Microbiological and color aspects of cooked sausages made from a standardized porcine blood cell concentrate

The objective of this study was to determine the potential for blood cell concentrates (BCCs) from pigs as an ingredient in food. Sausages were made for this study according to a basic recipe for a type of blood sausage that is common in Germany. First, sausages were produced with rind and kettle broth only, and different amounts (2.5 to 31%) of standardized blood cell concentrate (s-BCC) were added (15% table salt [NaCl] and 25% protein content). Then, sausages were made with whole blood and compared with s-BCC sausages; both the BCC and blood had been pretreated either with NaCl or curing salt (nitrite). The impact of BCC and blood on the color (La*b*) of these rind sausages was determined. Finally, blood sausages were made with 12% s-BCC and either natural spices or spice extracts. These sausages were investigated microbiologically and compared to customary commercial blood sausage products (with whole blood) in terms of aerobic plate count (APC), Enterobacteriaceae, sulfite-reducing anaerobic bacteria, coagulase-positive staphylococci, and spore-forming bacilli. The desired color parameters (L, 34.5; a*, 17.8; and b*, 10.6) were obtained with the addition of about 12% s-BCC. Curing the blood or BCC beforehand had no significant (P > 0.05) influence on the color. The microbial counts of both the blood (APC, 4.4 log CFU/g) and the natural spices (APC, 6.6 log CFU/g) were relatively high. The spices were responsible for the relatively high microbial counts in the sausages, particularly the bacilli (6.4 log CFU/g). However, these counts were comparable to those found in commercial blood sausages. The bacteria introduced into the sausage by the blood had no significant impact on the bacterial counts of the end product. The bacterial loads of the sausages produced with 12% s-BCC and spice extracts were significantly lower (APC and bacilli, 2.0 log CFU/g) than those of the other blood sausages (APC, -4.4 log CFU/g; bacilli, 3.2 to 4.0 log CFU/g).     

Effects of Trisodium Phosphate and Sodium Chloride Dipping on the Microbial Quality and Shelf Life of Refrigerated Tray-packaged Chicken Breasts

Effects of trisodium phosphate (TSP) and/or sodium chloride (NaCl) dipping on microbial quality and shelf life of chicken breasts were investigated during refrigeration. Chicken breasts were dipped in aqueous solution (w/v) of 10% TSP, 10% NaCl, combination of TSP and NaCl (7.5% + 7.5%) or distilled water (control) for 10 min, followed by tray-packaging storage at 2 degrees C. During storage, chicken breasts dipped in TSP maintained almost constant pH, while pH of control or NaCl-treated samples significantly increased (P<0.05). TSP dipping resulted in initial reduction of 0.48 and 0.91 log(10) CFU/g in aerobic plate counts and Enterobacteriaceae count, respectively, when compared with control. By storage day 6, APC of control chicken breasts reached 6.91 log(10) CFU/g, while TSP-treatment either alone or in combination with NaCl significantly delayed microbial growth (P<0.05) and extended shelf life of refrigerated chicken breasts up to 12 days, at which APC were 6.87 and 6.39, respectively, versus 9.58 log(10) CFU/g for control. Significant reductions in psychrotrophic and Enterobacteriaceae count were detected at the end of storage period in chicken breasts treated with TSP alone or in combination with NaCl, whereas such treatments had no significant effects on lactobacilli or mold and yeast populations.     

Microbiological quality and safety of quahog clams, Mercenaria mercenaria, during refrigeration and at elevated storage temperatures

The effects of storage temperatures and times on the microbiological quality and safety of hard-shelled quahog clams (Mercenaria mercenaria) were examined. Samples were stored at four different incubation temperatures (3.3, 7.2, 10.0, and 12.8 degrees C) for a period of 3 weeks, following their harvest from summer growing waters (> or = 27 degrees C) and winter waters (< or = 4 degrees C). Clams were analyzed for two naturally occurring pathogens, Vibrio parahaemolyticus and Vibrio vulnificus. During the summer, V. parahaemolyticus was isolated from 56% of the stored samples, with the highest concentration, 6,100/g, occurring on day 12 at 12.8 degrees C. Also, during the summer, V. vulnificus was isolated from 11% of the stored samples, with the highest concentration of 1,500/g occurring on day 15 at 7.2 degrees C. No Vibrio spp. were detected during the winter. During summer storage, aerobic mesophilic counts on plate count agar (PCA) containing 2% NaCl ranged from 10(4) to 10(8) CFU/g, and during storage of the winter samples, aerobic mesophilic PCA (with added NaCl) counts ranged from <100 to 10(4) CFU/g. Comparatively, summer storage mesophilic counts on PCA containing no added NaCl ranged from <100 to 10(5) CFU/g, and for the winter samples the range was <100 to 10(2) CFU/g. Coliform and fecal coliform counts ranged from <0.3 to 61.1/g and <0.3 to 24.4/g, respectively. There was no statistical correlation between the length of storage or the temperature of incubation and the presence of V. parahaemolyticus, V. vulnificus, coliforms, or fecal coliforms. However, storage time and incubation temperature affected the PCA counts (P < or = 0.05) in quahog clams.     

Effect of hydrogen peroxide treatment on microbial quality and appearance of whole and fresh-cut melons contaminated with Salmonella spp

The efficacy of hydrogen peroxide treatment on the inactivation of Salmonella spp. inoculated on the external surface of cantaloupe and honeydew melon was investigated. Salmonella was inoculated onto whole cantaloupe and honeydew melon to a final concentration of 4.65 log(10) CFU/cm(2) and 3.13 log(10) CFU/g, respectively. Inoculated whole melons stored at 5 degrees C for up to 7 days were washed with water, 2.5% and 5% hydrogen peroxide at day 0 and 5. Hydrogen peroxide (2.5% and 5%) treatments of whole melon for 5 min caused a 3 log(10) CFU/cm(2) reduction of the indigenous surface microflora and a 3.0 log(10) CFU/cm(2) reduction in Salmonella spp. on all melon surfaces. The efficacy of the hydrogen peroxide treatments was less when the interval between inoculation and treatment of cantaloupe exceeded 24 h. Unlike cantaloupe fresh-cut pieces, Salmonella was not recovered from fresh-cut pieces prepared from treated whole honeydew melon. Growth of Salmonella occurred in cantaloupe fresh-cut pieces stored at 10 or 20 degrees C, and by 2 weeks, levels reached approximately 1 log CFU/g. A rapid decline in appearance and overall acceptability was observed in fresh-cut pieces prepared from untreated whole cantaloupe. While Salmonella was recovered from fresh-cut pieces from and whole treated cantaloupe, sanitizing the surface of contaminated whole melons with hydrogen peroxide before and after cutting and storage of the fresh-cut pieces at 5 degrees C can enhance the microbial safety and acceptability rating for about 2 weeks after processing.     

Growth of Aeromonas hydrophila in the whey cheeses Myzithra, Anthotyros, and Manouri during storage at 4 and 12 degrees C

The fresh whey cheeses Myzithra, Anthotyros, and Manouri were inoculated with Aeromonas hydrophila strain NTCC 8049 (type strain) or with an A. hydrophila strain isolated from food (food isolate) at levels of 3.0 to 5.0 x 10(2) CFU/g of cheese and stored at 4 or 12 degrees C. Duplicate samples of cheeses were tested for levels of A. hydrophila and pH after up to 29 days of storage. At 4 degrees C, A. hydrophila grew in Myzithra and Anthotyros with a generation time of ca. 19 h, but no growth was observed in Manouri. In Myzithra, average maximum populations of 8.87 log CFU/g (type strain) and 8.79 log CFU/g (food isolate) were recorded after 20 and 22 days of storage at 4 degrees C, respectively. The average maximum populations observed in Anthotyros stored at 4 degrees C were 6.72 log CFU/g (food isolate) and 6.13 log CFU/g (type strain) and were observed after 15 and 16 days of storage, respectively. A. hydrophila grew rapidly and reached high numbers in cheeses stored at 12 degrees C. The average generation times were 3.7 and 3.9 h (Myzithra), 4.1 and 6.1 h (Anthotyros), and 8.0 and 9.2 h (Manouri) for the type strain and the food isolate, respectively. Among the different whey cheese trials, the highest A. hydrophila population recorded (10.13 log CFU/g) was in Myzithra that had been inoculated with the food isolate after 8 days of storage at 12 degrees C. To prevent A. hydrophila growth in whey cheeses, efforts must be focused on preventing postprocessing contamination and temperature abuse during transportation and storage.     

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.     

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.     

Influence of NaCl content and cooling rate on outgrowth of Clostridium perfringens spores in cooked ham and beef

The effect of NaCl concentration and cooling rate on the ability of Clostridium perfringens to grow from spore inocula was studied with the use of a process that simulates the industrial cooking and cooling of smoked boneless ham and beef roasts. NaCl was added to ground cooked hams A and B (which were commercially obtained) to obtain levels of 2.4, 3.1, 3.6, and 4.1% (wt/wt) and 2.8, 3.3, 3.8, and 4.3% (wt/wt), respectively, and to raw ground beef to obtain levels of 0, 1, 2, 3, and 4% (wt/wt). Ham C, a specially formulated, commercially prepared product, was supplemented with NaCl to obtain levels of 2.0, 2.5, 3.0, and 3.5%. The samples were inoculated with a three-strain mixture of C. perfringens spores to obtain concentrations of ca. 3 log10 CFU/g. Portions of meat (5 g each) were spread into thin layers (1 to 2 mm) in plastic bags, vacuum packaged, and stored at -40 degrees C. Thawed samples were heated at 75 degrees C for 20 min and subsequently cooled in a programmed water bath from 54.4 to < or = 8.5 degrees C in 15, 18, or 21 h. For the enumeration of C. perfringens, samples were plated on tryptose-sulfite-cycloserine agar and incubated in an anaerobic chamber at 37 degrees C for 48 h. Population densities for cooked ham and beef increased as cooling time increased, and NaCl exerted a strong inhibitory effect on the germination and outgrowth of C. perfringens. For beef, while 3% NaCl completely arrested growth, pathogen numbers increased by > or = 3, 5, and 5 log10 CFU/g in 15, 18, and 21 h, respectively, when the NaCl level was <2%. C. perfringens did not grow during cooling for 15, 18, or 21 h in ham samples containing > or = 3.1% NaCl. Results obtained in this study suggest that a 15-h cooling time for cooked ham, which is normally formulated to contain >2% NaCl, would yield an acceptable product (with an increase of <1 log10 CFU/g in the C. perfringens count); however, for beef containing <2% NaCl, C. perfringens populations may reach levels high enough to cause illness.     

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.     

Fermentation of low-salt miso as affected by supplementation with ethanol.

Steam-cooked soybeans and rice koji were combined (1:1, w/w), mixed with 5% (w/w) NaCl and ground into a fine paste. Samples (30 g) were deposited in nylon/polyethylene plastic bags and supplemented with 10 ml of aqueous ethanol solutions to give concentrations of 0, 2.5, 5, 7.5, 10, 15, 20, and 25% ethanol. Mixtures were homogenized, sealed, and incubated at 28 degrees C for eight weeks. Mold populations were less than 3 log10 CFU/g in all miso products after four weeks of fermentation. Yeast populations increased to 6.1 log10 CFU/g in the control (0% added ethanol) during the first week of fermentation and remained stable throughout the eight-week fermentation period. Yeasts were not detected in products containing 5-25% ethanol. Populations of lactic acid bacteria (LAB) increased to 6 log10 CFU/g after one week of fermentation in products containing 0 and 2.5% ethanol. However, after eight weeks of fermentation, LAB populations in all products were less than 4 log10 CFU/g. Rapid decreases in pH occurred only in products supplemented with 0 or 2.5% ethanol. Percentages of soluble protein in miso products containing various ethanol concentrations during the eight-week fermentation period revealed that protease activity was still active or not greatly inhibited in products supplemented with less than 10% ethanol. In comparison, koji enzymes were comparatively less affected by ethanol than were populations of molds, yeasts, and LAB. Total soluble carbohydrate and glucose contents were higher in products supplemented with 5, 7.5 and 10% ethanol than in other products. Discoloration (browning) during fermentation occurred most rapidly in products supplemented with 5 or 7.5% ethanol. Sensory evaluation of the low-salt (5%) product supplemented with 7.5% ethanol and fermented for eight weeks revealed normal or enhanced flavor ratings compared to ratings for a commercial product.     

Microbiological, sensory, and electronic nose evaluation of yellowfin tuna under various storage conditions.

Microbiological assessment, sensory evaluation, and electronic nose (AromaScan) analysis were performed on yellowfin tuna stored at 0, 4, 10, and 22 degrees C for 0, 1, 3, 5, and 9 days. Fish color, texture, appearance, and odor were evaluated by a trained sensory panel, while aroma-odor properties were evaluated using an AromaScan. Bacterial enumeration was performed using plate count agar containing 1.5% NaCl. Tuna fillets stored at 22 degrees C for 3 days or longer had a bacterial load of over 10(7) CFU/g and were rated not acceptable for consumption (grade C) by the sensory panel. Tuna fillets stored at 4 degrees C for 9 days or 10 degrees C for over 5 days were rated as grade C products and also had a bacterial load of over 10(7) CFU/g. The change in fish quality as determined by AromaScan followed increases in microbiological counts in tuna fillets, indicating that bacterial load can serve as a useful and objective indicator of gross spoilage. Electronic nose devices can be used in conjunction with microbial counts and sensory panels to evaluate the degree of decomposition in tuna during storage.     

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.     

Antibacterial effect of lactoferricin B on Escherichia coli O157:H7 in ground beef.

The antibacterial activity of lactoferricin B on enterohemorrhagic Escherichia coli O157:H7 in 1% peptone medium and ground beef was studied at 4 and 10 degrees C. In 1% peptone medium, 50 and 100 microg of lactoferricin B per ml reduced E. coli O157:H7 populations by approximately 0.7 and 2.0 log CFU/ml, respectively. Studies comparing the antibacterial effect of lactoferricin B on E. coli O157:H7 in 1% peptone at pH 5.5 and 7.2 did not reveal any significant difference (P > 0.5) at the two pH values. Lactoferricin B (100 microg/g) reduced E. coli O157:H7 population in ground beef by about 0.8 log CFU/g (P < 0.05). No significant difference (P > 0.5) was observed in the total plate count between treatment and control ground beef samples stored at 4 and 10 degrees C. The antibacterial effect of lactoferricin B on E. coli O157:H7 observed in this study is not of sufficient magnitude to merit its use in ground beef for controlling the pathogen.     

Reducing levels of Listeria monocytogenes contamination on raw salmon with acidified sodium chlorite

The antimicrobial activity of acidified sodium chlorite (ASC) against Listeria monocytogenes in salmon was studied. Raw salmon (whole fish and fillets) inoculated with L. monocytogenes (10(3) CFU/cm2 or 10(4) CFU/g) were washed with ASC solution (50 ppm) for 1 min and stored at -18 degrees C for 1 month (whole salmon) or in ice for 7 days (fillets). L. monocytogenes populations were determined for whole salmon after frozen storage and for fillets on days 1, 3, 5, and 7 of storage. A wash with ASC solution followed by ASC glazing did not reduce L. monocytogenes on the skin of whole salmon during frozen storage. However, the wash resulted in an L. monocytogenes reduction of 0.5 log CFU/g for salmon fillets. The populations of L. monocytogenes in fillets increased slowly during ice storage, but the growth of these populations was retarded by ASC ice. By day 7, the populations were 0.25 log units smaller in fillets stored in ASC ice and 0.62 log units smaller in fillets that had been washed with ASC solution and stored in ASC ice than in control fillets. Treatment with ASC also reduced total plate counts (TPCs) by 0.43 log CFU/cm2 on the skin of whole salmon and by 0.31 log CFU/g in fillets. The TPCs for skin decreased during frozen storage but increased gradually for fillets stored at 5 degrees C or in ice. However, TPCs of ASC-treated samples were lower than those for controls at any point during the study. Washing with ASC solution significantly (P < 0.05) reduced TPCs on the skin of whole salmon and in fillets, as well as L. monocytogenes in fillets. The antimicrobial activity of ASC was enhanced when salmon was washed with ASC solution and stored in ASC ice.     

Model for the combined effects of temperature, pH and sodium chloride concentration on survival of Shigella flexneri strain 5348 under aerobic conditions

Shigella is recognized as a major foodborne pathogen; however, relatively few studies have been reported on its growth and survival characteristics, particularly under conditions relevant to food. A fractional factorial design was used to measure the effects and interactions of temperature (4-37 degrees C), pH (2-6) and NaCl (0.5-9%) on survival kinetics of Shigella flexneri strain 5348 in BHI broth. Stationary-phase cells were inoculated into sterile media to give initial populations of 6-7 log(10) CFU/ml and bacterial populations were determined periodically by aerobic plate counts. A total of 267 cultures, representing 83 variable combinations of temperature, pH and NaCl concentration, were analyzed. Survivor curves were fitted from plate count data by means of a two-phase linear model to determine lag times and slopes of the curves, from which decimal reduction times (D-values) and times to a 4-log10 inactivation (t 4D) were calculated. Second order response surface models in terms of temperature, initial pH and NaCl concentration were obtained for the inactivation kinetics parameters of S. flexneri using regression analysis. The use of log10 transformation of the inactivation kinetics parameters yielded models with R2 values of >0.8. These models can provide an estimate of Shigella inactivation. The data obtained suggest that Shigella is resistant to acid and salt and that low pH foods stored at low temperatures may serve as vehicles for gastrointestinal illness.     

Microbiological quality of rabbit meat

World rabbit meat production is estimated to be over 1 million tons, and Spain is the third largest producer. Although rabbit meat is marketed and consumed worldwide, information on microbiological quality is very scarce. Here, we report indicator organisms, spoilage flora, sensory quality, and some physicochemical traits of 24 h postmortem chilled rabbit carcasses and prepackaged rabbit meat stored chilled in air for 0 to 3 days at the retail level. The mean total bacterial count (4.01 +/- 0.48 log CFU/g) for carcasses dressed at a small abattoir by a manual process was significantly lower (P < 0.05) than that (4.96 +/- 0.90 log CFU/g) for carcasses dressed at a large abattoir in automated slaughter lines. Both groups of carcasses had mean pH values of 5.98. The dominant contaminants on carcasses from the small abattoir were Pseudomonas, lactic acid bacteria, and yeasts. These microorganisms and Brochothrix thermosphacta were dominant on carcasses from the large abattoir. On prepacked hind legs (pH 6.26 +/- 0.18) stored at -1 to +1 degree C (supermarket 1), mean aerobic mesophilic count was 5.87 +/- 1.03 log CFU/g, and the major microbial groups were Pseudomonas, yeasts, lactic acid bacteria, and B. thermosphacta. On prepacked whole carcasses (pH 6.37 +/- 0.18) displayed at -1 to +5 degrees C (supermarket 2), mean aerobic mesophilic count was 6.60 +/- 1.18 and the same microbial groups were dominant. Relative Escherichia coli incidence was supermarket 2 > large abattoir > supermarket 1 > small abattoir. Overall, low numbers of coliforms, Enterobacteriaceae, psychrotrophic clostridia, coagulase-positive staphylococci, and molds were found. Sensory scores, pH values, and L-lactic acid content differentiated fresh carcasses from retail samples. Data obtained suggest that the microflora of chilled rabbit meat are different from those found on the meat of other animals.     

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 of Salmonella serovars introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21 °C

The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of Salmonella in low-salt compared to regular salt Cheddar cheese with 2 pH levels. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high-pH and aged for 12 wk resulting in four treatments: 0.7% NaCl and pH 5.1 (low-salt and low-pH); 0.7% NaCl and pH 5.5 (low-salt and high-pH); 1.8% NaCl and pH 5.7 (standard-salt and high-pH); and 1.8% NaCl and pH 5.3 (standard-salt and low-pH). Each treatment was comminuted and inoculated with a 5-serovar cocktail of Salmonella at a target level of 4 log CFU/g, then divided and incubated at 4, 10 and 21 °C for up to 90, 90, and 30 d, respectively. Salmonella counts decreased by 2.8 to 3.9 log CFU/g in all treatments. In the initial period of survival study, standard-salt treatments exhibited significantly lower Salmonella counts compared to low-salt treatments. The pH levels did not exhibit obvious significant effect in the Salmonella survival in low-salt treatments. Salmonella counts declined gradually regardless of a continuous increase in pH (end pH of 5.3 to 5.9) of low-salt treatments at all study temperatures. Salmonella counts were reduced faster at 21 °C storage. Although there were significant reductions in Salmonella counts, the treatments demonstrated survival of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross contamination remains. PRACTICAL APPLICATION: Low-salt aged Cheddar cheese could not support the growth of inoculated Salmonella and in fact gradual reduction in Salmonella count occurred during storage. Besides being nutritionally better, low or reduced salt Cheddar are safe as their full salt counterparts and that salt may only be a minor food safety hurdle regarding the post-aging contamination and growth of Salmonella. However, the treatments could not demonstrate complete destruction of Salmonella for up to 90 d when stored at 4 or 10 °C and for up to 30 d at 21 °C, the need for good sanitation practices to prevent postmanufacturing cross-contamination remains.     

Growth kinetics of Vibrio parahaemolyticus O3:K6 under varying conditions of pH, NaCl concentration and temperature

The growth responses of Vibrio parahamolyticus to pH, NaCl concentration and temperature changes were studied using serotype O3:K6 and other strains. Growth curves were obtained for 27 different sets of conditions, comprised of three levels of NaCl concentration, pH and temperature. The temperature, pH and NaCl concentrations most favorable for growth were in the order of 25 degrees C, 20 degrees C and 15 degrees C, pH 8, 7 and 5.8, and 1%, 3% and 7%, respectively. The bacteria grew most rapidly at 25 degrees C, at a pH of 7 or 8 in the presence of 1% or 3% NaCl, with the population (initial, ca. 2.5 log CFU/mL) reaching a level log 7 CFU/mL at 12 h. A growth predictive model using the Gompertz equation was generated from the experimental data for any combination of NaCl concentration, pH and temperature within the range used in this study.     

Fate of Escherichia coli O157:H7 in coleslaw during storage

An outbreak of Escherichia coli O157:H7 infection associated with the consumption of coleslaw in several units of a restaurant chain prompted a study to determine the fate of the pathogen in two commercial coleslaw preparations (pH 4.3 and 4.5) held at 4, 11, and 21 degrees C for 3 days. At an initial population of 5.3 log10 CFU/g of coleslaw, E. coli O157:H7 did not grow in either coleslaw stored at the three temperatures. Rather, the population of E. coli O157:H7 decreased by 0.1 to 0.5 log10 CFU/g within 3 days. The greatest reduction (0.4 and 0.5 log10 CFU/g) in population occurred at 21 degrees C, whereas only slight decreases (0.1 to 0.2 log10 CFU/g) occurred at 4 and 11 degrees C. A pH of 4.3 to 4.5 of coleslaw had little effect on reducing E. coli O157:H7 populations. Results suggest that the tolerance of E. coli O157:H7 to acid pH, not temperature abuse, is a major factor influencing the pathogen's fate in restaurant-prepared coleslaw.