Predictive modeling of the growth of Listeria monocytogenes in meat matrices containing sophorolipids produced by Starmerella bombicola.

Sophorolipids are microbial biosurfactants with antimicrobial properties and potential applications in food preservation. This study evaluated the in vitro antimicrobial activity of sophorolipids against Escherichia coli, Listeria monocytogenes, Salmonella spp. and Staphylococcus aureus, and their antilisterial capacity at different concentrations in beef broth, beef steak, beef meatballs and raw pork sausage stored at 8 °C, using challenge tests and predictive microbiological modeling. Sophorolipids were produced by Starmerella bombicola in submerged culture, recovered by liquid-liquid extraction, and characterized as acidic and lactonic congeners. Antimicrobial activity was confirmed, with concentrations causing 50% growth inhibition of 1.562 mg/mL for L.monocytogenes, 3.125 mg/mL for Salmonella sp. and S. aureus, and 12.5 mg/mL for E. coli. In meat-based broth, 0.12 mg/mL sophorolipids reduced the maximum growth rate of L.monocytogenes by approximately 50%. In meat matrices, growth rates ranged from 0.907 to 1.247 day-1 in beef steaks, 0.822 to 1.337 day-1 in meatballs, and 0 to 0.487 day-1 in raw pork sausages following sophorolipid treatment. Comparisons among matrices should consider the different analytical methods used to assess bacterial growth. Omnibus modeling showed that, in beef steaks, low concentrations (0-0.15 mg/cm2) decreased the maximum growth rate dose-dependently (p = 0.006), whereas higher concentrations (0.75-2.25 mg/cm2) reduced both maximum growth rate (p = 0.010) and population (p < 0.001). In meatballs, high concentrations reduced growth rate (p = 0.028), while very high doses (3.75-11.25 mg/g) extended the lag phase (p < 0.001). In pork sausage, 10-20 mg/g reduced growth, with a bacteriostatic effect at 20 mg/g.