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.