Interaction of pressure, time and temperature of pressurization on viability loss of Listeria innocua

In this study, the combined effectiveness of pressures of 137.9–344.7MPa, temperatures of 25–50°C and exposure times of 5–15min on Listeria innocua viability in peptone solution is examined. The results showed that under the study conditions only the combination of 344.7MPa, 50°C and 9.1min can reduce the viability of this species by 7 logs, with a z value of 173.1MPa.     

Inactivation of Alicyclobacillus acidoterrestris vegetative cells in model system,apple, orange and tomato juices by high hydrostatic pressure

The objective of this study is to determine the effect of high hydrostatic pressure (HHP) on inactivation of Alicyclobacillus acidoterrestris vegetative cells in a model system (BAM broth) and in orange, apple and tomato juices. The shelf-life stability of pressurized juices is also studied. In general the viability loss was enhanced significantly as the level of pressure and temperature were increased (P < 0.05). 4.70 log cycle reduction was obtained after pressurization at 350 MPa at 50 °C for 20 min in BAM broth whereas thermal treatment at 50 °C for 20 min caused only 1.13 log cycle inactivation showing the effectiveness of HHP treatment on inactivation. The D values for pressure (350 MPa at 50 °C) and temperature (50 °C) treatments were 4.37 and 18.86 min in BAM broth, respectively. All juices were inoculated with A. acidoterrestris cells to 10⁶ c.f.u./ml and were pressurized at 350 MPa at 50 °C for 20 min. More than 4 log cycle reduction was achieved in all juices studied immediately after pressurization. The pressurized juices were also stored up to 3 weeks at 30 °C and the viable cell numbers of A. acidoterrestris in orange, apple and tomato juices were 3.79, 2.59 and 2.27 log cycles, respectively after 3 weeks. This study has indicated that A. acidoterrestris vegetative cells can be killed by HHP at a predictable rate even at temperatures at which the microorganism would normally grow.     

Sister-chromatid exchange frequencies in postmenopausal hormone replacement patients

Our objective was to evaluate the frequency of sister-chromatid exchange (SCE) during hormone replacement therapy in postmenopausal women. Thirty-four asymptomatic postmenopausal women with a minimum 12 months since last menstrual period and surgical menopausal women were included in the study. Seventeen patients who were in spontaneous menopause were administered conjugated estrogen and medroxyprogesterone acetate (group A), and the others who were in surgical menopause were given 17beta-estradiol only (group B). Peripheral lymphocytes were obtained at the beginning and at the end of the third month of therapy. The mean age of the patients was 50. 67+/-4.79. There were statistically significant differences in terms of SCE frequencies between pre- and posttreatment levels of both groups (p<0.001 and p=0.003, respectively). It is likely that estrogens with or without progesterone have an effect in increased SCE frequency and this issue may be an evidence for the increased potential for malignancies.     

Efficiency of high pressure treatment for destruction of Listeria monocytogenes in fruit juices

The objective of this study was to compare high pressure resistance of Listeria monocytogenes strains at 25 degrees C and 50 degrees C at 350 MPa and to use high pressure (250 MPa and 350 MPa) at 30 degrees C and 40 degrees C for the inactivation of the relatively most pressure resistant strain inoculated in pasteurized apple, apricot, cherry and orange juices. L. monocytogenes CA was found to be the relatively most pressure resistant strain and increasing pressurization from 250 MPa to 350 MPa at 30 degrees C had an additional three to four log cycle reduction in viability, still leaving viable cells after 5 min. When 350 MPa at 40 degrees C for 5 min was applied more than eight log cycle reduction in cell population of all fruit juices was achieved. This study demonstrated that low temperature (40 degrees C) high pressure (350 MPa) treatment has the potential to inactivate relatively pressure resistant L. monocytogenes strains inoculated in different fruit juices within 5 min.     

Interaction of pressure,time and temperature of pressurization on viability loss of Listeria innocua

In this study, the combined effectiveness of pressures of 137.9–344.7MPa, temperatures of 25–50°C and exposure times of 5–15min on Listeria innocua viability in peptone solution is examined. The results showed that under the study conditions only the combination of 344.7MPa, 50°C and 9.1min can reduce the viability of this species by 7 logs, with a z value of 173.1MPa.     

A kinetic study on the plasmid stability of three <Emphasis Type="Italic">Lactococcus lactis</Emphasis> strains

Absract The plasmid stability of three wild type Lactococcus lactis strains and their mutants was investigated at different incubation time and temperatures in two different media [M17 broth and reconstituted skim milk (RSM)]. The results showed that both incubation times and temperature are effective on plasmid loss. The plasmid profiles of wild type strains exhibited 8 to 9 distinct plasmid species with molecular weights from 2.1 to 24.0 kb. Lactose fermentation ability was found to be encoded by 22.2 (strain U70), 23.6 (strain U29) and 24.0 (strain U52) kb plasmids in the wild type strains, respectively. The stabilities of the plasmids were explained by applying a second-order polynomial modeling system. Reasonable fittings were obtained for the model and the adjusted regression coefficients (R ² _adj) were between 0.76 and 0.99 for the overall data. Overall, it was found that incubation time had the most profound effect on plasmid stability, with plasmid loss occurring after 72 h, while temperatures in the range of 15–40°C also induced plasmid instability.     

Evaluation of Structural Changes Induced by High Hydrostatic Pressure in Leuconostoc mesenteroides

Scanning electron microcopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were used to evaluate structural changes in Leuconostoc mesenteroides cells as a function of high-hydrostatic-pressure treatment. This bacterium usually grows in chains of cells, which were increasingly dechained at elevated pressures. High-pressure treatments at 250 and 500 MPa also caused changes in the external surface and internal structure of cells. Dechaining and blister formation on the surface of cells increased with pressure, as observed in SEM micrographs. TEM studies showed that cytoplasmic components of the cells were affected by high-pressure treatment. DSC studies of whole cells showed increasing denaturation of ribosomes with pressure, in keeping with dense compacted regions in the cytoplasm of pressure-treated cells observed in TEM micrographs. Apparent reduction of intact ribosomes observed in DSC thermograms was related to the reduction in number of viable cells. The results indicate that inactivation of L. mesenteroides cells is mainly due to ribosomal denaturation observed as a reduction of the corresponding peak in DSC thermograms and condensed interior regions of cytoplasm in TEM micrographs.     

Sister chromatid exchange rate from pleural fluid cells in patients with malignant mesothelioma

This study assessed the impact of malignant mesothelioma on the frequencies of sister chromatid exchange (SCE) in the pleural effusion cells. Ten patients with mesothelioma and 20 control subjects were included in the study. The control subjects were the patients with tuberculosis pleurisy, and the remaining 10 subjects of control group were healthy volunteers and only heparinized blood samples were collected from these subjects. The pleural effusion cells were cultured with conventional culture methods. The samples were obtained from the patients after histopathologic confirmation of the malignancy but before the initiation of chemotherapy or radiotherapy. At the end of the culture period and 48 h prior the harvesting, BrdU was added into flasks. Totally, 100 metaphases were scored for each sample. In this study, we found that the SCE frequencies of malignant pleural mesotheliomas were significantly higher than the control subjects (P<0.001). Six of 10 patients came from central Anatolia, which is of great importance due to high rate of exposure to asbestosis in this region.     

Modeling the synergistic effect of high pressure and heat on inactivation kinetics of Listeria innocua: a preliminary study

The survival curves of Listeria innocua CDW47 by high hydrostatic pressure were obtained at four pressure levels (138, 207, 276, 345 MPa) and four temperatures (25, 35, 45, 50 degrees C) in peptone solution. Tailing was observed in the survival curves. Elevated temperatures and pressures substantially promoted the inactivation of L. innocua. A linear and two non-linear (Weibull and log-logistic) models were fitted to these data and the goodness of fit of these models were compared. Regression coefficients (R2), root mean square (RMSE), accuracy factor (Af) values and residual plots suggested that linear model, although it produced good fits for some pressure-temperature combinations, was not as appropriate as non-linear models to represent the data. The residual and correlation plots strongly suggested that among the non linear models studied the log-logistic model produced better fit to the data than the Weibull model. Such pressure-temperature inactivation models form the engineering basis for design, evaluation and optimization of high hydrostatic pressure processes as a new preservation technique.     

Evaluation of structural changes induced by high hydrostatic pressure in Leuconostoc mesenteroides

Scanning electron microcopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were used to evaluate structural changes in Leuconostoc mesenteroides cells as a function of high-hydrostatic-pressure treatment. This bacterium usually grows in chains of cells, which were increasingly dechained at elevated pressures. High-pressure treatments at 250 and 500 MPa also caused changes in the external surface and internal structure of cells. Dechaining and blister formation on the surface of cells increased with pressure, as observed in SEM micrographs. TEM studies showed that cytoplasmic components of the cells were affected by high-pressure treatment. DSC studies of whole cells showed increasing denaturation of ribosomes with pressure, in keeping with dense compacted regions in the cytoplasm of pressure-treated cells observed in TEM micrographs. Apparent reduction of intact ribosomes observed in DSC thermograms was related to the reduction in number of viable cells. The results indicate that inactivation of L. mesenteroides cells is mainly due to ribosomal denaturation observed as a reduction of the corresponding peak in DSC thermograms and condensed interior regions of cytoplasm in TEM micrographs.