冷海水保藏下鲐鱼(Pneumatophorus japonicus)菌相变化规律及优势腐败菌的分离鉴定

以冷海水保鲜的鲐鱼为研究对象,通过选择性培养基和16S r DNA序列分析法探究其在冷海水保鲜过程中的菌相变化,确定了鲐鱼在冷海水保鲜条件下的优势腐败菌,并通过MEGA5.2软件构建了贮藏末期代表菌株的系统发育树。结果表明:冷海水保鲜鲐鱼样品在贮藏初期(第0 d)的微生物比较复杂,优势种群是假单胞菌属(Pseudomonas sp.)和嗜冷菌属(Psychrobacter sp.),还有少量的类芽孢杆菌属(Paenibacillus sp.)、希瓦氏菌属(Shewanella sp.)、蜡状芽孢杆菌(Bacillus anthracis)、枯草芽孢杆菌属(Brevibacterium sp.);随着贮藏时间的延长,鲐鱼样品中的菌相逐渐变的单一,假单胞菌属迅速下降,希瓦氏菌属迅速增加;贮藏末期希瓦氏菌属和肠杆菌属(Enterobacter sp.)的比例迅速增加,其中希瓦氏菌属呈上升趋势且到贮藏后期数量占绝对优势,被确定为鲐鱼冷海水保鲜条件下的优势腐败菌。     

Effects of specific egg yolk antibody (IgY) on the quality and shelf life of refrigerated Paralichthys olivaceus

BACKGROUND: The spoilage of fishery food has been attributed to limited types of microorganisms called specific spoilage organisms (SSO). Unlike traditional food‐preserving techniques which usually exploit broad‐spectrum antimicrobial agents, here, based on the specific antimicrobial activity of egg yolk antibodies (IgY) against two SSO in refrigerated fish (Shewanella putrefaciens and Pseudomonas fluorescens), a novel strategy for fish preservation was suggested and evaluated. RESULTS: During storage of Paralichthys olivaceus fillets at 4 ± 1 °C, the bacteria growth (including total microorganisms and the two SSO) in test groups was significantly inhibited in comparison to that of controls (P < 0.05). This antibacterial activity of the specific IgY was also confirmed by chemical analysis (pH, total volatile base nitrogen and 2‐thiobarbituric acid value) and sensory evaluation, and the shelf life of samples was extended approximately from 9 days to 12–15 days in the presence of the specific IgY. CONCLUSION: These results indicated a significant antimicrobial activity of the anti‐SSO IgY for refrigerated fish products, which allowed us to suggest its potential as a bio‐preservative for seafood. Copyright © 2011 Society of Chemical Industry     

不同时期鲳鱼冷藏期间优势腐败菌的多样性变化

目的：比较分析不同时期冷藏鲳鱼（Pampus argenteus）贮藏期间的感官品质、pH值、微生物指标与主要微生物菌群的变化规律。方法：冷藏（4±1） ℃条件下,以感官评定、pH值与菌落总数为品质评价指标,采用聚合酶链式反应（polymerase chain reaction,PCR）扩增结合生理生化鉴定法分别对冬、春两个时期的鲳鱼进行优势腐败菌的变化规律研究。将经细菌培养与分离纯化得到单菌落按其形态特征进行分类,再通过生理生化鉴定与革兰氏染色,初步得到菌落种类,对单菌落进行DNA提取与PCR扩增并测序。结果：冬季样品获得12 种菌株,春季样品获得9 种菌株。贮藏末期时,冬季样品中优势腐败菌的种类与比例分别为嗜冷杆菌（Psychrobacter spp.）21.51%、草莓假单胞菌（Pseudomonas fragi）16.13%、荧光假单胞菌（Pseudomonas fluorescens）52.68%与热杀索丝菌（Brochothrix thermosphacta）9.68%;春季样品为草莓假单胞菌（Pseudomonas fragi）8.62%、荧光假单胞菌（Pseudomonas fluorescens）64.66%与腐败希瓦氏菌（Shewanella putrefaciens）26.72%。结论：冬、春时期中冷藏鲳鱼贮藏期间优势腐败菌的种类基本一致,以革兰氏阴性菌为主,但在细菌种类与比例上存在差异,冬季样品的微生物种类较春季丰富。贮藏期间,随着荧光假单胞菌所占比例的增加,使腐败希瓦氏菌的生长受到明显抑制。     

Proteolytic activity of four strains of Pseudomonas on crude extracts of contractile proteins

Hydrolytic activities of exogenous proteases obtained from Pseudomonas upon crude extracts of contractile proteins were studied. Four strains were used: C61 and C20, isolated from beef samples, and P. fragi (ATCC-4973) and P. fluorescens (NRRL-B-1244). Proteolytic activity was tested on crude extracts of actomyosin, myosin+ actin+regulatory proteins, actin and high molecular weight proteins obtained from postrigor beef by differential precipitation according to their solubility in salt solutions of various ion strengths. Electrophoresis analysis showed considerable degradation of actomyosin in samples treated with a C61 enzymatic extract. Myosin degradation was similar for treatments with proteases obtained from C61 and P. fragi. Actin degradation was similar for all enzymatic extracts. The most active protease was a 46.8 kDa enzyme produced by C60. P. fragi produced two proteases of 49.2 kDa and 34.2 kDa, P. fluorescens one of 46.1 kDa, and C20 one of 49.2 kDa.     

Use of Desirability Approach to Predict the Inhibition of Pseudomonas fluorescens, Shewanella putrefaciens and Photobacterium phosphoreum in Fish Fillets Through Natural Antimicrobials and Modified Atmosphere Packaging

The main goal of this paper was the prolongation of the microbiological acceptability limit (MAL) of gilthead sea bream fillets, added with some natural antimicrobials and packed under modified atmosphere; desirability approach was used, and the research was divided into two different steps. The first phase addressed fish fillet preservation through chitosan (0–4 %), grape fruit seed extract (GFSE) and thymol (0–6,000 ppm); Pseudomonas fluorescens, Shewanella putrefaciens and Photobacterium phosphoperum, inoculated onto the surface of fillets, were used as microbial targets. The concentration of the three antimicrobials were combined through a three variables/five levels central composite design; after fish inoculation and dipping into active solutions containing the natural compounds, fillets were stored at 4 °C and analysed periodically. Data of microbiological counts were fitted through a primary model (modified Gompertz equation), for the evaluation of MAL; MALs were used to build a polynomial model, able to draw a desirability profile for each antimicrobial. These outputs (desirability and polynomial equation) highlighted that Pseudomonas fluorescens was the most resistant microorganism; it could be inhibited through an active solution containing 2 % of chitosan and 6,000 ppm of GFSE and thymol. Therefore, in the second step of the research, fish fillets were dipped in this active solution and packed under two different atmospheres (30:40:30 O₂/CO₂/N₂ and 5:95 O₂/CO₂) and stored at 4 °C. For each microorganism, the stability time was evaluated, thus pointing out that the best sample was that packed under 5:95 O₂/CO₂.     

传统生理生化鉴定技术结合PCR法分析复合保鲜剂对冷藏带鱼贮藏期间菌相变化的影响

将微生物传统生理生化鉴定技术与PCR法相结合,研究了复合保鲜剂对冷藏带鱼贮藏期间菌相变化的影响。通过对冷藏对照组与保鲜剂处理组样品贮藏期间的主要微生物进行分离纯化、16SrDNA序列分析与生理生化鉴定,并作系统发育树分析,最终鉴定出13株具有典型特征的纯菌株。对照组样品在货架期终点时,其主要微生物的种类与所占比例依次为:腐败希瓦氏菌(34.7%)、荧光假单胞菌(14.5%)、松鼠葡萄球菌(10.2%)、嗜水气单胞菌(8.2%)、弧菌(6.1%)、恶臭假单胞菌(6.1%)、绿色气球菌(4.1%)、金黄色葡萄球菌(4.1%)、蜡样芽孢杆菌(4.0%)、铜绿假单胞菌(2.0%)、嗜冷杆菌(2.0%)、成团肠杆菌(2.0%)、约氏不动杆菌(2.0%)。其中,腐败希瓦氏菌为特定优势腐败微生物。假单胞菌属在带鱼冷藏过程中所占比例大小依次为荧光假单胞菌>恶臭假单胞菌>铜绿假单胞菌。经复合保鲜剂处理后,能够使冷藏带鱼的二级鲜度货架期延长9d,并使其贮藏期间的细菌菌相组成比例发生变化,细菌种类减少到9种。主要优势菌的比例明显减少,表明复合保鲜剂对带鱼体内腐败菌具有不同程度的抑制作用。     

The antibacterial activity and antibacterial mechanism of the tea polyphenol liposomes/lysozyme–chitosan gradual sustained release composite coating

To obtain long-lasting preservation materials, the tea polyphenol liposomes (TP-Lips)/lysozyme (LZM)–chitosan (CS) composite coating with the gradual sustained property was prepared by tape casting method. These coatings were characterised, and their physicochemical properties were measured. Meanwhile, the antibacterial mechanisms of coatings were studied using the spoilage bacteria of aquatic products (Shewanella putrefaciens and Pseudomonas fluorescens) as target strains. Compared with CS coating, the incorporation of TP-Lips makes the cracks and granular matter of the coatings increase. Except for the oxygen permeabilities (OP) and carbon dioxide permeabilities (CDP), the rest of the physicochemical properties are decreased, including tensile strength (Ts), elongation at break (EB) and light transmittance (T). Antibacterial mechanisms indicate that TP and LZM have a synergistic antibacterial effect. The slow-release system composed of liposomes and coating prolongs the action time of TP and LZM. Hence, the TP-Lips/LZM-CS coating could be a hopeful material in food preservation field with excellent antibacterial properties.     

Microbial competition: effect of Pseudomonas fluorescens on the growth of Listeria monocytogenes

Listeria monocytogenes Scott A was cultured alone and in coculture with Pseudomonas fluorescens ATCC 33231 to characterize quantitatively the effects of microbial competition on the growth of this psychrotrophic pathogen. The bacteria were cultured in brain–heart infusion broth (BHI), using a 3×3×3×2 complete factorial design to assess the impact of temperature (4, 12, 19°C), initial pH (5·0, 6·0, 7·0), and sodium chloride content (5, 25, 45 gl⁻¹) on the interaction between the two micro-organisms. Samples were periodically plated on BHI agar and Vogel Johnson agar to obtain total counts and L. monocytogenes counts, respectively. Growth curves were generated by fitting the data to the Gompertz equation, and the derived growth kinetics were compared. WhenP. fluorescens did influence the growth of L. monocytogenes, the primary effect was a suppression of the maximum population density (MPD) reached by the pathogen. Suppression of L. monocytogenes was generally associated with low incubation temperatures (4°C) and sodium chloride levels (5 and 25 gl⁻¹). Slight increases (<1·0 log cfu ml⁻¹) in the MPD attained by L. monocytogenes were observed when grown in the presence of P. fluorescens at higher temperatures (12 and 19°C) and sodium chloride levels (25 and 45 gl⁻¹) when the pH was 5·0. The current study supports earlier work that indicates that reliance on microbial competition as a barrier to control L. monocytogenes in refrigerated foods will require detailed knowledge of how the interaction between the pathogen and the microflora is affected by environmental and food characteristics such as storage temperature, pH, and water activity.     

Quality of Norway lobster (Nephrops norwegicus) treated with a 4-hexylresorcinol-based formulation

In the present work, the effect on biochemical indexes and microbial growth was studied in Norway lobster (Nephrops norwegicus), using a formulation containing 4-hexylresorcinol (0.1 and 0.05%) in combination with organic acids (citric, ascorbic and acetic) and chelating agents (ethylenediaminetetraacetic acid [EDTA] and di-sodium di-hydrogen pyrophosphate [PPi]). Lobsters treated with 4% of a commercial formula based on sulphites were used for control purposes. The treatment with 4-hexylresorcinol-based formulations delayed the increase in K-value and total volatile bases, while evolution of pH and trimethylamine was similar regardless of the treatment. No relation was found between biochemical and microbiological indexes. Regarding microflora, although commercial sulphites slightly slowed the growth of seafood spoiler organisms, as Shewanella putrefaciens and luminescent colonies, these organisms were not found in a very high number (∼6 log cfu/g) at the end of storage. Moreover, the formulation containing 4-hexylresorcinol 0.1% appeared to stimulate the growth of lactic acid bacteria. The sensory quality of lobster, in terms of melanosis, remained with a good appearance for 12 days. Formulations based on 4-hexylresorcinol preserved the quality and could therefore replace the traditional sulphites during storage of Norway lobster.     

Survival of indicator/pathogenic bacteria in orange soft drink

Experiments were undertaken to determine the survival of indicator and pathogenic bacteria in samples of a popular orange soft drink having pH 3.0 and held at 8°C. The fizzy orange drink was inoculated withc.10⁶cell ml^–1ofEscherichia coli(two strains, EAC1 and EAC75) andc.10⁶cell ml^–1ofSalmonella derby(two strains) andListeria monocytogenes(one strain). None of the strains ofS. derbyandL. monocytogeneswas detected 35h after inoculation. Numbers of theE. colidecreased, reaching a final concentration of 1.1×10²CFUml^–1and 1.3×10³CFUml^–1for strain EAC1 and strain EAC75, respectively. These results indicate the safety of this type of soft drink with respect to these organisms.     

Characterization of Extracellular Polymeric Substances Produced by Pseudomonas fragi Under Air and Modified Atmosphere Packaging

Extracellular polymeric substances (EPS) play an important role in bacterial biochemical properties. The characteristics of EPS from 2 strains of Pseudomonas fragi cultured in meat aerobically (control) and in modified atmosphere packaging (MAP) were studied. The amount and components of EPS, the surface properties, and the effect on biofilm formation of several spoilage organisms were evaluated. The results showed that MAP inhibited the growth of the P. fragi strains. Compared with the control, more loose and less bound EPS (containing protein and carbohydrate) were produced by P. fragi in MAP samples. MAP also caused increased cell autoaggregation and surface hydrophobicity. After the removal of the EPS, the surface property changes were strain‐dependent, suggesting that membrane compositions were also changed. In addition, the EPS displayed significant antibiofilm activity on Pseudomonas fluorescens and Serratia liquefaciens. In conclusion, P. fragi strains not only modified the amount, components, and surface properties of EPS but also changed the cell membrane compositions to adapt to MAP stress. Moreover, EPS may play an important role in microbial community competitions.     

The influence of oxygen and carbon dioxide on the growth of prevalent Enterobacteriaceae andPseudomonasspecies isolated from fresh and controlled-atmosphere-stored vegetables

To obtain more insight into the specific impact of modified gas conditions on the composition of microflora of minimally processed vegetables, the prevalent bacteria on mungbean sprouts and cut chicory endive were determined during storage under controlled atmospheric (CA) conditions at 8°C. Enumeration of the total mesophilic counts, Enterobacteriaceae,Pseudomonasspecies, and lactic acid bacteria indicated that Enterobacteriaceae andPseudomonasspecies constituted the major populations found on these products before and after CA storage. Identification of the predominant species within these populations revealed that on fresh and CA-stored mungbean sprouts,Enterobacter cloacae, Pantoea agglomerans, Pseudomonas fluorescens, Ps. viridilividaandPs. corrugatawere the prevalent species. On chicory endive,Rahnella aquatilisand severalPseudomonasspecies were found on the fresh product, while after CA storage,Escherichia vulnerisandPs. fluorescenswere the main species. Growth of the predominant epiphytes was subsequently quantified in pure culture, using an agar model system at 8°C under 1.5 or 21% O₂with 0, 5, 20, or 50% CO₂. In general, these CA conditions did not strongly influence maximum population densities and lag times were not detected. For each of the strains, however, maximum specific growth rates were reduced at increased CO₂concentrations, independent of the 0₂concentration applied. This effect was more pronounced forPseudomonasspecies than forEnterobacteriaceae. Notably, the agar model study showed that individual species ofEnterobacteriaceaeorPseudomonasresponded similarly to the specific CA conditions applied. This did not correlate with the shift in predominant species observed on chicory endive. Our data underline the complexity of the ecological conditions to which micro-organisms on vegetables are subjected during storage under modified gas conditions.     

The effect of a competitive microflora,pH and temperature on the growth kinetics of Escherichia coli O157:H7

Growth curves were generated for Escherichia coli O157:H7 in brain–heart infusion broth incubated at 37 or 15°C in the presence of individual and combinations of competing microflora. Broths were inoculated withE. coli O157:H7 (log₁₀3·00 cfu ml⁻¹) and competitors (log₁₀4·00 cfu ml⁻¹) and the initial pH of the broth was either neutral (7·0) or adjusted to 5·8 and then sequentially reduced to 4·8 over 10 h to simulate fermentation conditions. Growth curves were also generated for the competitors in these cultures, including Pseudomonas fragi, Hafnia alvei, Pediococcus acidilactici (pepperoni starter culture) and Brochothrix thermosphacta . Gompertz equations were fitted to the data and growth kinetics including lag phase duration, exponential growth rates and maximum population densities (MPD) calculated. In pure culture, the growth parameters for E. coli O157:H7 in neutral pH broths were significantly different from those recorded in simulated fermentation broths (P<0·05). The presence of competitors in the broth also had a significant effect on the growth kinetics of the pathogen. H. alvei significantly inhibited the growth (lag phase, growth rate and MPD) of E. coli O157:H7 at 37°C, neutral pH and outgrew the pathogen under these conditions. In neutral pH cultures, two other competitors, B. thermosphacta and P. acidilactici also inhibited the lag phase of the pathogen but had no effect on the other growth parameters. In simulated fermentation broths, the growth rate of E. coli O157:H7 was consistently slower and the MPD lower in the presence of a competitive microflora than when grown individually. At 15°C, only one competitor, P. fragi significantly inhibited the lag phase of the pathogen. The implications of these findings for food safety are discussed.     

Colonization of Beef Muscle Surfaces by Pseudomonas fluorescens and Pseudomonas fragi

Attached and unattached cell densities were determined for Pseudomonas fluorescens and Pseudomonas fragi growing on the surface of beef muscle stored at 4 and 25°C, in presence of NaCl, KCl, and CaCl₂. A mechanical rinsing procedure was developed for this purpose. Both species colonized the surface at both temperatures and were enhanced at low (4°C) temperature. Attached cells represented up to 90% of the total until a density of 10⁵-10⁶ CFU cm^?2 was reached. At that point, a proportion of attached cells to unattached cells declined but colonization of the surface continued. In presence of CaCl₂, ratios of attached to unattached cells did not decline, suggesting a significant role for the calcium ion in colonization. Ability to colonize meat surfaces may be a significant competitive advantage for meat spoilage bacteria such as Pseudomonas fragi and Pseudomonas fluorescens.     

The ability of biogenic amines and ammonia production by single bacterial cultures

The amino acid decarboxylating activity and production of biogenic amines, trimethylamine and ammonia by Morganella morganii (two strains), Klebsiella pneumoniae (three strains), Hafnia alvei (two strains), Enterococcus faecalis, Photobacterium phosphoreum, Micrococcus sp., Psychrobacter immobilis, Corynebacterium sp., Vibrio fischeri, Vibrio harveyi and Pseudomonas putida were investigated using a rapid HPLC method. In a laboratory medium containing amino acid (histidine, ornithine, lysine, tyrosine and arginine), not all bacterial strains produced the biogenic amines but most of them produced histamine, putrescine, cadaverine and ammonia. Cadaverine production by Klebsiella pneumoniae (8152), Klebsiella pneumoniae (673), Klebsiella pneumoniae (2122), Hafnia alvei (6578), Hafnia alvei (11999), Vibrio fischeri (25) Vibrio harveyi (42) and Pseudomonas putida (10936) was 531, 422, 532, 485, 472, 343, 547 and 343 mg/l, respectively in lysine decarboxylase broth. Tyramine was produced in highest concentration (526 mg/l) by Enterococcus faecalis (775). Agmatine was not produced apart from Psychrobacter immobilis (100) in an arginine decarboxylase broth.     

Changes in aerobic microflora of skin and gills of Mediterranean sardines (Sardina pilchardus) during storage in ice

Sardines from the Adriatic Sea were examined fresh and after 4 and 8 days of storage in ice. A total of 1500 strains isolated were identified from the gills and the surface of the fish. Pseudomonadaceae, Neisseriaceae, Flavobacterium/Cytophaga, Enterobacteriaceae, coryneform bacteria and Micrococcaceae were the most common bacteria in fresh fish. During storage the pseudomonads (mainly the non-fluorescent strains) increased and became the dominating microflora; the Neisseriaceae (Moraxella, Psychrobacter and Acinetobacter) showed a distinct increase during the first 4 days in ice; the percentage of the other bacterial groups clearly decreased. On the gills the quantitative changes in the microflora were less pronounced than on the surface.     

Use of surface-smear bacteria for inhibition ofListeria monocytogeneson the rind of smear cheese

Surface-smear micro-organisms isolated from Taleggio cheese were screened for their ability to inhibitListeria monocytogenes. Most of the isolates showing antilisterial activity (19% of the total) consisted of coryneform bacteria, mainly belonging to theMicrobacterium lacticumspecies. The inhibitory activity was observed also after growth at 5°C and pH 6·0. After cross-inhibition tests among inhibitory strains and between these and other pigmented, non-inhibitory strains, two bacterial mixtures were assayed as surface-smear starter of Taleggio cheese. At different ripening stages (1, 20 and 40 days), the cheese surface was contaminated with 2·5×10²cfu cm⁻²L. monocytogenes(Ohio strain) and the growth evaluated over 15 days of incubation at 5°C. Contrary to the laboratory experiments,Listeriacould not be completely inhibited on the cheese surface. With 5·5–6·0 pH range of the cheese rind, (lower than usual values), the growth of surface-smear bacteria was delayed, or even stopped. Nevertheless, a listeriostatic effect was achieved on the surface of cheese samples contaminated at the end of ripening. This seemed to confirm the essential role played by surface-smear bacteria, within the rind microflora, in controlling the development of contaminant micro-organisms, and by competitive bacteria in reducing the overall risks associated with soft cheese. The mechanisms involved in the selection and the growth of competing bacteria on the cheese surface are also discussed.     

The bacteriology of fresh and spoiling Lake Victorian Nile perch (Lates niloticus)

A total of 177 bacterial cultures isolated from Lake Victorian Nile Perch (Lates niloticus) were investigated. The flora on newly caught Nile perch consisted of organisms belonging to the genera Moraxella, Alcaligenes, Acinetobacter, Pseudomonas, Aeromonas, Micrococcus and other Gram-positive organisms. 39% were identified as Gram-positive species and 61% were negative in the Gram-reaction. Three cultures out of 53 investigated caused weak rotten off-odours in sterile fish broth and one culture, an Aeromonas spp. produced strong rotten, fishy, hydrogen sulphide off-odours. From Nile perch spoiled at ambient temperature, 15 of the 42 strains isolated caused rotten, fishy, hydrogen sulphide off-odours. These specific spoilage bacteria were all identified as Aeromonas and all reduced trimethylamine oxide to trimethylamine and produced hydrogen sulphide. From spoiled iced Nile perch, 74 out of 82 (90%) of the bacteria isolated were identified as Pseudomonas. A small proportion of these (13 out of 74) produced off-odours in sterile fish broth resembling the spoiling fish. These specific spoilers could not be separated from the non-spoilers based on biochemical activities used in classical taxonomy. While the Pseudomonas spp. isolated did not produce trimethylamine or H₂S, a few of the remaining isolates (two Shewanella putrefaciens and five Aeromonas spp.) did produce these compounds. The role of Shewanella putrefaciens in the iced spoilage of Nile perch was, however, insignificant, since they only very late in the storage reached numbers where their spoilage could be detected.     

Preparation of a bilayer edible film incorporated with lysozyme and its effect on fish spoilage bacteria

An edible bilayer film incorporated with lysozyme based on chitosan and sodium alginate was prepared via the layer-by-layer method. The film was characterized and its effects against the fish spoilage bacteria Pseudomonas fluorescens and Shewanella putrefaciens were investigated and compared to the monolayer films. The results suggest that electrostatic interactions such as hydrogen bonds occurred between the two layers of the bilayer film. Compared with monolayer films, the mechanical and gas barrier properties of the bilayer film were improved and higher inhibitory activity against both bacteria was exhibited. After treatment with the bilayer film, scanning electron microscopy revealed the serious damage to the bacterial cell surface, and cell membrane permeability and nucleic acid leakage increased. The bilayer film also affected the activity of alkaline phosphatase and adenosine triphosphatase. SDS-PAGE of bacterial total protein revealed that the protein concentration n decreased, which may be due to the leakage of proteins from the damaged bacterial cell. All the results indicate that the bilayer film possesses good physicochemical properties and can destroy the bacterial cell membrane. Such superior antibacterial properties against fish spoilage bacteria indicate a good potential application of bilayer films in fish preservation.     

Spoilage potential and sensory profile associated with bacteria isolated from cold-smoked salmon

Off-odours/flavours associated with cold-smoked salmon spoilage are due to the activity of microflora. This study evaluated the spoilage potential of nine bacterial groups (Shewanella putrefaciens, Brochothrix thermosphacta, Aeromonas spp., Lactobacillus alimentarius, Lactobacillus sake,Lactobacillus farciminis, Carnobacterium piscicola, Photobacterium phosphoreum and Serratia liquefaciens) isolated from cold-smoked salmon. Five different isolates from each group were inoculated into sterile cold-smoked salmon blocks, and chemical and sensory changes were studied after five weeks of storage in vacuum packs at 6°C. Bacterial growth was monitored weekly during the storage period. A sensory profile was assigned to each group. Principal component analysis allowed some bacterial species to be characterised by a specific odour, and correspondence factorial analysis discriminated among the species according to their spoilage potential. The bacteria mainly responsible for spoilage were L. sake, L. farciminis and B. thermosphacta, which produced sulphurous, acidic and rancid off-odours respectively. Some strains of S. liquefaciens produced rubbery, cheesy or acidic off-odours. Some P. phosphoreum isolates were characterised by an acidic effect.