Leuconostoc Mesenteroides Research Articles

Antilisterial Properties of Selected Strains from the Autochthonous Microbiota of a Swiss Artisan Soft Smear Cheese

High incidences of the foodborne pathogen Listeria monocytogenes have been reported on smear cheeses, and despite increased hygiene efforts, this incidence has remained stable in recent years. Applying antilisterial strains may increase the safety of smear cheeses. To find and test antilisterial strains, we inoculated fresh soft cheeses from nine dairies with the surrogate species Listeria innocua and assessed its growth under standardized ripening conditions. Acetic acid at day 23 (r = −0.66), lactose in fresh cheese (r = −0.63), and glucose at day 10 (r = −0.62), as well as seven amplicon sequence variants (ASVs), were negatively correlated with L. innocua growth. Two of these ASVs were assigned to the genus Leuconostoc of Lactobacillaceae (r = −0.82 and −0.71). Isolates from this family, from Aerococcaceae, and Carnobacteriaceae were characterized according to their inhibitory properties, and those showing antilisterial properties were applied as protective cultures in challenge tests. The combined application of strains of Leuconostoc mesenteroides, Aerococcaceae, and Carnobacteriaceae successfully eliminated low levels of L. innocua in the final products. This is likely explained by antimicrobial compounds, including mesentericin Y105 and acetate, and competition for carbon sources and iron. This study shows a promising way to improve the safety of soft smear cheeses by applying defined protective cultures.

Regional microbial content of fermented traditional and industrial East Mediterranean sausages from the islands of Cyprus and Mytilini

Objective: To characterize the microbial biodiversity of fermented sausages from the East Mediterranean islands of Cyprus and Mytilini, and to identify differences between the microbial diversity of traditionally and industrially produced Cypriot sausages. Method: The microbial diversity of thirty sausages from Cyprus and Mytilini (traditionally and industrially produced) was analyzed using high throughput sequencing (HTS) (amplicon sequencing) of 16S rRNA gene and ITS loci fragments. By applying microbial signature detection and machine learning algorithms, we identified key microbes that distinguish traditionally produced sausages from those produced industrially. Focusing on selected microbial taxa and using interaction network analysis, we identified associations among the sausages’ microbiota that may affect the shaping of the sausages’ microbial consortia. Results: Cypriot and Mytilini sausages indicated increased relative representation of Lactobacillus and Leuconostoc . Cypriot sausages were distinguished by the presence of the fungi Debaryomyces hansenii and Candida spp. , whereas Mytilini sausages by the bacteria Lactococcus and Streptococcus . Traditionally produced sausages from the Pitsilia region of Cyprus were differentiated by the presence of the species Lactobacillus helveticus , whereas industrially produced sausages were differentiated by the species Leuconostoc mesenteroides . Focusing mainly on Lactobacillus and Leuconostoc , negative associations with pathogenic bacteria, such as Salmonella , and spoilage fungi, such as Fusarium poae , were revealed. Conclusion: The present metataxonomic analysis provided insights into the microbial communities that characterize Cypriot and Mytilini sausages. The findings provide an indication that the microbial diversity might be applied as an additional marker of Cypriot sausages’ authenticity.

Lock, stock, and Leuconostoc: an unusual presentation of a rare pathogen

Leuconostoc mesenteroides is a Gram-positive bacterium in the Lactobacillaceae family. This species is rarely encountered clinically and in the past was regarded as a contaminant when cultured. Recently it is being recognized as a pathogen responsible for opportunistic infections in immunocompromised patients. Compared to other Gram-positive cocci, Leuconostoc spp. carry intrinsic resistance to vancomycin. It is not common for clinical microbiology laboratories to isolate this organism and instead incorrectly report enterococcus and streptococcus organisms. Here, we present a case of bacteremia resulting in febrile illness and pneumonia in an 81-year-old woman with a history of rheumatoid arthritis and a notable lapse between immunomodulator therapy exposure. She was successfully treated when this organism was identified, and her antibiotic therapy was switched from vancomycin to ampicillin-sulbactam. This case highlights the importance of considering L. mesenteroides as a source of infection in patients predisposed to an immunocompromised state despite this organism’s being a rare pathogen. Keywords: Leuconostoc mesenteroides, rheumatoid arthritis, immunomodulators; vancomycin resistance

Leuconostoc koreense sp. nov., isolated from kimchi, a fermented vegetable.

The novel strain CBA3628T was isolated from kimchi, a Korean fermented vegetable. CBA3628T is a cocci-shaped, Gram-stain-positive, catalase- and oxidase-negative and facultatively anaerobic bacterium. The results of phylogenetic analysis based on 16S rRNA gene sequencing indicated that CBA3628T represented a member of the genus Leuconostoc of the family Leuconostocaceae. CBA3628T has a circular chromosomal genome and three plasmids of 1 864 558 bp (37% DNA G+C content), containing 1,887 genes, 1,762 predicted protein-coding genes, 4 complete rRNA loci and 70 tRNA genes. The cells were non-haemolytic, non-motile and non-spore forming. The optimal growth of CBA3628T occurred at 30 °C, pH 6.0 and with 0-2% (w/v) NaCl. The major polar lipids of CBA3628T were diphosphatidylglycerol and phosphatidylglycerol. The major fatty acids (>10%) of CBA3628T were C16 : 0, C20 : 0 and C19 : 0 cyclo ω8c. CBA3628T contained A3α-type peptidoglycans. CBA3628T was most closely related to Leuconostoc mesenteroides subsp. mesenteroides ATCC 8293T, L. mesenteroides subsp. dextranicum DSM 20484T and L. suionicum DSM 20241T with 99.52% 16S rRNA gene sequence similarity. However, the average nucleotide identities of 91.9%, 91.7% and 91.1% and the digital DNA-DNA hybridisation values of 45.6%, 45.4% and 45.4% indicated that the novel isolate represented a distinct species. Phylogenetic analyses of both the 16S rRNA gene and genome sequences revealed that CBA3628T formed a distinct phylogenetic lineage within the genus Leuconostoc and was most closely related to Leuconostoc litchii MB7T. The ANI and dDDH values between CBA3628T and L. litchii MB7T were 84.9 and 22.8%, respectively. Functional genes belonging to COG categories E, J and K were enriched in the genome of CBA3628T (>7.9%). On the basis of its physiological, chemotaxonomic, phylogenetic and genomic properties, strain CBA3628T represents a novel species from the genus Leuconostoc, for which we propose the name Leuconostoc koreense sp. nov., with the type strain CBA3628T (= KACC 23049T = DSM 116836T).

Efficacy and Safety of Wilac L Probiotic Complex Isolated from Kimchi on the Regulation of Alcohol and Acetaldehyde Metabolism in Humans.

Alcohol-related hangovers impact both physical and mental wellness, largely due to acetaldehyde levels produced through alcohol metabolism. The present study investigated the efficacy and safety of the Wilac L probiotic complex (Levilactobacillus brevis WiKim0168 and Leuconostoc mesenteroides WiKim0172 isolated from kimchi) in improving hangovers post-alcohol consumption. This study was conducted as a randomized, double-blind, crossover placebo-controlled clinical trial from August 2023 to February 2024. Subjects (n = 26) were randomized into six test groups consuming three products, the Wilac L probiotic complex, Wilac L35 (Wilac L probiotic complex with Pyrus pyrifolia Nakai), or placebo, in different orders with crossover after a wash-out interval of 7-10 days. Blood alcohol and acetaldehyde concentrations were measured 0, 0.25, 0.5, 1, 2, 4, 6, and 15 h after alcohol consumption. The blood acetaldehyde levels measured with Wilac L probiotic complex supplementation were significantly lower than the control at 0.25 (p = 0.0381), 0.5 (p = 0.0498), and 1 h (p = 0.0260) post-consumption. The blood acetaldehyde levels after Wilac L35 consumption compared to the control are significant at 0.25 (p = 0.0115), 0.5 (p = 0.0054), 1 (p = 0.0285), 2 (p = 0.0113), and 6 h (p = 0.0287) post-consumption. No significant adverse events were reported. The Wilac L probiotic complex is associated with decreased blood acetaldehyde levels and improved subjective hangover symptoms.

Probiotic and fermentation properties of Leuconostoc mesenteroides strain I1/53 from sugarcane juice by a multi-omics approach

Previous studies have demonstrated the presence of microorganisms in sugarcane juice, but the species composition and characteristics of dominant strains remain ambiguous. In this study, the most abundant strain Leuconostoc mesenteroides accounted for 39.89% of the total sequences in sugarcane juice. Subsequently, a L. mesenteroides, here named as strain I1/53, was isolated on a typical MRS medium. The whole genome size of the isolate was 2,044,872 bp with a GC content of 37.5% and 2027 coding DNA sequences with average length of 907 bp. Notably, the strain involved no antibiotic-related and virulence factor-producing genes, not producing endotoxins. In contrast, the L. mesenteroides I1/53 contained abundant adaptability and stress tolerance response genes of the human gastrointestinal environment. Additionally, strain I1/53 potentially encoded bacteriocin lactococcin G by expressing lagD, and demonstrated its antibacterial efficacy against Gram-positive and negative foodborne pathogens by in-vitro experiments. The fermentation of the strain I1/53 significantly elevated beneficial metabolites such as SCFAs, liquiritigenin, L-catechin, α-solanine and indoleacetic acid, whereas deleted harmful compounds for human wellness, including valdecoxib. Therefore, this study demonstrates the probiotic and fermentation properties of the dominant L. mesenteroides in sugarcane juice, which provide a robust theoretical foundation for its application in foods as a probiotic.

Potential Prebiotic Effects of Artemisia capillaris-Derived Transglycosylated Product.

This study investigated the impact of a transglycosylated product (ACOD) catalyzed by Leuconostoc mesenteroides MKSR dextransucrase using sucrose as a glucosyl donor and both maltose and Artemisia capillaris as acceptors on gut microbiota through fecal fermentation. ACOD promoted the growth of probiotics such as Lactiplantibacillus plantarum, Lacticaseibacillus casei, Lacticaseibacillus rhamnosus GG, and Leuconostoc mesenteroides MKSR, while inhibiting the growth of pathogenic bacteria such as Escherichia coli, E. coli O157:H7, Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus, Shigella flexneri, Streptococcus mutans, Pseudomonas aeruginosa, and Bacillus cereus during independent cultivation. Fecal fermentation for 24 h revealed that ACOD significantly increased the production of short-chain fatty acids (SCFAs) compared to the blank and fructoooligosaccharide (FOS) groups. Specifically, ACOD led to a 4.5-fold increase in acetic acid production compared to FOSs and a 3.3-fold increase in propionic acid production. Both the ACOD and FOS groups exhibited higher levels of butyric acid than the blank. Notably, ACOD significantly modulated the composition of the gut microbiota by increasing the relative abundances of Lactobacillus and decreasing Escherichia/Shigella and Salmonella. In contrast, FOSs remarkably promoted the growth of Salmonella. These findings suggest that ACOD is a potential candidate for prebiotics that improve the intestinal environment by being actively used by beneficial bacteria.

Antioxidant Activity and Other Characteristics of Lactic Acid Bacteria Isolated from Korean Traditional Sweet Potato Stalk Kimchi.

The aim of this study was to examine the biological activity and probiotic properties of lactic acid bacteria (LAB) isolated from sweet potato stalk kimchi (SPK). Various LAB and Bacillus spp. are active in the early stages of the fermentation of kimchi made from sweet potato stalk. Four strains of LAB were identified, including SPK2 (Levilactobacillus brevis ATCC 14869), SPK3 (Latilactobacillus sakei NBRC 15893), SPK8 and SPK9 (Leuconostoc mesenteroides subsp. dextranicum NCFB 529). SPK2, SPK3, SPK8, and SPK9 showed 64.64-94.23% bile acid resistance and 78.66-82.61% pH resistance. We identified over 106 CFU/mL after heat treatment at 75 °C. Four strains showed high antimicrobial activity to Escherichia coli and Salmonella Typhimurium with a clear zone of >11 mm. SPK2 had the highest antioxidative potentials, higher than the other three bacteria, with 44.96 μg of gallic acid equivalent/mg and 63.57% DPPH scavenging activity. These results demonstrate that the four strains isolated from sweet potato kimchi stalk show potential as probiotics with excellent antibacterial effects and may be useful in developing health-promoting products.

Okra (Abelmoschus esculentus L.) Flour Integration in Wheat-Based Sourdough: Effect on Nutritional and Technological Quality of Bread.

The aim of this study was to develop an innovative sourdough using dehydrated okra (Abelmoschus esculentus L.) pod flour and to use it in the production of bread. Three different flours (sun-dried S, freeze-dried F, oven-dried O) were individually mixed at 9% with wheat flour (Dough Yield 300) and fermented (N0: 8.0 log10 CFU/g) for 14 h, using Lactiplantibacillus plantarum ITM21B, Weissella cibaria C43-11 or Leuconostoc mesenteroides C43-2M. The results showed that after fermentation, the content of organic acids (lactic, acetic and propionic), exopolysaccharides (EPS), l-glutamic acid and total free amino acids (TFAA) increased and the high molecular weight proteins were converted into smaller proteins. Sourdough based on Leuc. mesenteroides and O flour (O_LeuMes) was selected to evaluate its applicability in bread making. It was included in the yeast-leavened bread formulation at 20 or 40% (0.6% and 1.21% w/w O flour replacement). The results showed that fermentation limited the negative effects of unfermented O flour on bread quality attributes, mainly the specific volume and firmness. Bread with O_LeuMes at 40% was improved in TFAA, EPS and l-glutamic acid content and showed a higher specific volume and lower moisture and firmness compared to bread with the unfermented O flour.

Enhancing the flavor quality of Chinese rice wine (Huangjiu) through inoculation with Lactobacillus plantarum and Leuconostoc mesenteroides

This study investigates the modulation of flavor in Chinese rice wine (Huangjiu) by inoculating with Lactobacillus plantarum (L. plantarum) and Leuconostoc mesenteroides (L. mesenteroides). Firmicutes and lactic acid bacteria (LAB) were predominant in both inoculated and spontaneously fermented samples. We observed an enhanced bacterial diversity in treatments involving single and combined inoculations, which corresponded with increases in volatile components, organic acids, and amino acids compared to spontaneously fermented controls. Sensory evaluations, assessing alcohol aroma, sourness, and full-bodiedness, identified the co-inoculated samples as superior, outperforming those from single inoculations and spontaneous fermentations. These results elucidate the impact of starter cultures on the fermentation process and flavor profile of Huangjiu, providing insights for selecting optimal starters to engineer desired flavor characteristics.

Continental-scale insights into the sugarbeet diffusion juice microbiomes

ABSTRACT Bacterial contamination of raw diffusion juice poses unique challenges during the sugar extraction process. This study profiled bacterial communities by using full-length 16S rRNA amplicon sequencing and quantified the carbohydrate concentrations in raw diffusion juice samples received from sugar factory regions across the USA and Canada. Juice samples were collected at four time points during the 2021 and 2022 processing campaigns. Firmicutes was the dominant phylum from the raw diffusion juice samples collected during both campaigns and comprised 85.5% of total bacterial abundance. Lactic acid bacteria such as Leuconostoc and Lactobacillus were among the core genera which also dominated the bacterial community in raw diffusion juice. Positive correlations in the abundance of functionally and taxonomically related bacterial communities were identified. During the 2021 campaign, 44 bacterial genera were differentially abundant in raw diffusion juice extracted from sugarbeet roots in Periods 1 to 4. This number declined sixfold during the 2022 campaign to three genera. The concentration of raffinose in raw diffusion juice positively correlated to the relative abundance of Leuconostoc . Furthermore, an in vitro assay was performed to assess the growth dynamics of Leuconostoc mesenteroides in sucrose or raffinose-rich medium and observed the rapid consumption of both carbohydrates by this bacterium. This finding is important for deciphering microbial growth dynamics in raw diffusion juice that can be useful in minimizing sugar loss during the factory processing. IMPORTANCE Findings additionally provide baseline information that can be used to develop mitigation strategies that reduce losses due to microbial contamination of sucrose processing streams.

Design Optimization of a Novel Catalytic Approach for Transglucosylated Isomaltooligosaccharides into Dietary Polyols Structures by Leuconostoc mesenteroides Dextransucrase.

Polyols, or sugar alcohols, are widely used in the industry as sweeteners and food formulation ingredients, aiming to combat the incidence of diet-related Non-Communicable Diseases. Given the attractive use of Generally Regarded As Safe (GRAS) enzymes in both academia and industry, this study reports on an optimized process to achieve polyols transglucosylation using a dextransucrase enzyme derived from Leuconostoc mesenteroides. These enzyme modifications could lead to the creation of a new generation of glucosylated polyols with isomalto-oligosaccharides (IMOS) structures, potentially offering added functionalities such as prebiotic effects. These reactions were guided by a design of experiment framework, aimed at maximizing the yields of potential new sweeteners. Under the optimized conditions, dextransucrase first cleared the glycosidic bond of sucrose, releasing fructose with the formation of an enzyme-glucosyl covalent intermediate complex. Then, the acceptor substrate (i.e., polyols) is bound to the enzyme-glucosyl intermediate, resulting in the transfer of glucosyl unit to the tested polyols. Structural insights into the reaction products were obtained through nuclear maneic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analyses, which revealed the presence of linear α(1 → 6) glycosidic linkages attached to the polyols, yielding oligosaccharide structures containing from 4 to 10 glucose residues. These new polyols-based oligosaccharides hold promise as innovative prebiotic sweeteners, potentially offering valuable health benefits.

Exopolysaccharide (EPS) Produced by Leuconostoc mesenteroides SJC113: Characterization of Functional and Technological Properties and Application in Fat-Free Cheese

A Leuconostoc mesenteroides strain (SJC113) isolated from cheese curd was found to produce large amounts of a mucoid exopolysaccharide (EPS). An analysis revealed the glucan nature of the EPS with 84.5% (1→6)-linked α-d-glucose units and 5.6% (1,3→6)-linked α-d-glucose units as branching points. The EPS showed 52% dextranase resistance and a yield of 7.4 ± 0.9 g/L from MRS medium supplemented with 10% sucrose within 48 h. Ln. mesenteroides SJC113 was also characterized and tested for the production of EPS as a fat substitute in fresh cheese. Strain SJC113 showed high tolerance to a wide range of NaCl concentrations (2, 5 and 10%), high β-galactosidase activity (2368 ± 24 Miller units), cholesterol-reducing ability (14.8 ± 4.1%), free radical scavenging activity (11.7 ± 0.7%) and hydroxyl scavenging activity (15.7 ± 0.4%). The strain had no virulence genes and was sensitive to clinically important antibiotics such as ampicillin, tetracycline and chloramphenicol. Ln. mesenteroides SJC113 produced highly viscous EPS during storage at 8 °C in skim milk with 5% sucrose. Therefore, these conditions were used for EPS production in skim milk before incorporation into fresh cheese. Four types of fresh cheese were produced: full-fat cheese (FF) made from pasteurized whole milk, non-fat cheese (NF) made from pasteurized skim milk, non-fat cheese made from skim milk fermented with Ln. mesenteroides without added sugar (NFLn0) and non-fat cheese made from skim milk fermented with Ln. mesenteroides with 5% sucrose (NFLn5). While the NF cheeses had the highest viscosity and hardness, the NFLn5 cheeses showed lower firmness and viscosity, higher water-holding capacity and lower weight loss during storage. Overall, the NFLn5 cheeses had similar rheological properties to full-fat cheeses with a low degree of syneresis. It was thus shown that the glucan-type EPS produced by Ln. mesenteroides SJC113 can successfully replace fat without altering the texture of fresh cheese.

Bioconversion of sugar beet molasses into functional exopolysaccharides by beet juice-derived lactic acid bacteria

Sugar beet molasses, a sugar-rich byproduct of sugar beet industry, have great potential as a biorefinery feedstock for the production of value-added bio-products by microbial fermentation. The production of functional exopolysaccharides (EPS) by lactic acid bacteria (LAB) represents a promising strategy for valorizing sugar processing waste. This study screened and identified high-efficiency EPS-producing LAB isolates from beet juice. Among the 32 isolates, six LAB strains including Limosilactobacillus fermentum YL7, Lactiplantibacillus plantarum YL4, TC10, and CJ10, Leuconostoc mesenteroides TCT3 and TCT4, exhibited efficient bio-conversion of beet molasses to LAB-EPS, with yields varying from 13.96 to 22.26 g/L. Antioxidant activity analysis revealed that EPS from these strains displayed significant scavenging activities against ABTS+, DPPH, and -OH radicals. Notably, EPS produced by L. plantarum TC10 and L. fermentum YL7 exhibited superior ABTS + scavenging capacity, with rates up to 99.48% and 95.89% at 4 mg/mL, respectively. Additionally, EPS from strains YL4, YL7, TCT3 and TCT4 showed significant antibiofilm activity against S. aureus and E. coli, with EPS-YL7 inhibiting S. aureus biofilm formation by up to 90.49% at 8.0 mg/mL. Furthermore, EPS from strains TCT4 demonstrated great tolerance to digestive fluid compared to EPS from other strains, with a retention rate of 72% at the end of intestinal digestion. These findings suggest that EPS-producing LAB strains from beet juice can efficiently convert beet molasses into valuable EPS utilized as functional food ingredients.

Investigating the Effect of Bacilli and Lactic Acid Bacteria on Water Quality, Growth, Survival, Immune Response, and Intestinal Microbiota of Cultured Litopenaeus vannamei.

Shrimp is one of the most important aquaculture industries. Therefore, we determined the effect of nitrifying-probiotic bacteria on water quality, growth, survival, immune response, and intestinal microbiota of Litopenaeus vannamei cultured without water exchange. In vitro, only Bacillus licheniformis used total ammonia nitrogen (TAN), nitrites, and nitrates since nitrogen bubbles were produced. TAN decreased significantly in the treatments with B. licheniformis and Pediococcus pentosaceus and Leuconostoc mesenteroides, but no differences were observed in nitrites. Nitrates were significantly higher in the treatments with bacteria. The final weight was higher only with bacilli and bacilli and LAB treatments. The survival of shrimp in the bacterial treatments increased significantly, and superoxide anion increased significantly only in lactic acid bacteria (LAB) treatment. The activity of phenoloxidase decreased significantly in the treatments with bacteria compared to the control. Shrimp treated with bacilli in the water showed lower species richness. The gut bacterial community after treatments was significantly different from that of the control. Linoleic acid metabolism was positively correlated with final weight and superoxide anion, whereas quorum sensing was correlated with survival. Thus, bacilli and LAB in the water of hyperintensive culture systems act as heterotrophic nitrifers, modulate the intestinal microbiota and immune response, and improve the growth and survival of shrimp. This is the first report on P. pentosaceus and L. mesenteroides identified as nitrifying bacteria.

Exploring the Diversity and Potential Use of Flower-Derived Lactic Acid Bacteria in Plant-Based Fermentation: Insights into Exo-Cellular Polysaccharide Production.

Isolation of new plant-derived lactic acid bacteria (LAB) is highly prioritized in developing novel starter cultures for plant-based fermentation. This study explores the diversity of LAB in Danish flowers and their potential use for plant-based food fermentation. A total of 46 flower samples under 34 genera were collected for LAB isolation. By introducing an enrichment step, a total of 61 LAB strains were isolated and identified using MALDI-TOF and 16S rRNA sequencing. These strains represent 24 species across 9 genera, predominantly Leuconostoc mesenteroides, Fructobacillus fructosus, Apilactobacillus ozensis, and Apilactobacillus kunkeei. Phenotypic screening for exo-cellular polysaccharide production revealed that 40 strains exhibited sliminess or ropiness on sucrose-containing agar plates. HPLC analysis confirmed that all isolates produced exo-cellular polysaccharides containing glucose, fructose, or galactose as sugar monomers. Therefore, the strains were glucan, fructan, and galactan producers. The suitability of these strains for plant-based fermentation was characterized by using almond, oat, and soy milk. The results showed successful acidification in all three types of plant-based matrices but only observed texture development in soy by Leuconostoc, Weissella, Lactococcus, Apilactobacillus, and Fructobacillus. The findings highlight the potential of flower-derived LAB strains for texture development in soy-based dairy alternatives.

Comparative assessment of plate count and PMA-qPCR methods for modeling the growth of lactic acid bacteria in smoked Turkey ham

This study compared the quantitative polymerase chain reaction (qPCR) method combined with propidium monoazide (PMA) and the plate count (PC) method, both combined with predictive modeling, to describe the behavior of lactic acid bacteria (LAB) in vacuum-packaged sliced smoked turkey ham (STH). The PMA-qPCR method does not allow the DNA amplification of died cells but allow the amplification of viable cells, including the non-culturable. The standard curves relating quantification cycle (Cq) and log10 CFU/g demonstrated good linearity (R2 > 0.95), evidencing its accuracy and reproducibility. These curves were used to quantify Leuconostoc mesenteroides and Weissella viridescens in artificially inoculated STH samples stored at different isothermal temperatures (8, 10, 12, 16 and 20 °C). Firstly, the PMA-qPCR and PC methods were compared, and the analysis demonstrated a good correlation (R2 = 0.99) and agreement between the results. However, the PC method underestimated the quantification of W. viridescens cells by 0.76 log10 CFU/g at 8 °C, suggesting bacterial stress at this temperature, which was not observed for L. mesenteroides. In terms of growth, the maximum specific growth rate increased with rising temperature for both LAB. Predictive modeling indicated that the growth of L. mesenteroides and W. viridescens at 8 °C suggests a shelf life of approximately 4.25 days for STH based on PC data, and 4.13 days based on PMA-qPCR data. In conclusion, the PMA-qPCR method presented an advantage in terms of accuracy, especially under bacterial stress conditions, and proved to be a promising alternative for the quantification of LAB in refrigerated ready-to-eat meat products. The predictive models used were suitable for describing microbial growth, reinforcing the importance of the PMA-qPCR method in shelf life and food safety studies.

Exopolysaccharide from Leuconostoc mesenteroides XR1: Yield optimization, partial characterization and properties

The production conditions of exopolysaccharide (EPS) from Leuconostoc mesenteroides XR1 were optimized by response surface methodology (RSM). Maximum EPS yield was 56.59 ± 0.51 g/L under fermentation conditions with 2.6 g/L ammonium citrate, initial pH 6.5 and temperature 23 °C, which was 6.21-fold greater than the EPS yield before optimization. Characterization of the chain conformation using Congo red test and circular dichroism (CD) showed that EPS exhibited a random coil structure in aqueous solution. The CD results revealed that the EPS concentration altered its hydrogen-bond interactions and chirality, but did not change its chain conformation. The average polydispersity index (PDI) of the EPS solution was only 27.16 %, indicating that it was uniformly distributed in the aqueous solution with high stability. The degradation temperature of EPS was 253.11 °C, indicating high thermal stability. EPS possessed the ability to scavenge activities of free radicals and was protective against oxidative stress-induced plasmid DNA damage. In addition, stable hydrogels could be formed at EPS concentrations above 5 % (w/v). These results collectively showed that EPS can be used commercially as an antioxidant and drug delivery carrier.

A Novel C-Terminal Truncated Bacteriocin Found by Comparison between Leuconostoc mesenteroides 406 and 213M0 Isolated from Mongolian Traditional Fermented Milk, Airag.

Bacteriocins produced by lactic acid bacteria are known to be useful tools for food biopreservation and fermentation control. Leuconostoc mesenteroides subsp. mesenteroides 406 and 213M0 isolated from different samples of Mongolian traditional fermented milk, airag, had been reported to produce listericidal bacteriocin-like inhibitory substances with similar but slightly different properties. In this study, the antibacterial properties and the related gene sequences of both strains were compared, and then their bacteriocins were purified and identified. Strain 406 was superior to strain 213M0 in cell growth and antibacterial activity against many strains. However, the activity of 213M0 was stronger than that of 406 against a few strains. DNA sequencing revealed two and three plasmids in 406 and 213M0, respectively, and each one of them harbored an almost identical mesentericin Y105-B105 gene cluster. Removal of these plasmids resulted in a complete loss of activity, indicating that the antibacterial activity of both strains was generated by bacteriocins encoded on the plasmids. Mesentericins Y105 and B105 were purified from both cultures, and another novel bacteriocin, named mesentericin M, was identified from the 213M0 culture only. Its structural gene was coded on a 213M0 plasmid and, surprisingly, its C-terminal three amino acid residues were post-translationally cleaved. To our knowledge, this is the first report of a C-terminal truncated bacteriocin. In conclusion, the novel bacteriocin should be mainly responsible for the difference in antibacterial properties between the two strains.

Organic acid type in kimchi is a key factor for determining kimchi starters for kimchi fermentation control

This study was conducted to confirm the effectiveness of kimchi starters (KSs) by investigating their growth characteristics. First, we assessed the growth characteristics of five lactic acid bacteria (LAB) strains (Lactococcus lactis WiKim0124; Companilactobacillus allii WiKim39; and Leuconostoc mesenteroides WiKim0121, WiKim33, and WiKim32) and assessed the effects of different parameters, including organic acids, salinity, acidity, and temperature, on the growth of these LAB. The findings showed that organic acids, particularly acetic and lactic acids that accumulated with the progress in fermentation, were the major players determining the microbial composition of kimchi and the growth of the KSs. Leuconostoc mesenteroides grew well in the presence of acetic and lactic acids than other starts, so it is confirmed that Leuconostoc mesenteroides can dominant in kimchi. In addition, malic acid, which is derived from kimchi ingredients, is used to induce malolactic fermentation by Lactobacillus species, and the progression of malolactic fermentation can be controlled through KSs. Our results suggest that KSs promote the production of organic acids, and the profiling of organic acids, as well as the progress of malolactic fermentation, can be controlled by selecting the suitable KS. Overall, this study demonstrates that kimchi fermentation can be controlled more effectively if the characteristics of KS are understood and used appropriately.