Developing microbial spoilage population in vacuum-packaged charcoal-broiled European river lamprey (Lampetra fluviatilis)

Microbiological and sensory changes in vacuum-packaged charcoal-broiled river lampreys from three lamprey processing plants were monitored as a function of time at 8 degrees C. The lampreys were examined every 7 days up to 8 weeks for aerobic plate count (APC) and lactic acid bacteria (LAB). The highest mean APC and LAB were 6.01 log CFU/g and 4.86 log CFU/g, respectively. Only 6 out of 15 lots reached an APC value of 7.0 log CFU/g during storage. The sensory scores remained at the baseline levels after 8 weeks' storage. Twenty-seven isolates were randomly picked from MRS agar and identified to species level using a 16S and 23S rDNA HindIII RFLP (ribotyping) database and sequencing of the 16S rRNA gene if no database match was obtained. Twelve of the 27 isolates were identified as Lactobacillus curvatus subsp. curvatus, and two Leuconostoc mesenteroides and one Weissella halotolerans strain were also detected. Twelve isolates were not identified by the LAB database. However, they possessed very high (99.9%) 16S gene sequence similarity with either Staphylococcus warneri or Staphylococcus pasteuri type strains. The LAB detected, with the exception of W. halotolerans, have commonly been associated with spoilage of fishery products, but in these vacuum-packaged lampreys, they were not the dominant organisms within the developing spoilage population.     

The prevalence of Clostridium botulinum in European river lamprey (Lampetra fluviatilis) in Finland

The prevalence of Clostridium botulinum types A, B, E and F in river lampreys caught in Finnish rivers was determined for the first time using a quantitative PCR-MPN (most probable number) analysis. One of 67 raw whole lampreys (1.5%) was positive for the botulinum neurotoxin type E gene, with the estimated C. botulinum count being 100spores/kg. Two type E strains were isolated from the positive sample and confirmed as different genotypes by pulsed-field gel electrophoresis. Although the current procedure of bringing the charcoal-broiled lampreys to market has been without any further packaging or extended storage, interest towards increasing the shelf life of the product by vacuum-packaging is increasing. Our results demonstrate that C. botulinum type E may constitute a safety hazard in processed lampreys from the Baltic Sea area if packaging and extended shelf lives are to be used. To control the potential risk, a storage temperature of 3 degrees C or below should be recommended for these products.     

Bacteriological quality of aquacultured freshwater fish portions in prepackaged trays stored at 3 degrees C

Fresh trout fillets and salmon slices packed in trays were obtained from two multinational chain supermarkets and evaluated for freshness and bacteriological quality immediately after packaging and during storage at 3 degrees C. Initial aerobic counts at 30 and 25 degrees C were significantly (P < 0.05) lower in trout fillets (5.27 +/- 0.57 and 4.87 +/- 0.80 log CFU/g, respectively) than in salmon slices, where levels in excess of 6 log CFU/g were found. In both products, initial Enterobacteriaceae counts were slightly higher than 3 log CFU/g and increased significantly during shelf life by approximately 3 log CFU/g. Most of the enterobacteria were identified as Citrobacter freundii, Hafnia alvei, and Enterobacter cloacae. On day 0, most probable number (MPN) counts of total and fecal coliforms were not significantly different, numbers of the latter group being approximately 4 MPN/g. Escherichia coli was only detected when fish was spoiled. Although initial presumptive Staphylococcus aureus counts were approximately 3 log CFU/g, only 4 of 84 selected colonies belonged to this species. Neither Salmonella nor antimicrobial residues were detected in any sample. Ethanol content in salmon slices did not significantly (P > 0.05) increase until they became inedible. Significant correlation (r = +0.72, P < 0.05) was observed between this chemical index and viable counts at 30 degrees C only when salmon slices were inedible. Trout fillets were acceptable for 7 days, and salmon slices showed signs of spoilage after 4 days. Although public health concerns associated with packed trout and salmon appear to be minimal, data on sensory quality, shelf life, and total viable and Enterobacteriaceae counts strongly suggest the need to improve the quality control systems used by European multinational retailers, especially for imported salmon.     

Sensory, chemical and bacteriological changes in vacuum-packed pressurised squid mantle (Todaropsis eblanae) stored at 4 degrees C

Sensory, chemical and bacteriological changes were studied in vacuum-packed squid mantles (Todaropsis eblanae) that were pressurised at 150, 200, 300 and 400 megapascal (MPa) for 15 min at ambient temperature and stored at 4 degrees C. Sensory analysis showed that the higher the pressurisation the longer the shelf-life. Thus, the lot pressurised at 400 MPa was rejected after 28 days' storage compared with 7 days for the untreated lot. The chemical results generally corresponded with the sensory ones. Furthermore, ammonia (NH3) and trimethylamine (TMA) were produced in the pressurised lots after a pressure dependent delay. Urea decreased to low levels in all lots with the exception of the 400 MPa lot. Onset of production of agmatine, the dominant amine in this species, and other biogenic amines was delayed by increasing pressure, but still, high concentrations of these amines were detected in pressurised lots of acceptable sensory quality. Microbial counts conducted after 1 day of storage showed that the bacterial load was reduced by all pressures, reaching levels below the detection limit in the lots treated with 200-400 MPa. However, growth was resumed in all lots after a pressure dependent delay. Luminous bacteria predominated initially in the lots pressurised at 300 and 400 MPa, but were outnumbered by Enterobacteriaceae and lactic acid bacteria at the time of sensory rejection of these lots. All colonies isolated prior to pressurisation were identified as Photobacterium phosphoreum. This bacterium also resumed growth faster than other members of the endogenous microflora after pressurisation. All luminous colonies were identified as P. phosphoreum. Lactic acid bacteria isolated at the final sampling point of the lot pressurised at 400 MPa were identified as Carnobacterium piscicola and Carnobacterium divergens, while Serratia liquefaciens and Proteus vulgaris make up Enterobacteriaceae.     

Microbiological and physicochemical properties of red claw crayfish (Cherax quadricarinatus) stored in different package systems at 2 degrees C

ABSTRACT:  This study compared 3 package systems for their influence on the stability of shell-on red claw crayfish tail meat stored at 2 °C for 14 d. Modified atmosphere packaging (MAP, with 80% CO₂/10% O₂/10% N₂) suppressed ( P < 0.05) the growth of aerobic bacteria and coliforms when compared with aerobic packaging using polyvinylchloride (PVCP) and vacuum packaging (VP). MAP and VP tended to retard lipid oxidation, inhibited Ca-ATPase activity change, but produced more intense protein denatuation when compared with PVCP. The MAP packaging enhanced proteolysis and resulted in more ( P < 0.05) cooking losses and a higher ( P < 0.05) shear force than VP and PVCP for samples stored for 6 and 14 d ( P < 0.05). Sensory panel results were in general agreement with the physicochemical changes, suggesting that the specific package systems had a significant impact on the quality of refrigerated red claw crayfish raw meat.     

Foodborne pathogenic bacteria in prepackaged fresh retail portions of farmed rainbow trout and salmon stored at 3 degrees C

Twelve lots of fresh unskinned fillets of rainbow trout (Oncorhynchus mykiss) and 10 lots of fresh sliced salmon (Salmo salar) prepacked in trays wrapped with an oxygen-permeable film were obtained immediately after packing from two supermarkets having in-plant facilities for packaging wet fish. During storage at 3 degrees C, Listeria innocua was detected in eight lots of trout fillets after 4 days storage. L. monocytogenes was recovered from a single lot also contaminated with L. innocua. Initial numbers of aeromonads were significantly (p < 0.05) lower in trout fillets (3.35 +/- 0.62 log cfu g(-1)) than in salmon slices (4.20 +/- 0.89 log cfu g(-1)). In both fish products, these bacteria significantly (p < 0.05) increased up until spoilage. Most Aeromonas spp. isolates from trout fillets were assigned to A. veronii biovar sobria HG8 (hybridisation group 8), A. caviae HG4, A. eucrenophila HG6, A. hydrophila HG1 and A. veronii biovar veronii HG10. Strains of HG12 (A. schubertii), HG4 and HG8 formed the majority of aeromonads recovered from salmon slices.     

Quality attributes of farmed eel (Anguilla anguilla) stored under air, vacuum and modified atmosphere packaging at 0 degrees C

The shelf life of fresh eel in various packaging conditions of atmospheric air, vacuum and modified atmosphere packaging (MAP) (40% CO(2), 30% N(2) and 30% O(2)) at 0 degrees C was investigated. All raw eel samples received acceptable sensory scores during the first 11+/-1 days of storage in atmospheric air, 11+/-1 days of storage in vacuum and finally 18+/-1 days of storage in MAP conditions. Using the microbial quality indicators the shelf life of eel packed in air, vacuum and MAP was estimated to be more than 18, 28 and 34 days, respectively. The main spoilage microorganisms under MAP conditions were lactic acid producing bacteria followed by Shewanella spp., pseudomonads, Enterobacteriaceae and yeasts. Chemical data revealed that pH, ammonia, glucose and lactate examinations might not be useful for monitoring eel quality differences.     

Iron (III) hydrolysis and solubility at 25 degrees C

UV-vis spectrophotometric measurements, potentiometric titrations, and solubility measurements were performed to evaluate the hydrolysis constants for aqueous Fe(III) and the solubility of 2-line ferrihydrite over a wide concentration range (0-3 M NaClO4 and p[H+] 1.54-11.23). From these measurements, Fe3+ was found to hydrolyze to form FeOH2+, Fe2(OH)24+, Fe(OH)2+, Fe(OH)3(0), and Fe(OH)4-. The hydrolysis and solubility constants of these species were determined together with their dependence on ionic strength. The iron (III) hydrolysis constants at infinity dilution were (logbeta(1,1) to logbeta(1,4) and logbeta(2,2))-2.19 +/- 0.02, -5.76 +/- 0.06, -14.30 +/- 0.32, -21.71 +/- 0.24, and -2.92 +/- 0.02, respectively. The solubility product for 2-line ferrihydrite was (logK(s,0)) +3.50 +/- 0.20. The results have been compared with literature values.     

Fate of Salmonella Tennessee in peanut butter at 4 and 22 degrees C

ABSTRACT:  This study was undertaken to determine survival characteristics of inocula of a 3-strain mixture of Salmonella Tennessee in 5 commercial brands of peanut butter (A, B, C, D, and E). Inoculated peanut butter was stored at 4 (refrigerator temperature) and 22 °C (room temperature) for up to 14 d. After 1, 3, 5, 7, and 14 d, surviving cells, including injured cells, were enumerated on appropriate selective agar, including use of the agar overlay method. Populations in samples inoculated with 10^6–7 CFU/g and stored for 14 d at 4 and 22 °C decreased by 0.15 to 0.65 and 0.34 to 1.29 log CFU/g, respectively, depending on the formulation. Peanut butter A showed a significantly lower number of S . Tennessee cells when stored at 22 °C for 14 d, compared to 4 °C ( P < 0.05). However, there was no significant difference between the levels of S. Tennessee at 4 and 22 °C in products B, C, D, and E ( P > 0.05).     

Survival of Listeria monocytogenes in vanilla-flavored soy and dairy products stored at 8 degrees C

The survival of Listeria monocytogenes V37 in vanilla-flavored yogurt (low-fat and nonfat) and soy milk (low-fat and Plus) stored at 8 degrees C for 31 days was investigated. Commercial samples of yogurt and soy milk were used. These samples were inoculated with either 10(4) or 10(7) CFU of L. monocytogenes per ml. Sampling was carried out every 3 to 4 days initially and was then carried out weekly, for a total storage time of 31 days. Each time a sample was collected, the pH of the sample was measured. After 31 days, low-fat plain, low-fat vanilla, and nonfat plain yogurt samples inoculated with 10(4) CFU/ml showed 2.5-log reductions in viable cell populations, and nonfat vanilla yogurt showed a 3.5-log reduction. For yogurt inoculated with 10(7) CFU/ml, reductions of 2.5 log CFU/ml were observed for plain low-fat and nonfat yogurts, and reductions of 5 log CFU/ml were observed for vanilla-flavored low-fat and nonfat yogurts. In vanilla-flavored and plain low-fat and Plus soy milk samples, cell counts increased from 10(4) and 10(7) CFU/ml to 10(9) CFU/ml at 7 and 3 days of storage, respectively, at 8 degrees C. Coagulation in soy milk samples was observed when the cell population reached 10(9) CFU/ml. In soy milk, the L. monocytogenes population did not change for up to 31 days. Vanillin had an inhibitory effect on L. monocytogenes in yogurt but not in soy milk.     

Fate of Staphylococcus aureus on vacuum-packaged ready-to-eat meat products stored at 21 degrees C

The U.S. Department of Agriculture has established standards for the composition and shelf stability of various ready-to-eat meat products. These standards may include product pH, moisture:protein ratio, and water activity (aw) values. It is unclear how closely these standards are based on the potential for pathogen growth or toxin production. Because the vacuum packaging used on most ready-to-eat meat products inhibits mold, Staphylococcus aureus is the pathogen most likely to grow on products with reduced aw and increased percentage of water-phase salt. In this study, 34 samples of various ready-to-eat meat products were inoculated with a three-strain mixture of S. aureus, vacuum packaged, and stored at 21 degrees C for 4 weeks. S. aureus numbers decreased by 1.1 to 5.6 log CFU on fermented products (pH < or = 5.1) with a wide range of salt concentrations and moisture content. Similarly, S. aureus numbers decreased by 3.2 to 4.5 log CFU on dried nonacidified jerky (aw < or = 0.82; moisture:protein ratio of < or =0.8). Products that were not fermented or dried clearly supported S. aureus growth and cannot be considered shelf stable. The product pH and moisture:protein ratio were the two compositional factors most highly correlated (R2 = 0.84) with S. aureus survival and growth for the types of products tested, but pH and aw or pH and percentage of water-phase salt also may provide useful predictive guidance (R2 = 0.81 and 0.77, respectively).     

Effect of packaging atmosphere on the microbial attributes of pearlspot (Etroplus suratensis Bloch) stored at 0-2 degrees C

Effect of packaging atmosphere (air and under different modified atmospheres (MAs), 40% CO2/60% O2, 50%/50% O2, 60% CO2/40% O2, 70% CO2/30% O2 and 40% CO2/30% O2/30% N2) on the microbial and biochemical attributes of fresh pearlspot (Etroplus suratensis Bloch) stored at 0-2 degrees C was investigated. Trimethylamine nitrogen (TMA-N) and thiobarbituric acid (TBA) values remained lower than the proposed acceptability limits throughout the storage period. Results demonstrated that storage of pearlspot under air and MA 40% CO2/30% O(2)/30% N(2) resulted in growth of Enterobacteriaceae, Aeromonas and H(2)S-producing bacteria including Shewanella putrefaciens, while all other packaging atmospheres did not allow multiplication of Enterobacteriaceae and Aeromonas within 3 weeks. Aeromonas spp. identified were Aeromonas hydrophila, Aeromonas veronii biovar sobria and A. veronii biovar veronii. Significant reduction (p<0.01) was noticed in Aeromonas population of pearlspot stored under MA 60% CO2/40% O2 and 70% CO2/30% O2. A delay of growth of Pseudomonas below 5.0log(10)cfug(-1) was observed during the 15th day of storage at 0-2 degrees C under modified atmosphere packaging (MAP) conditions. Growth of faecal streptococci was significantly inhibited in all the packaging atmospheres at 0-2 degrees C during the entire storage period. Survival of coagulase positive Staphylococci (<50cfug(-1)) in low numbers was noticed during storage in all the packaging atmospheres. Clostridium botulinum toxin was not detected. All the packaging atmospheres did not allow multiplication of sulphite-reducing clostridia at 0-2 degrees C during the entire storage period. Packaging in MA 60% CO2/40% O2 resulted in the inhibition of growth of Aeromonas and Enterobacteriaceae, and the slowest growth of psychrotrophic bacteria, H(2)S-producing bacteria, including Shewanella putrefaciens and Pseudomonas and extended microbiological shelf life to 9-10 days. This study confirms the survival of potentially pathogenic A. hydrophila, A. veronii biovar sobria and A. veronii biovar veronii capable of growth at low temperature in pearlspot stored under MA.     

Control of Listeria monocytogenes with combined antimicrobials on beef franks stored at 4 degrees C

Contamination of ready-to-eat meat products such as beef franks with Listeria monocytogenes has become a major concern for the meat processing industry and an important food safety issue. The objective of this study was to determine the effectiveness of combinations of antimicrobials as aqueous dipping solutions to control L. monocytogenes on vacuum-packaged beef franks stored at 4 degrees C for 3 weeks. Commercial beef franks were dipped for 5 min in three antimicrobial solutions: pediocin (6,000 AU), 3% sodium diacetate and 6% sodium lactate combined, and a combination of the three antimicrobials. Samples were then inoculated with 10(7) CFU/g of either four L. monocytogenes strains individually or a cocktail of the four strains, vacuum packaged, and stored at 4 degrees C for 3 weeks. Sampling was carried out at day 0 and after 2 and 3 weeks of storage. Individual strains, as well as the cocktail, exhibited different responses to the antimicrobial treatments. After 2 and 3 weeks of storage at 4 degrees C, pediocin-treated beef franks showed a less than 1-log reduction for all bacterial strains. Samples treated with the sodium diacetate-sodium lactate combination showed about a 1-log reduction after 2 weeks of storage for all strains and between a 1- and 2-log reduction after 3 weeks of storage, depending on the bacterial strain. When the three antimicrobials were combined, reductions ranged between 1 and 1.5 log units and 1.5 to 2.5 log units after 2 and 3 weeks of storage, respectively, at 4 degrees C. These results indicate that the use of combined antimicrobial solutions for dipping treatments is more effective at inhibiting L. monocytogenes than treatments using antimicrobials such as pediocin separately.     

Biogenic amines in vacuum-packaged and carbon dioxide-controlled atmosphere-packaged fresh pork stored at -1.50 degrees C

Biogenic amines are formed in foods as a result of amino acid decarboxylation catalyzed by bacterial enzymes. When consumed in sufficient quantities, these compounds will cause headache, hypertension, fever, and heart failure. Technologies such as vacuum packaging and carbon dioxide-modified atmosphere packaging (CO2-MAP), when combined with low-temperature storage (-1.5 degrees C), allow fresh pork to have a storage life long enough for export to overseas markets. During low-temperature storage of pork in these packaging systems, the lactic acid bacteria (LAB), which possess the enzymes for biogenic amine formation, dominate the microflora. The objectives of this study were to determine the quantities of biogenic amines in packaged fresh pork, to monitor LAB growth, and to determine the storage life by sensory evaluation. Vacuum-packaged and CO2-MAP pork were stored at -1.5+/-0.5 degrees C for 9 and 13 weeks, respectively. Phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine, and spermine concentrations were determined weekly by high-performance liquid chromatography and capillary gel electrophoresis. LAB and carnobacteria were enumerated weekly. Samples were evaluated for odor and appearance. The CO2-MAP was successful in delaying bacterial growth and the development of unacceptable off-odors compared with the vacuum packaging. The storage lives of the vacuum-packaged and CO2-MAP pork were 5 and 13 weeks, respectively. High-performance liquid chromatography was the superior method for biogenic amine quantification. Tyramine and phenylethylamine in pork of both packaging treatments approached levels considered to be potentially toxic. Given Canada's increasing role in the export of fresh meat to foreign markets, it is recommended that the formation of biogenic amines in vacuum-packaged and CO2-MAP pork be further investigated.     

Combined effects of mustard flour,acetic acid,and salt against Esherichia coil O157:H7 stored at 5 and 22 degrees C

The combined effects of acetic acid and mustard flour were investigated to ascertain their impact on Escherichia coli O157:H7 stored at 5 and 22 degrees C. Samples were prepared with various concentrations of acetic acid (0, 0.25, 0.5, 0.75, and 1% [vol/vol]) combined with 10% (wt/vol) Baltimore or Coleman mustard flour and 2% (fixed; wt/vol) sodium chloride. An acid-adapted mixture of three E. coli O157:H7 strains (10(6) to 10(7) CFU/ml) was inoculated into prepared mustard samples that were stored at 5 and 22 degrees C, and samples were assayed periodically for the survival of E. coli O157:H7. The numbers of E. coli O157:H7 were reduced much more rapidly at 22 degrees C than at 5 degrees C. E. coli O157:H7 was rapidly reduced to below the detection limit (<0.3 log10, CFU/ml) after 1 day at 22 degrees C, whereas it survived for up to 5 days at 5 degrees C. There was no synergistic or additive effect with regard to the killing of E. coli O157:H7 with the addition of small amounts of acetic acid to the mustard flour. When stored at 5 degrees C, mustard in combination with 0.25 (M-0.25), 0.5 (M-0.5), and 0.75% (M-0.75) acetic acid exerted less antimicrobial activity than the control (M-0). The order of lethality at 5 degrees C was generally M-0.25 = M-0.5 < M-0.75 = M-0 < M-1. The addition of small amounts of acetic acid (<0.75%) to mustard retards the reduction of E coli O157:H7. Statistical reduction in populations of E. coli O157:H7 (P < 0.05) was enhanced relative to that of the control (mustard alone) only with the addition of 1% acetic acid. This information may help mustard manufacturers to understand the antimicrobial activity associated with use of mustard flour in combination with acetic acid.     

Changes in lipids during the storage of krill (Euphausia superba Dana) at 3 degrees C

Lipid content and composition (classes), susceptibility to UV-catalysed oxidation and carotenoid content were determined in Antarctic krill (Euphausia superba Dana) stored for 72 h at 3 degrees C. Phospholipids making up 80% of krill lipids were observed to undergo the most drastic changes during storage. After 72 h of storage, their content dropped by about 20%; the largest drop was recorded in phosphatidylcholine, its content being reduced by almost half. The amount of free fatty acids increased to about 6% of lipids. No degradation was observed in triacylglycerols, diacylglycerols, and wax esters. Monoglycerides did not appear. The UV-catalysed lipid oxidation rate decreased with deteriorating freshness of krill, as evidenced by a slower oxidation reaction, much lower oxidation maximum attained by lipids from spoiled krill, slower carotenoid decomposition, slower coloration of lipids and a slower absorbance increase at 320 nm. As no significant differences were found between iodine numbers and the carotenoid content of the samples tested, differences in the oxidation rate can be explained by hyperoxide decomposition brought about by products of phosphatidylcholine break-down.     

Microbiological quality of maatjes herring stored in air and under modified atmosphere at 4 and 10 degrees C

Microbiological and sensory changes of maatjes herring stored in air (experiment I) and under modified atmosphere (MAP) (experiments II and III) were evaluated during storage at 4 and 10 degrees C. Microbial (total and psychrotrophic viable bacteria, lactic acid bacteria and Enterobacteriaceae) counts and chemical analyses (chloride content, fat content, dry matter, ash and pH) were performed. A Quality Index Method (QIM) scheme developed for maatjes herring was used for sensory evaluation. The main reasons for sensory rejections at both storage temperatures were a strong rancid taste for herring stored in air (Experiment I) and a sour, bitter, rotten taste and an aftertaste like old flower water for MAP herring (Experiments II and III). A soft texture of freshly produced samples (Experiment II) was noticed. The sensory shelf-life of maatjes herring stored in air (Experiment I) was three days at both 4 and 10 degrees C. The MAP herring in Experiments II and III had a shelf-life of 5 and 6 days, respectively, at both storage temperatures. Rancidity due to oxidation of fat was the main spoilage indicator for air-stored maatjes herring. Autolytic enzymes may affect textural deterioration. The characteristic off-odour and off-taste in the MAP herring (Experiments II and III) were may well be attributable to microbial metabolism. On the day of sensory rejection, total viable counts for herring in all three experiments (Experiments I-III) stored at 4 degrees C did not reach 10(6)cfu/g, which is considered the limit of acceptability for maatjes herring given by the Dutch fishery authorities. It appears that total viable counts have minor significance in the sensory assessment of maatjes herring.     

Survival of Staphylococcus aureus and Listeria monocytogenes on vacuum-packaged beef jerky and related products stored at 21 degrees C

In the manufacture of beef jerky, a thermal lethality step is followed by drying to prevent growth of pathogenic bacterial postprocessing contaminants on the finished product. Recent guidelines from the U.S. Department of Agriculture have raised the question of the maximum water activity (a(w)) in jerky products that will inhibit growth of pathogenic bacteria. The survival of the potential postprocessing contaminants Staphylococcus aureus and Listeria monocytogenes was evaluated on 15 vacuum-packaged beef jerky and related products with a(w) values ranging from 0.47 to 0.87, just below the 0.88 limit reported for anaerobic growth of S. aureus. Small individual product pieces were inoculated on the outer surface with five strains each of S. aureus and L. monocytogenes, repackaged under vacuum, and stored at room temperature (21 degrees C) for 4 weeks. Pathogen numbers were determined before storage and after 1 and 4 weeks. None of the 15 jerky products supported growth of either pathogen. Counts of S. aureus fell by 0.2 to 1.8 log CFU after 1 week of storage and by 0.6 to 5.3 log CFU after 4 weeks of storage. Numbers of L. monocytogenes fell by 0.6 to 4.7 log CFU and by 2.3 to 5.6 log CFU after 1 and 4 weeks of storage, respectively. Although factors other than a(w) may have some effect on pathogen survival, the results of the present study clearly support drying beef jerky to an a(w) of < or = 0.87 to ensure that bacterial pathogens cannot grow on vacuum-packaged product stored at room temperature.     

Postprocessing antimicrobial treatments to control Listeria monocytogenes in commercial vacuum-packaged bologna and ham stored at 10 degrees C

The antilisterial effect of chemical dipping solutions on commercial bologna and ham slices, inoculated (3 to 4 log CFU/ cm2) after processing, was evaluated during storage in vacuum packages at 10 degrees C. Samples were inoculated with a 10-strain composite of Listeria monocytogenes and subsequently immersed (25+/-2 degrees C) for 2 min in 2.5% acetic acid (AA), 2.5% lactic acid (LA), 5% potassium benzoate (PB), or 0.5% Nisaplin (commercial form of nisin, equivalent to 5,000 IU/ml of nisin) solutions, either singly or sequentially (Nisaplin plus AA, Nisaplin plus LA, or Nisaplin plus PB), and then vacuum packaged and stored at 10 degrees C for 48 days. In addition to microbiological analysis, sensory evaluations were performed on uninoculated samples treated with AA, LA, or PB. Initial reductions (day 0) of the pathogen, compared with the controls, on bologna and ham samples treated with AA, LA, or PB ranged from 0.4 to 0.7 log CFU/cm2. Higher (P < 0.05) initial reductions (2.4 to 2.9 log CFU/cm2) were obtained for samples treated with Nisaplin alone and when followed by AA, LA, or PB. L. monocytogenes populations on control bologna and ham samples increased from 3.4 log CFU/cm2 (day 0) to 7.4 and 7.8 log CFU/ cm2, respectively, in 8 days at 10 degrees C. Listericidal effects were observed for all treatments tested, except for Nisaplin applied on its own, during storage at 10 degrees C. The sequential treatment of Nisaplin plus LA reduced L. monocytogenes to undetectable levels in both products at the end of storage. The sequential treatments were also found to inhibit growth of spoilage microorganisms. Sensory evaluations indicated that dipping (2 min) of ham samples in AA (2.5%), LA (2.5%), or PB (5%) led to lower sensory scores. However, since results of this study indicated that these treatments caused extensive listericidal effects, there is possibly a potential to reduce the levels of chemicals applied and still achieve adequate antilisterial activity without major negative effects on product quality.     

Survival of Escherichia coli O157:H7 in Galotyri cheese stored at 4 and 12 degrees C

Post-process contamination of fresh acid-curd cheeses with Escherichia coli O157:H7 may pose a risk considering the low infectious dose and the ability of the pathogen to survive in acidic foods. To evaluate its survival in Galotyri, a traditional Greek acid-curd cheese, portions (0.5 kg) of two commercial fresh products, one artisan (pH 3.9+/-0.1) and the other industrial (pH 3.7+/-0.1), were inoculated with approximately 3.0 or 6.5 log cfu g(-1) of a five-strain cocktail of E. coli O157:H7, including rifampicin-resistant derivatives of the strains ATCC 43895 and ATCC 51657, and stored aerobically at 4 and 12 degrees C. Survival was monitored for 28 days by plating cheese samples on tryptic soy agar with 100 mg l(-1) rifampicin (TSA+Rif), SMAC and Fluorocult E. coli O157:H7 agar media. The pathogen declined much faster (P<0.05) in the industrial as compared to the artisan cheeses at both temperatures. Thus, while E. coli O157:H7 became undetectable by culture enrichment after 14 days at 4 degrees C in industrial samples, irrespective of the inoculation level, populations of 1.4-1.9 and 4.2-5.1 log cfu g(-1) survived after 28 days in the corresponding artisan cheeses with the low and high inocula, respectively. Survival was longer and greater (P<0.05) on TSA+Rif than on SMAC and Fluorocult, indicating the presence of acid-injured cells. Interestingly, survival of E. coli O157:H7 after 14-28 days in cheeses was better at 12 degrees C than at 4 degrees C, probably due to yeasts which grew on the surface of temperature-abused cheeses. The large difference in the pathogen's inactivation between the industrial and artisan cheeses at 4 degrees C could not be associated with major differences in pH or type/concentration of organic acids, suggesting another anti-E. coli O157:H7 activity by the industrial starter. The high survival of the pathogen in artisan Galotyri under conditions simulating commercial storage should be of concern.