Use of the Weibull model for lactococcal bacterlophage inactivation by high hydrostatic pressure

Four lactococcal bacteriophages (phi L16-2, phi L135-6, phi Ld66-36 and phi Ld67-42) in M17 broth were pressurized at 300 and 350 MPa at room temperature and their survival curves were determined at various time intervals. Tailing (monotonic upward concavity) was observed in all survival curves. The resulting non-linear semi-logarithmic survival curves were described by the Weibull model and goodness of fit of this model was investigated. Regression coefficients (R 2), root mean square error (RMSE), residual and correlation plots strongly suggested that Weibull model produced a better fit to the data than the traditional linear model. Hazard plots suggested that the Weibull model was fully appropriate for the data being analyzed. These results have confirmed that the Weibull model, which is mostly utilized to describe the inactivation of bacterial cells or spores by heat and pressure, could be successfully used in describing the lactococcal bacteriophage inactivation by high hydrostatic pressure

Modeling high pressure inactivation of Escherichia coli and Listeria innocua in whole milk

The survival curves of Escherichia coli and Listeria innocua inactivated by high hydrostatic pressure (HHP) were obtained at room temperature (∼22 °C) and at five pressure levels (400, 450, 500, 550 and 600 MPa) in whole milk. These curves were described by the Weibull model and parameters of this model were reduced from two to one with slight loss of goodness-of-fit. The logarithm of the time constant parameter (δ) of the reduced Weibull model was described with respect to high pressure (P). This approach can be used to define a z p value analogous to the modeling of the classical D value (increase in pressure that results in one log unit decrease of δ values). The development of accurate survival models under high pressure, as presented here, can be very beneficial to food industry for designing, evaluating and optimizing HHP processes as a new preservation technology

Multi-pulsed high hydrostatic pressure treatment for inactivation and injury of Escherichia coli

Escherichia coli cells in peptone water were pressurized at 300 MPa at ambient temperature with no holding time (pulse series) and with a total holding duration of 300 s for single- (300 s × 1 pulse) and multi-pulsed (150 s × 2 pulses, 100 s × 3 pulses, 75 s × 4 pulses, 60 s × 5 pulses, 50 s × 6 pulses and 30 s × 10 pulses) high hydrostatic pressure (HHP) treatments. Multi-pulsed HHP treatment with no holding time indicated that as the pulse number increased the number of inactivated and injured cells also increased. Holding time had significant effect on the inactivation of E. coli. There was low inactivation difference between single- and multi-pulsed HHP treatments with holding time. Escherichia coli cells showed at least 1.6 log10 more reduction on selective medium than the non-selective medium indicating that more than 95 % of the survivors severely injured for both single- and multi-pulsed treatments with holding time. Although the inactivation difference was low between single- and multi-pulsed HHP treatments, storage at 4 °C revealed that there was less recovery from injury for multi-pulsed HHP treatment