Synergistic effects of pressure, temperature, shear, and their interactions on Clostridium sporogenes PA3679 spore inactivation during ultra-shear processing

Ultra-shear technology (UST) is a semi-continuous high-pressure method for processing liquid foods. By pressurizing liquid foods up to 400 MPa and decompressing them through a shear valve, UST is designed for pasteurizing or sterilizing foods and modifying their structure and rheological characteristics. This study evaluated the lethal effects of pressure, holding time, temperature, shear, and their interactions for inactivating endospores of Clostridium sporogenes PA3679 suspended in pressure-stable 4-(2-hydroxyethyl)-1-piper-azineethanesulfonic acid (HEPES) buffer solution (0.1 M, pH 7.0, initial concentration = 6.3 log CFU/mL). Results indicated while thermal treatment at 105 degrees C did not have appreciable spore inactivation, isostatic treatment at 400 MPa and 105 degrees C for 5 min resulted in a 3.3-log inactivation. UST treatment at 400 MPa and 85 degrees C for 5 min, followed by 125 degrees C shear discharge resulted in 3.3-log reduction. Our analysis also revealed that thermal-pressure treatment history as well as their intensities also influence magnitude of spore reduction. This study revealed the sporicidal capability of UST and evaluated the relative importance of different lethal factors on spore inactivation.Industrial relevance: Ultra-shear technology (UST) is a novel processing method that has a potential to help produce value-added liquid foods, sauces, gels, and nanoemulsions, while helping to preserve the foods by inactivating undesirable microorganisms using the combination of pressure, shear, and temperature. This research provided an insight on the effects of key UST lethal factors on spores of C. sporogenes PA3679 for commercial sterilization validation. The results of this study could help the industry select the safe-harbor UST processing parameters for sterilizing food products in the future.