Abstract/Summary

This study explores the combined effect of different High Hydrostatic Pressures (HHP; 200–300 MPa) with various chitosan concentrations (up to 0.2%) on five Listeria monocytogenes strains and one of Escherichia coli, at temperatures 20 & 35 ◦C. Cells were resuspended in ACES buffer 1 h prior to HHP. A synergistic effect of chitosan and HHP was reported for first time in the above bacterial species tested. Synergistic effect up to 1 log reduction was observed at 300 MPa and chitosan at 20 ◦C against L.monocytogenes LO28 with FBR13 being the most sensitive strain at 250 MPa and 0.1% chitosan. Higher combined effect was found at 35 ◦C compared to 20 ◦C at 200 MPa highlighting for first time the significant role of temperature in the above synergistic action. Pressure and temperature had a greater impact on inactivation and synergism than chitosan concentrations. Synergistic effect (1 log reduction) was also observed in E. coli K12 at 0.1% chitosan and 200 MPa. Industrial relevance: This study presents the significance of combining HHP with natural antimicrobials to control L. monocytogenes and E. coli. Even though the technology is used for 3 decades in the food industry, its cost is still relatively high. Therefore, it is important to investigate novel ways to reduce the pressure intensity resulting in reduced costs, lower energy consumption and a broader product portfolio. This research demonstrates for first time the synergistic action of chitosan and HHP on L. monocytogenes and E. coli and the significant role of temperature that could contribute in the enhancement of the antimicrobial effect and optimization of the processing conditions. This aligns also with the growing demand for more sustainable and natural systems regarding the food production.