Psychrotrophic lactic acid bacteria used to improve the safety and quality of vacuum-packaged cooked and peeled tropical shrimp and cold-smoked salmon

Selection of lactic acid bacteria for biopreservation of salmon products applying processing-dependent growth kinetic parameters and antimicrobial mechanisms

Biopreservation using lactic acid bacteria (LAB) is a promising technology to prevent the growth of pathogenic microorganisms in fresh and mildly processed food. The main aim of this study was to select LAB, originally isolated from ready-to-eat (RTE) seafood, for biopreservation of fresh salmon and processed salmon products. Ten LAB strains (five Carnobacterium and five Leuconostoc) were selected based on previously demonstrated bioprotective properties to investigate their antimicrobial mechanisms and temperature-dependent growth kinetics in a sterile salmon juice model system. Furthermore, five strains (three Carnobacterium and two Leuconostoc) were selected to test process-dependent growth kinetic parameters relevant to the secondary processing of salmon. Two strains (Carnobacterium maltaromaticum 35 and C. divergens 468) showed bacteriocin-like activity against Listeria innocua, while inhibitory effect of cell-free supernatants (CFS) was not observed against Escherichia coli. All selected strains were able to grow in sterile salmon juice at tested temperatures (4, 8, 12 and 16 °C), with specific growth rates (μ) ranging from 0.01 to 0.04/h at 4 °C and reaching a maximum population density of 8.4-9 log CFU/ml. All five strains tested for process-dependent growth kinetic parameters were able to grow in the range of 0.5-5% NaCl and 0.13-0.26% purified condensed smoke (VTABB and JJT01), with inter- and intraspecies variation in growth kinetics. According to the temperature-dependent growth kinetics and antimicrobial assay results, two strains, Leuconostoc mesenteroides 68 (Le.m.68) and C. divergens 468 (C d.468), were selected for in situ test to validate their ability to grow in vacuum-packed fresh salmon at 4 °C. Both strains were able to grow at maximum growth rates of 0.29 ± 0.04/d for Le. m.68 and 0.39 ± 0.06/d for C.d.468, and their final concentrations were 7.91 ± 0.31 and 8.02 ± 0.25 log CFU/g, respectively. This study shows that LAB, originally isolated from RTE seafood, have promising potential as bioprotective strains in fresh and processed salmon products.

Microbiome data reveal significant differences in the bacterial diversity in freshwater rohu (Labeo rohita) across the supply chain in Dhaka, Bangladesh

The present study aimed to characterize and compare the skin and gut microbial communities of rohu at various post-harvest stages of consumption using quantitative real-time polymerase chain reaction and 16S rRNA-based amplicon sequencing. Real-time PCR amplification detected higher copy numbers for coliform bacteria-Escherichia coli, Salmonella enterica and Shigella spp. in the marketed fish-compared to fresh and frozen samples. The 16S rRNA data revealed higher alpha diversity measurements in the skin of fish from different retail markets of Dhaka city. Beta ordination revealed distinct clustering of bacterial OTUs for the skin and gut samples from three different groups. At the phylum level, Proteobacteria was most abundant in all groups except the Fusobacteria in the control fish gut. Although Aeromonas was found ubiquitous in all types of samples, diverse bacterial genera were identified in the marketed fish samples. Nonetheless, low species richness was observed for the frozen fish. Most of the differentially abundant bacteria in the skin samples of marketed fish are opportunistic human pathogens enriched at different stages of postharvest handling and processing. Therefore, considering the microbial contamination in the aquatic environment in Bangladesh, post-harvest handling should be performed with proper methods and care to minimize bacterial transmission into fish.

Improving the Shelf-Life of Fish Burgers Made with a Mix of Sea Bass and Sea Bream Meat by Bioprotective Cultures

Seafood products are one of the most perishable foods, and their shelf life is limited by enzymatic and microbial spoilage. Developing methods to extend the shelf life of fresh fish could reduce food waste in the fishery industry, retail stores, and private households. In recent decades, the application of lactic acid bacteria (LAB) as bioprotective cultures has become a promising tool. In this study, we evaluated the use of four starter cultures, previously selected for their properties as bioprotective agents, for sea bass and sea bream burgers biopreservation. Starter cultures impacted the microbial populations, biochemical parameters (pH, TVB-N), and sensory properties of fish burgers, during 10 days of storage at 4 °C and then 20 days at 8 °C in modified atmosphere packaging (MAP). Also, storage time influenced the microbial and physicochemical characteristics of all the tested samples, except for TVB-N values, which were significantly higher in the uninoculated burgers. The volatilome changed in the different treatments, and in particular, the samples supplemented with starter presented a profile that described their rapid growth and colonization, with the production of typical molecules derived from their metabolism. The addition of bioprotective cultures avoided bloating spoilage and improved the sensory parameters of the burgers. The shelf life of the fish burgers supplemented with starter cultures could be extended up to 12 days.

Impact of lactic acid bacteria on the control of Listeria monocytogenes in ready-to-eat foods

Due to the increased demand for ready-to-eat (RTE) minimally processed foods, alternatives to chemical and thermal preservation methods to maintain food safety are highly demanded. A significant safety hazard in RTE food products is the growth of the foodborne pathogen Listeria monocytogenes. After processing, recontamination or cross-contamination of L. monocytogenes in RTE food products may occur and the lack of cooking can lead to an increased risk of listeriosis. Further, some RTE food products (e.g., cheese and cured meat) can have a long processing period and shelf life, thus allowing for the growth and proliferation of L. monocytogenes in the food matrix. Lactic acid bacteria (LAB) are generally recognized as safe (GRAS) probiotics and have been proposed as a biological control approach to eliminate foodborne pathogens including L. monocytogenes. LAB have been reported to extend the shelf life of food products and inhibit pathogen proliferation via growth competition and metabolite production. LAB are native microflora of many RTE foods, but only certain LAB may inhibit pathogen growth. Therefore, specificity of LAB species should be employed into their use in RTE foods. This review will discuss the antimicrobial mechanisms of LAB against L. monocytogenes, selective use of LAB in food matrices, and their uses in food processing and packaging.

Development of a rapid qPCR method to quantify lactic acid bacteria in cold-smoked salmon

Quantification of lactic acid bacteria (LAB) is essential to control quality of seafood products like cold-smoked salmon (CSS). In the present study, we report the design and optimization of a dual-labelled TaqMan ™ probe targeting the V7 region of 16S rRNA gene for the detection of LAB in CSS. This quantitative PCR (qPCR) assays is useful for the simultaneous detection of the ten LAB genera communally encountered in CSS as Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Macrococcus, Streptococcus, Vagococcus and Weissella. The specificity of this method was demonstrated against 14 genera (44 isolates, 35 species) of Gram-positive bacteria and 19 genera of Gram-negative (40 isolates, 34 species). Calibration of the method was performed in CSS matrix using a mix of equimolar cultured solution of five LAB. Quantification with the qPCR method range from 3.5 to 8.5 Log CFU/g in CSS matrix, covering 5 orders of magnitude. On these artificially contaminated CSS slices, PCR method results correlated successfully (R² = 0.9945) with the conventional enumeration on Elliker medium. In addition, the new method was successful on commercial CSS from five different origins with a quantification range from 3.7 Log CFU/g to 8.0 Log CFU/g. This one-step quantitative methodology is proposed as a rapid and complementary tool of the cultural methods to investigate the LAB microbiota and biodiversity of CSS.

Effect of the Manufacturing Process on the Microbiota, Organoleptic Properties and Volatilome of Three Salmon-Based Products

Lightly preserved seafood products, such as cold-smoked fish and fish gravlax, are traditionally consumed in Europe and are of considerable economic importance. This work aimed to compare three products that were obtained from the same batch of fish: cold-smoked salmon (CSS) stored under vacuum packaging (VP) or a modified atmosphere packaging (MAP) and VP salmon dill gravlax (SG). Classical microbiological analyses and 16S rRNA metabarcoding, biochemical analyses (trimethylamine, total volatile basic nitrogen (TVBN), biogenic amines, pH, volatile organic compounds (VOCs)) and sensory analyses (quantitative descriptive analysis) were performed on each product throughout their storage at a chilled temperature. The three products shared the same initial microbiota, which were mainly dominated by Photobacterium, Lactococcus and Lactobacillus genera. On day 28, the VP CSS ecosystem was mainly composed of Photobacterium and, to a lesser extent, Lactococcus and Lactobacillus genera, while Lactobacillus was dominant in the MAP CSS. The diversity was higher in the SG, which was mainly dominated by Enterobacteriaceae, Photobacterium, Lactobacillus and Lactococcus. Although the sensory spoilage was generally weak, gravlax was the most perishable product (slight increase in amine and acidic off-odors and flavors, fatty appearance, slight discoloration and drop in firmness), followed by the VP CSS, while the MAP CSS did not spoil. Spoilage was associated with an increase in the TVBN, biogenic amines and spoilage associated VOCs, such as decanal, nonanal, hexadecanal, benzaldehyde, benzeneacetaldehyde, ethanol, 3-methyl-1-butanol, 2,3-butanediol, 1-octen-3-ol, 2-butanone and 1-octen-3-one. This study showed that the processing and packaging conditions both had an effect on the microbial composition and the quality of the final product.

Recent Developments in Seafood Packaging Technologies

Seafood products are highly perishable, owing to their high water activity, close to neutral pH, and high content of unsaturated lipids and non-protein nitrogenous compounds. Thus, such products require immediate processing and/or packaging to retain their safety and quality. At the same time, consumers prefer fresh, minimally processed seafood products that maintain their initial quality properties. The present article aims to review the literature over the past decade on: (i) innovative, individual packaging technologies applied to extend the shelf life of fish and fishery products, (ii) the most common combinations of the above technologies applied as multiple hurdles to maximize the shelf life of seafood products, and (iii) the respective food packaging legislation. Packaging technologies covered include: Modified atmosphere packaging; vacuum packaging; vacuum skin packaging; active food packaging, including oxygen scavengers; carbon dioxide emitters; moisture regulators; antioxidant and antimicrobial packaging; intelligent packaging, including freshness indicators; time–temperature indicators and leakage indicators; retort pouch processing and edible films; coatings/biodegradable packaging, used individually or in combination for maximum preservation potential.

Antilisterial Potential of Lactic Acid Bacteria in Eliminating Listeria monocytogenes in Host and Ready-to-Eat Food Application

Listeriosis is a severe food borne disease with a mortality rate of up to 30% caused by pathogenic Listeria monocytogenes via the production of several virulence factors including listeriolysin O (LLO), transcriptional activator (PrfA), actin (Act), internalin (Int), etc. It is a foodborne disease predominantly causing infections through consumption of contaminated food and is often associated with ready-to-eat food (RTE) and dairy products. Common medication for listeriosis such as antibiotics might cause an eagle effect and antibiotic resistance if it is overused. Therefore, exploration of the use of lactic acid bacteria (LAB) with probiotic characteristics and multiple antimicrobial properties is increasingly getting attention for their capability to treat listeriosis, vaccine development, and hurdle technologies. The antilisterial gene, a gene coding to produce antimicrobial peptide (AMP), one of the inhibitory substances found in LAB, is one of the potential key factors in listeriosis treatment, coupled with the vast array of functions and strategies; this review summarizes the various strategies by LAB against L. monocytogenes and the prospect in development of a ‘generally regarded as safe’ LAB for treatment of listeriosis.

Innovative Seafood Preservation Technologies: Recent Developments

Fish and fishery products are among the food commodities of high commercial value, high-quality protein content, vitamins, minerals and unsaturated fatty acids, which are beneficial to health. However, seafood products are highly perishable and thus require proper processing to maintain their quality and safety. On the other hand, consumers, nowadays, demand fresh or fresh-like, minimally processed fishery products that do not alter their natural quality attributes. The present article reviews the results of studies published over the last 15 years in the literature on: (i) the main spoilage mechanisms of seafood including contamination with pathogens and (ii) innovative processing technologies applied for the preservation and shelf life extension of seafood products. These primarily include: high hydrostatic pressure, natural preservatives, ozonation, irradiation, pulse light technology and retort pouch processing.

Salmon Gravlax Biopreservation With Lactic Acid Bacteria: A Polyphasic Approach to Assessing the Impact on Organoleptic Properties, Microbial Ecosystem and Volatilome Composition

Seafood and fishery products are very perishable commodities with short shelf-lives owing to rapid deterioration of their organoleptic and microbiological quality. Microbial growth and activity are responsible for up to 25% of food losses in the fishery industry. In this context and to meet consumer demand for minimally processed food, developing mild preservation technologies such as biopreservation represents a major challenge. In this work, we studied the use of six lactic acid bacteria (LAB), previously selected for their properties as bioprotective agents, for salmon dill gravlax biopreservation. Naturally contaminated salmon dill gravlax slices, with a commercial shelf-life of 21 days, were purchased from a French industrial company and inoculated by spraying with the protective cultures (PCs) to reach an initial concentration of 106 log CFU/g. PC impact on gravlax microbial ecosystem (cultural and acultural methods), sensory properties (sensory profiling test), biochemical parameters (pH, TMA, TVBN, biogenic amines) and volatilome was followed for 25 days of storage at 8°C in vacuum packaging. PC antimicrobial activity was also assessed in situ against Listeria monocytogenes. This polyphasic approach underlined two scenarios depending on the protective strain. Carnobacterium maltaromaticum SF1944, Lactococcus piscium EU2229 and Leuconostoc gelidum EU2249, were very competitive in the product, dominated the microbial ecosystem, and displayed antimicrobial activity against the spoilage microbiota and L. monocytogenes. The strains also expressed their own sensory and volatilome signatures. However, of these three strains, C. maltaromaticum SF1944 did not induce strong spoilage and was the most efficient for L. monocytogenes growth control. By contrast, Vagococcus fluvialis CD264, Carnobacterium inhibens MIP2551 and Aerococcus viridans SF1044 were not competitive, did not express strong antimicrobial activity and produced only few organic volatile compounds (VOCs). However, V. fluvialis CD264 was the only strain to extend the sensory quality, even beyond 25 days. This study shows that C. maltaromaticum SF1944 and V. fluvialis CD264 both have a promising potential as bioprotective cultures to ensure salmon gravlax microbial safety and sensorial quality, respectively.

Natural products with preservative properties for enhancing the microbiological safety and extending the shelf-life of seafood: A review

Seafood is highly perishable, presenting a rapid loss of its quality soon after capture. Temperature is the critical parameter that impacts on seafood shelf-life reduction, allowing the growth of foodborne pathogens and spoilage microorganisms. In recent years, the search by additional methods of preserving seafood has increased, able to ensure quality and safety. Several natural preservatives have highlighted and gained considerable attention from the scientific community, consumers, industry, and health sectors as a method with broad action antimicrobial and generally economical. Natural preservatives, from different sources, have been widely studied, such as chitosan from animal sources, essential oils, and plant extracts from a plant source, lactic acid bacteria, and bacteriocins from microbiological sources and organic acid from different sources, all with great potential for use in seafood systems. This review focuses on the natural preservatives studied in seafood matrices, their forms of application, concentrations usually employed, their mechanisms of action, factors that interfere in their use and the synergistic effect of the interactions among the natural preservatives, with a focus for maintenance of quality and ensure of food safety.

Modelling the interaction of the sakacin-producing Lactobacillus sakei CTC494 and Listeria monocytogenes in filleted gilthead sea bream (Sparus aurata) under modified atmosphere packaging at isothermal and non-isothermal conditions

The objective of this work was to quantitatively evaluate the effect of Lactobacillus sakei CTC494 (sakacin-producing bioprotective strain) against Listeria monocytogenes in fish juice and to apply and validate three microbial interaction models (Jameson, modified Jameson and Lotka Volterra models) through challenge tests with gilthead sea bream (Sparus aurata) fillets under modified atmosphere packaging stored at isothermal and non-isothermal conditions. L. sakei CTC494 inhibited L. monocytogenes growth when simultaneously present in the matrix (fish juice and fish fillets) at different inoculation ratios pathogen:bioprotector (i.e. 1:1, 1:2 and 1:3). The higher the inoculation ratio, the stronger the inhibition of L. monocytogenes growth, with the ratio 1:3 yielding no growth of the pathogen. The maximum population density (N_max) was the most affected parameter for L. monocytogenes at all inoculation ratios. According to the microbiological and sensory analysis outcomes, an initial inoculation level of 4 log cfu/g for L. sakei CTC494 would be a suitable bioprotective strategy without compromising the sensory quality of the fish product. The performance of the tested interaction models was evaluated using the Acceptable Simulation Zone approach. The Lotka Volterra model showed slightly better fit than the Jameson-based models with 75-92% out of the observed counts falling into the Acceptable Simulation Zone, indicating a satisfactory model performance. The evaluated interaction models could be used as predictive modelling tool to simulate the simultaneous behaviour of bacteriocin-producing Lactobacillus strains and L. monocytogenes; thus, supporting the design and optimization of bioprotective culture-based strategies against L. monocytogenes in minimally processed fish products.

Bioprotective Effect of Lactococcus piscium CNCM I-4031 Against Listeria monocytogenes Growth and Virulence

Listeria monocytogenes is a Gram-positive pathogen occurring in many refrigerated ready-to-eat foods. It is responsible for foodborne listeriosis, a rare but severe disease with a high mortality rate (20-30%). Lactococcus piscium CNCM I-4031 has the capacity to prevent the growth of L. monocytogenes in contaminated peeled and cooked shrimp and in a chemically defined medium using a cell-to-cell contact-dependent mechanism. To characterize this inhibition further, the effect of L. piscium was tested on a collection of 42 L. monocytogenes strains. All strains were inhibited but had different sensitivities. The effect of the initial concentration of the protective and the target bacteria revealed that the inhibition always occurred when L. piscium had reached its maximum population density, whatever the initial concentration of the protective bacteria. Viewed by scanning electron microscopy, L. monocytogenes cell shape and surface appeared modified in co-culture with L. piscium CNCM I-4031. Lastly, L. monocytogenes virulence, evaluated by a plaque-forming assay on the HT-29 cell line, was reduced after cell pre-treatment by the protective bacteria. In conclusion, the bioprotective effect of L. piscium toward L. monocytogenes growth and virulence was demonstrated, and a hypothesis for the inhibition mechanism is put forward.

Lactococcus piscium: a psychrotrophic lactic acid bacterium with bioprotective or spoilage activity in food-a review

The genus Lactococcus comprises 12 species, some known for decades and others more recently described. Lactococcus piscium, isolated in 1990 from rainbow trout, is a psychrotrophic lactic acid bacterium, probably disregarded because most of the strains are unable to grow at 30°C. During the last 10 years, this species has been isolated from a large variety of food: meat, seafood and vegetables, mostly packed under vacuum (VP) or modified atmosphere (MAP) and stored at chilled temperature. Recently, culture-independent techniques used for characterization of microbial ecosystems have highlighted the importance of Lc. piscium in food. Its role in food spoilage varies according to the strain and the food matrix. However, most studies have indicated that Lc. piscium spoils meat, whereas it does not degrade the sensory properties of seafood. Lactococcus piscium strains have a large antimicrobial spectrum, including Gram-positive and negative bacteria. In various seafoods, some strains have a protective effect against spoilage and can extend the sensory shelf-life of the products. They can also inhibit the growth of Listeria monocytogenes, by a cell-to-cell contact-dependent. This article reviews the physiological and genomic characteristics of Lc. piscium and discusses its spoilage or protective activities in food.

Selection of bioprotective cultures for preventing cold-smoked salmon spoilage

Biopreservation is a natural technology of food preservation, which consists of inoculating food with microorganisms selected for their antibacterial properties. The objective of this study was to select lactic acid bacteria (LAB) to improve the quality of cold-smoked salmon (CSS). In this work, different strains representative of the 4 dominant species, identified in a previous study by pyrosequencing the 16S rRNA gene, were isolated and their spoiling potential in CSS blocks, sterilized by ionization, was assessed by twelve trained panelists along the vacuum storage at 8°C. Photobacterium phosphoreum, Brochothrix thermosphacta and Serratia proteamaculans released strong off-odors whereas the spoiling potential of Carnobacterium divergens was weaker. The spoiling capacity of Lactococcus piscium EU2241, Leuconostoc gelidum EU2247, Lactobacillus sakei EU2885, Staphylococcus equorum S030674 and 4 commercial starters was tested by the same method and 2 strains were eliminated due to off-odor production. The effect of the 6 selected LAB against the 4 specific spoiling organisms (SSOs) selected was tested by challenge tests in sterile CSS blocks. The protective effect of the LAB differed from one SSO to another and no correlation could be established between the sensory improvement, SSO inhibition, and the implantation or acidification of protective cultures (PCs). All the PCs except L. piscium reduced the off-odors released by P. phosphoreum although some of them had no effect on its growth. S. equorum, which did not grow in CSS, favored the implantation of P. phosphoreum but prevented its off-odor formation. L. piscium was the only strain that prevented the spoilage of B. thermosphacta and S. proteamaculans although it did not grow very well and did not acidify the product. L. gelidum EU2247 inhibited the growth of these 2 SSOs and lowered the pH but had no effect on the sensory quality. Finally, L. piscium was tested in 2 naturally contaminated products, with a positive effect on 1 batch. This effect was not correlated with the microbial ecosystem as determined by acultural and cultural techniques. Based on these results, the selection strategy is discussed.

Inhibition mechanism of Listeria monocytogenes by a bioprotective bacteria Lactococcus piscium CNCM I-4031

Listeria monocytogenes is a pathogenic Gram positive bacterium and the etiologic agent of listeriosis, a severe food-borne disease. Lactococcus piscium CNCM I-4031 has the capacity to prevent the growth of L. monocytogenes in contaminated peeled and cooked shrimp. To investigate the inhibititory mechanism, a chemically defined medium (MSMA) based on shrimp composition and reproducing the inhibition observed in shrimp was developed. In co-culture at 26 °C, L. monocytogenes was reduced by 3-4 log CFU g(-1) after 24 h. We have demonstrated that the inhibition was not due to secretion of extracellular antimicrobial compounds as bacteriocins, organic acids and hydrogen peroxide. Global metabolomic fingerprints of these strains in pure culture were assessed by liquid chromatography coupled with high resolution mass spectrometry. Consumption of glucose, amino-acids, vitamins, nitrogen bases, iron and magnesium was measured and competition for some molecules could be hypothesized. However, after 24 h of co-culture, when inhibition of L. monocytogenes occurred, supplementation of the medium with these compounds did not restore its growth. The inhibition was observed in co-culture but not in diffusion chamber when species were separated by a filter membrane. Taken together, these data indicate that the inhibition mechanism of L. monocytogenes by L. piscium is cell-to-cell contact-dependent.

Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage

The microbial spoilage of meat and seafood products with short shelf lives is responsible for a significant amount of food waste. Food spoilage is a very heterogeneous process, involving the growth of various, poorly characterized bacterial communities. In this study, we conducted 16S ribosomal RNA gene pyrosequencing on 160 samples of fresh and spoiled foods to comparatively explore the bacterial communities associated with four meat products and four seafood products that are among the most consumed food items in Europe. We show that fresh products are contaminated in part by a microbiota similar to that found on the skin and in the gut of animals. However, this animal-derived microbiota was less prevalent and less abundant than a core microbiota, psychrotrophic in nature, mainly originated from the environment (water reservoirs). We clearly show that this core community found on meat and seafood products is the main reservoir of spoilage bacteria. We also show that storage conditions exert strong selective pressure on the initial microbiota: alpha diversity in fresh samples was 189±58 operational taxonomic units (OTUs) but dropped to 27±12 OTUs in spoiled samples. The OTU assemblage associated with spoilage was shaped by low storage temperatures, packaging and the nutritional value of the food matrix itself. These factors presumably act in tandem without any hierarchical pattern. Most notably, we were also able to identify putative new clades of dominant, previously undescribed bacteria occurring on spoiled seafood, a finding that emphasizes the importance of using culture-independent methods when studying food microbiota.

Characterization and evaluation of the spoilage potential of Lactococcus piscium isolates from modified atmosphere packaged meat

A total of 222 psychrotrophic lactococci isolated from use-by day, modified atmosphere packaged (MAP) meat were identified to the species level by numerical analyses of EcoRI and ClaI ribopatterns and phylogenetic sequence analyses of 16S, rpoA and pheS genes. In addition, their meat spoilage potential was studied. The majority of the isolates (n=215) were identified as Lactococcus piscium, while seven isolates belonged to Lactococcus raffinolactis. L. piscium was shown to be adapted to growing in a variety of MAP meat products including broiler, turkey, pork, and minced meat from beef and pork, where they belonged to the predominating microbiota at the end of the storage. Numerical analyses of EcoRI and ClaI ribopatterns, and phylogenetic sequence analyses of rpoA and pheS genes were shown to be reliable tools in species level identification of meat lactococci. The spoilage potential of L. piscium was evaluated by inoculating representative isolates to MAP pork stored at 6 °C for 22 days. Development of spoilage population was monitored using a culture-independent T-RFLP approach. The sensory shelf life of pork inoculated with L. piscium was shortened compared to the uninoculated control. Alongside with the inoculated L. piscium isolates, Leuconostoc spp. present as initial contaminants in the samples thrived. This shows that even though lactococci were inoculated at higher levels compared to the natural microbiota, they did not occupy the niche and prevent the growth of other lactic acid bacteria.

Adaptation to cold and proteomic responses of the psychrotrophic biopreservative Lactococcus piscium strain CNCM I-4031

There is considerable interest in the use of psychrotrophic bacteria for food biopreservation and in the understanding of cold adaptation mechanisms. The psychrotrophic biopreservative Lactococcus piscium strain CNCM I-4031 was studied for its growth behavior and proteomic responses after cold shock and during cold acclimation. Growth kinetics highlighted the absence of growth latency after cold shock, suggesting a very high promptness in cold adaptation, a behavior that has never been described before for lactic acid bacteria (LAB). A comparative proteomic analysis was applied with two-dimensional gel electrophoresis (2-DE), and upregulated proteins were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Both cold shock and cold acclimation triggered the upregulation of proteins involved in general and oxidative stress responses and fatty acid and energetic metabolism. However, 2-DE profiles and upregulated proteins were different under both conditions, suggesting a sequence of steps in cold adaptation. In addition, the major 7-kDa Csp protein was identified in the L. piscium CNCM I-4031 genome but was not cold regulated. The implication of the identified cold shock proteins and cold acclimation proteins in efficient cold adaptation, the possible regulation of a histidyl phosphocarrier protein, and the roles of a constitutive major 7-kDa Csp are discussed.