The Synergistic Effect of High Pressure and Nisin on the Inactivation of Heat-Resistant and Pathogenic Spores in Food Matrices
Résumé
[Technical Session 7 – Food Processing Technologies]Introduction: The high demand for minimally processed food makes high pressure processing (HPP) one of the most promising non-thermal technologies for food application. While HPP efficiently inactivates vegetative bacteria, bacterial spores show strong resistance, especially at mild temperatures. To ensure spore inactivation in food matrices, the addition of other hurdle(s), such as mild heat or antimicrobial agents, is necessary.Purpose: HPP in combination with nisin was investigated as a non-thermal method for the inactivation of pathogenic and thermoresistant bacterial spores in food matrices.Methods: Six bacterial strains were studied with regard to the diversity of their origins and properties: Bacillus pumilus, Bacillus sporothermodurans, Bacillus licheniformis, Bacillus weihenstephanensis, Bacillus subtilis and Clostridium sp. (botulinum type E-like). Spores were treated in a buffer, skim milk or a liquid medium simulating cooked ham. Pressure levels ranging from 200 MPa to 600 MPa were applied for 10 min at 20°C or 50°C. Nisin was added during and/or after HPP to a final concentrations of 50 or 20 UI/mL.Results: While no significant reduction of spore cultivability was observed at any pressure at 20 °C, the addition of nisin at low concentration (ten times lower than the legal concentration) during and after HPP treatment induced a highly synergistic effect on Bacillus spp. inactivation, with spore count below the detection limit (inactivation > 6 log/mL). Moreover, spores remained sensitive to nisin up to 6h after HPP.Significance: The food industry usually pressurizes foods at room temperature, resulting in, only, inactivation of vegetative cells. The present work shows that combining HPP with nisin can lead to a synergistic Bacillus spp. spore inactivation, even after treatments at 20°C. The addition of nisin in foods before their pressurization can, therefore, be an efficient way to ensure the inactivation of bacterial spores.