Psychrotrophic Lactic Acid Bacteria Research Articles

Effect of Dry Aging of Pork on Microbiological Quality and Instrumental Characteristics

Meat aging is an important process that affects the quality of meat and is traditionally used mainly for beef. However, in recent years, there has been an increasing demand for pork products subjected to dry aging. The aim of this study was to compare selected parameters (microbiological quality, instrumental analyses of texture and color of meat, weight loss) of pork neck and loin with bone and skin together subjected to dry aging for 14 days. The microbiological profile (total viable psychrotrophic count, Enterobacteriaceae, psychrotrophic lactic acid bacteria, Pseudomonas spp.) on the surface of the meat with the skin and the lateral cutting surfaces without skin was compared on the first day after slaughter and after 14 days of dry aging. The results of this study demonstrated that dry aging did not significantly deteriorate the microbiological profile. Statistically significant weight losses were observed after 14 days of aging. The dry aging of pork had no significant effect on lightness (L*), redness (a*), and shear force. Significant differences were observed for yellowness (b*) and meat hardness (p < 0.05).

Development a modified MRS medium for enhanced growth of psychrotrophic lactic acid bacteria isolated from kimchi

When culturing psychrotrophic lactic acid bacteria (LAB) isolated from kimchi, the commonly used de Man, Rogosa and Sharpe (MRS) medium does not sufficiently satisfy the nutritional requirements for all bacteria. To overcome this limitation, a modified MRS medium (m-MRS) and culture conditions tailored for psychrotrophic LAB were developed via statistical optimization using response surface methodology (RSM) and partial least squares–genetic algorithm (PLS–GA). A one–factor method based on the MRS medium was used to determine the medium composition. Glucose, sucrose, and mannose (6.7 g/L each) were selected as carbon sources, and soy peptone (19.11 g/L), a plant-based alternative, was used as a nitrogen source, replacing beef extract. Tomato juice (1 g/L) and L-ascorbic acid (0.1 g/L) were selected as growth factors. These factors were treated as independent variables and optimized using RSM, and PLS–GA. Temperature, incubation time, and pH were utilized as independent variables for RSM and PLS-GA to optimize the culture conditions. Compared to the MRS medium, the m-MRS broth provided better support for the growth of most psychrotrophic LAB strains tested. Thus, m-MRS medium and optimized conditions can be effectively applied to culture psychrotrophic LAB isolated from kimchi.

Polar-Region Soils as Novel Reservoir of Lactic Acid Bacteria from the Genus Carnobacterium.

Polar habitats offer excellent sites to isolate unique bacterial strains due to their diverse physical, geochemical, and biological factors. We hypothesize that the unique environmental conditions of polar regions select for distinct strains of lactic acid bacteria (LAB) with novel biochemical properties. In this study, we characterized ten strains of psychrotrophic LAB isolated from hitherto poorly described sources-High Arctic and maritime Antarctic soils and soil-like materials, including ornithogenic soils, cryoconites, elephant seal colonies, and postglacial moraines. We evaluated the physiological and biochemical properties of the isolates. Based on 16S rRNA and housekeeping genes, the four LAB strains were assigned to three Carnobacterium species: C. alterfunditum, C. maltaromaticum, and C. jeotgali. The remaining strains may represent three new species of the Carnobacterium genus. All isolates were neutrophilic and halophilic psychrotrophs capable of fermenting various carbohydrates, organic acids, and alcohols. The identified metabolic properties of the isolated Carnobacterium strains suggest possible syntrophic interactions with other microorganisms in polar habitats. Some showed antimicrobial activity against food pathogens such as Listeria monocytogenes and human pathogens like Staphylococcus spp. Several isolates exhibited unique metabolic traits with potential biotechnological applications that could be more effectively exploited under less stringent technological conditions compared to thermophilic LAB strains, such as lower temperatures and reduced nutrient concentrations. Analysis of extrachromosomal genetic elements revealed 13 plasmids ranging from 4.5 to 79.5 kb in five isolates, featuring unique genetic structures and high levels of previously uncharacterized genes. This work is the first comprehensive study of the biochemical properties of both known and new Carnobacterium species and enhances our understanding of bacterial communities in harsh and highly selective polar soil ecosystems.

Microbiological characteristics and applied preservation method of novel ready-to-eat vegetarian spreads and dips

A range of spreads and dips as novel vegetarian ready-to-eat foods are being introduced on the (European) retail market to response to an increasing number of vegetarian’/flexitarian’ consumers and the shift towards plant-based foods consumption. This innovative food group was explored by a product survey (n = 369) in Belgium. The spreads and dips were classified on the presence of main ingredients, the applied preservation mode, the remaining shelf-life period, and the presence of additives. The majority of the products have soybeans or other seeds as the main ingredient, are containing preservatives (e.g. potassium sorbate; E202) and organic acids/acid regulators (e.g. lactic acid; E270 and citric acid; E330) as additives. 45% of the products were marketed under the organic label and 36% of them were indicated as so-called ‘clean label’. From a selection (78 refrigerated and 23 ambient stored products), the physicochemical characteristics (i.e. pH, water activity, and headspace gas composition) were determined as well as the microbiological quality, hygiene, and safety at the moment of purchase and the end of the indicated shelf-life. The analyzed microbiological quality indicators for refrigerated samples demonstrated a psychrotrophic total plate count range of 1.0–9.4 log CFU/g, psychrotrophic lactic acid bacteria range of 1.0–8.8 log CFU/g, yeast and fungi range of 2.0–9.5 log CFU/g and sulfite reducing Clostridia range of 1.0–3.7 log CFU/g. E. coli and coliforms were analyzed as hygiene indicators and solely coliforms were detected on three samples with a maximum count of 3.6 log CFU/g. Listeria monocytogenes was not detected in 10g. Bacillus cereus never exceeded 3.5 log CFU/g. For the ambient stored samples, mesophilic total plate count, mesophilic lactic acid bacteria, yeast and fungi, sulfite reducing Clostridia, B. cereus, B. cereus spores, aerobic spores, and anaerobic spores were determined. Most of the products showed cell counts below the limit of detection (= 1.0 log CFU/g). Only products based on chickpeas, sesame seeds, and other seeds showed cell counts for mesophilic total plate count and aerobic plate count ranging respectively from 1.0 to 4.3 log CFU/g and 1.0 to 5.1 log CFU/g. The research gives insight into the variable microbiological composition and multiple applied preservation modes of this innovative food group of ready-to-eat vegetarian dips and spreads.

Isolation and identification of psychrotrophic lactic acid bacteria in godo, the traditional fermented soy food in Japan.

Godo is a traditional fermented soy food made in Aomori prefecture, Japan. It is mainly made of soybeans, rice koji, and salt. Since godo ripens during the long and severe winter in northeast Japan, it is assumed that lactic acid bacteria inhabiting godo have cold tolerance. We aimed to investigate the presence or absence of psychrotrophic lactic acid bacteria in godo. The viable counts of estimated lactic acid bacteria ranged from 106 to 108 cfu/g. In addition, aerobic and anaerobic microorganisms were detected in four godo products though the microbial population differed from sample to sample. Twenty-two bacterial strains were able to be isolated from godo, and all of the isolated strains were Gram-positive and catalase-negative. Some of the isolates grew well at 10°C. The carbohydrate fermentation profile of the selected three strains was determined by API50 CHL analysis. These strains were identified as Leuconostoc mesenteroides, and Latilactobacillus sakei by 16S rRNA gene sequence analysis. Leuconostoc mesenteroides strains HIT231 and HIT252, and Latilactobacillus sakei strain HIT273 could grow at 5°C in MRS broth, but their optimum growth temperature was 20°C-30°C. These results suggest that psychrotrophic lactic acid bacteria presumed to be derived from rice koji are present in godo, which is one of the factors in the low temperature ripening of godo in winter.

Exploring the microbiological quality and safety of dry-aged beef: A cross-sectional study of loin surfaces during ripening and dry-aged beef steaks from commercial meat companies in Belgium

A cross-sectional survey was undertaken in Belgian beef producing companies to study the current practices and the microbiological load of dry-aged loins (during production) and trimmed steaks (final product). In each company, the temperature and relative humidity of the ripening chamber were measured, and two loins (each in a different stage of the ripening process) were sampled. From the surface of each loin, a lean meat and adipose tissue sample was analysed separately, and different groups of bacteria, yeasts and moulds were enumerated. The average relative humidity in the ripening chambers was 72 ± 13% and the temperature ranged between 0.0 °C and 5.9 °C. During the drying process, most of the lean meat and adipose tissue samples showed high numbers of total psychrotrophic aerobic bacteria, Pseudomonas spp., psychrotrophic lactic acid bacteria, and yeasts, but the variation between loins was high. The microbiological load on freshly cut dry-aged steaks was generally lower than on loin surfaces, but both psychrotrophic aerobic and anaerobic bacteria were present inside several steaks. The water activity inside dry-aged beef steaks was high (aw ≥ 0.98), which could allow growth of psychrotrophic pathogens, though more in-depth studies are necessary to determine potential growth during the storage of (trimmed) steaks or even inside loins during the dry-aging process.

Characterization of the Psychrotrophic Lactic Acid Bacterium Leuconostoc gelidum subsp. aenigmaticum LS4 Isolated from Kimchi Based on Comparative Analyses of Its Genomic and Phenotypic Properties.

With the aim of developing a new food starter culture, twenty-three psychrotrophic lactic acid bacteria (LAB) were isolated from 16 kimchi samples. One strain, Leuconostoc gelidum subsp. aenigmaticum LS4, which had typical psychrotrophic characteristics, was selected, and its phenotypic and genomic properties as a starter culture were investigated. The complete genome of L. aenigmaticum LS4 consisted of one circular chromosome (1,988,425 bp) and two plasmids (19,308 bp and 11,283 bp), with a guanine–cytosine content of 36.8%. L. aenigmaticum LS4 could grow at 5 °C but not at 37 °C, and maximum cell growth was obtained at 15~25 °C. L. aenigmaticum LS4 did not show any harmful characteristics such as hemolysis, undesirable enzyme activities, biogenic amine production, or antibiotic resistance. L. aenigmaticum LS4 was investigated for its suitability for technological processes (pH, temperature and NaCl treatment). L. aenigmaticum LS4 exhibited strong antimicrobial activity caused by the production of organic acids and bacteriocin, and it produced an exopolysaccharide composed of glucose with a molecular weight of 3.7 × 106 Da. Furthermore, L. aenigmaticum LS4 improved the organoleptic qualities of kimchi juice. Our results indicate that L. aenigmaticum LS4 could be used as a functional starter culture for food (vegetable or fruit) fermentation at low temperatures.

Transcriptomic time-series analysis of cold- and heat-shock response in psychrotrophic lactic acid bacteria

BackgroundPsychrotrophic lactic acid bacteria (LAB) species are the dominant species in the microbiota of cold-stored modified-atmosphere-packaged food products and are the main cause of food spoilage. Despite the importance of psychrotrophic LAB, their response to cold or heat has not been studied. Here, we studied the transcriptome-level cold- and heat-shock response of spoilage lactic acid bacteria with time-series RNA-seq for Le. gelidum, Lc. piscium, and P. oligofermentans at 0 °C, 4 °C, 14 °C, 25 °C, and 28 °C.ResultsWe observed that the cold-shock protein A (cspA) gene was the main cold-shock protein gene in all three species. Our results indicated that DEAD-box RNA helicase genes (cshA, cshB) also play a critical role in cold-shock response in psychrotrophic LAB. In addition, several RNase genes were involved in cold-shock response in Lc. piscium and P. oligofermentans. Moreover, gene network inference analysis provided candidate genes involved in cold-shock response. Ribosomal proteins, tRNA modification, rRNA modification, and ABC and efflux MFS transporter genes clustered with cold-shock response genes in all three species, indicating that these genes could be part of the cold-shock response machinery. Heat-shock treatment caused upregulation of Clp protease and chaperone genes in all three species. We identified transcription binding site motifs for heat-shock response genes in Le. gelidum and Lc. piscium. Finally, we showed that food spoilage-related genes were upregulated at cold temperatures.ConclusionsThe results of this study provide new insights on the cold- and heat-shock response of psychrotrophic LAB. In addition, candidate genes involved in cold- and heat-shock response predicted using gene network inference analysis could be used as targets for future studies.

Microbiomes in the Context of Refrigerated Raw Meat Spoilage

Meat spoilage is a complicated biological phenomenon taking place over the course of time. Several factors influence it, mainly external factors related to packaging and storage temperature but also internal ones related to contamination diversity and product ingredients. We conducted genomic studies of specific spoilage organisms (SSO) and investigated the spoilage microbiomes providing information about the factors that make a specific organism a competitive SSO, as well as the interactions between certain SSO and the most active species and pathways in packaged raw meat. Our studies showed that spoilage microbiomes are diverse, but certain aspects, such as oxygen content or added marinades, shape this diversity strongly. We have also characterized a new spoilage-associated pathway, i.e., heme-dependent respiration capability, in Leuconostoc gelidum subsp. gasicomitatum. The microbiome studies we conducted explain why this species has become a competitive SSO. It is a fast grower and gains advantage for its growth if oxygen is present in the packages. Since the contamination of psychrotrophic lactic acid bacteria is difficult to avoid in meat manufacture, leuconostocs cause spoilage problems from time to time especially in marinated products or those packaged under high-oxygen–containing atmospheres.

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 10years, 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.

Improving the fermentation quality of wheat straw silage stored at low temperature by psychrotrophic lactic acid bacteria.

This study aimed to explore the feasible approaches to develop a silage production technique in regions with low temperatures. An effective low-temperature silage technology system was constructed and two frigostable Lactobacillus (L.) strains isolated from alpine pastures were selected and proved to be available for wheat straw silage at 5°C. The strains QZ227 and QZ887 were both identified as L. plantarum according to the phenotype, 16S rRNA, and RecA gene analysis. QZ227, QZ887 and a commercial inoculant FG1 consisting of L. plantarum were effective for improving the fermentation quality of wheat straws silage at 5°C for 30 days as indicated by the higher content of lactic acid and for 60 days by lower pH values, while the control with sterile water instead conferred reduced benefits. Additionally, silages fermented at low temperature proved to be acceptable for feeding livestock after being placed in a simulated environmental temperature of 20°C for 14 days to detect its edibility during the early spring when the temperature begins to rise. Both QZ227 and QZ887 showed potential applications of silage making in frigid areas and were effective inoculants in a low-temperature silage technology system.

Microflora of farm and hunted pheasants in relation to biogenic amines production

The aim of the study was to compare, within 3-week cold storage, the content of eight biogenic amines (BA) and the development of microflora in different parts of bodies (breast and thigh muscles and liver) of farm pheasants and pheasants hunted in the wild. Killed and untreated bodies of pheasants were stored hanging in an air-conditioned chamber at a cold temperature (5 ± 1 °C). The pheasant bodies were subjected to microbiological analysis and identification of isolated microorganisms whose decarboxylase activity was detected. The production of biogenic amines and polyamines was determined by means of HPLC after pre-column derivatisation with dansylchloride. The total number of microorganisms in all parts of the pheasant bodies as well as the number of psychrotrophic bacteria, enterobacteria and lactic acid bacteria was increasing during storage (P < 0.05). A total of 127 strains of bacteria from the pheasant bodies were isolated and identified. Production of at least one biogenic amine was found in vitro in 107 isolates. Three strains were found to produce four biogenic amines—histamine, tyramine, putrescine and cadaverine. Production of phenylethylamine, tryptamine, spermidine and spermine in the isolated bacteria was not detected. Within all the biogenic amines detected in the analysed samples of pheasant bodies, the lowest concentration was found in histamine and the highest one in tyramine and cadaverine. The amount of BA detected in the individual parts of pheasant bodies was increasing during the storage period. The total amounts of seven biogenic amines (histamine, tyramine, putrescine, cadaverine, phenylethylamine, spermidine and spermine) in the individual parts of pheasant bodies were ranging between 9 and 708 mg/kg.

Genome Sequence and Transcriptome Analysis of Meat-Spoilage-Associated Lactic Acid Bacterium Lactococcus piscium MKFS47.

Lactococcus piscium is a psychrotrophic lactic acid bacterium and is known to be one of the predominant species within spoilage microbial communities in cold-stored packaged foods, particularly in meat products. Its presence in such products has been associated with the formation of buttery and sour off-odors. Nevertheless, the spoilage potential of L. piscium varies dramatically depending on the strain and growth conditions. Additional knowledge about the genome is required to explain such variation, understand its phylogeny, and study gene functions. Here, we present the complete and annotated genomic sequence of L. piscium MKFS47, combined with a time course analysis of the glucose catabolism-based transcriptome. In addition, a comparative analysis of gene contents was done for L. piscium MKFS47 and 29 other lactococci, revealing three distinct clades within the genus. The genome of L. piscium MKFS47 consists of one chromosome, carrying 2,289 genes, and two plasmids. A wide range of carbohydrates was predicted to be fermented, and growth on glycerol was observed. Both carbohydrate and glycerol catabolic pathways were significantly upregulated in the course of time as a result of glucose exhaustion. At the same time, differential expression of the pyruvate utilization pathways, implicated in the formation of spoilage substances, switched the metabolism toward a heterofermentative mode. In agreement with data from previous inoculation studies, L. piscium MKFS47 was identified as an efficient producer of buttery-odor compounds under aerobic conditions. Finally, genes and pathways that may contribute to increased survival in meat environments were considered.

Complete genome sequence and analysis of Lactobacillus hokkaidonensis LOOC260(T), a psychrotrophic lactic acid bacterium isolated from silage.

BackgroundLactobacillus hokkaidonensis is an obligate heterofermentative lactic acid bacterium, which is isolated from Timothy grass silage in Hokkaido, a subarctic region of Japan. This bacterium is expected to be useful as a silage starter culture in cold regions because of its remarkable psychrotolerance; it can grow at temperatures as low as 4°C. To elucidate its genetic background, particularly in relation to the source of psychrotolerance, we constructed the complete genome sequence of L. hokkaidonensis LOOC260T using PacBio single-molecule real-time sequencing technology.ResultsThe genome of LOOC260T comprises one circular chromosome (2.28 Mbp) and two circular plasmids: pLOOC260-1 (81.6 kbp) and pLOOC260-2 (41.0 kbp). We identified diverse mobile genetic elements, such as prophages, integrated and conjugative elements, and conjugative plasmids, which may reflect adaptation to plant-associated niches. Comparative genome analysis also detected unique genomic features, such as genes involved in pentose assimilation and NADPH generation.ConclusionsThis is the first complete genome in the L. vaccinostercus group, which is poorly characterized, so the genomic information obtained in this study provides insight into the genetics and evolution of this group. We also found several factors that may contribute to the ability of L. hokkaidonensis to grow at cold temperatures. The results of this study will facilitate further investigation for the cold-tolerance mechanism of L. hokkaidonensis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1435-2) contains supplementary material, which is available to authorized users.

Processing Environment and Ingredients Are Both Sources of Leuconostoc gelidum, Which Emerges as a Major Spoiler in Ready-To-Eat Meals.

Mesophilic and psychrotrophic organism viable counts, as well as high-throughput 16S rRNA gene-based pyrosequencing, were performed with the aim of elucidating the origin of psychrotrophic lactic acid bacteria (LAB) in a ready-to-eat (RTE) meal manufacturing plant. The microbial counts of the products at the end of the shelf life were greatly underestimated when mesophilic incubation was implemented due to overlooked, psychrotrophic members of the LAB. Pseudomonas spp., Enterobacteriaceae, Streptococcaceae, and Lactobacillus spp. constituted the most widespread operational taxonomic units (OTUs), whereas Leuconostoc gelidum was detected as a minor member of the indigenous microbiota of the food ingredients and microbial community of the processing environment, albeit it colonized samples at almost every sampling point on the premises. However, L. gelidum became the most predominant microbe at the end of the shelf life. The ability of L. gelidum to outgrow notorious, spoilage-related taxa like Pseudomonas, Brochothrix, and Lactobacillus underpins its high growth dynamics and severe spoilage character under refrigeration temperatures. The use of predicted metagenomes was useful for observation of putative gene repertoires in the samples analyzed in this study. The end products grouped in clusters characterized by gene profiles related to carbohydrate depletion presumably associated with a fast energy yield, a finding which is consistent with the fastidious nature of highly competitive LAB that dominated at the end of the shelf life. The present study showcases the detrimental impact of contamination with psychrotrophic LAB on the shelf life of packaged and cold-stored foodstuffs and the long-term quality implications for production batches once resident microbiota are established in the processing environment.

Identification and evaluation of psychrotrophic lactic acid bacteria from imitation crab sticks to develop a microbial time temperature integrator

Ten strains of psychrotrophic Weissella species from imitation crab sticks (ICSs) were isolated and characterized to develop a microbial-based time temperature integrator (TTI). The strains were selected according to their hemolytic activity, gram staining, and catalase reaction. All the strains grew well in modified imitation crab (MIC) broth at 5 and 15°C. Significant acid production, an associated drop in pH values, and a color change were observed in most of the strains after 7-days of incubation at both temperatures. Furthermore, the strains produced a time-temperature dependent color change due to the production of lactic acid. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the ten strains belonged to the genus Weissella.

Multilocus sequence typing of Leuconostoc gelidum subsp. gasicomitatum, a Psychrotrophic lactic acid bacterium causing spoilage of packaged perishable foods.

Leuconostoc gelidum subsp. gasicomitatum is a psychrotrophic lactic acid bacterium (LAB) that causes spoilage of a variety of modified-atmosphere-packaged (MAP) cold-stored food products. During the past 10 years, this spoilage organism has been increasingly reported in MAP meat and vegetable products in northern Europe. In the present study, the population structure within 252 L. gelidum subsp. gasicomitatum strains was determined based on a novel multilocus sequence-typing (MLST) scheme employing seven housekeeping genes. These strains had been isolated from meat and vegetable sources over a time span of 15 years, and all 68 previously detected pulsed-field gel electrophoresis (PFGE) genotypes were represented. A total of 46 sequence types (STs) were identified, with a majority of the strains (>60%) belonging to three major STs, which were grouped into three clonal complexes (CCs) and 17 singletons by Global Optimal eBURST (goeBURST). The results by Bayesian analysis of population structure (BAPS) mostly correlated with the grouping by goeBURST. Admixture analysis by BAPS indicated a very low level of exchange of genetic material between the subpopulations. Niche specificity was observed within the subpopulations: CC1 and BAPS cluster 1 consisted mostly of strains from a variety of MAP meats, whereas vegetable strains grouped together with strains from MAP poultry within CC2 and BAPS cluster 2. The MLST scheme presented in this study provides a shareable and continuously growing sequence database enabling global comparison of strains associated with spoilage cases. This will further advance our understanding of the microbial ecology of this industrially important LAB.

Exploring the strain-specific attachment of Leuconostoc gelidum subsp. gasicomitatum on food contact surfaces

The psychrotrophic lactic acid bacterium (LAB) Leuconostoc gelidum subsp. gasicomitatum has emerged as one of the most prevalent specific spoilage organisms (SSOs) of packaged, cold-stored food products in Northern Europe. The whole genome sequencing of the type strain L. gelidum subsp. gasicomitatum LMG 18811T revealed genes encoding for proteins related to adhesion. In the present study the attachment of six food and environmental isolates was monitored on stainless steel (SS) and glass surfaces incubated (7°C for 5–9days) in two food simulating substrates (i.e. sweet bell pepper juice and boiled eggs in brine). The selection encompassed unique genotypes, isolated from different food products or sampling sites as well as slime-forming biotypes. The evaluation of the attached cells was performed with the bead vortexing method and a viability staining assay coupled with epifluorescence microscopy. On SS surfaces the slime-formers showed the lowest attachment (3.3–4.5logCFU/cm2), while strain L. gelidum subsp. gasicomitatum ab2, which was isolated from an acetic acid bath in a vegetable salad company, reached significantly higher populations of attached cells exceeding 7logCFU/cm2. Strain ab2 formed dense cell aggregations on SS after 9days of incubation in sweet bell pepper juice. The attachment ability of L. gelidum subsp. gasicomitatum on surfaces documented in the present study extends our knowledge and understanding of the spoilage potential and intra-subspecies diversity of this microbe.

Psychrotrophic lactic acid bacteria associated with production batch recalls and sporadic cases of early spoilage in Belgium between 2010 and 2014

Between 2010 and 2014 several spoilage cases in Belgium occurring in retail foodstuffs prior to the end of shelf-life have been reported to our laboratory. Overall, seven cases involved strictly psychrotrophic lactic acid bacteria (LAB) contamination in packaged and chilled-stored food products. The products derived either from recalls of entire production batches or as specimens of sporadic spoilage manifestations. Some of these samples were returned to the manufacturing companies by consumers who observed the alterations after purchasing the products.The products covered a wide range of foodstuffs (i.e. meat, dairy, vegetable, egg products and composite food) and denoted different spoilage defects. However, the microbiota determined by means of 16S rRNA gene high-throughput sequencing analysis underpin few LAB genera (i.e. Leuconostoc, Lactobacillus, Weissella and Lactococcus), which are frequently encountered nowadays as specific spoilage organisms (SSO) albeit overlooked by mesophilic enumeration methods due to their strictly psychrotrophic character. The present study confirms the spreading of psychrotrophic LAB in Belgian food processing environments leading to unexpected spoilage, corroborating their spoilage dynamics and prevalence in all kinds of packaged and refrigerated foodstuffs in Northern Europe.

Monitoring psychrotrophic lactic acid bacteria contamination in a ready-to-eat vegetable salad production environment

A study monitoring lactic acid bacteria contamination was conducted in a company producing fresh, minimally processed, packaged and ready-to-eat (RTE) vegetable salads (stored at 4°C) in order to investigate the reason for high psychrotrophic LAB levels in the products at the end of shelf-life. Initially, high microbial counts exceeding the established psychrotrophic thresholds (>107–108CFU/g) and spoilage manifestations before the end of the shelf-life (7days) occurred in products containing an assortment of sliced and diced vegetables, but within a one year period these spoilage defects became prevalent in the entire processing plant. Environmental sampling and microbiological analyses of the raw materials and final products throughout the manufacturing process highlighted the presence of high numbers of Leuconostoc spp. in halved and unseeded, fresh sweet bell peppers provided by the supplier. A combination of two DNA fingerprinting techniques facilitated the assessment of the species diversity of LAB present in the processing environment along with the critical point of their introduction in the production facility. Probably through air mediation and surface adhesion, mainly members of the strictly psychrotrophic species Leuconostoc gelidum subsp. gasicomitatum and L. gelidum subsp. gelidum were responsible for the cross-contamination of every vegetable handled within the plant.