In-situ monitoring of inactivation of Listeria innocua under high hydrostatic pressure using electrical conductivity measurement

Abstract

The effect of high hydrostatic pressure on electrical conductivity of samples of Listeria innocua ATCC 33090 bacterial suspension (~1010 CFU/ml) was investigated, to determine if its inactivation could be monitored via such measurements. HHP treatment was applied at 300, 400 and 500 MPa, and the electrical conductivity, temperature and pressure were continuously recorded during experiments. Microbiological concentrations were also monitored by plate-counting over a 60 min hold period. With increasing pressure the degree of cell damage increased resulting in higher final electrical conductivity and higher reduction in Listeria innocua CFU. The log reduction in bacterial counts increased with increasing conductivity ratio. Conductivity ratio increased during pressurization and holding, but did not change during depressurization, suggesting that little or no inactivation occurred during this phase. Data on conductivity ratio, calibrated against microbial count reduction could be used to fit to inactivation kinetics models. A log-linear model with tail was found to provide the best fit.