Soo Rin Kim

Analysis of survival rates and cellular fatty acid profiles of Listeria monocytogenes treated with supercritical carbon dioxide under the influence of cosolvents

In the present study, we identified several process variables that significantly affect the efficiency of supercritical carbon dioxide inactivation of the food-borne pathogen Listeria monocytogenes. Treatment with SC-CO(2) completely disabled the colony-forming activity of the cells (8-log reduction) within specific treatment time (10-50 min), pressure (80-150 bar), and temperature ranges (35-45 degrees C). Microorganism inactivation rates increased proportionally with pressure and temperature, but the inactivation rate decreased significantly when cells were suspended in phosphate-buffered saline rather than in physiological saline. Additionally, when the microbial cell suspension was 80-100% (w/w) of water, the SC-CO(2)-mediated reduction in CFU ml(-1) was 4-8 log higher at the same treatment conditions than in typical cell suspensions (a water content of 800-4000% [w/w]) or dry preparations that had only 2-10% (w/w) of water. The addition of a fatty acid, oleic acid, decreased the effectiveness of the microbial inactivation by SC-CO(2), but the addition of a surfactant, sucrose monolaurate, increased the effectiveness. Therefore, cosolvents for SC-CO(2), including water, a fatty acid, and a surfactant in this study, were found to greatly influence on the inactivation effectiveness. The extraction of cellular substances, such as nucleic acid- and protein-like materials and fatty acids, was monitored by spectrophotometry and GC/MS and increased with SC-CO(2) treatment time. Additionally, using scanning and transmission electron microscopies, we investigated morphological changes in the SC-CO(2)-treated cells. The effects of the variables we have described herein represent a significant contribution to our current knowledge of this method of inactivating food-borne pathogens.

Fatty acid profiling and proteomic analysis of Salmonella enterica serotype Typhimurium inactivated with supercritical carbon dioxide

Non-thermal sterilization and microbial inactivation processes are currently receiving much attention in food and pharmaceutical industries. In particular, since supercritical carbon dioxide (SC-CO2) treatment, which is conducted at relatively low temperatures, is considered to be a promising alternative method to replace thermal sterilization processes that cannot be safely used in foods and bioactive materials. Although SC-CO2 has been applied to many microorganisms, the inactivation of microbial cells by SC-CO2 has only been evaluated by using a conventional viable cell count such as a plating method, by which it is not possible to systematically elucidate the microbial cell inactivation process. Therefore, in this study the physiological status of SC-CO2 treated Salmonella enterica serotype Typhimurium was analyzed by using GC-MS analysis of fatty acids with principal component analysis and two-dimensional electrophoresis for protein profiling. From the results of these systemic analyses, it was revealed that SC-CO2 caused significant alterations to the profiles of fatty acids and proteins of the cells.