The fate of Escherichia coli O157 : H7 in Myzithra,Anthotyros, and Manouri whey cheeses during storage at 2 and 12°C

Myzithra, Anthotyros and Manouri whey cheeses were inoculated the day after production withEscherichia coli O157 : H7 at concentrations of approx. 1·8×10⁶cfu g⁻¹, and stored at 2 and 12°C for 30 and 20 days, respectively. The pH of the whey cheeses decreased from an initial value of approx. 6·20 to 5·83 or 5·60 (Myzithra) 5·75 or 5·20 (Anthotyros) and 5·80 or 5·30 (Manouri) by the end of the corresponding storage periods at 2 and 12°C, respectively. Escherichia coli O157 : H7 populations in the whey cheeses at the end of the 12°C storage period, had grown with an increase of approx. 1·3 log₁₀cfu g⁻¹. E. coli O157 : H7 populations in whey cheeses at the end of the 2°C storage period did not grow and decreased, with an approx. 2·5 log₁₀cfu g⁻¹reduction. Results showed that E. coli O157 : H7 can grow at 12°C and survive at 2°C storage in Myzithra, Anthotyros and Manouri whey cheeses, and therefore post-manufacturing contamination with this pathogen must be avoided by employing hygienic control programmes such as HACCP.     

Enumeration and confirmation of Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria isolated from raw milk and other milk products in Northern Greece.

A total of 138 raw cow's and 57 raw ewe's milk samples; 80 pasteurized cow's milk samples; 39 Anthotyros cheese, 36 Manouri cheese, and 23 Feta cheese samples; and 15 rice pudding samples were examined for the presence and any countable population of Aeromonas species. Twenty-two (15.9%) of the 138 cow's milk samples analyzed were contaminated with A. hydrophila. In 13 of these samples, populations of 3.0x10(2) to 5.0x10(3) CFU/ml were counted in starch ampicillin agar (SAA). Eighteen cow's milk samples (13.0%) were contaminated with A. caviae, and in eight of these samples, populations of 2.0x10(2) to 3.0x10(3) CFU/ml were counted in SAA. Five cow's milk samples (3.6%) were contaminated with A. sobria, and in two of these samples, populations of 2.5x10(3) and 5.0x10(3) CFU/ml were counted in SAA. Eleven cow's milk samples (7.9%) were contaminated with other Aeromonas spp. not classified. Eight (14.0%) of the 57 ewe's milk samples analyzed were contaminated with A. hydrophila. In these samples, populations of 5.0x10(2) to 5.0x10(3) CFU/ml were counted in SAA. Six ewe's milk samples (10.5%) were contaminated with A. caviae, and populations of 1.5x10(2) to 1.0x10(3) CFU/ ml were counted in SAA. Two ewe's milk samples (3.5%) were contaminated with A. sobria, and populations counted in SAA were 5.0x10(2) and 1.0x10(3) CFU/ml. Four samples (7.0%) were contaminated with other Aeromonas spp. not classified. A. hydrophila was recovered in 4 (10.2%) and 3 (8.3%) of the Anthotyros and Manouri cheese samples analyzed, respectively, but no countable populations were noted in SAA. None of the pasteurized milk, Feta cheese, and rice pudding samples yielded Aeromonas spp. The results of this work indicate that motile Aeromonas are common in raw milk in Greece. Also, the presence of A. hydrophila in the whey cheeses Anthotyros and Manouri indicates that postprocessing contaminations of these products with motile Aeromonas may occur during production.     

Effect of salting and cold-smoking process on the culturability, viability, and virulence of Listeria monocytogenes strain Scott A

The aim of the present study was to determine the effect of the different steps of the cold-smoking process and vacuum storage on the culturability and viability of Listeria monocytogenes strain Scott A inoculated in sterile salmon samples. Additionally, the virulence of L. monocytogenes cells was assessed by intravenous inoculation of immunocompetent mice. Salmon (Salmo salar) portions were inoculated with L. monocytogenes at a level of 6 log CFU/g and were then dry salted (5.9%), smoked (0.74 mg phenol per 100 g), partially frozen (-7 degrees C), vacuum packed, and stored for 10 days at 4 degrees C followed by 18 days at 8 degrees C. Salting represented the only step of the process with a weak but significant listericidal effect (0.6 log reduction). Although the other processing steps had no immediate reduction effect on L. monocytogenes, the combination of steps significantly lowered by 1.6 log CFU/g the number of L. monocytogenes. The culturable count remained less than 7 log CFU/g until the end of the storage period, whereas in unprocessed samples (control) the culturable counts reached values up to 9 log CFU/g. To mimic a postprocess contamination, salmon portions were also inoculated with L. monocytogenes after being cold-smoke processed. A reduction of the culturable count during the 2 first weeks of storage was observed, but then growth occurred and identical values observed for preprocess contamination were reached at the end of the storage. A viable but nonculturable state transition of strain Scott A was not observed, and the cold-smoking process did not affect the virulence of bacteria isolated at the beginning and end of the storage.     

The antimicrobial properties of chitosan in mayonnaise and mayonnaise-based shrimp salads

The potential for using chitosan glutamate as a natural food preservative in mayonnaise and mayonnaise-based shrimp salad was investigated. Mayonnaise containing 3 g/liter of chitosan combined with acetic acid (0.16%) or lemon juice (1.2 and 2.6%) was inoculated with log 5 to 6 CFU/g of Salmonella Enteritidis, Zygosaccharomyces bailii, or Lactobacillus fructivorans and stored at 5 and 25 degrees C for 8 days. In mayonnaise containing chitosan and 0.16% acetic acid, 5 log CFU/g of L. fructivorans were inactivated, and numbers remained below the sensitivity limit of the plate counting technique for the duration of the experiment. Z. bailii counts were also reduced by approximately 1 to 2 log CFU/g within the first day of incubation at 25 degrees C, but this was followed by growth on subsequent days, giving an overall growth delay of 2 days. No differences in counts of Z. bailii in mayonnaise stored at 5 degrees C or of Salmonella Enteritidis stored at either temperature were observed. In mayonnaise containing lemon juice at both 1.2 and 2.6%, no substantial differences were observed between the controls and the samples containing chitosan. In shrimp salads stored at 5 degrees C, the presence of a coating of chitosan (9 mg/g of shrimp) inhibited growth of the spoilage flora from approximately log 8 CFU/g in the controls to log 4 CFU/g throughout 4 weeks. However, at 25 degrees C, chitosan was ineffective as a preservative. The results demonstrated that chitosan may be useful as a preservative when combined with acetic acid and chill storage in specific food applications.     

Survival of Escherichia coli O157:H7 in ground-beef patties during storage at 2, -2, 15 and then -2 degrees C, and -20 degrees C

The survival of Escherichia coli O157:H7 and of a nonpathogenic control strain of E. coli was monitored in raw ground beef that was stored at 2 degrees C for 4 weeks, -2 degrees C for 4 weeks, 15 degrees C for 4 h and then -2 degrees C for 4 weeks, and -20 degrees C. Irradiated ground beef was inoculated with one E. coli control strain or with a four-strain cocktail of E. coli O157:H7 (ca. 10(5) CFU/g), formed into patties (30 to 45 g), and stored at the appropriate temperature. The numbers of the E. coli control strain decreased by 1.4 log 10 CFU/g, and pathogen numbers declined 1.9 log 10 CFU/g when patties were stored for 4 weeks at 20 degrees C. When patties were stored at -2 degrees C for 4 weeks, the numbers of the E. coli control strain and the serotype O157:H7 strains decreased 2.8 and 1.5 log 10 CFU/g, respectively. Patties stored at 15 degrees C for 4 h prior to storage at -2 degrees C for 4 weeks resulted in 1.6 and 2.7 log 10-CFU/g reduction in the numbers of E. coli and E. coli O157:H7, respectively. Storage of retail ground beef at 15 degrees C for 4 h (tempering) did not result in increased numbers of colony forming units per gram, as determined with violet red bile, MRS lactobacilli, and plate-count agars. Frozen storage (-20 degrees C) of ground-beef patties that had been inoculated with a single strain of E. coli resulted in approximately a 1 to 2 log 10-CFU/g reduction in the numbers of the control strain and individual serotype O157:H7 strains after 1 year. There was no significant difference between the survival of the control strain and the O157:H7 strains, nor was there a difference between O157:H7 strains. These data demonstrate that tempering of ground-beef patties prior to low-temperature storage accelerated the decline in the numbers of E. coli O157:H7.     

Survival differences of Escherichia coli O157:H7 strains in apples of three varieties stored at various temperatures

Differences in survival and growth among five different Escherichia coli O157:H7 strains in three apple varieties were determined at various temperatures. Jonathan, Golden Delicious, and Red Delicious apples were wounded and inoculated with E coli O157:H7 strains C7929 (apple cider isolate), 301C (chicken isolate), 204P (pork isolate), 933 (beef isolate), and 43890 (human isolate) at an initial level of 6 to 7 log CFU/g. The inoculated apples were stored at a constant temperature of 37, 25, 8, or 4 degrees C or at 37 degrees C for 24 h and then at 4 degrees C, and bacterial counts were determined every week for 28 days. By day 28, for Jonathan apples at 25 degrees C, the apple isolate counts were significantly higher than the chicken and human isolate counts. At 4 degrees C for 28 days, the human isolate inoculated into Jonathan, Golden Delicious, and Red Delicious apples was present in significantly smaller numbers than the other strains. The apple isolate survived significantly better at 4 degrees C, yielding the highest number of viable cells. By days 21 and 28, for apples stored at 37 degrees C for the first 24 h and then at 4 degrees C, the counts of viable E. coli O157:H7 apple and human isolates were 6.8 and 5.8 log CFU/g at the site of the wound, whereas for apples kept at 4 degrees C for the duration of storage, the respective counts were 5.6 and 1.5 log CFU/g. Our study shows that E. coli O157:H7 strains responded differentially to their ability to survive in these three apple varieties at 25 or 4 degrees C and produced higher viable counts when apples were temperature abused at 37 degrees C for 24 h and then stored at 4 degrees C for 27 days.     

Inhibition of nonproteolytic,psychrotrophic clostridia and anaerobic sporeformers by sodium diacetate and sodium lactate in cook-in-bag turkey breast

A nonproteolytic, psychrotrophic Clostridium isolate, designated strain OMFRI1, was recovered from cook-in-bag turkey breasts (CIBTB) that displayed an intense pink discoloration and an off-odor following extended refrigerated storage. The viability of strain OMFRI1 in CIBTB containing sodium diacetate (at 0, 0.25, and 0.5%) and/or sodium lactate (at 0, 1.25, and 2.5%) was subsequently evaluated. Raw CIBTB batter was inoculated with 9 to 30 spores of strain OMFRI1 per g, vacuum packaged, cooked to an instantaneous internal temperature of 71.1 degrees C, chilled, and incubated at 4 degrees C for up to 22 weeks. In the absence of food-grade antimicrobial agents, spoilage (i.e., an off-odor) occurred within 6 weeks, and anaerobic plate counts reached 6.6 log10 CFU/g. The CIBTB containing sodium diacetate (0.25%) and that containing sodium lactate (1.25%) required 12 weeks for spoilage to occur and for anaerobic plate counts to reach 7.0 and 6.0 log10 CFU/g, respectively. When sodium diacetate (0.25%) and sodium lactate (1.25%) were used in combination, no off-odor was detected and anaerobic plate counts did not exceed 2.3 log10 CFU/g over 22 weeks of storage at 4 degrees C. In related experiments, sodium diacetate (at 0, 0.25, and 0.5%), sodium lactate (at 0, 1.25, and 2.5%), and combinations of both ingredients were evaluated in uninoculated CIBTB incubated at 25 degrees C for up to 22 days. In the absence of antimicrobial agents and in CIBTB containing sodium diacetate (0.5%), spoilage occurred within 8 days and anaerobic plate counts reached 6.8 and 6.6 log10 CFU/g, respectively. Samples of CIBTB containing sodium lactate (2.5%) showed signs of spoilage within 22 days, and anaerobic plate counts for these samples ranged from < or = 1.0 to 6.3 log10 CFU/g. In CIBTB containing both sodium lactate (2.5%) and sodium diacetate (0.25%), spoilage was not evident and anaerobic plate counts were < or = 1.0 log10 CFU/g within 22 days. These data validate the efficacy of sodium lactate and sodium diacetate in extending the shelf life of CIBTB.     

Contamination flows of Bacillus cereus and spore-forming aerobic bacteria in a cooked,pasteurized and chilled zucchini purée processing line

A food processing plant producing pasteurized purées and its zucchini purée processing line were examined for contamination with aerobic and facultative anaerobic bacterial spores during a day's operation. Multiplication of spores was also monitored in the product stored under different conditions. High concentrations of Bacillus cereus spores were found in the soil in which the zucchinis were grown (4.6+/-0.3 log CFU/g), with a background spore population of 6.1+/-0.2 log CFU/g. In the processing plant, no B. cereus or psychrotrophic bacterial spores were detected on equipment. B. cereus and psychrotrophic bacterial spores were detected after enrichment in all samples of raw zucchinis, washed zucchinis, of two ingredients (starch and milk proteins) and in processed purée at each processing step. Steam cooking of raw zucchinis and pasteurization of purée in the final package significantly reduced spore numbers to 0.5+/-0.3 log CFU/g in the processed food. During storage, numbers of spore-forming bacteria increased up to 7.8+/-0.1 log CFU/g in purée after 5 days at 20-25 degrees C, 7.5+/-0.3 log CFU/g after 21 days at 10 degrees C and 3.8+/-1.1 log CFU/g after 21 days at 4 degrees C. B. cereus counts reached 6.4+/-0.5 log CFU/g at 20-25 degrees C, 4.6+/-1.9 log CFU/g at 10 degrees C, and remained below the detection threshold (1.7 log CFU/g) at 4 degrees C. Our findings indicate that raw vegetables and texturing agents such as milk proteins and starch, in spite of their low levels of contamination with bacterial spores and the heat treatments they undergo, may significantly contribute to the final contamination of cooked chilled foods. This contamination resulted in growth of B. cereus and psychrotrophic bacterial spores during storage of vegetable purée. Ways to eliminate such contamination in the processing line are discussed.     

Viability of a five-strain mixture of Listeria monocytogenes in vacuum-sealed packages of frankfurters, commercially prepared with and without 2.0 or 3.0% added potassium lactate, during extended storage at 4 and 100 degrees C

The viability of Listeria monocytogenes was monitored on frankfurters containing added potassium lactate that were obtained directly from a commercial manufacturer. Eight links (ca. 56 g each) were transferred aseptically from the original vacuum-sealed bulk packages into nylon-polyethylene bags. Each bag then received a 4-ml portion of a five-strain mixture of the pathogen. Frankfurters containing 2.0 or 3.0% potassium lactate were evaluated using 20 CFU per package, and frankfurters containing 3.0% potassium lactate were evaluated using 500 CFU per package. The packages were vacuum-sealed and stored at 4 or 10 degrees C for up to 90 or 60 days, respectively. During storage at 4 degrees C, pathogen numbers remained at about 1.6 log10 CFU per package over 90 days in packages containing frankfurters with 2.0% potassium lactate that were inoculated with about 20 CFU. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 20 CFU and stored at 4 degrees C, pathogen numbers remained at about 1.4 log10 CFU per package over 90 days. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 500 CFU and stored at 4 degrees C, pathogen numbers remained at about 2.4 log10 CFU per package over 90 days. However, in the absence of any added potassium lactate, pathogen numbers increased to 4.6 and 5.0 log10 CFU per package after 90 days of storage at 4 degrees C for starting levels of 20 and 500 CFU per package, respectively. During storage at 10 degrees C, pathogen numbers remained at about 1.4 log10 CFU per package over 60 days in packages containing frankfurters with 2.0% potassium lactate that were inoculated with about 20 CFU. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 20 CFU and stored at 10 degrees C, pathogen numbers remained at about 1.1 log10 CFU per package over 60 days of storage. In the absence of any added potassium lactate, pathogen numbers increased to 6.5 log10 CFU per package after 28 days and then declined to 5.0 log10 CFU per package after 60 days of storage at 10 degrees C. In packages containing frankfurters with 3.0% potassium lactate that were inoculated with about 500 CFU per package, pathogen numbers remained at about 2.4 log10 CFU per package over 60 days of storage at 10 degrees C, whereas in the absence of any added potassium lactate, pathogen numbers increased to about 6.6 log10 CFU per package within 40 days and then declined to about 5.5 log10 CFU per package after 60 days of storage. The viability of L. monocytogenes in frankfurter packages stored at 4 and 10 degrees C was influenced by the pH and the presence or levels of lactate but not by the presence or levels of indigenous lactic acid bacteria or by the proximate composition of the product. These data establish that the addition of 2.0% (P < 0.0004) or 3.0% (P < 0.0001) potassium lactate as an ingredient in frankfurters can appreciably enhance safety by inhibiting or delaying the growth of L. monocytogenes during storage at refrigeration and abuse temperatures.     

Survival of Salmonella typhimurium and Escherichia coli O157:H7 in cheese brines

Survival of Salmonella typhimurium and Escherichia coli O157:H7 was studied in model brines and brine from three cheese plants. Three strain mixtures of S. typhimurium and E. coli O157:H7 (10(6) CFU/ml) were inoculated separately into 23% model brine with or without added pasteurized whey (2%) and as a combined inoculum into the commercial brines. The model brines were incubated at 8 and 15 degrees C for 28 days, and the commercial brines at 4 and 13 degrees C for 35 days. Populations of both pathogens in the model brine + whey decreased slowly over 28 days (1.0-2.0 log CFU/ml) with greater survival at 8 degrees C than at 15 degrees C. Corresponding decreases in model brine without whey were 1.9-3.0 log CFU/ml, with greater survival at 8 degrees C than at 15 degrees C. Both S. typhimurium and E. coli O157:H7 survived significantly better (P < 0.05) at 4 degrees C than at 13 degrees C in two of the commercial brines. The survival of each pathogen in the commercial brines at 13 degrees C was significantly influenced by brine pH. Both pathogen populations decreased most rapidly in commercial brines during the first week of storage (2.5-4.0 and 2.3-2.8 log CFU/ml for S. typhimurium and E. coli O157:H7, respectively) with significant recovery (ca. 0.5 log CFU/ml increase) often occurring in the second week of storage. Counts changed little thereafter. Overall, E. coli O157:H7 survived better than S. typhimurium, with differences of 0.1-1.2 log CFU/ml between the two pathogens. Results of this study show that cheese brine could support the survival of contaminating S. typhimurium and E. coli O157:H7 for several weeks under typical brining conditions.     

Nisin treatments to control Listeria monocytogenes post-processing contamination on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages

Post-processing contamination and growth of Listeria monocytogenes in whey cheeses stored under refrigeration is an important safety concern. This study evaluated commercially available nisin (Nisaplin^®) as a biopreservative to control L. monocytogenes introduced post-processing on Anthotyros, a traditional Greek whey cheese, stored at 4°C in vacuum packages for up to 45 days. The whey used (pH 6.5–6.7) was from Feta cheese manufacture, and it was subjected either to natural acidification (pH 5.3, readjusted to 6.2 with 10% NaOH) prior to heating, or to direct acidification (pH 6.0–6.2) at 80°C with 10% citric acid. Nisin was added either to the whey (100 or 500 IU g⁻¹) prior to heating, or to the cheese (500 IU g⁻¹) prior to packaging, also inoculated with ca. 10⁴ cfu g⁻¹ of L. monocytogenes strain Scott A. In cheese samples without nisin, L. monocytogenes (PALCAM agar) exceeded 7 log cfu g⁻¹ after the first 10 days of storage, irrespective of the whey acidification method. All nisin treatments had an immediate lethal effect (0.7–2.2 log reduction) on L. monocytogenes populations at inoculation (day 0), which was more pronounced with 500 IU g⁻¹ added to the whey. This treatment also suppressed L. monocytogenes growth below the inoculation level for 30 and 45 days in naturally and directly acidified samples, respectively. All other treatments had weak antilisterial effects. Nisin reversed the natural spoilage flora of Anthotyros cheese from Gram-positive to Gram-negative, and this ecological alteration was far more pronounced in the most effective antilisterial treatments.     

Microbiology of charcoal-broiled European river lampreys (Lampetra fluviatilis) stored at 3 and 22 degrees C

The microbiological quality of 30 production lots of charcoal-broiled river lampreys was studied at three lamprey processing plants (plants A, B, and C). Samples were taken directly after charcoal broiling and stored at 22 and 3 degrees C. Lampreys were examined on the day of manufacture, and those kept at 22 degrees C were examined every second day for 6 days. Samples kept at 3 degrees C were examined every fourth day for up to 24 days. On the production day, the mean aerobic plate counts (APCs) for broiled lampreys from plants A, B, and C were 2.29 log CFU/g, 1.88 log CFU/g, and undetectable (1.67 log CFU/g), respectively. At 22 degrees C, the mean APCs for samples from plants A, B, and C increased markedly within 4 days, and after 6 days the counts for samples from these plants were 8.56, 5.04, and 6.23 log CFU/g, respectively. Chilling and storage at 3 degrees C remarkably improved the shelf life of the product. The levels of bacteria in charcoal-broiled river lampreys from plant A were higher than those in lampreys from plants B and C. No significant increases in APCs were observed during storage at 3 degrees C for 24 days; mean APCs did not exceed 2.80 log CFU/g for samples from any plant. Staphylococcus aureus was found in two samples. No lactic acid bacteria, thermotolerant coliforms, enterococci, Clostridium perfringens, or Listeria monocytogenes was detected. Microbiological data from this study will be used for the development of a hazard analysis for the determination of critical control points.     

Survival of Streptococcus pyogenes on foods and food contact surfaces

Streptococcus pyogenes causes septic sore throat in millions of Americans each year and may be transmitted from food handlers to food contact surfaces, foods, and consumers. This study examined the individual survival of six S. pyogenes strains on food contact surfaces (plastic and ceramic plates, plastic cups, and stainless steel utensils) held at 21 degrees C for 2 h and on tomatoes stored aerobically at 21 degrees C for 2 h and at 5 degrees C for 24 h. Survival of a cocktail of the six S. pyogenes strains was also evaluated on vacuum-packaged ready-to-eat meats and cheeses held at 21 degrees C for 8 h and at 5 degrees C for 24 h. Populations generally did not change on tomatoes, cheeses, or beef bologna; however, there were small (0.1 to 0.7 log CFU) but statistically significant decreases (P < 0.05) in average S. pyogenes populations on turkey luncheon meat and beef summer sausage stored for 8 h at 21degrees C and on beef summer sausage stored for 24 h at 5 degrees C. On food contact surfaces, average populations either decreased slightly (P > or = 0.05) or remained constant, with the exception of three strains that significantly decreased in number on ceramic plates (P < 0.05; average decreases, 0.3 log CFU). Results of this study suggest the importance of preventing the contamination of foods and food contact surfaces with S. pyogenes by infected workers.     

Behavior of aeromonas hydrophila in bottled mineral waters.

The growth and survival of Aeromonas hydrophila in three types of natural mineral waters were investigated. Mineral waters with different levels of mineral content (low, medium, and high) were experimentally contaminated with A. hydrophila, stored at different temperatures (10 degrees C and 20 degrees C), and analyzed at intervals over a 60-day period. Water samples that were not experimentally contaminated were investigated for indigenous A. hydrophila. The results confirmed that A. hydrophila may occur naturally in mineral waters and showed that the level of mineral content, temperature, length of storage, and, in some cases, the type of container used may favor the growth of A. hydrophila. The greatest proliferation was observed in water with a low mineral content stored in PET bottles at 10 degrees C, in which A. hydrophila peaked at day 28 (4.47 +/- 0.01 log CFU/100 ml). At 20 degrees C, the same load was observed at day 60. The presence of high densities of A. hydrophila in bottled mineral water can constitute a risk for some groups of consumers, such as elderly and immunocompromised persons.     

Validation of a manufacturing process for fermented, semidry Turkish soudjouk to control Escherichia coli O157:H7

Two soudjouk batters were prepared from ground beef (20% fat) and nonmeat ingredients and inoculated with a five-strain mixture of Escherichia coli O157:H7 to yield an initial inoculum of 7.65 log10 CFU/g. One batter contained a commercial-starter culture mixture (approximately 8.0 log10 CFU/g) and dextrose (1.5%), while the other batter relied upon a natural fermentation with no added carbohydrate. Following mixing, sausage batters were held at 4 degrees C for 24 h prior to stuffing into natural beef round casings. Stuffed soudjouk sticks were fermented and dried at 24 degrees C with 90 to 95% relative humidity (RH) for 3 days and then at 22 degrees C with 80 to 85% RH until achieving a product moisture level of approximately 40%. After fermentation and drying with an airflow of 1 to 1.5 m/s, the sticks were either not cooked or cooked to an instantaneous internal temperature of 54.4 degrees C (130 degrees F) and held for 0, 30, or 60 min. The sticks were then vacuum packaged and stored at either 4 or 21 degrees C. For each of three trials, three sticks for each treatment/batter were analyzed for numbers of E. coli O157:H7 after inoculation, after fermentation, after cooking, and after storage for 7, 14, 21, and 28 days. Reductions in numbers of E. coli O157:H7 after fermentation and drying for sticks fermented by the starter culture (pH 4.6) and for sticks naturally fermented (pH 5.5) were 1.96 and 0.28 log10 CFU/g, respectively. However, cooking soudjouk sticks produced with a starter culture and holding at 54.4 degrees C for 0, 30, or 60 min reduced pathogen numbers from an initial level after fermentation and drying of 5.69 log10 CFU/g to below a detectable level by either direct plating (<1.0 log10 CFU/g) or by enrichment. In contrast, cooking soudjouk sticks produced without an added starter culture decreased pathogen numbers from an initial level after fermentation and drying of 7.37 to 5.65 log10 CFU/g (54.4 degrees C, no hold), 5.04 log10 CFU/g (54.4 degrees C, 30 min hold), and 4.67 log10 CFU/g (54.4 degrees C, 60 min hold). In general, numbers of E. coli O157:H7 within both groups of soudjouk sticks decreased faster during storage at 21 degrees C compared to 4 degrees C. After 28 days of storage, total reductions in pathogen numbers in soudjouk sticks produced using a starter culture but that were not subsequently cooked were 7.65 and 3.93 log10 CFU/g at 21 and 4 degrees C, respectively. For naturally fermented soudjouk, total reductions varied from 4.47 to 0.45 log10 CFU/g, depending on the cooking time and storage temperature. These data provide guidelines for manufacturers of dry sausage of ethnic origin, including soudjouk, to assess the safety of their processes for control of E. coli O157:H7.     

Survival of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes on inoculated walnut kernels during storage

The survival of single strains or cocktails of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was evaluated on walnut kernels. Kernels were separately inoculated with an aqueous preparation of the pathogens at 3 to 10 log CFU/g, dried for 7 days, and then stored at 23°C for 3 weeks to more than 1 year. A rapid decrease of 1 to greater than 4 log CFU/g was observed as the inoculum dried. In some cases, the time of storage at 23°C did not influence bacterial levels, and in other cases the calculated rates of decline for Salmonella (0.05 to 0.35 log CFU/g per month) and E. coli O157:H7 (0.21 to 0.86 log CFU/g per month) overlapped and were both lower than the range of calculated declines for L. monocytogenes (1.1 to 1.3 log CFU/g per month). In a separate study, kernels were inoculated with Salmonella Enteritidis PT 30 at 4.2 log CFU/g, dried (final level, 1.9 log CFU/g), and stored at -20, 4, and 23°C for 1 year. Salmonella Enteritidis PT 30 declined at a rate of 0.10 log CFU/g per month at 23°C; storage time did not significantly affect levels on kernels stored at -20 or 4°C. These results indicate the long-term viability of Salmonella, E. coli O157:H7, and L. monocytogenes on walnut kernels and support inclusion of these organisms in hazard assessments.     

Porcine blood cell concentrates for food products: hygiene, composition, and preservation

The objective of this study was to determine whether porcine blood cell concentrates (BCC) can be produced and stored using hygienic measures independent of the temperature acting upon the substrate. A number of additives widely accepted by the consumer (NaCl, sugars, food-grade acids) were used to form so-called hurdles (water activity [a(w)], pH) to spoilage, and their impact was tested on microbiological and sensory parameters of the BCC. BCC, whole blood, plasma, and the anticoagulant were collected on 23 days in a slaughterhouse. The BCC with the additives were stored for 27 days at + 3 degrees C and at +20 degrees C. Microbiological and chemical tests were carried out on the raw materials, and a(w) and the pH values of the stored BCC combinations were determined; the combinations were also submitted to sensory testing. The amounts of protein (33.4%) and hemoglobin (29.5 g/dl) in the BCC were significantly higher than in whole blood (19.4%; 13.8 g/dl). The mean total aerobic plate count was similar in all three substrates. However, the highest count (4.83 log CFU/g) was found in BCC; the count was lower in whole blood (4.62 log CFU/g) and lowest in plasma (4.22 log CFU/g). Storability (defined as a count of <5 log CFU/g) for 27 days at +20 degrees C was achieved only with two additive types: 15% NaCl and 10% NaCl plus 10% glucose plus 1% of a food-grade acid. Spoilage of the BCC was inhibited by an a(w) of 0.824 (with 15% NaCl) and by the combination of a(w) 0.87 and a pH of 5 (with 10% NaCl, 10% sugar, 1% acid). Both substrates retained their red color and fresh odor over the entire storage time.     

Influence of blanching treatments on Salmonella during home-type dehydration and storage of potato slices

Recommended drying treatments may not enhance destruction of pathogens that could be present on home-dried foods. In this study, the effects of traditional and modified treatments on Salmonella were evaluated during preparation, home-type dehydration (60 degrees C for 6 h), and storage of potato slices. Potato slices inoculated with five strains of Salmonella (8.4 log CFU/ g) were left untreated or were treated by steam blanching (88 degrees C for 10 min), water blanching (88 degrees C for 4 min), 0.105% citric acid blanching (88 degrees C for 4 min), or 0.210% citric acid blanching (88 degrees C for 4 min). Slices were then dried (6 h for 60 degrees C) and aerobically stored for up to 30 days at 25 +/- 3 degrees C. Cells were enumerated on tryptic soy agar with 0.1% pyruvate (TSAP) and on xylose lysine deoxycholate agar. Salmonella populations were reduced by 4.5 to 4.8 CFU/g and by >5.4 log CFU/g immediately following steam and water blanching, respectively. Populations were below the detection limit (0.80 log CFU/g) immediately following acid blanching, except for samples blanched in 0.105% citric acid and recovered on TSAP. After dehydration (6 h for 60 degrees C), Salmonella reductions on blanched potato slices (5.3 to 5.6 log CFU/g) were significantly greater (P < 0.05) than those on untreated samples (1.9 to 2.7 log CFU/g). Populations on all samples continued to decrease throughout 30 days of storage but still were 3.1 to 3.9 log CFU/g on untreated samples. In comparison, bacterial populations on blanched samples were undetectable by direct plating following 30 days of storage (regardless of blanching method). Blanching treatments used in this study improved the effectiveness of drying for inactivating Salmonella inoculated onto potato slices and, therefore, may enhance the safety of the product.     

Inhibitory effect of Melastoma candidum D. Don acetone extract on foodborne pathogenic bacteria survival in food products

Melastoma candidum D. Don, a Taiwanese folk medicinal plant, has high levels of antibacterial and bactericidal activity. Our aim was to determine whether and to what extent an acetone extract of this plant inhibits the growth of foodborne pathogenic bacteria. M. candidum acetone extract had marked inhibitory effect on test bacteria introduced into sliced pork, which was then stored at 4 degrees C. At the end of storage (day 12), the bacterial concentrations dropped by 1.59 to 2.91 log CFU/g compared with the control. In steamed rice stored at 30 degrees C, a 0.2% extract decreased initial (before storage) concentrations of Bacillus cereus from 2.01 log CFU/g to an undetectable level, which remained for at least 24 h. After 72 to 168 h of storage, test bacterial concentrations were reduced by 2.59 to 5.66 log CFU/g. In fresh noodles stored at 30 degrees C, both initial and final bacterial concentrations were decreased. At the end of storage (72 to 168 h), test bacteria concentrations were reduced by 1.85 to 2.88 log CFU/g. Overall, M. candidum acetone extract had an inhibitory effect on foodborne pathogenic bacteria in different food model systems.     

Growth and survival of Vibrio parahaemolyticus in postharvest American oysters

Oysters at the retail stage of distribution generally contain greater densities of Vibrio parahaemolyticus than do oysters at harvest. The objective of this study was to determine the effects of postharvest storage at 26 and 3 degrees C on the growth and survival of naturally occurring V. parahaemolyticus in shellstock American oysters (Crassostrea virginica). Oysters were collected monthly from May 1998 through April 1999 from Mobile Bay, Alabama, and their V. parahaemolyticus densities were determined after 0, 5, 10, and 24 h of postharvest storage at 26 degrees C. After 24 h of storage at 26 degrees C, oysters were transferred to a refrigerator at 3 degrees C and analyzed 14 to 17 days later. V. parahaemolyticus numbers were determined by a direct plating method involving an alkaline-phosphatase-labeled DNA probe that targets the species-specific thermolabile hemolysin gene (tlh-AP) to identify suspect isolates. From April to December, when water temperatures at harvest were >20 degrees C, the geometric mean harvest density of V. parahaemolyticus was 130 CFU/g. When water temperatures were <20 degrees C, the geometric mean harvest density was 15 CFU/g. After harvest, V. parahaemolyticus multiplied rapidly in live oysters held at 26 degrees C, showing a 50-fold increase (1.7 log CFU/g) at 10 h and a 790-fold increase (2.9 log CFU/g) at 24 h (April through December). Average V. parahaemolyticus numbers showed a sixfold decrease (0.8 log CFU/g) after approximately 14 days of refrigeration. These results indicate that V. parahaemolyticus can grow rapidly in unrefrigerated oysters.