Abstract
The objective of this study was to investigate the inactivation mechanism of Bacillus subtilis spores by high pressure CO2 (HPCD) processing. The spores of B. subtilis were subjected to heat at 0.1 MPa or HPCD at 6.5-20 MPa, and 64-86°C for 0-120 min. The germination, the permeability of inner membrane (IM) and cortex, the release of pyridine-2, 6-dicarboxylic acid (DPA), and changes in the morphological and internal structures of spores were investigated. The HPCD-treated spores did not lose heat resistance and their DPA release was lower than the inactivation, suggesting that spores did not germinate during HPCD. The flow cytometry analysis suggested that the permeability of the IM and cortex of HPCD-treated spores was increased. Furthermore, the DPA of the HPCD-treated spores were released in parallel with their inactivation and the fluorescence photomicrographs showed that these treated spores were stained by propidium iodide, ensuring that the permeability of IM of spores was increased by HPCD. The scanning electron microscopy photomicrographs showed that spores were crushed into debris or exhibited a hollowness on the surface, and the transmission electron microscopy photomicrographs exhibited an enlarged core, ruptured and indistinguishable IM and a loss of core materials in the HPCD-treated spores, indicating that HPCD damaged the structures of the spores. These findings suggested that HPCD inactivated B. subtilis spores by directly damaging the structure of the spores, rather than inducing germination of the spores.
Highlights
Spores of a number of Bacillus and Clostridium species are extremely resistant to a variety of severe stresses including extreme temperatures, desiccation, chemicals and radiation because of their unique structures (Setlow, 1995, 2006)
As it is known that spores will lose heat resistance and release almost all the DPA after germination (Setlow, 2003; Yi and Setlow, 2010; Setlow et al, 2016), the loss of heat resistance and DPA release were used as indicators for spore germination (Shah et al, 2008; Setlow et al, 2016)
A previous report indicated that the germination of Bacillus cereus, Clostridium sporogenes, and Clostridium perfringens spores was inhibited completely by carbon dioxide at atmospheric pressure, 1.0 and 2.5 MPa, respectively (Enfors and Molin, 1978), and this inhibition of spore germination might be caused by low pH under the HPCD conditions
Summary
Spores of a number of Bacillus and Clostridium species are extremely resistant to a variety of severe stresses including extreme temperatures (steam at 121◦C), desiccation, chemicals and radiation because of their unique structures (Setlow, 1995, 2006) These spores are common agents of food spoilage, foodborne illnesses, and detrimental changes to the organoleptic quality of food (Brown, 2000; Logan, 2012), which make them a significant problem in the food industry. High temperature can effectively inactivate spores, it can impart undesirable organoleptic changes and cause some detrimental effects to the nutritional quality of heat-sensitive food. Nonthermal technologies such as irradiation, pulsed electric fields, pulsed magnetic fields, high hydrostatic pressure (HHP), and high pressure CO2 (HPCD), have been proposed as foodprocessing methods. The large investment cost due to the extremely high processing pressure and the non-continuous nature of the process hamper the industrial applications and commercialization of the HHP (Devlieghere et al, 2004; Estrada-Girón et al, 2005; Garcia-Gonzalez et al, 2007; Perrut, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
