Growth of Escherichia coli and Salmonella typhimurium on Beef Tissue at 25°C

At 25°C, growth of Escherichia coli and Salmonella typhimurium on beef was influenced by type of tissue, pH, gaseous atmosphere, and physiological state of the cells used to inoculate the tissue. These organisms grew after only a short lag period, both aerobically and anaerobically, on beef fatty-tissue, and on high pH muscle (pH ≥ 6). The lag period was considerably extended on low pH muscle (pH ≤ 5.7) incubated aerobically. On low pH lean tissue stored anaerobically at 25°C for 24 hr, cells from aerobically grown broth cultures did not grow whereas cells from anaerobically grown cultures grew after an extended lag. These results suggest that during the cooling of hot-boned meat growth of E. coli and salmonellae is more likely on fatty tissue or muscle of high pH than on lean tissue of low pH.     

Fabricated Beef Product: Effect of Handling Conditions on Microbiological, Chemical, and Sensory Properties

Total microbial count was not adversely affected by lowering the holding temperature of fabricated beef roast from 60°C to 54°C or by 12 hr holding time. If a reduction in holding temperature is anticipated, then initial roast contamination and sanitation of the food facility are of critical importance. A stabilizing period of 20 min at room temperature (～23°C) did not decrease yield, but caused a slight lowering of sensory scores. Tenderness was more acceptable in product held at 54°C compared to 60°C. In general, all sensory evaluation ratings were slightly lower with increased holding time.     

Oscillatory Compared with Continuous High Pressure Sterilization on Bacillus stearothermophilus Spores

TO ESTABLISH a sterilization method with minimal heating, the effect of high pressure on bacteriostasis was studied using thermoduric spores of Bacillus stearothermophilus. After exposure to 800 MPa for 60 min at 60°C, the spore count decreased from 10⁶ to 10²/mL. However, exposure to the same pressure at room temperature did not cause significant change in spore numbers. The synergistic effect of high pressurization on the bacteriostatic action of sucrose fatty acid ester at low concentration (< 10 ppm) was pronounced with sucrose palmitic acid ester but not with sucrose stearic acid ester. Oscillatory pressurization was more effective for spore sterilization. Six cycles oscillation of 5-min pressurization with 400 MPa at 70°C decreased the spore count from 10⁶ to 10²/mL, and with 600 MPa, complete sterilization was achieved.     

Some Effects on the Mechanical Properties of Meat Produced by Cooking at Temperatures between 50° and 60°C

Peak force (PF) shear values obtained for stretched muscles from beef animals of three ages (2–3 months, 2–6 year and 12–17 years) decreased when heated for 1 hr at temperatures above 50°, 55° and 60°C respectively. PF values obtained for veal muscles were unaffected by heating at 50°C for up to 8 hr but rapidly decreased with increased time of heating at 55° or 60°C. The decrease in shear values with heating time was still evident after the connective tissue contribution was eliminated by a further cook at 80°C. Samples from the oldest animals required 24–48 hr at 60°C to produce a large decrease in the connective tissue contribution. Tenderization by prolonged cooking at 50–60°C was achieved by accelerated aging of the myofibrillar structure and, at ≥ 55°C, by a weakening of the collagenous connective tissue also.     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

Bacterial Histamine Production as a Function of Temperature and Time of Incubation

Optimal temperature, lower temperature limit, extent, and rate of histamine production in a tuna fish infusion broth (TFIB) varied for the strains of Proteus morganii, Klebsiella pneumoniae, Hafnia alvei, Citrobacter freundii, and Escherichia coli studied. P. morganii and K. pneumoniae produced large quantities of histamine in a relatively short incubation period (<24 hr) at 15°C, 30°C, and 37°C; production was fastest at 37°C. H. alvei, C. freundii, and E. coli produced toxicologically significant levels of histamine (>2500 nmoles/ml) only at 30°C and 37°C on prolonged incubation (≥48 hr). At 72 hr of incubation, optimal temperature for histamine production was 37°C for E. coli and C freundii; 30°C for P. morganii strain 110SC2, K. pneumoniae, and H. alvei; and 15°C for P. morganii strain JM. The lower temperature limits for production of toxicologically significant levels of histamine in TFIB were 7°C for K. pneumoniae; 15°C for both P. morganii strains; and 30°C for H. alvei, C. freundii, and E. coli.     

Thermal Inactivation of Escherichia coli O157:H7 in Strawberry Puree and Its Effect on Anthocyanins and Color

Raw whole strawberries, if contaminated with pathogens, such as Escherichia coli O157:H7, must be pasteurized prior to consumption. Therefore, the objective of this research was to investigate the thermal inactivation kinetics of E. coli O157:H7 in strawberry puree (SP), and evaluate the changes in anthocyanins and color, and the survival of yeasts and molds (YM) after thermal processing. Inoculated with a 5‐strain cocktail, fresh SP, with or without added sugar (20 and 40 °Brix), was heated at 50, 52, 54, 57.5, 60, and 62.5 °C to determine the thermal resistance of E. coli O157:H7. In raw SP, the average D‐values of E. coli O157:H7 were 909.1, 454.6, 212.8, 46.1, and 20.2 s at 50, 52, 54, 57.5, and 60 °C, respectively, with a z‐value of 5.9 °C. While linearly decreasing with temperature, the log D‐values of E. coli O157:H7 increased slightly with sugar concentration. The log degradation rates of anthocyanins increased linearly with temperature, but decreased slightly with sugar concentrations. These results suggest that sugar may provide some protection to both E. coli O157: H7 and anthocyanins in SP. The browning index was not affected by heating at 50 and 52 ºC at low sugar concentrations, but increased by an average of 1.28%, 2.21%, and 10.1% per min when SP was exposed to heating at 54, 57.5, and 60 °C, respectively. YM was also inactivated by heating. This study demonstrated that properly designed thermal processes can effectively inactivate E. coli O157:H7 and YM in contaminated SP, while minimizing the changes in anthocyanins and color.     

Survival and growth of B. cereus group and presumptive Cronobacter spp. contaminated naturally in rehydrated sunsik

Survival and growth of Bacillus cereus group and presumptive Cronobacter in the rehydrated sunsik were investigated to control the pathogens. Five sunsik contaminated naturally by the pathogens were rehydrated with hot waters of 50, 60, 65, and 70°C and kept for 24 hr at 5 and 25°C. Survival and growth of B. cereus seemed to be influenced not by rehydration water temperature, but by storage temperature and time after rehydration. However, survival and growth of Cronobacter was influenced by both rehydration temperature and storage conditions. Especially, storage temperature and time seemed to be more important than the rehydration temperature to limit the growth of Cronobacter. Therefore, it is required to take immediately the sunsik after rehydration with at least 65°C water, otherwise within 6 hr at room temperature for the risk reduction of B. cereus and Cronobacter.     

Shelf Life of Shrimp (Penaeus merguiensis) Stored at Different Temperatures

The sensory, microbiological and biochemical changes were determined in shrimp (Penaeus merguiensis) stored at 0° to 35°C. Mean aerobic plate count of fresh shrimp, initially 5.0 × 10⁵ CFU/g, increased with time and temperature to 6.4 × 10⁹ CFU/g at 35°C after 24 hr. A total of 560 different bacteria were isolated and identified. In addition, the dominant organisms were tested for ability to reduce TMAO, produce indole and hydrolyze protein. The initial bacteria were 30% Gram + organisms but changed to predominantly Grampsychrotrophs at lower temperatures and to mesophiles at higher temperatures. Odor, texture and color qualities decreased; TMA, TVB, pH and Indole increased with time and temperature. Shelf life of shrimp ranged from 7 hr at 35°C to 13 days at 0°C.     

Fate of Escherichia coli O157: H7 in Chinese-Style Sausage During the Drying Step of the Manufacturing Process as Affected by the Drying Condition and Curing Agent

In this study, Chinese-style sausage was subjected to three different air-blast drying conditions commonly employed during the manufacturing process. The fate of Escherichia coli O157: H7 during the drying period was determined and compared. The effect of curing agents on the survival of E coli O157: H7 was also identified. Results showed that populations of E coli O157: H7 decreased ca 1.51 Log CFU g^-1 in sausage containing curing agents after a 6-h drying period at 50°C. However, the number of viable cells of E coli O157: H7 increased slightly in sausage without curing agents. When subjected to air-blast drying at 55°C for 6 h or at 55°C for 2·5 h and then 60°C for 3·5 h, a reduction in the number of viable cells of E coli O157: H7 was observed in sausage with or without curing agents. The reduction was more significant in sausage containing curing agents than in those without curing agents. No viable E coli O157: H7 was detected after 6 h of drying in samples containing curing agents, while the control samples still contained a viable E coli O157: H7 population of ca 2·65–4·36 Log CFU g^-1. After drying the sausage at 55°C for 4 h, inactivation of E coli O157: H7 increased in the presence of 30·00 g kg^-1 sodium chloride or 1·50 g kg^-1 sodium sorbate. On the other hand, the presence of 0·07–0·15 g kg^-1 sodium nitrite did not increase the inactivation of E coli O157: H7 compared to that in the control. © 1997 SCI.     

Fate of Escherichia coli in apple and reduction of its growth using the postharvest biocontrol agent Candida sake CPA‐1

BACKGROUND: Generally, acidic fruits and fruit juices are considered ‘safe’ from a microbiological point of view. However, some outbreaks of foodborne illnesses have been linked to the consumption of unpasteurised cider. The aim of this work was to study the survival of Escherichia coli in apple juice, wounds and flesh and on apple surfaces at different temperatures and to determine the effect of the fungal biocontrol agent Candida sake CPA‐1 against the colonisation of apple by E. coli. RESULTS: Trials were conducted with a mixture of five strains of E. coli isolated from apples. E. coli was unable to grow in apple juice at 5, 15 and 25 °C but survived. At 10 °C and above, E. coli thrived in fresh‐cut apple and wounds. At 5 °C it survived in apple wounds after 27 days of storage and after 21 days in fresh‐cut apples. When E. coli was inoculated in apple wounds together with the yeast antagonist C. sake, its growth was reduced by approximately 1 log cfu wound^?1 at 25 °C. At 5 °C no effect of the biocontrol agent was observed. CONCLUSION: Despite the low pH of apple, a rapid increase in the bacterial population is possible if the temperature is not kept low enough. The biocontrol agent C. sake, developed to prevent fruit decay during storage, could also reduce E. coli growth in wounded apples at abusive temperatures. This would represent an additional benefit of using this biocontrol agent when applied to control postharvest diseases. Copyright © 2009 Society of Chemical Industry     

In-milk inactivation of Escherichia coli O157:H7 by the environmental lytic bacteriophage ECPS-6

Shiga toxin-producing Escherichia coli is a common foodborne pathogen which transmission includes dairy products. In the search for novel biocontrol methods, bacteriophages have become important candidates for the eradication of foodborne pathogens. The aim of this study was to evaluate the bacteriophage-mediated reduction of E. coli O157:H7 in raw and filtered milk. Laboratory-scale tests showed that the bacteriophage ECPS-6 efficiently adsorbed to E. coli O157: H7 cells. Furthermore, ECPS-6 remained stable when heated at 70°C for 20 min and in a wide pH range from 3.0 to 11.0. The trials on contaminated milk were performed using filtered and unfiltered raw milk contaminated with 1 × 10⁵ CFU × ml⁻¹ of E. coli O157: H7. Bacteriophage was added at multiplicity of infection (MOI) 5 and 50. The ECPS-6 reached the highest lytic activity at MOI = 5 (25°C) which resulted in 4.74 Log₁₀ CFU × ml⁻¹ and 7.3 Log₁₀ CFU × ml⁻¹ reduction after 10 days for both tested strains, respectively. Under refrigerated conditions (4°C) the quantity of E. coli decreased to 1.5 Log₁₀ CFU × ml⁻¹ and 3.04 Log₁₀ CFU × ml⁻¹ for these strains, respectively. Usage of MOI = 50 for the treatment unfiltered milk led to the reduction of E. coli O157:H7 A-2 below the detection limit after 6 hr.     

Heat resistance in Escherichia coli and its implications on ground beef cooking recommendations in Canada

This study assessed the adequacy of the current cooking recommendations in relation to heat resistant Escherichia coli by evaluating eight potentially heat resistant E. coli strains (four generic and four E. coli O157:H7) along with AW1.7. The D_60°C-values for these strains varied from 1.3 to 9.0 min, with J3 and AW1.7 being the least and most heat resistant strains, respectively. The D_60°C-values for E. coli 62 and 68 were similar and were not affected by growth medium, while the heat resistance of C37, J3, and AW1.7 varied with the growth medium. When heated in extra lean ground beef (100 g) in vacuum pouches, the mean D_54°C, D_57°C, and D_60°C-values were 44.8, 18.6, and 2.9 min for C37, 13.8, 6.9, and 0.9 min for J3, and 40.5, 9.1, and 6.1 min for AW1.7. Burger temperatures continued to rise after being removed from heat when the target temperature was reached, by 3–5°C, and resting of 1 min would result in a destruction of 133, 374 and 14 log C37, J3 and AW1.7. These findings along with the very low occurrence of heat resistant E. coli expected in ground beef show that cooking ground beef to 71°C should be adequate.     

Relationship Between the Growth Phase of Pseudomonas fragi and Its Attachment to Stainless Steel.

Attachment of Pseudomonas fragi ATCC 4973 to a sterile stainless steel surface was followed under stationary and dynamic growth conditions at 25°C and 4°C using scanning electron microscopy techniques. The organism was grown in 10% reconstituted nonfat dry milk for 28 hr at 25°C and 9 days at 4°C. Attachment was ob served in both the stationary and dynamic environments at 1/2 hr at 25°C and at 2 hr at 4°C. There appeared to be no difference in the development of attachment fibrils on the organisms in the two environments or at the two temperatures. The extent of attachment increased as the microbial population increased over the growth cycle under both environments at both temperatures.     

Packaging Film Permeability in Conjunction with Sodium Nitrite, Potassium Sorbate or Lactic Acid Starter Culture for Control of Clostridium sporogenes (PA3679) Growth in Sliced Bologna

A sliced bologna was prepared and inoculated with Clostridium sporogenes (PA3679), packaged in films ranging in oxygen permeability from 0.1 cc/m²/24 hr to 120 cc/m²/24 hr and stored at 5°C, 15°C or 25°C. Subsequent bologna preparations included either 156 ppm sodium nitrite, 0.26% potassium sorbate or a lactic acid starter culture. Water activity, pH, TBA number and PA3679 counts were monitored during 28 days of storage. TBA numbers increased in packages with over 60 cc/m²/24 hr permeability but PA3679 counts did not change as a function of packaging film. Nitrite and sorbate were equally effective as inhibitors. At 15°C and 25°C, the lactic acid culture allowed the least PA3679 growth. Oxygen permeability did not alter any inhibitory effects even when increased TBA numbers resulted from using an oxygen-permeable film.     

Influence of gamma irradiation on growth and survival of Escherichia coli O157:H7 and quality of cig kofte, a traditional raw meat product

Cig kofte is a traditional Turkish food containing raw ground meat. Samples inoculated with Escherichia coli O157:H7 were irradiated at 0.5–6 kGy with a ⁶⁰Co source and stored at 4 and 25 °C. Total aerobic mesophilic count decreased with increasing irradiation doses, D₁₀ value was 0.83 kGy. Escherichia coli O157:H7 count decreased from 5.1 log₁₀ CFU g^?1 to an undetectable level (<1 log₁₀ CFU g^?1) after 1‐day storage at 4 °C following irradiation at 2 kGy, D₁₀‐value was 0.29 kGy. Irradiation doses up to 2 kGy did not affect sensory quality after 1 day. There was colour loss in samples irradiated at 2 kGy or above and stored for longer periods. Storage of the irradiated products at abused temperature must be avoided for safety assurance. Irradiation at 2 kGy has a great potential for extending the shelf‐life of cig kofte and assuring safety by decreasing the number of E. coli O157:H7 and other bacteria, but further studies with suitable package designs are needed to decrease quality degradation during extended storage.     

Optimization of Fermentation Parameters for the Production of Concentrated Starters from Nonbitter Streptococcus lacti INIA 12

Streptococcus lactis INIA 12, a selected nonbitter strain, reached its maximum counts and its highest lactic acid production in a culture medium containing 125 g/L skim milk powder, fortified with 5 g/L yeast extract and digested with 10 ppm papain for 20 min at 65°C. Lactose added to the medium did not enhance growth rate or biomass production. A growth temperature of 32°C and the maintenance of pH at 6.80, with 10N NaOH as the neutralizer, were the optimum fermentation parameters in batch cultures. In ten 40-L fermentations carried out at 32°C and pH 6.80, with a 5% inoculum, a 0.2 kg/cm² nitrogen head space pressure and a stirring rate of 80 rpm, maximum counts of S. lactis (10¹⁰ CFU/mL) were reached after incubation for 6 hr at 32°C and pH 6.80.     

Changes in the Tenderness of Meat Cooked at 50–65°C

Warner-Bratzler (WB) shear force values obtained for stretched veal muscles decreased as cooking temperatures were increased from 50 to 60°C. Increased proteolytic enzyme activity at these temperatures to give accelerated aging did not appear to explain the effects since there was still a substantial decrease in shear force with increase in cooking temperature from 50 to 60°C, even when well aged (7 wk at 5–6°C) meat and meat cooked for 24 hr was used. A more likely explanation was that, even at these relatively low temperatures, changes in connective tissue were involved since (a) the magnitude and direction of the change in shear force with increasing temperature was dependent on animal age and cooking time; (b) the effect of recooking at 80°C was dependent on animal age; and (c) the effects of increasing the cooking temperature and/or time on adhesion between the meat fibres was significantly greater for the samples from the younger animals.     

Microwave Processing to Destroy Salmonellae in Corn-Soy-Milk Blends and Effect on Product Quality

Enriched corn-soy-milk (CSM) blends were inoculated with Salmonella senftenberg and packed in 50-lb (22.7 kg) bags. The inoculated product and CSM bags containing natural salmonellae contamination were heated from 21° to 56.7°C through 82.2°C in 3.9 – 10 min, respectively, using a 60 Kw (2450 MHz) continuous microwave tunnel, and then palletized with and without 4-cm spacers between rows. Spacer palletized bags cooled to 43°C after 9.7 hr with moving air and after 23.3 hr without moving air, but 60 hr was required with no spacers. Initial most probable numbers (MPN) of 4 × 10² cells/g for S. senftenberg were reduced 10²-fold to 10⁵-fold after processing at 56.7° through 82.2°C, respectively. Nutritional damage occurred at process temperatures of 77.8° and 82.2°C. At 61.1° and 67.2°C, MPN were reduced 2 × 10³-fold with no significant change in rheology, moisture, color, vitamins A and B₁, available lysine, and protein efficiency ratios.     

Comparative Growth ofEscherichia coli0157:H7, Spoilage Organisms and Shelf-Life of Shredded Iceberg Lettuce Stored under Modified Atmospheres

The objective of this work was to compare organoleptic and microbiological spoilage with the survival of Escherichia coli 0157:H7 in modified atmosphere (MA) stored shredded lettuce. The rates of growth of E coli 0157:H7, increase in aerobic plate counts (APC g⁻¹), and rates of visual spoilage of shredded lettuce held under air or MA at 13 and 22°C were compared. Samples were inoculated with nalidixic acid-resistant E coli 0157:H7 (ATCC 35150) and placed in a chamber which was continuously flushed with gas mixtures of 0/10/90, 3/0/97, 5/30/65, 20/0/80 (O₂/CO₂/N₂, v/v) and held at 13 or 22°C. APC growth was inhibited in 5/30/65 (O₂/CO₂/N₂) at 13°C compared to all other atmospheres which were not significantly different from each other. The growth rates for both E coli 0157:H7 and APC were greatest in air at 22°C. Carbon dioxide concentration had no significant effect on the growth of E coli 0157:H7 at either temperature. The shelf-life of shredded lettuce, as judged by appearance, was extended in atmospheres containing 30% CO₂ by approximately 300% compared to air. The APC were similar at the time when the shredded lettuce samples were judged unacceptable regardless of shelf-life. However, the extended shelf-life provided by the MA allowed E coli 0157:H7 to grow to higher numbers compared to air-held shredded lettuce.