J. Yuste

High-pressure processing applied to cooked sausages: bacterial populations during chilled storage.

Vacuum-packaged cooked sausages were pressurized at 500 MPa for 5 or 15 min at mild temperature (65 degrees C) and later stored at 2 and 8 degrees C for 18 weeks. Counts of aerobic mesophiles and psychrotrophs, lactic acid bacteria, enterobacteria, Baird-Parker microbiota, and Listeria spp. were determined 1 day and 3, 6, 9, 12, 15, and 18 weeks after treatment and compared with those of cooked sausages treated at 80 to 85 degrees C for 40 min. Pressurization generated reductions of about 4 log CFU/g in psychrotrophs and lactic acid bacteria. Enterobacteria and Listeria proved the most pressure sensitive; insignificant or no growth was detected throughout the study. Heat treatment inactivated psychrotrophs and enterobacteria similarly to pressure treatment. Listeria monocytogenes and enterotoxigenic Staphylococcus aureus were not found in treated samples. In general, there was no significant difference in counts of any bacterial populations either among treatments or between storage temperatures. High-pressure processing at mild temperature is an effective preservation method that can replace heat pasteurization applied to some cooked meat and poultry products after packaging.

Application of high-pressure processing and nisin to mechanically recovered poultry meat for microbial decontamination

Abstract The combined effect of high-pressure, nisin and acidification on the mesophilic and psychrotrophic microbiota of mechanically recovered poultry meat (MRPM) was evaluated. Nisin (0, 12.5, 100 and 200 ppm) and 1% of glucono-delta-lactone were added to MRPM. Samples were treated by combinations of pressure (350 and 450 MPa), time (5 and 15 min) and temperature (−20 and 20 °C). Both alone or in combination with nisin, pressurization at 20 °C was more lethal than that at −20 °C. The significantly highest decreases in counts occurred in samples with 200 ppm of nisin treated at 450 MPa: 5.3 log CFU/g for mesophiles and above 7.5 log CFU/g (nondetected growth) for psychrotrophs. So, this combined treatment can improve the safety and shelf-life of MRPM.

Listeria innocua and aerobic mesophiles during chill storage of inoculated mechanically recovered poultry meat treated with high hydrostatic pressure

Mechanically recovered poultry meat (MRPM) was inoculated with Listeria innocua 910 CECT at a level of approximately 10(8) CFU g(-1). Vacuum-packaged samples were treated by combinations of pressure (350, 400, 450 and 500 MPa), time (5, 10, 15 and 30 min) and temperature (2, 10 and 20°C) and later stored at 2°C for 2 months. Counts of L. innocua and aerobic mesophilic bacteria were determined 1, 4, 7, 15, 30 and 60 days after pressurisation. For mesophiles, in most treatments, pressurization at 2°C gave the significantly best results. High pressure caused a marked bactericidal effect on L. innocua: reductions higher than 7.5 log units were achieved in several cases. Some cells were just sublethally injured by pressure. Samples treated at 500 MPa for 30 min at 2°C had counts of only 2.3 log units after 60 days of chill storage. Noninoculated pressurised MRPM did not show Listeria growth throughout storage. These results suggest that high pressure processing can enhance the microbiological quality of MRPM.

Salmonella enteritidis and aerobic mesophiles in inoculated poultry sausages manufactured with high‐pressure processing

Salmonella enteritidis‐inoculated poultry sausages were pressurized at 500 MPa by combining different times (10 and 30 min) and temperatures (50, 60 and 70 °C) or heat treated with the same temperature–time combinations and a standard cooking (75 °C for 30 min). Counts of Salm. enteritidis and mesophilic bacteria were determined. Most pressure treatments generated statistically higher reductions than the corresponding heat treatments alone. Lethalities of about 7·5 and 6·5 log cfu g−1 for Salm. enteritidis and mesophiles, respectively, were found in pressurized sausages. There was no significant difference in counts between pressurization at 60 °C for 30 min or at 70 °C and the standard cooking. High‐pressure processing is a suitable alternative method in poultry sausage manufacture.

Pressure- vs. heat-induced bacterial stress in cooked poultry sausages: a preliminary study.

Vacuum‐packaged poultry cooked sausages were pressure‐treated at 500 MPa by combinations of time (5–45 min) and temperature (2–80 °C) and later stored at 6–8 °C for 12 we. Mesophile and psychrotrophe counts were determined 1 d, 3, 6, 9 and 12 we after treatment and compared with those of cooked sausages pasteurized at 80–85 °C for 40 min. Both pressure and heat treatments offer great possibilities for preservation. Sausages pressurized at 65 °C for 15 min showed mesophile numbers below 2 log cfu g−1 throughout the chill storage. Pressurization, unlike heat treatment, causes a reversible bacterial stress. Thus, injured cells recovered during storage and, at 6 and 12 we, after a temperature abuse (room temperature for approx. 24 h), counts increased up to 6.5–7.5 log units. Psychrotrophes were more sensitive to both treatments; no growth was detected the day after (a lethality of more than 4 log units).

Microbiological Aspects of High-Pressure Processing

Abstract High-pressure processing can be performed at room or lower temperatures, obtaining the inactivation of pathogenic and spoilage microorganisms. The presence of this technology in food industries is increasing and will be quite common in the near future. Pressure treatment can be performed at room or lower temperatures, resulting in foods with good nutritional and organoleptic qualities, great safety and long shelf-life. Furthermore, in recent years, studies are being conducted to combine the effect of high pressure with medium-high temperatures in order to obtain bacterial spore inactivation. Treatment conditions (pressure, time and temperature) influence the decrease in microbial counts. To be able to set these conditions is necessary to know in which sites the microorganisms are inactivated (cells walls, membranes, genetic mechanisms and key enzymes) and take into account the mechanisms of sublethal recuperation forms.

High Pressure Processing at Subzero Temperature: Effect on Spoilage Microbiota of Poultry

Mechanically recovered poultry meat (MRPM) was treated at 350 and 450 MPa for 5 and 15 min at m 20 °C and then stored at 2 °C. Counts of mesophilic, psychrotrophic and lactic acid bacteria were determined at 1, 4 and 15 days of storage. Initial counts were ca. 7 log CFU/g for the three populations. High pressure induced lethalities of ca. 1.5 log CFU/g for mesophiles and psychrotrophs and, in some cases, ca. 2.5 log CFU/g for lactic acid bacteria. At 4 days, counts in pressurized samples increased less for mesophiles and psychrotrophs ( h 0.5 CFU/g) than for lactic acid bacteria ( S 1 log CFU/g). At 15 days, counts of the three populations were ca. 9 log CFU/g in all samples. High pressure processing at subzero temperature does not extend shelf-life of MRPM.

Flow cytometry immunodetection and membrane integrity assessment of Escherichia coli O157:H7 in ready-to-eat pasta salad during refrigerated storage.

Over the past years, products of non-animal origin have been increasingly linked to foodborne diseases caused by the enterohemorrhagic pathogen Escherichia coli O157:H7. Contaminated fresh produce and derived ready-to-eat meals are of major concern, since no further or only minimal processing is applied. In this study, flow cytometry was evaluated as a rapid technique to detect E. coli O157:H7 by immunofluorescence, using polyclonal antibodies conjugated to R-phycoerythrin, in refrigerated ready-to-eat pasta salad containing acetic acid and benzoic acid. Signal filtering strategies were applied during sample analysis to reduce the limit of detection of the technique to 5 log CFU/g. Simultaneously with pathogen detection, physiological state was assessed by staining with the membrane integrity indicators propidium iodide and SYBR Green I. Fine tuning of dye concentrations and ratios allowed discrimination of not only cells with intact or damaged membranes, but also of cells with partially damaged membranes, which were considered injured cells. Then, changes in membrane integrity of inoculated E. coli O157:H7 cells were monitored throughout 14-day refrigerated storage. Most cells were injured at the beginning of refrigeration, but showed an intact membrane at the end. This suggests that injured E. coli O157:H7 cells underwent a membrane repair during exposure to refrigeration and acid stresses, and survived in ready-to-eat pasta salad. This highlights the importance of the implementation of control measures to limit the presence of this pathogen in non-animal origin food products. Additionally, the proposed immunodetection and membrane integrity three-color assay in food is a good tool to monitor the effect of a number of food-related treatments on E. coli O157:H7 cell membrane.

Chapter 5 – Microbiological Aspects of High-Pressure Processing

High-pressure processing can be performed at room or lower temperatures, obtaining the inactivation of pathogenic and spoilage microorganisms. The presence of this technology in food industries is increasing and will be quite common in the near future. Pressure treatment can be performed at room or lower temperatures, resulting in foods with good nutritional and organoleptic qualities, great safety and long shelf-life. Furthermore, in recent years, studies are being conducted to combine the effect of high pressure with medium-high temperatures in order to obtain bacterial spore inactivation. Treatment conditions (pressure, time and temperature) influence the decrease in microbial counts. To be able to set these conditions is necessary to know in which sites the microorganisms are inactivated (cells walls, membranes, genetic mechanisms and key enzymes) and take into account the mechanisms of sublethal recuperation forms.