EXTENDED VALIDATION OF DYNAMIC IRREVERSIBLE THERMOPORATION: A NOVEL THERMAL PROCESS FOR MICROBIAL INACTIVATION

Abstract

A novel thermal treatment for microorganism inactivation, characterized by a very rapid temperature increase (up to 30C/s) and a low final temperature (up to 65C) maintained for a relatively short holding time, has been recently presented and tested by the authors, showing microbial load reduction greater than 5 log units against several common bacteria and yeasts. With the aim of extending the possible use of the new thermal treatment to a wider microorganisms class, in this work the dynamic irreversible thermoporation (DIT) treatment was further tested on a well-known thermoresistant strain, the Enterococcus hirae: The results of these new experimental tests confirmed the reliability of the process, which allowed to reach the 5 log microbial reduction once the adequate holding time was employed. The comparison with simple immersion in a thermostatic bath, where the very slow heating process with 0.3C/s has been performed, confirmed the crucial role of the thermal shock for the success of the treatment. The inactivation kinetics of E. hirae in isothermal conditions immediately after the application of thermal shock has also been studied. Finally, the morphological analysis performed by using a scanning electron microscope clearly revealed the rupture of the cell membrane, leading to identification of the process called dynamic irreversible thermoporation (DIT).