The influence of packaging methodology on the microbiological and fatty acid profiles of refrigerated African catfish fillets

AIMS: The shelf-life of refrigerated catfish fillets was determined at 2 degrees C, to simulate retail conditions, using two types of packaging materials, vacuum packing (VP) and oxygen permeable packaging (OPP). METHODS AND RESULTS: Representative samples (n=5) from both types of packaging methods were drawn at random every 2 d until a microbiological count of 106 cfu g-1 was reached. Samples were pooled and screened microbiologically using standard methods. Fatty acid analyses of total lipids, neutral lipid, glycolipid and phospholipid fractions were also conducted, to determine at which point the fish was regarded as spoiled and which packaging method provided a longer shelf-life. OPP limits storage to a maximum of 4 d (aerobic plate count of 8.2 x 105 cfu g-1), whereas VP extends the shelf-life of the fillets to between 6 and 8 d (aerobic plate count of 9.2 x 104 cfu g-1 and 1.66 x 106 cfu g-1, respectively). Similarly, coliform counts increased with time; however, packaging material had no statistical influence thereon. CONCLUSION: Until d 13, when the experiment was terminated, no deterioration in lipid composition of the various fractions was noted. SIGNIFICANCE AND IMPACT OF THE STUDY: An extended shelf-life microbiologically-speaking, for potential processors, could thus be obtained by using VP instead of OPP.     

Nisin and ALTATM 2341 inhibit the growth of Listeria monocytogenes on smoked salmon packaged under vacuum or 100% CO2

The effects of nisin and ALTA 2341 on the growth of Listeria monocytogenes were assessed on smoked salmon packaged under vacuum or 100% CO2. Smoked salmon slices (pH 6.3) were inoculated with a cocktail of seven L. monocytogenes isolates at a level of approximately 2.5 log10 colony forming units (cfu) g-1. After inoculation, the surface of the smoked salmon slices was treated with either nisin (400 or 1250 IU g-1) or ALTA 2341 (0.1 or 1%). The smoked salmon was packaged and stored at 4 degrees C (28 d) or 10 degrees C (9 d). On untreated vacuum-packaged smoked salmon, L. monocytogenes grew by 3.8 log10 cfu g-1 at 4 degrees C and 5.1 log10 cfu g-1 at 10 degrees C. Growth was reduced on nisin- and ALTA 2341-treated vacuum-packaged smoked salmon. On the nisin-treated samples, L. monocytogenes increased by 2.5 (400 IU g-1) and 1.5 (1250 IU g-1) log10 cfu g-1 at 4 degrees C, and by 4.3 (400 IU g-1) and 2.7 (1250 IU g-1) log10 cfu g-1 at 10 degrees C. With the ALTA 2341-treated samples, L. monocytogenes increased by 2.8 (0.1%) or 1.6 (1.0%) log10 cfu g-1 at 4 degrees C, and 3.3 (0.1%) or 3.6 (1.0%) log10 cfu g-1 at 10 degrees C. The growth of L. monocytogenes was retarded by packaging the smoked salmon in 100% CO2. On untreated smoked salmon, only a 0.8 log10 cycle increase was observed at 10 degrees C. Under all the other conditions tested with 100% CO2, L. monocytogenes was detected but growth was prevented.     

The bacterial flora of vacuum-packed cold-smoked salmon stored at 7 degrees C, identified by direct 16S rRNA gene analysis and pure culture technique

AIMS: The indigenous flora of freshly chilled cold-smoked salmon just after the vacuum packaging, and the spoilage flora after storage, in vacuum package at 7 degrees C for 19 days, were to be investigated with two different sampling strategies. METHODS AND RESULTS: Identification was performed using 16S rRNA sequencing of both isolated bacteria and bacterial DNA from tissue extract. The indigenous flora of fresh cold-smoked vacuum-packed salmon was dominated by, in order, Brochothrix thermosphacta, Yersinia ruckeri, Photobacterium and Carnobacterium, whereas the spoilage flora of the same product stored at 7 degrees C for 19 days was dominated by Lactobacillus and Photobacterium. The two sampling strategies showed similar results on the fish flora. Several new types of Photobacterium sequences, closely related to Photobacterium iliopiscarium and Photobacterium phosphoreum, were found from both the freshly processed and the stored salmon, indicating that smoked salmon harbours at least three different, as yet unknown, Photobacterium species. CONCLUSIONS: Ten per cent of the bacterial flora multiplying on chilled, vacuum-packed, cold-smoked salmon comprised unknown species. The two sampling strategies complement each other. SIGNIFICANCE AND IMPACT OF THE STUDY: As cold-smoked salmon is consumed without heat-treatment, the presence of undefined bacteria in high numbers should be considered in public health assessments.     

Carvacrol and cinnamic acid inhibit microbial growth in fresh-cut melon and kiwifruit at 4 degrees and 8 degrees C

AIM: To establish whether or not carvacrol and cinnamic acid delay microbial spoilage of fresh-cut fruit. METHODS AND RESULTS: Dipping of fresh-cut kiwifruit in carvacrol solutions at 5-15 mM reduced total viable counts from 6.6 to < 2 log cfu g-1 for 21 d at 4 degrees C; however, undesirable colour and odour changes were also observed. Treatment with 1 mM of carvacrol or cinnamic acid reduced viable counts on kiwifruit by 4 and 1.5 log cfu g-1 for 5 d at 4 degrees C and 8 degrees C, respectively. Treatment of fresh-cut honeydew melon with 1 mM of carvacrol or cinnamic acid extended the lag phase of the microbial flora from less than 1 d in the untreated controls to 3 d at 8 degrees C and 5 d at 4 degrees C. Viable counts on the treated melon were 6 log cfu g-1 lower on Day 3 at 8 degrees C and 4 log cfu g-1 lower on Day 5 at 4 degrees C, compared with the untreated controls. IMPACT OF THE STUDY: Treatment with 1 mM of carvacrol or cinnamic acid delays spoilage of fresh-cut kiwifruit and honeydew melon at chill temperatures without adverse sensory consequences.     

Production of acylated homoserine lactones by psychrotrophic members of the Enterobacteriaceae isolated from foods.

Bacteria are able to communicate and gene regulation can be mediated through the production of acylated homoserine lactone (AHL) signal molecules. These signals play important roles in several pathogenic and symbiotic bacteria. The following study was undertaken to investigate whether AHLs are produced by bacteria found in food at temperatures and NaCl conditions commercially used for food preservation and storage. A minimum of 116 of 154 psychrotrophic Enterobacteriaceae strains isolated from cold-smoked salmon or vacuum-packed chilled meat produced AHLs. Analysis by thin-layer chromatography indicated that N-3-oxo-hexanoyl homoserine lactone was the major AHL of several of the strains isolated from cold-smoked salmon and meat. AHL-positive strains cultured at 5 degrees C in medium supplemented with 4% NaCl produced detectable amounts of AHL(s) at cell densities of 10(6) CFU/ml. AHLs were detected in cold-smoked salmon inoculated with strains of Enterobacteriaceae stored at 5 degrees C under an N(2) atmosphere when mean cell densities increased to 10(6) CFU/g and above. Similarly, AHLs were detected in uninoculated samples of commercially produced cold-smoked salmon when the level of indigenous Enterobacteriaceae reached 10(6) CFU/g. This level of Enterobacteriaceae is often found in lightly preserved foods, and AHL-mediated gene regulation may play a role in bacteria associated with food spoilage or food toxicity.     

Microbiological composition of raw milk from selected farms in the Camembert region of Normandy

Raw milk from 27 farms was sampled over 6 months for listerias, salmonellas, Yersinia enterocolitica and campylobacters. Total bacterial counts and somatic cell counts were measured. Lactococci, lactobacilli, dextran-producing leuconostocs, Brevibacterium linens , yeasts and moulds, Staphylococcus aureus and other Micrococcaceae, Pseudomonas , coliforms, Escherichia coli , enterococci, Clostridium perfringens and spores of anaerobic lactate-fermenting bacteria were also counted. Pseudomonas (2000 cfu ml⁻¹), lactococci (760 cfu ml⁻¹) and Micrococcaceae (720 cfu ml⁻¹) were the most numerous groups. Lactic acid bacteria were detected in all samples. Coliforms were present in most samples, but 84% of samples had counts <100 cfu ml⁻¹. Staphylococcus aureus was detected in 62% of milks, the average count was 410 cfu ml⁻¹. About 80% of supplies had ≤10 E. coli cfu ml⁻¹ and all samples had 1 Cl. perfringens cfu ml⁻¹. Two of the tested milks were positive for salmonellas (2·9%), four were positive for Listeria monocytogenes (5·8%), 25 for Yersinia enterocolitica (36%) and one for campylobacters (1·4%).     

Growth and survival of E. coli O157:H7 during the manufacture and ripening of a smear-ripened cheese produced from raw milk

AIMS: The behaviour of Escherichia coli O157:H7 was studied during the manufacture and ripening of a smear-ripened cheese produced from raw milk. METHODS AND RESULTS: Cheese was manufactured on a laboratory scale using milk (20 l) inoculated with E. coli O157:H7, and enumeration was carried out using CT-SMAC. From an initial level of 1.52 +/- 0.03 log cfu ml-1 in the milk (34 +/- 2 cfu ml-1), the numbers increased to 3.4 +/- 0.05 log cfu g-1 in the cheese at day 1. During ripening, the numbers decreased to <1 cfu g-1 and <10 cfu g-1 in the rind and core, respectively, after 21 days, although viable cells were detected by enrichment after 90 days. The presence of E. coli O157:H7 in the cheese was confirmed by latex agglutination and by multiplex PCR. CONCLUSION: The results indicate that the manufacturing procedure encouraged substantial growth of E. coli O157:H7 to levels that permitted survival during ripening and extended storage. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of low numbers of E. coli O157:H7 in milk, destined for raw milk cheese manufacture, could constitute a threat to the consumer.     

Factors affecting growth and lipase production by meat lactobacilli strains and Brochothrix thermosphacta

Lipolytic activity of lactobacilli strains and Brochothrix thermosphacta was cellrelated; no significant activity was found in the supernatant fluids. Most lipase was produced during the logarithmic phase of growth and was greatly affected by growth conditions. The optimal temperatures for growth and lipase production were respectively 24°C for B. thermosphacta and 30°C for lactobacilli. For all strains, an initial pH of around 7-0 for the medium and low glucose concentration stimulated lipase production. Tributyrin inhibited both growth and lipase production at a concentration of 0-1% for B. thermosphacta or 1% for lactobacilli. Butyric acid (0-1%) and anaerobic culture inhibited lipase production by B. thermosphacta while these two factors had no effect on enzyme production by lactobacilli.     

Impact of two probiotic Lactobacillus strains feeding on fecal lactobacilli and weight gains in chicken

Two probiotic strains, Lactobacillus agilis JCM 1048 and L. salivarius subsp. salicinius JCM 1230 isolated from chicken intestine, exhibited probiotic characteristics that can be applied for chicken production. After 7 days of probiotic feeding (FD7), the count of intestinal lactobacilli in the probiotic group (group P, n=10) was significantly (p<0.05) higher than that in the control group (group C, n=9). After 40 days of probiotic feeding (FD40), the lactobacilli and enterococci counts were stable but the Enterobacteriaceae number was significantly reduced (p<0.05). A total of 163 isolated lactobacilli were identified as the L. acidophilus/gallinarum group (49.7%), L. agilis (30.7%), L. salivarius (9.2%), L. reuteri (9.2%), and Lactobacillus spp. (1.2%). The probiotic lactobacilli positively affected the Lactobacillus biota in chickens at FD7, with a significant increase in the number (p<0.05) of L. agilis and group P. The viable counts of each Lactobacillus species at FD40, however, showed no differences between two groups. An increasing incidence of L. agilis was also noted with probiotic feeding. The probiotic effect of two strains resulted in significantly increased weight gains (10.7%) of group P in comparison with group C at FD40 (p<0.01).     

Reduction of Escherichia coli O157:H7 by stimulated Pediococcus acidilactici

This study was conducted to determine if stimulating the growth of meat starter culture (Pediococcus acidilactici) in a laboratory medium (Brain Heart Infusion broth +2.3% NaCl + 1.5% sucrose; LBHI) and during meat fermentation would control Escherichia coli O157:H7. In LBHI medium without P. acidilactici, the numbers of E. coli O157:H7 increased from 4.00 to 8.34 log10 cfu ml-1, whereas in the presence of P. acidilactici (approximately 6.0 log10 cfu ml-1) in LBHI, LBHIM (LBHI + 0.005% MnSO4), LBHIO (LBHI + 0.3 unit ml-1 Oxyrase), and LBHIMO (LBHI + M + O), the numbers of E. coli O157:H7 increased from 4.00 to 8.05, 7.50, 7.99, and 6.50 log10 cfu ml-1, respectively, after incubation at 40 degrees C for 15 h. During salami fermentation, the numbers of E. coli O157:H7 changed from 7.00 to 6.40 and 5.10 log10 cfu g-1 without and with P. acidilactici (approximately 7.0 log10 cfu g-1), respectively. Stimulated P. acidilactici by M, O, and MO further reduced the number of E. coli O157:H7 from 7.00 to 4.00, 4.80, and 3.65 log10 cfu g-1, respectively. The combination of MO was a better growth stimulator for P. acidilactici, which controlled E. coli O157:H7 in both systems (P < 0.05).     

Microbiological characteristics of anevato: a traditional greek cheese

Nine batches of Anevato, raw goat milk cheese, were examined throughout a 60 day storage time at three different periods within the lactation season of the goat. High mean log counts per gram of cheese for aerobic bacteria (7·92–9·56), lactic acid bacteria (7·78–9·32), Gram-negative organisms 5·64–9·67), psychrotrophs (7·90–11·79) and proteolytic bacteria (7·57–9·36) were found. Enterobacteriaceae, coliforms and yeasts were considerably lower. Enterobacteriaceae and coliforms in the curd of cheese made in May were lower by approximately 3·0 log₁₀ cfu g⁻¹ than counts in curd made in January, and were lower by about 2·5 log₁₀ cfu g⁻¹ than those in cheese made in March. This coincided with lower pH and higher counts of lactic acid bacteria in cheese made in March and May. Yeast populations were affected by the season and were higher in May than March and/or January. Lactococci dominated in the cheese until 15 days, but lactobacilli became predominant after 30 days. Lactococcus lactis was the most abundant species of lactic acid bacteria found in Anevato cheese. Results suggest the need for improving milk quality and/or using heat-treated milk to produce Anevato cheese; the use of L. lactis as a starter would possibly eliminate or suppress the growth of undesirable organisms.     

The effect of biogenic amine production by single bacterial cultures and metabiosis on cold-smoked salmon

AIM: Biogenic amines are important indicators of spoilage in vacuum-packed cold-smoked salmon. It is the aim of this study to identify bacteria responsible for biogenic amine production in cold-smoked salmon. METHODS AND RESULTS: The present study identified spoilage microflora from cold-smoked salmon and determined biogenic amine production of single and co-cultures growing in cold-smoked salmon. Photobacterium phosphoreum was the only species that produced histamine when inoculated on sterile cold-smoked salmon. Production of putrescine was enhanced 10-15 times when cultures of Serratia liquefaciens or Hafnia alvei were grown with Carnobacterium divergens or Lactobacillus sakei subsp. carnosus. This phenomenon was explained by interspecies microbial metabolism of arginine, i.e., metabiosis. CONCLUSIONS: The amounts of biogenic amines produced by single and co-cultures corresponded to those observed during spoilage of naturally-contaminated cold-smoked salmon. Photobacterium phosphoreum and Lact. curvatus were identified as the specific spoilage organisms in cold-smoked salmon. SIGNIFICANCE AND IMPACT OF THE STUDY: Determination of the specific spoilage organism is needed before a model can be developed for shelf-life predictions of cold-smoked salmon.     

Seasonal variation in the microbial contamination of game carcasses in an Austrian hunting area

In 2003, 50 game carcasses (ungulates) originating from one Austrian hunting ground were subject to visual examination for (fecal) contamination of the body cavities and microbiological testing of the body cavities in order to assess variations in microbial surface contamination in the season June–August compared to October–December. No carcass tested positive for the bacterial pathogens Salmonella or Listeria. Bacterial surface counts in October–December (median values: total aerobic count: 4.12 log₁₀ colony-forming-units (cfu)/cm²; Enterobacteriaceae: 2.48 log₁₀ cfu/cm²) were significantly lower than those in June–August (median values: total aerobic count: 5.65 log₁₀ cfu/cm²; Enterobacteriaceae: 3.45 log₁₀ cfu/cm²). The cooling regime (0.4 °C, 62% relative humidity) allowed no microbial growth for 96 h but was associated with weight loss of the carcasses. All carcasses had undergone a precooling phase of 8–12 h, with temperatures of 17.8±1.2 °C in the season June–August and 9.8±1.2 °C in October–December. This temperature difference was identified as the most probable effector for the observed seasonal variation. The results demonstrate the need for a continuous cool chain after evisceration of game carcasses.     

Factors affecting growth and lipase production by meat lactobacilli strains and Brochothrix thermosphacta

Lipolytic activity of lactobacilli strains and Brochothrix thermosphacta was cell-related; no significant activity was found in the supernatant fluids. Most lipase was produced during the logarithmic phase of growth and was greatly affected by growth conditions. The optimal temperatures for growth and lipase production were respectively 24 degrees C for B. thermosphacta and 30 degrees C for lactobacilli. For all strains, an initial pH of around 7.0 for the medium and low glucose concentration stimulated lipase production. Tributyrin inhibited both growth and lipase production at a concentration of 0.1% for B. thermosphacta or 1% for lactobacilli. Butyric acid (0.1%) and anaerobic culture inhibited lipase production by B. thermosphacta while these two factors had no effect on enzyme production by lactobacilli.     

Growth of Escherichia coli O157 in poorly fermented laboratory silage: a possible environmental dimension in the epidemiology of E. coli O157

Laboratory silages, inoculated with either c. 1000 cfu g-1, an atoxigenic Escherichia coli O157 or a toxigenic E. coli O157 isolate, were made in plastic bags which permitted limited aerobic spoilage. Replicate bags of each treatment were opened at weekly intervals after incubation at 20 degrees C. In all silages the fermentation was slow and aerobic spoilage with visible moulding ocurred at the tie ends after 7 d. In all the aerobically spoiled silages Enterobacteriaceae reached over 107 cfu g-1 within 1 week. The E. coli in control silages increased from barely detectable levels to 104 cfu g-1 within 13 d; over the same period both strains of E. coli O157 increased from 103 to 107 cfu g-1. The increases in the poorly fermented interior of the silage bags were initially similar but declined slightly as the pH fell. It is suggested that faecal contamination of grass followed by poor silage management may be a factor in the persistence of E. coli O157 carriage in ruminants.     

泥螺养殖滩涂异养菌群和弧菌的检测

1　引　　言泥螺 (Ｂｕｌｌａｃｔａｅｘａｒａｔａ)隶属腹足纲软体动物 ,肉质鲜嫩、营养丰富 ,是浙江沿海重要的滩涂养殖品种 .至 2 0 0 0年浙江省养殖面积已达 1.13× 10 4ｈｍ2 ,由于实行生态养殖 ,本轻利厚 ,广受养农的青睐 .随着泥螺养殖生产的发展 ,养殖业的自身污染和陆源排污水的大量入海 ,养殖生态环境越趋恶化 ,使生物病原大量滋生 ,自 1995年以来常诱发养殖泥螺的暴发性死亡 .有关海洋滩涂环境细菌的研究至今未见报道 .为探明泥螺养殖周期内暴发性死亡与滩涂环境的关系 ,对养殖滩涂的细菌菌群组成及其生态特性进行了检测分析 .2…     

Microbiological and chemical analysis of fermented sorghum dough for Kisra production

Summary Sorghum flour was fermented in the traditional way for Kisra production. Wet or dry preparations of fermented sorghum dough from Sudanese households were employed as inocula. Microbiological and chemical analysis was performed throughout the fermentation process. Cell counts reached values of up to 9 × 10⁸ cfu/g and contained >99% lactobacilli. Strains of Lactobacillus fermentum, L. reuteri and L. amylovorus or L. fermentum and L. amylovorus were found as dominant organisms in doughs inoculated with wet or dry sorghum dough preparations, respectively. The ratios of the lactobacilli remained constant after up to four consecutive fermentations. After inoculation with the dry dough preparation the yeast Candida krusei was detected at 10⁶ cfu/g. During the fermentation the pH declined from 5.5 to values of approximately 3.4. The maltose content of the dough decreased continuously, wheraas glucose was accumulated as an intermediate. The relative content of most amino acids in the doughs did not significantly change during the fermentation. However, the concentrations of cysteine and methionine decreased, whereas threonine was enriched in the dough. Correspondence to: R. F. Vogel     

A note on yeast growth in media used for the cultivation of lactobacilli

Yeast species found in mayonnaise-based salads are capable of growth in media used for the isolation of lactobacilli. Many counts of lactobacilli from such products may, therefore, inadvertently include counts of yeasts. A method is presented whereby the use of media with and without chloramphenicol makes it possible to deduce a differential count of bacteria. It was not possible to prevent yeast growth in de Man, Rogosa and Sharpe agar by the addition of cycloheximide since many isolates were resistant to it.     

Modelling and predicting the simultaneous growth of Listeria monocytogenes and spoilage micro-organisms in cold-smoked salmon

Aims: To evaluate and model the simultaneous growth of Listeria monocytogenes and spoilage micro-organisms in cold-smoked salmon. Methods and Results: Growth kinetics of L. monocytogenes, lactic acid bacteria (LAB), Enterobacteriaceae, enterococci and Photobacterium phosphoreum were determined in two series of challenge tests with sliced and vacuum-packed cold-smoked salmon (SVP-CSS). The product contained a high level of smoke components and at 2°C levels of L. monocytogenes increased <100-fold in 193 days. Without the addition of spoilage micro-organisms, L. monocytogenes reached ca 10⁸ CFU g⁻¹ at 5, 10, 17·5 and 25°C. Inoculation with spoilage micro-organisms reduced this level to 10²–10⁴ CFU g⁻¹. LAB dominated the spoilage microfora of SVP-CSS and competition between LAB and L. monocytogenes in SVP-CSS was appropriately described by a simple expansion of the Logistic model. This interaction model aided in predicting the growth of L. monocytogenes in naturally contaminated SVP-CSS when it was used in combination with expanded versions of existing secondary models for L. monocytogenes and LAB. Conclusions: Temperature, water activity/NaCl, simultaneous growth of LAB, smoke components and to a lesser extent lactate and pH control growth of L. monocytogenes in SVP-CSS. These factors must be included in mathematical models to predict growth of the pathogen in this product. Significance and Impact of the Study: The suggested predictive model can be used to support assessment and management of the human health risk due to L. monocytogenes in SVP-CSS.     

Production of Acylated Homoserine Lactones by Psychrotrophic Members of the Enterobacteriaceae Isolated from Foods

Bacteria are able to communicate and gene regulation can be mediated through the production of acylated homoserine lactone (AHL) signal molecules. These signals play important roles in several pathogenic and symbiotic bacteria. The following study was undertaken to investigate whether AHLs are produced by bacteria found in food at temperatures and NaCl conditions commercially used for food preservation and storage. A minimum of 116 of 154 psychrotrophic Enterobacteriaceae strains isolated from cold-smoked salmon or vacuum-packed chilled meat produced AHLs. Analysis by thin-layer chromatography indicated that N-3-oxo-hexanoyl homoserine lactone was the major AHL of several of the strains isolated from cold-smoked salmon and meat. AHL-positive strains cultured at 5°C in medium supplemented with 4% NaCl produced detectable amounts of AHL(s) at cell densities of 10⁶ CFU/ml. AHLs were detected in cold-smoked salmon inoculated with strains of Enterobacteriaceae stored at 5°C under an N₂ atmosphere when mean cell densities increased to 10⁶ CFU/g and above. Similarly, AHLs were detected in uninoculated samples of commercially produced cold-smoked salmon when the level of indigenous Enterobacteriaceae reached 10⁶ CFU/g. This level of Enterobacteriaceae is often found in lightly preserved foods, and AHL-mediated gene regulation may play a role in bacteria associated with food spoilage or food toxicity.