Enterococcus species dominating in fresh modified-atmosphere-packaged, marinated broiler legs are overgrown by Carnobacterium and Lactobacillus species during storage at 6 degrees C

In order to show which of the initial lactic acid bacteria (LAB) contaminants are also causing spoilage of a modified-atmosphere-packaged (MAP), marinated broiler leg product at 6 degrees C, LAB were enumerated and identified on the 2nd and 17th days following manufacture. A total of 8 fresh and 13 spoiled packages were studied for LAB levels. In addition, aerobic mesophilic bacteria and Enterobacteriaceae were determined. The average CFU/g values in the 8 fresh packages were 1.3 x 10(3), 9.8 x 10(3) and 2.6 x 10(2) on de Man Rogosa Sharpe agar (MRS), Plate Count Agar (PCA) and Violet Red Bile Glucose agar (VRBG), respectively. The commercial shelf life for the product had been set as 12 days, and all packages analyzed on the 17th day were deemed unfit for human consumption by sensory analysis. The corresponding CFU/g averages in the spoiled product were 1.4 x 10(9), 1.1 x 10(9) and 3.9 x 10(7) on MRS, PCA and VRBG agar, respectively. For characterization of LAB population, 104 colonies originating from the fresh packages and 144 colonies from the spoiled packages were randomly picked, cultured pure and identified to species level using a 16 and 23S rDNA HindIII RFLP (ribotyping) database. The results showed that enterococci (35.7% of the LAB population) were dominating in the fresh product, whereas carnobacteria (59.7%) dominated among the spoilage LAB. Enterococcus faecalis, Carnobacterium piscicola and Carnobacterium divergens were the main species detected. In general, when the initial LAB population is compared to the spoilage LAB, a shift from homofermentative cocci towards carnobacteria, Lactobacillus sakei/curvatus and heterofermentative rods is seen in this marinated product.     

Spoilage of value-added, high-oxygen modified-atmosphere packaged raw beef steaks by Leuconostoc gasicomitatum and Leuconostoc gelidum

Moisture-enhancing and marinating of meats are commonly used by the meat industry to add value to raw, retail products. Recently in Finland, certain value-added beef steak products have proven to be unusually susceptible to microbial spoilage leading to untoward quality deteriorations during producer-defined shelf-life. This study was conducted to evaluate the role of lactic acid bacteria (LAB) in the premature spoilage of value-added beef packaged under high-oxygen modified atmospheres. Spoilage was characterised by green discolouration and a buttery off-odour. The predominant LAB in eight packages of spoiled, marinated or moisture-enhanced beef steaks were identified by reference to a 16 and 23S rRNA gene restriction fragment length polymorphism pattern (ribotype) database. Leuconostoc gasicomitatum, Leuconostoc gelidum, Lactobacillus algidus, Lactobacillus sakei and Carnobacterium divergens were found to predominate in the LAB populations at numbers above 10(8) CFU/g. Inoculation of moisture-enhanced steaks with LAB strains and strain mixtures originating from the spoiled products demonstrated the spoilage potential of L. gasicomitatum and L. gelidum isolates. These two species produced green surface discolouration and buttery off-odours similar to these found in the spoiled, commercial products.     

Leuconostoc gelidum and Leuconostoc gasicomitatum strains dominated the lactic acid bacterium population associated with strong slime formation in an acetic-acid herring preserve

Spoilage characterised by strong slime and gas formation affected some manufacture lots of an acetic-acid Baltic herring (Culpea haerengus membras) preserve after few weeks of storage at 0-6 degrees C. The product consisted of herring filets in acetic acid marinade containing sugar, salt, allspice and carrot slices. Microbiological analyses of the spoiled product showed high lactic acid bacterium (LAB) levels ranging from 4.5x10(8) to 2.4x10(9) CFU/g. Yeasts were not detected in any of the herring samples. Since LAB contaminants are seldom associated with fresh fish, LAB populations associated with marinade ingredients (carrots, allspice) were also analyzed. The highest LAB levels exceeding 10(7) CFU/g were detected in equilibrium modified atmosphere packaged baby carrots whereas the levels detected in the allspice samples did not exceed 4.3x10(5). A total of 176 randomly selected LAB isolates originating from herring, carrot and allspice samples were further identified to species level using a 16 and 23S rRNA gene RFLP (ribotyping) database. Leuconostoc gelidum and Leuconostoc gasicomitatum strains dominated both in the spoiled herring and carrot samples. These species are heterofermentative-producing CO(2) from glucose and they also produce dextran from sucrose. Inoculation of some commercial-herring products with spoilage-associated L. gelidum and L. gasicomitatum strains verified that these strains have the capability of producing slime and gas in herring preserves although slime formation was not as strong as in the original samples. Since L. gelidum and L. gasicomitatum strains were commonly detected in carrots, carrot slices used for the fish marinade were considered to be the probable source of these specific spoilage organisms.     

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.     

Characterization and identification of lactic acid bacteria in "morcilla de Burgos"

A total of 176 lactic acid bacteria (LAB) isolated from a typical Spanish blood sausage called "morcilla de Burgos" were identified by means of phenotypic characteristics and 16S rDNA RFLP (ribotyping). LAB were isolated from "morcilla" of different producers and in different storage periods, which includes unpackaged, vacuum and modified atmosphere packaged "morcilla" and vacuum packed and pasteurised "morcilla". The knowledge of specific spoilage bacteria of "morcilla de Burgos" will be useful to design new preservation methods to extend the shelf-life of this product. Identification made according to phenotypic and biochemical characteristics shows the majority of the isolates were heterofermentative LAB (93.2%) and eight different bacterial groups could be distinguished (A-G). Weisella viridescens was the main species detected (42%). In addition, Leuconostoc spp. (23.9%), Weissella confusa (11.4%) and Lactobacillus fructosus (5.7%) species were found. Few strains were phenotypically misidentified as Lactobacillus sanfrancisco, Pediococcus spp., Lactobacillus sakei/curvatus and Carnobacterium spp. and 11 strains remained unknown. Most of the leuconostocs were identified as Leuconostoc mesenteroides and Leuconostoc carnosum species. Ribotyping shows a quite good correlation with phenotypic methods, although it has been possible to identify 15 different clusters. W. viridescens and leuconostocs were also the predominant LAB. Strains identified as W. confusa by phenotypic characteristics were resolved in W. confusa and Weissella cibaria by ribotyping. Neither Carnobacterium piscicola nor Lb. sanfrancisco were identified by means of genotypic method. All Lb. fructosus strains and some more included in different phenotypic groups (17 strains in total) could not be associated with any reference strain (cluster VII).     

Change in the composition of the microflora on vacuum-packaged beef during chiller storage

Five fresh beefcut samples were divided into 10 pieces, respectively, vacuum-packaged and stored at 2 degrees C for up to 6 weeks. The average pH values of five pieces from five beef samples were 5.62 +/- 0.04 at the start of storage and 5.12 +/- 0.07 after 6 weeks of storage. The pieces were homogenized, diluted and cultivated at weekly intervals on glucose-blood-liver (BL), de Man Rogosa and Sharpe (MRS) and trypticase soya (TS) agars at 7 degrees C for 10-14 days. From plates with 30-300 colonies, or the highest number if below 30, 15 colonies were randomly picked from each of the three media used for each beef sample. Based on morphologies, SDS-PAGE whole-cell protein profiles and physio-chemical characteristics, a total of 1493 strains isolated were identified as Brochothrix thermosphacta (64), Carnobacterium divergens (79), Carnobacterium piscicola (27), Lactobacillus algidus (637), Lactobacillus sp. (4), Lactococcus piscium (270), Leuconostoc gelidum (375), Acinetobacter (3), Aeromonas (1), Bacillus (10), Corynebacterium (3), Enterobacteriaceae (1), Pseudomonas (13) or Psychrobacter (6). A wider range of organisms was isolated from TS (13 organisms) and BL (7) agars than from MRS agar (3). Leuc. gelidum, Lc. piscium and L. algidas increased in numbers during the first 3 weeks of storage from about 5 x 10(3) cfu/g to the level of about 10(8) cfu/g and persisted at this level thereafter. C. divergens and C. piscicola were inconsistently detected, but seemed to persist at the relatively low level of about 5 x 10(7) cfu/g during the last 3 weeks of storage. B. thermosphacta increased to the level of about 7 x 10(5) cfu/g during the first 2 weeks of storage, but was not detected thereafter. Remaining organisms were detected sporadically at levels of <3.5 x 10(2) cfu/g during the first 2 weeks of storage.     

Comparison of microbial communities in marinated and unmarinated broiler meat by metagenomics

Most raw poultry sold in Finland at the retail level is mixed with marinades containing oil, sugar, spices and acetic acid and packaged under modified atmosphere. Premature spoilage of marinated poultry preparations has been observed and associated with high levels of Leuconostoc spp. in meat. In this study we investigated whether marination of broiler fillet strips increased the proportion of Leuconostoc spp. in the microbial communities. To obtain a comprehensive view of the microbiota, we sequenced total DNA and 16S rRNA gene amplicons from the microbial communities. The lactic acid bacterial communities were characterized also by identification of colonies. The results showed that marinade increased the proportions of the spoilage-associated Leuconostoc gasicomitatum in the communities as well as the proportions of Leuconostoc gelidum and Lactobacillus spp. The proportions of Carnobacterium, Vagococcus, Brochothrix thrermosphacta, Clostridium, Enterobacteriaceae and Vibrio were diminished in marinated meat. Analysis of 16S rRNA gene amplicons resulted in 312 and 284 operational taxonomical units (dissimilarity 0.03) in unmarinated and marinated meat, respectively, indicating that the meat communities were more diverse than hitherto shown. Metagenomic analysis revealed a number of bacterial taxa that have not been associated with late shelf-life meat before, including Vagococcus and Vibrio that belonged to the predominating part of the microbial community in unmarinated meat. According to the functional analysis of the metagenomes, the communities in both marinated and unmarinated poultry were characterized by high proportions (15.6% or 17.9%) of genes involved in carbohydrate metabolism.     

有机白萝卜表皮附生乳酸菌抗生素耐药性分析

以市售有机白萝卜为研究对象,分析其表皮附生乳酸菌对四环素（tetracycline,TET）、链霉素（streptomycin,STR）和青霉素G（penicillin G,PEN）的耐药性。分离菌株的生理生化特征、随机扩增多态性DNA聚类（random amplified polymorphic DNA,RAPD）、16S rRNA、耐药性和耐药表型多态分析表明：有机白萝卜表皮附生有约4.67×103 CFU/cm2的乳酸菌。分离的187 株乳酸菌分别属于Pediococcus pentosaceus（114/187）、Weissella cibaria（9/187）、Leuconostoc mesenteroides（18/187）、Leuconostoc pseudomesenteroides（7/187）、Leuconostoc citreum（20/187）和Leuconostoc holzapfelii（19/187）。其中,25 株（13.37%）对TET、STR和PEN表现出单一或多重耐药性。在P. pentosaceus中,分别有2 株对STR、TET和PEN三重耐药,13 株对STR和TET二重耐药和4 株对TET单一耐药;L. citreum中,分别有1 株对STR、TET和PEN三重耐药和1 株对STR单一耐药;L. mesenteroides中,分别有1 株对TET单一耐药和1 株对TET和PEN二重耐药;L. pseudomesenteroides和W. cibaria中,分别有1 株对STR和TET、STR和PEN二重耐药。     

Lactic acid bacteria in marinades used for modified atmosphere packaged broiler chicken meat products

Lactic acid bacteria (LAB) in some marinades commonly used in Finland for modified atmosphere packaged poultry meat products were enumerated and identified to determine whether the marinades contained LAB species that cause meat spoilage. The concentrations of LAB in 51 marinade samples ranged from less than 100 to 8.0 x 10(5) CFU/ml. Seventeen of the samples produced LAB growth only after enrichment, and in five samples no growth was detected either by direct culturing or enrichment. Eighty-eight randomly selected isolates, 51 from the enumerated plates and 37 from enriched samples, were identified using a database of 16S and 23S rRNA gene HindIII restriction fragment length polymorphism patterns of over 300 type and references LAB strains as operational taxonomic units in numerical analyses. The predominating LAB in the enumerated samples was Lactobacillus plantarum (25 of 51 isolates). Eleven isolates were identified as Lactobacillus paracasei subsp. paracasei, and nine were Lactobacillus parabuchneri. None of these species are considered specific spoilage LAB in marinated modified atmosphere packaged poultry meat products nor have they been reported to dominate in unspoiled late-shelf-life products. These results indicate that even though marinades may contain high numbers of LAB, they are not necessarily sources of specific meat spoilage LAB. Therefore, risks associated with meat quality are not predicted by quantitative enumeration of LAB in marinades.     

Study of the microbial ecology of wild and aquacultured Tunisian fresh fish

Eighty samples of fresh fish were collected in Tunisia and analyzed for microbial load. Quality and hygienic safety of the meat and intestines of wild and aquacultured fresh fish were determined. The mesophilic aerobic plate count and populations of psychrotrophic lactic acid bacteria (LAB) and other psychrotrophic bacteria ranged from 5.67 to 7.29, 4.51 to 6, and 5.07 to 6.21 log CFU/g, respectively. For all microbiological determinations, bacterial counts were lower in meat than in the intestines of fresh fish. For all samples lower microbial populations were found in most of the wild fish than in the aquacultured fish. No isolates of the pathogenic genera Salmonella and Listeria were detected in any sample. Among the 160 strains of biopreservative psychrotrophic LAB and the 150 strains of spoilage psychrotrophic gram-negative bacteria identified by biochemical and molecular methods, Lactobacillus (six species) and Pseudomonas (six species) predominated. Lactococcus, Leuconostoc, Carnobacterium (C. piscicola and C. divergens), Aeromonas, and Photobacterium were the most common genera, and Lactococcus lactis, Lactobacillus plantarum, Pseudomonas fluorescens, and Aeromonas hydrophila were the most common species. These findings indicate that the microbiological quality of fresh fish in Tunisia can be preserved by controlling pathogenic and psychrotrophic bacteria.     

Diversity of lactic acid bacteria from modified atmosphere packaged sliced cooked meat products at sell-by date assessed by PCR-denaturing gradient gel electrophoresis

The predominant lactic acid bacteria (LAB) microbiota associated with three types of modified atmosphere packaged (MAP) sliced cooked meat products (i.e. ham, turkey and chicken) was analyzed at sell-by date using a combination of culturing and molecular population fingerprinting. Likewise routine analyses during industrial MAP production, meat samples were plated on the general heterotrophic Plate Count Agar (PCA) and on the LAB-specific de Man, Rogosa, Sharpe (MRS) agar under different temperature and atmosphere conditions. Subsequently, community DNA extracts were prepared from culturable bacterial fractions harvested from both media and used for PCR targeting the V3 hyper-variable region of the 16S rRNA gene followed by denaturing gradient gel electrophoresis (DGGE) of PCR amplicons (PCR-DGGE). Irrespective of aerobic or anaerobic incubation conditions, V3-16S rDNA DGGE fingerprints of culturable fractions from PCA and MRS medium displayed a high level of similarity indicating that LAB constituted the most dominant group in the culturable bacterial community. Comparison of DGGE profiles of fractions grown at 20, 28 or 37 °C indicated that part of the culturable community consisted of psychrotrophs. Four DGGE bands were common among cooked ham, turkey and chicken products, suggesting that these represent the microbiota circulating in the plant where all three MAP product types were sliced and packaged. Based on band sequencing and band position analysis using LAB reference strains, these four bands could be assigned to Lactobacillus sakei and/or the closely related Lactobacillus fuchuensis, Lactobacillus curvatus, Carnobacterium divergens and Leuconostoc carnosum. In conclusion, the PCR-DGGE approach described in this study allows to discriminate, identify and monitor core and occasional LAB microbiota of MAP sliced cooked meat products and provides valuable complementary information to the current plating procedures routinely used in industrial plants.     

Isolation and Selection of Lactic Acid Bacteria as Biocontrol Agents for Nonacidified, Refrigerated Pickles

ABSTRACT: A nonacidified, deli-type pickle product was used as a model system to study the potential use of biocontrol as a means to prevent the growth of pathogens in minimally processed fruits and vegetables (MPFV). Fresh pickling cucumbers were blanched and brined with sterile spices and garlic oil. The product was stored at 5 °C for 3 wk and then transferred to various abuse temperatures (16 °C, 25 °C, 30 °C). Lactic acid bacteria (LAB) were isolated and characterized as potential biocontrol agents, and the isolates were tested for bacteriocin-like activity. A total of 118 LAB isolates were obtained. Among the LAB identified were species of Lactococcus, Leuconostoc, Lactobacillus, Weissella , and Enterococcus . Three isolates showed transient bacteriocin activity against— Listeria monocytogenes , and 7 isolates ( Lactococcus ) had bacteriocin-like activity against other LAB. Although it did not produce a bacteriocin, a Lactobacillus curvatus isolate (LR55) was found to have desirable characteristics for use as a biocontrol (competitive exclusion) culture to enhance the safety of nonacidified deli-type pickles.     

Empirical model building based on Weibull distribution to describe the joint effect of pH and temperature on the thermal resistance of Bacillus cereus in vegetable substrate

A total of 296 lactic acid bacteria (LAB) isolated from spoiled, vacuum-packaged 'gravad' rainbow trout stored at 3 and 8 degrees C were characterised and identified using a molecular approach. The isolates were initially grouped according to their HindIII restriction endonuclease profiles and further identified to species level using an rRNA gene restriction pattern (ribotype) identification database. Lactobacillus sakei, L. curvatus and Carnobacterium piscicola were the three main species detected. Only one isolate was identified as C. divergens. Most of the carnobacteria were found in the samples stored at 3 degrees C. The relative proportion of L. sakei was higher in the samples stored at 8 degrees C.     

新疆不同地域发酵乳品中Lactobacillus多样性的研究

利用MRS,M17等5种不同培养基从12份采自新疆北部伊犁、博乐、塔城、阿勒泰地区牧民家庭传统方法制作的乳品中分离乳酸菌,并进行了生理生化表型特征鉴定。对这些乳酸菌进行16Sr RNA基因序列的测序,构建系统发育树,初步建立其属水平的进化地位,再利用乳杆菌种间特异性引物对其进行种水平的鉴定和分类。共分离164株疑似乳酸菌,大部分菌株对温度适应性较强。以杆菌为主,系统发育表明:样品中乳酸菌主要有7个属,其中Lactobacillus(78株)、Carrobacterium(3株)、Weissella(1株)、Lactococcus(22株)、Enterococcus(47株)、Streptococcus(8株)、Vagococcus(5株)。种特性扩增显示乳杆菌存在种水平的差异。主要有4个种。利用牛津杯从样品中筛选出了10株对大肠杆菌(Escherichia coli)、枯草芽孢杆菌(Bacillus subtilis)、李斯特氏菌(Listeria monocytogenes)金黄色葡萄球菌(Staphylococcus aureus)均具有明显抑制作用的乳杆菌,为乳酸菌作为生物型防腐剂应用到食品工业中奠定基础。     

Characterisation of lactic acid bacteria from spoiled, vacuum-packaged, cold-smoked rainbow trout using ribotyping

A total of 405 lactic acid bacteria (LAB) isolated from spoiled, vacuum-packaged, salted, sodium nitrite- or potassium nitrate-treated, cold-smoked rainbow trout stored at 4 degrees C or 8 degrees C were characterised and identified using a molecular method. The isolates were initially classified according to their restriction endonuclease profiles using HindIII and EcoRI restriction endonucleases and further characterised by rRNA gene restriction patterns (ribotypes). Numerical analysis of these ribopatterns was performed together with 19 reference LAB strain patterns in order to identify the isolates to species level. The strains were divided with HindIII and EcoRI ribopatterns into ten and nine clusters at the similarity level of 65% and 50%, respectively. The Leuconostoc-clusters and the Lb. sakei/Lb. curvatus-clusters formed the two main groups. Only one isolate was identified as Lactobacillus plantarum and no Carnobacterium strains were discovered. For both enzymes, the 35 isolates possessing six individual ribotypes and forming five clusters could not be identified further with the reference strains used. The relative proportion of Leuconostoc mesenteroides subsp. mesenteroides was higher in all samples stored at 4 degrees C. Most of the Leuconostoc citreum were found in the samples stored at 8 degrees C, and particularly in the nitrite-treated samples.     

Nonstarter lactobacilli isolated from soft and semihard Argentinean cheeses: genetic characterization and resistance to biological barriers

Nonstarter lactic acid bacteria isolated from Argentinean cheeses were identified and characterized by focusing on their resistance to biological barriers, along with other physiological features of potential interest, in the search for future probiotic organisms. Lactobacilli were enumerated and isolated from semihard and soft cheeses made with multistrain Streptococcus thermophilus starters. Lactobacilli counts in 1-week-old cheeses were between 10(5) and 10(7) CFU/g and then reached 10(7) CFU/ g in all 1-month samples, while streptococci were always above 10(9) CFU/g. A total number of 22 lactobacilli isolates were retained, identified, and characterized by in vitro tests. Species identity was determined by carbohydrate metabolism and species-specific PCR assays. Genetic diversity was explored by random amplified polymorphic DNA (RAPD) PCR analysis. The Lactobacillus strains were assigned to the species L. casei, L. plantarum, L. rhamnosus, L. curvatus, L. fermentum, and L. perolens. All the strains studied tolerated 25 ppm of lysozyme, and most of them showed resistance to 0.3% bile. After incubation in gastric solution (pH 2.0), counts decreased by several log units, ranging from 3.2 to 7.0. The strains were able to grow in the presence of bile salts, but only three isolates were capable of deconjugation. The nonstarter lactobacilli that were assayed fermented the prebiotic substrates (especially lactulose and inulin). Some strains showed high cell hydrophobicity and beta-galactosidase activity, as well as inhibitory activity against pathogenic bacteria. It was concluded that most of the lactobacilli isolated in this study demonstrated resistance to biological barriers and physiological characteristics compatible with probiotic properties, which make them suitable for further research in in vivo studies aimed at identifying new probiotic organisms.     

Numbers and types of microorganisms in vacuum-packed cold-smoked freshwater fish at the retail level

Fifty-four packages (each one belonging to a different lot) of vacuum-packed cold-smoked salmon (30) and trout (24) produced by six Spanish smokehouses were obtained at retail level after 3 weeks storage at 2+/-1 degrees C. Sensorial, chemical, physicochemical and microbiological characteristics were examined. Overall, pH, a(w), salt content in water phase, aerobic plate counts at 30 and 25 degrees C. levels of Enterobacteriaceae, lactic acid bacteria (LAB), fungi and presumptive aeromonads and staphylococci are in agreement with available data on lightly preserved fish products. Psychrotrophic clostridia ranged between 1.71 and 2.21 log CFU/g. Levels of ethanol were highly variable and not significantly related (p > 0.05) to sensory scores or to microbial numbers. Salmonella, Escherichia coli and Listeria monocytogenes were not detected in any sample. Listeriae other than L. monocytogenes were isolated from three packages. Levels of Staphylococcus aureus lower than 4 log CFU/g were also found in three packages. Among 377 bacteria randomly isolated from aerobic 25 degrees C plate counts, LAB predominated, with Carnobacterium (C. piscicola) and Lactobacillus (eight species) being the genera most frequently found. The second and third major groups were Enterobacteriaceae and Micrococcaceae, respectively. Proteus vulgaris, P. mirabilis and Serratia liquefaciens were dominant among Enterobacteriaceae and coagulase-negative staphylococci among Micrococcaceae. Minor microbial groups such as aerobic gram-negative bacilli (Acinetobacter; Moraxella and Pseudomonas), Brochothrix, Aeromonas, Bacillus and Vibrio constituted less than 17% of the total flora.     

冷鲜牛肉贮藏中菌群结构及优势菌致腐性的分析

为探究牛肉在0?℃冷藏下微生物菌群变化和优势腐败菌,采用培养依赖的16S rRNA结合高通量测序技术分析牛肉样品的微生物多样性变化。通过定期测定接种牛肉汁的生长、感官、蛋白酶活性、pH值和挥发性盐基氮（total volatile basic nitrogen,TVB-N）值,分析分离株的致腐特征。结果表明,牛肉冷藏中感官品质保持良好,15?d出现异味,18?d有腐臭味。而样品中菌落总数第3天快速上升,15?d菌落总数为8.73（lg（CFU/g））,之后呈现稳定,假单胞菌（Pseudomonas spp.）、热死环丝菌（Brochothrix thermosphacta）、肠杆菌（Enterobacter）和乳酸菌4 种分离培养基中细菌与菌落总数增长趋势相似,其中假单胞菌增长最快,肠杆菌数和乳酸菌数生长最慢。两种菌群鉴定结果显示,冷鲜牛肉初始微生物构成复杂,包括热死环丝菌、不动杆菌属（Acinetobacter spp.）、气单胞菌属（Aeromonas spp.）和假单胞菌等多种菌属构成,而腐败末期菌群构成趋于单一,假单胞菌和热死环丝菌为优势腐败菌,特别是莓实假单胞菌（P. fragi）。将腐败分离株10?株假单胞菌、4?株热死环丝菌和1?株蜂房哈夫尼菌（Hafnia alve）接种于冷藏的牛肉汁,发现假单胞菌和蜂房哈夫尼菌的接种组感官评分、pH值和TVB-N值高于热死环丝菌,且假单胞菌有较强的蛋白酶活性。研究表明,结合感官和微生物评价冷鲜牛肉贮藏期为15?d,且菌群多样性下降,假单胞菌和热死环丝菌是优势腐败菌,其中假单胞菌致腐性较强。     

Identification of lactic acid bacteria isolated from kimchi and studies on their suitability for application as starter culture in the production of fermented sausages

The aim of the investigation was to identify strains of lactobacilli coming from kimchi with properties suitable for use as starter cultures in sausage fermentation. A total of 31 strains of lactobacilli were isolated from kimchi on the 4-6th day of fermentation at 20°C using MRS agar plates and identified on the basis of morphological, biochemical, and physiological characteristics. The isolates were identified as Leuconostoc mes.mes./dent (12.9%), Lactobacillus curvatus (9.7%), Lactobacillus brevis (35.5%), Lactobacillus sake (25.8%), and Lactobacillus plantarum (16.1%). Thus, 51.6% of the isolates were homo-fermentative or facultative hetero-fermentative bacteria and the rest (48.4%) were hetero-fermentative bacteria. Among them L. brevis, L. curvatus, L. plantarum, and L. sake were investigated for their growth profile and metabolism characteristics in the fluid (submerged) model-medium modified according to the special conditions of fermented sausages. Relatively good growth properties were found for L. brevis, L. plantarum, and L. sake with maximum numbers of 8.18, 8.51 and 8.17cfu/ml, respectively, whereas L. curvatus could not adapt to the special environmental conditions. Regarding souring properties, L. brevis showed little ability to decrease pH, whereas L. curvatus, L. plantarum, and L. sake showed relatively good acidifying properties. According to the results of glucose fermentation and its products, only L. plantarum exhibited homo-fermentative characteristics. As a result only L. plantarum among the isolates from kimchi had an ability to adapt to the complex environment of fermented sausage, which will thereby allow them to act as starter cultures and natural preservatives in sausage production.     

Lactic acid bacteria isolated from artisanal dry sausages: characterization of antibacterial compounds and study of the factors affecting bacteriocin production

Lactic acid bacteria (LAB) were isolated from artisanal dry sausages sampled from north-eastern region of Chaco, Argentina. Among 141 isolates, 27 showed antimicrobial activity against Listeria innocua, Staphyloccus aureus or Brochothrix spp. One isolate, identified as Lb. curvatus/sakei, produced bacteriocin like substances (BLIS). These BLIS were heat stable, effective after refrigerated storage and freeze/thaw cycles and even active against pathogens when produced under refrigeration at 3% NaCl concentration. The influence of several factors on production of BLIS was assessed in MRS broth added with: EDTA, ascorbic acid, KCl, potassium sorbate, sodium citrate, 3 and 6% NaCl, Tween 20 or Brij 35. These additives showed different effects towards the effectiveness of the bacteriocin produced by Lb. sakei/curvatus against L. innocua and S. aureus. Conditions that provided high cell density favored high bacteriocin production. BLIS production by this LAB strain was greatly influenced by NaCl concentration and the presence of surfactants.