R. Pla

Inactivation of Listeria innocua Inoculated in Liquid Whole Egg by High Hydrostatic Pressure

The resistance of Listeria innocua, as a model microorganism for Listeria monocytogenes, to high hydrostatic pressure in liquid whole egg was studied at several pressures (300, 350, 400, and 450 MPa),temperatures (- 15, 2, and 20 degrees C), and times (5, 10, and 15 min). Listeria innocus was added to liquid whole egg at approximately 10(6) CFU/ml. Listeria innocua was not totally inactivated in any of the treatments. In general, reduction was better at 2 degrees than at room temperature, but the greatest inactivation was obtained at 450 MPa at 20 degrees C for 15 min (over 5 log of reduction), The results indicate that microbial inactivation was increased with prolonged exposure to pressure. D values for Listeria innocua were obtained at 400 MPa for two temperatures (2 and 20 degrees C), and different times (0 to 20 min). The microbial inactivation followed apparent first-order kinetics, exhibiting a decimal reduction time of 7.35 min at 2 degrees C and 8.23 min at 20 degrees C.

Combined effect of nisin and high hydrostatic pressure on destruction of Listeria innocua and Escherichia coli in liquid whole egg.

High hydrostatic pressure inactivation of Escherichia coli and Listeria innocua inoculated in liquid whole egg was improved significantly (P < 0.05) with nisin addition at concentrations of 1.25 and 5 mg/1. A reduction of almost 5 log10 units in E. coli counts and more than 6 log10 units for L. innocua was obtained at 450 MPa and 5 mg/l of nisin. For this treatment, the two microorganisms were not detectable after 1 month of storage at 4 degrees C. The amount of nisin added did not affect E. coli inactivation at 300 MPa. For L. innocua, 5 mg/l of nisin was more effective than 1.25 mg/l. Nisin showed no effect when samples were stored at 20 degrees C after pressurization, except for samples with L. innocua containing 5 mg/l of nisin and treated with 450 MPa.

Populations of Aerobic Mesophils and Inoculated E. coli during Storage of Fresh Goat's Milk Cheese Treated with High Pressure

Pasteurized goats milk inoculated with Escherichia coli 405 CECT was manufactured into cheese containing 108CFU/g. The fresh cheese was treated by combinations of pressure (400, 450, and 500 MPa), temperature (2, 10, and 25°C) and time (5, 10, and 15 min). Once treated, cheeses were stored at 2 to 4°C. Counts of surviving Escherichia coli and aerobic mesophilic bacteria were determined 1, 15, 30, and 60 days after treatment. No colonies of surviving E. coli were detected 1 day after pressurization, except in samples treated for 5 min at 25°C at pressures of 400 and 450 MPa. No surviving E. coli were detected at 15, 30, or 60 days in any case. Aerobic mesophilic bacteria counts after treatment were between 2 and 3 log CFU/g in most cases and only a slight increase during refrigerated storage could be detected in samples treated at 400 MPa.

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).

Revisión: Irradiación de alimentos.—aspectos generales/Review: Food irradiation.—General aspects:

Irradiation has been proposed for disinfestation, inhibition of sprouting, destruction of parasites in meat and fish, to delay maturation of fruit and pasteurization and sterilization. In some applications it could replace or supplement chemical preservatives; in other cases it may have unique advantages (dry or frozen foods). Generalizations about effects of irradiation may be misleading if the dose and commodities are not specified. Radioactivity cannot be induced in foods by treatment with approved sources. Toxicological and nutritional evaluation has confirmed the safety of irradiated foods at doses below 10 KGy. Food irradiation is limited by organoleptical changes; irradiation in the absence of oxygen and at the frozen state could reduce undesirable changes. Food irradiation is not a panacea for all food preservation; it cannot replace proper food sanitation, packaging, storage and preparation. The public and political debate of whether or not irradiation of foods should be permitted in the European Community has become a confused dialogue about the real consequences of food irradiation. Owing to the timeliness of the question, it is important to present and discuss the results of this research.

A survey on the microbiological quality of a semi-soft on-farm manufactured goat cheese

The microbiological quality of a sixty day ripened, on-farm manufactured, semi-soft, mixed coagulation cheese was evaluated. Samples from 42 cheeses were analysed for their aerobic mesophilic counts, lactic acid bacteria in three solid media (MRS Agar, M17 Agar and MSE Agar), yeasts and moulds, psychotrophs, Enterobacteriaceae, coliforms and faecal coliforms, coagulase-positive staphylococci, sulphite-reducing clostridia and Salmonella spp. The aerobic mesophile bacteria constituted the largest group of micro-organisms found. The largest number of lactic acid bacteria was obtained with MRS Agar; M17 Agar and MSE Agar gave similar counts although the latter was generally lower. The mean log cfu g−1 of psychrotrophic micro-organisms was 4·77 and for moulds and yeasts 4·30. Thirteen, 25 and 45·8% of the samples were found negative for enterobacteria, coliforms and coagulase-positive staphylococci, respectively. Sulphite-reducing clostridia, faecal coliforms and Salmonella was not detected. The mean pH of the samples was 4·07 ± 0·5.