat and rhamnolipids against Listeria monocytogenes: Influence of water activity and pH

Foodborne diseases remain a major public health concern, with Listeria monocytogenes being one of the most significant foodborne pathogens due to its high mortality rate and persistence in food-processing environments. This study evaluated the combined effects of heat, pH, and water activity on the antimicrobial activity of rhamnolipids (RL) against L. monocytogenes within the framework of hurdle technology. Treatments were performed at 62 °C for 10 min under different pH and water activity (a w ) conditions adjusted with NaCl or sucrose. Increasing NaCl concentrations reduced the efficacy of heat treatment alone; however, its combination with RL produced a synergistic effect, achieving reductions exceeding 5 log CFU/mL in low-a w media containing NaCl. In sucrose-containing media, the combined treatment reduced viable populations by 4–5 log CFU/mL across all pH and a w conditions evaluated. The hurdles also showed potential as a sanitizer formulation against L. monocytogenes attached to stainless steel surfaces, while scanning electron microscopy revealed extensive structural damage to treated cells. The combination of moderate heat and rhamnolipids exhibited synergistic antimicrobial activity under a range of pH and water activity conditions, representing a prospective strategy for controlling L. monocytogenes , particularly in low-water-activity foods with high salt or sugar contents.