Lactic Acid Bacteria Cultures Research Articles

Fermentation of Kalamata Natural Black Olives Using Selected Lactic Acid Bacteria as Starters

Fermented foods such as table olives are produced through a spontaneous process that has been improved over the years, ensuring the safety and quality of the final product. The aim of the present work was to study the action of starter cultures of lactic acid bacteria (Lacticaseibacillus rhamnosus GG ATCC53103, Levilactobacillus brevis ATCC8287, and Lactiplantibacillus plantarum ATCC14917) which were previously shown to have probiotic and antioxidant potential during the fermentation of natural Greek-style black olives (Kalamata) in brine containing 6% (w/v) NaCl at a temperature of 20 °C for a period of 150 days. At a molecular level, the main metabolites in every fermentation process were identified using an HPLC method. The results showed that the concentration of the metabolites increased gradually, developing a stable pattern after the 90th day of fermentation. In addition, the DL-p-hydroxyphenyllactic acid (OH-PLA) was identified as the phenolic acid with the highest concentration, independently of the selected starter culture. Microbial genomic DNA was also extracted from the olives’ surface at the final stages of fermentation (150 days) and was subjected to 16S rRNA sequencing using the Nanopore MinION™ NGS tool, enabling a comprehensive analysis of the microbial community. According to the findings, the most abundant genera were Lactobacillus and Leuconostoc. To the best of our knowledge, this is the first study exploring these particular starters for olive fermentation.

Vitamin B12 production in solubilized protein extract of bioprocessed wheat bran with Propionibacterium freudenreichii

Wheat bran, a nutrient-rich byproduct of wheat milling, has the potential to be used for the production of vitamin B12 (B12) in order to fortify plant-based foods that are lacking in this vitamin. This study aimed to investigate B12 production in the soluble extract of bioprocessed wheat bran using Propionibacterium freudenreichii. The optimal conditions for B12 production were found to be a bioprocessing time of 24 h, along with the use of a commercial starter culture of lactic acid bacteria and yeast, with pH adjusted from 4.0 to 6.4. The highest B12 production (55 ng/mL) was achieved within three days of fermentation. Cobalt supplementation (as CoCl2 or food-grade yeast extract) resulted in up to four-fold increase in B12 production. Similar results (50–70 ng/mL) were obtained when the processes were scaled up, with bioprocessing involving up to 15 kg and B12 fermentation involving up to 5 L, demonstrating the robustness of the procedure. Microbiological safety was ensured with the absence of Enterobacteriaceae in the extracts after bioprocessing and B12 fermentation. Overall, this study highlights the potential of under-utilized wheat bran as a raw material for producing B12-enriched bran extract, which can be used to fortify plant-based products in various food applications.

Application of an oxidative-biological treatment strategy for production of lactic acid and biomass from vinasse of sugarcane bioethanol industry

In this study, the cultivation of lactic acid bacteria was done using vinasse (with a chemical oxygen demand of 378 ± 5 g O2/L) to harness its organic content. The potential for biomass and lactic acid production was evaluated by using strains Lactococcus lactis subsp. Cremoris and Lactococcus lactis subsp. Lactis. Before medium preparation, vinasse was pretreated with air and ozone to reduce inhibitory load. The effects of pretreated vinasse addition on lactic acid bacteria growth were in the range of 0–33% v/v. The optimal vinasse concentration for obtaining high biomass and lactic acid concentrations was 17% v/v, leading to maximum concentrations of biomass and lactic acid of 2.2 ± 0.14 and 16.0 ± 0.9 g/L, respectively. Fed-batch operation was also studied as a strategy for extending the production phase of lactic acid bacteria using vinasse (17% v/v) as feeding. These results highlight the underexplored potential of vinasse as an economical source of raw material for obtaining value-added products through biotechnological processes.

THE INFLUENCE OF NUTRIENTS AND LACTULOSE PREBIOTIC ON THE FERMENTATION PROCESSES IN THE TECHNOLOGY OF RECEIVING A FUNCTIONAL FOOD PRODUCT WITH AN INCREASED TITER OF VIABLE LACTIC ACID BACTERIA

A study of the influence of biologically active substances (fat-soluble vitamins, omega-3 fatty acids and vitamin D, as well as water-soluble vitamin C), prebiotic lactulose on the titer of viable cells of lactic acid bacteria was carried out for the further use of the obtained research results in the biotechnology of functional food products, obtained thanks to the successful course fermentation processes. Experiments have proven the expediency of using biologically active substances as stimulators of the growth of lactic acid bacteria, which contribute to the increase of biomass and support of their vital activity for 192 hours. Research has established that at the end of the experiment (192 hours), the highest titer of lactic acid bacteria was recorded in samples 1, 2, 3, 4, to which the prebiotic lactulose was added in the amount of 1, 3, 5 and 7 %, respectively. This is due to the fact that the prebiotic acts as a specific substrate that is used by the symbiosis of pure cultures of lactic acid bacteria for a long time, unlike milk sugar. Analyzing the obtained data, it is indicated that thanks to the addition of fat-soluble nutrients omega-3 fatty acids and vitamin D, as well as water-soluble vitamin C, there is a significant increase in the titer of viable cells of probiotic cultures at 6 and 24 hours of the experiment, although at the end of the experiment (by 192 hour) in these samples, an insignificant decrease of this indicator was recorded — from 10 to 8.9 log cells/ml. In the control sample (without the addition of biologically active substances and lactulose prebiotic), a significant decrease in the titer of viable cells of lactic acid bacteria was noted, compared to the test samples to which nutrients were added. The titer of lactic acid bacteria cells in the control sample was reduced by 192 hours from 8.5 to 5.5 log cells/ml. It is recommended to use the studied nutrients in the indicated concentrations to stimulate the growth and maintain the viability of lactic acid bacteria cultures in the technology of production of functional food products.

Effects of Different Lactic Acid Bacteria in Single or Mixed Form on the Fermentative Parameters and Nutrient Contents of Early Heading Triticale Silage for Livestock.

Lactic acid bacteria (LAB) are excellent anaerobic fermenters that produce highly valuable grass-based animal feed containing essential nutrients. In the present study, an ensiling process was used to improve anaerobic fermentation in triticale silage under different moisture conditions with LAB. The triticale was treated with either a single bacterium or combined LAB and then vacuum-sealed. After 180 and 360 days of storage, the silage's fermentation characteristics, microbial changes and nutrient contents were analyzed. The pH of the silage was significantly lower than the control silage. There was a significant difference in the pH values between the silages treated with single or mixed LAB. The LAB treatment led to a substantial increase in lactic acid (LA), a decrease in butyric acid (BA), and marginal levels of acetic acid (AA). The LA content after the mixed LAB treatment was significantly higher than that after the single culture LAB treatment. After single or combined inoculant treatments, the LAB population in the silage increased, while the yeast and mold levels decreased. These findings suggest that the addition of LAB to silage during ensiling could enhance the nutritional quality and reduce unwanted microbial growth. The mixed LAB treatments produced silage with a significantly higher nutritional value than the single LAB treatments.

Development of a low pollution medium for the cultivation of lactic acid bacteria

Protein rich culture media are employed in the production of lactic acid bacteria (LAB); however, production costs are high. In this work media formulation and evaluation for LAB production were conducted considering physiological properties of lactic acid bacteria. Consumption efficiency (E), yield production (Y) and specific substrate consumption rate (qS) values as response variables were used. Four culture media were used: (1) Man Rogosa Sharp (MRS); (2) cabbage liquor (MC); (3) a new balanced culture medium (MX); and (4) MX supplemented with cabbage liquor (MXC). The culture media were evaluated using two strains: Lactobacillus acidophilus ATCC 4356 and Lactiplantibacillus plantarum ATCC 10241. The EGLU for L. plantarum was 100 % in the three media and YX/S value was 0.02 ± 0.003 in MRS and MX, while YLAC/S was 0.57 ± 0.03 in MRS and 0.51 ± 0.02 in MX. In MXC, the value obtained for YX/S was 0.07 ± 0.002 while YLAC/S was 0.47 ± 0.04. Specific glucose consumption and lactate formation rates for L. plantarum in MRS and MX media did not show significant differences. These results suggest that MX and MXC can be used for efficient production of the LAB at low cost.

Bioprotection Potential of Lacticaseibacillus rhamnosus LRH01 and Lactiplantibacillus plantarum LP01 against Spoilage-Associated Penicillium Strains in Yoghurt

Penicillium spp. are considered a major spoilage fungus in dairy products. Due to the growing concerns over food safety issues and the demand for “clean label” food products from consumers, the use of lactic acid bacteria (LAB) as a bioprotective tool to control fungal spoilage of dairy products appears to be a promising alternative. Here, the antifungal activities of ten LAB cultures against five dairy-spoilage-associated Penicillium strains were studied in a model system, and the most potent bioprotective cultures were further tested in yoghurt. Lacticaseibacillus rhamnosus (L. rhamnosus) LRH01 and Lactiplantibacillus plantarum (L. plantarum) LP01 exhibited potent antifungal efficacy at low concentrations. The inhibitory effects of cell-containing fermentates (C-fermentates), cell-free fermentates (CF-fermentates), and volatiles produced by the two cultures were tested in a yoghurt serum medium. The C-fermentates showed antifungal effects, while the removal of cells from C-fermentates led to decreased antifungal activities. Volatiles alone displayed some antifungal efficiency, but less than the fermentates. In a yoghurt matrix, the specific effect of manganese depletion by the bioprotective cultures on mold growth was investigated. Here, the LAB cultures could completely suppress the growth of molds, while addition of manganese partially or fully restored the mold growth, demonstrating that manganese depletion played a key role in the antifungal activity of the tested LAB cultures in the yoghurt matrix. Both L. plantarum LP01 and L. rhamnosus LRH01 showed efficient antifungal activities in the yoghurt serum, while L. rhamnosus LRH01 exhibited the most potent inhibitory effects on Penicillium strains when added during the processing of the yoghurt with subsequent storage at 7 °C for 22 days. Our findings suggested that L. rhamnosus LRH01 could be a promising bioprotective culture for yoghurt biopreservation.

Characterization of potential probiotic starter cultures of lactic acid bacteria isolated from Ethiopian fermented cereal beverages, Naaqe and Cheka.

To test the in vitro probiotic potential and starter culture capacity of lactic acid bacteria (LAB) isolated from Naaqe and Cheka, cereal-based Ethiopian traditional fermented beverages. 44 strains were isolated from spontaneously fermented Ethiopian cereal-based beverages, Naaqe and Cheka, with 24 putatively identified as LAB and 14 identified up to the species level. The species Limosilactobacillus fermentum (6/12; 50%) and Weissella confusa (5/12, 41.67%) were the predominant species identified from Naaqe, while the two Cheka isolates were Limosilactobacillus fermentum and Pediococcus pentosaceus. Six LAB strains inhibited eight of the nine gastrointestinal indicator key pathogens in Ethiopia, including Escherichia coli, Salmonella enterica subsp. enterica var. Typhimurium, Staphylococcus aureus, Shigella flexneri, and Listeria monocytogenes. Three of the LAB isolates exhibited strain-specific immunostimulation in human monocytes. Based on these probiotic properties and growth, six strains were selected for in situ evaluation in a mock fermentation of Naaqe and Cheka. During primary fermentations, L. fermentum 73B, P. pentosaceus 74D, L. fermentum 44B, Weissella confusa 44D, L. fermentum 82C and Weissella cibaria 83E and their combinations demonstrated higher pH-lowering properties and colony-forming unit counts compared to the control spontaneous fermentation. The same pattern was also observed in the secondary mock fermentation by the Naaqe LAB isolates. In this study, we selected six LAB strains with antipathogenic, immunostimulatory and starter culture potentials that can be used as autochthonous probiotic starters for Naaqe and Cheka fermentations, once their health benefit is ascertained in a clinical trial as a next step.

Inoculation with Lentilactobacillus buchneri alone or in combination with Lentilactobacillus hilgardii modifies gene expression, fermentation profile, and starch digestibility in high-moisture corn.

Inoculants combining Lentilactobacillus buchneri and Lentilactobacillus hilgardii have been shown to improve the aerobic stability of high-moisture corn (HMC) and whole-plant corn silage, but the mode of action of this co-inoculation remains to be elucidated. This study used metatranscriptomics to evaluate the effects of inoculation with L. buchneri alone or combined with L. hilgardii on the bacterial community, gene expression, fermentation profile, and starch digestibility in HMC. High-moisture corn not inoculated (Control) or inoculated with L. buchneri NCIMB 40788 (LB) or L. buchneri NCIMB 40788 combined with L. hilgardii CNCM-I-4785 (Combo) was ensiled in mini silo bags for 30, 60, 120, and 180 days. The fermentation profile was evaluated at all time points. Metatranscriptomics was performed on samples collected on day 120. Combo had a greater alpha diversity richness index of contigs than LB and Control, and inoculation with Combo and LB modified the beta-diversity of contigs compared to Control. Out of 69 genes of interest, 20 were differentially expressed in LB compared to Control and 25 in Combo compared to Control. Of those differently expressed genes, 16 (10 of which were associated with carbohydrate metabolism and six with amino acid metabolism) were differently expressed in both LB and Combo compared to Control, and all those genes were upregulated in the inoculated silages. When we compared Combo and LB, we found seven genes expressed differently, four associated with carbohydrate metabolism and downregulated in Combo, and three associated with amino acid metabolism and upregulated in Combo. At day 120, the inoculated silages had more culturable lactic acid bacteria, higher Lactobacillus relative abundance, and lower Leuconostoc relative abundance than Control. The concentration of acetic acid remained low throughout ensiling in Control, but in LB and Combo, it increased up to day 60 and remained stable from day 60 to 180. The 1,2-propanediol was only detected in LB and Combo. Inoculation did not affect the concentration of starch, but starch digestibility was greater in Combo than in Control. Inoculation of HMC with Combo modified the gene expression and fermentation profile compared to Control and LB, improving starch digestibility compared to uninoculated HMC.

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The article considers the issues of providing the dairy industry with Russian-made bacterial sourdough, ways to solve the problem of import substitution, providing biofactories with collection cultures of lactic acid bacteria, the assortment and classification of bacterial starter cultures, features of the use of additional and protective cultures, compliance of the species composition of starter cultures with the requirements of the legislation of the Customs Union.

Water-in-water Pickering emulsion: A fascinating microculture apparatus for embedding and cultivation of Lactobacillus helveticus

Currently, the cultivation of lactic acid bacteria is mainly carried out by improving the fermentation process and culture conditions, which was difficult to ensure the survival quantity and culture efficiency. The primary purpose of this work was to construct water-in-water (W/W) Pickering emulsion as a microculture for probiotics. The W/W Pickering emulsion consisting of maltodextrin (MD) and hydroxypropylmethylcellulose (HPMC) was constructed by using microcrystal celluloses (MCC) as the Pickering stabilizers. The effects of MCC concentration, NaCl concentration, MRS broth concentration, and pH value on the formation and stability of W/W Pickering emulsion have been investigated. The stability of W/W Pickering emulsions was driven by the electrostatic repulsion provided by the MCC. The stability of the emulsion was reduced by increasing NaCl and MRS broth concentrations, primarily because their charge shielding effect weakened the electrostatic repulsion between the MCC particles. The W/W Pickering emulsion had higher stability in a weakly acidic environment. The results from another trial revealed that Lactobacillus helveticus CICC 22,536 had little influence on the stability of the W/W Pickering emulsion when it was encapsulated in the emulsion. Moreover, Lactobacillus helveticus was able to be cultured in the emulsion, and the numbers of Lactobacillus helveticus after being cultured for 16 h were increased to 1.1 × 109 CFU/mL. These findings indicated that the W/W Pickering emulsion provided a new approach and an attractive platform for the cultivation of probiotic bacteria.

Detection of Lactic Acid Bacteria (LAB) In Soaking Water of Arabica Coffee Cherries on Mount Sindoro

Coffee is one of the major commodities in Indonesia's agricultural sector, where Indonesia is the fourth largest coffee producer in the world. Arabica coffee is the only type of coffee produced on Mount Sindoro. The used water is wasted in the sewers when washing and sorting coffee. Even though the skin covering the cherry flesh is likely to contain natural microorganism life since the coffee cherries grow during ripening on the tree. Therefore, this study aims to determine whether there is the presence or absence of Lactic Acid Bacteria (LAB) groups in the water used to soak the Arabica coffee cherries. The research method was carried out with 200 ml of water samples soaked in Arabica coffee cherries for 4 hours, isolating microorganisms from the 10-1 to 10-3 dilution series of soaking water using the spread plate method and reinoculation to obtain pure LAB cultures, then detected macroscopically through observation of colony morphology and microscopically detected, including physiological and biochemical reaction tests. Data analysis was conducted in a fully descriptive-qualitative manner concerning Bergey's Manual of Determinative Bacteriology and other books supporting the detection of the BAL groups obtained. The study results obtained three isolates, but only one isolate was detected as LAB. The isolate belongs to the Streptococcaceae family's LAB group- the Lactococcus genus.

Optimization of lactic acid bacterial starter culture to improve the quality and flavor characteristics of traditional Hurood

Hurood is a traditional fermented milk product prepared by traditional Mongolian techniques of fermenting raw milk, partial degreasing, heating, whey drainage, emulsification of curd, and molding. Currently, Hurood available in the market is generally prepared by small-scale enterprises at home or in open air. Therefore, lack of standardization of bacterial starter culture leads to variation in the flavor and sensory properties of Hurood from batch to batch. In this study, we aimed to assess the best starter culture combination obtained from 37 lactic acid bacterial strains isolated from traditional Hurood. The solidification state and sensory quality were used as indexes for determining the fermentation efficiency of the bacterial starter culture combinations. The yield and texture characteristics were used to determine the optimal ratio of bacterial strains in a combination and the processing conditions for traditional Hurood production. The most optimal bacterial culture combination was observed to be NF 9-3:NF 10-4:CH 3-1 in 5:4:1 ratio and in 3% amount. The most optimal whey temperature and heating-stirring temperature were observed to be 55°C to 60°C and 85°C to 90°C, respectively. Hurood prepared with the optimal combination of bacterial strains exhibited significantly enhanced sensory quality, flavor, and contents of AA and fatty acids. Therefore, the use of optimal starter culture of lactic acid bacteria could produce Hurood with significantly superior sensory qualities, making the product more acceptable to consumers.

Identification of Lactic Acid Bacteria from Fermented Kimchi Sawi Ansabi (Brassica juncea L.) using Phenotypic Similarities

Latic acid bacteria play a significant role in the fermentation of food, such as kimchi, which is fermented vegetables. Sawi kampung ansabi is a vegetable cultivated by the Dayak people in Kalimantan during the rice farming season which can be fermented into kimchi. Based on phenotypic similaities, the aim of this study was to identify and acquire cultures of lactic acid bacteria on MRSA media (De Man Rogosa and Sharpe Agar) enriched 1% CaCO3 from kimchi sawi ansabi fermented food sawi ansabi. The results of the isolations were used to test 10 isolates of lactic acid bacteria using the MVSP (Multivariate Statistical Package) program, the UPGMA (Unweighted Pair Group Method with Arithmetic Average Mean) method based on the Simple Matching Coefficient and Jaccard Coefficient to form dendrograms. Simple Matching Coefficient analysis resulted 8 isolates suspected to be Lactobacillus plantarum with a similarity index of 94.6%, 1 suspected 91.9% to Lactobacillus dellbrueckii, and 1 suspected 91.9% to Pediococcus cerevisiae. The Jaccard Coefficient analysis resulted in 8 isolates suspected of Lactobacillus plantarum with a similarity index of 92.6%, 1 isolate suspected 87% to Lactobacillus dellbrueckii, and 1 isolate 88% to Pediococcus cerevisiae.

Comprehensive studies on the stability of yogurt-type fermented soy beverages during refrigerated storage using dairy starter cultures.

This study aimed to assess the feasibility of utilizing commercially available dairy starter cultures to produce yogurt-type fermented soy beverages and evaluate the fundamental properties of the resulting products. Sixteen different starter cultures commonly used in the dairy industry for producing fermented milks, such as yogurt, were employed in the study. The study investigated the acidification curves, acidification kinetics, live cell population of starter microflora during refrigerated storage, pH changes, water-holding capacity, texture analysis, carbohydrates content, and fatty acid profile of the yogurt-type fermented soy beverage. The results demonstrated that the starter cultures exhibited distinct pH changes during the fermentation process, and these changes were statistically significant among the cultures. The acidification kinetics of different cultures of lactic acid bacteria showed characteristic patterns, which can be used to select the most suitable cultures for specific product production. The study also revealed that the choice of starter culture significantly influenced the starter microorganisms population in the yogurt-type fermented soy beverage. Additionally, the pH values and water-holding capacity of the beverages were affected by both the starter cultures and the duration of refrigerated storage. Texture analysis indicated that storage time had a significant impact on hardness and adhesiveness, with stabilization of these parameters observed after 7-21 days of storage. Furthermore, the fermentation process resulted in changes in the carbohydrate content of the soy beverages, which varied depending on the starter culture used.

Exploring the Possibility of Enriching Fermented Milks with Young Barley Leaves Powder Preparation

Barley (Hordeum vulgare L.) is one of the first cereals that humans began to cultivate. This study aimed to investigate the possibility of enriching fermented dairy products, using fermented milk as an example, with young barley leaves powder (YBLP) preparation including different starter cultures of lactic acid bacteria (LAB). The addition of YBLP did not affect the maximum rate of acidification and the time at which the maximum acidification rate was achieved. However, it did impact the time required to reach the desired pH level (4.6) for specific starter cultures. Over a 28-day storage period, gradual acidification of the fermented milk was observed. The addition of YBLP has a limited effect on the pH of the fermented milk, with the pH value primarily dependent on the type of starter culture and storage time. The addition of YBLP may have a positive effect on the survival of bacterial cells during the storage of the fermented milk; however, a gradual decrease in the number of LAB cells was observed during refrigerated storage. Furthermore, the addition of YBLP had a significant effect on the hardness, adhesion, and water-holding capacity of some fermented milk immediately after fermentation, depending on the specific starter culture used.

Effects of Different Fermenting Agents on Proximate Composition and Sensory Evaluation of Masa - A Fermented Puff Fried Batter

Fermentation improves the shelf life, texture, taste and aroma, nutritional value and digestibility and also lowers the content of antinutrients of fermented meals. This study investigated the effect of different fermenting agents on the quality of masa. The rice grains were sorted, cleaned, washed and soaked, wet milled and fermented separately with baker’s yeast, lactic acid culture (yogourmet) and tsamiyan gaye (citric acid) respectively. The final batter was fried and package for analysis. The different fermenting agent had significant (p<0.05) effect on all parameters measured. Masa fermented with lactic acid bacteria culture (LAB) had the highest value of 9.25% 0.83%, 1.01% and 18.51% for protein, crude fibre ash and fat content respectively while yeast fermented masa had higher respective value of 21.46% and 50.12% for moisture and carbohydrate content. The pH of masa sample is within the r range of 3.76-5.57 and titritable acidity of 0.05-0.17. The sensory evaluation was carried out to assess the acceptability of the masa samples. However, all masa samples were generally accepted but baker’s yeast fermented masa had higher means scores for overall acceptability (7.40). Tsamiyan gaye (citric acid) and LAB culture can be used as an alternative to baker’s yeast for preparation of masa.

Modelling and Predicting the Growth of Escherichia coli and Staphylococcus aureus in Co-Culture with Geotrichum candidum and Lactic Acid Bacteria in Milk

The growth of two pairs of co-cultures (Escherichia coli/Geotrichum candidum and Staphylococcus aureus/Geotrichum candidum) with a starter culture of lactic acid bacteria was studied in milk at temperatures ranging from 15 °C to 21 °C, related to the ripening of artisanal cheese. For an inoculum of approximately 106 CFU/mL, LAB not only induced an early stationary phase of E. coli (two isolates BR and PS2) and S. aureus (isolates 2064 and 14733) but also affected their death phase. In co-cultures with LAB and G. candidum, the numbers of E. coli and S. aureus increased in 2 logs and 1 log, respectively, reaching maximum population densities (MPDs) of less than 5 and 4 logs, respectively. After that, the populations of both bacteria represented with two isolates decreased in more than 2 logs and 3 logs within 2 days compared to their MPDs, respectively. G. candidum was found to be the subject of interactions with LAB within a given temperature range only partially. To develop a tertiary model for the growth curves of the populations, a one-step approach was used, combining the Huang-Gimenez and Dalgaard primary model with secondary square-root models for growth rate and lag time. Furthermore, the reparametrized Gompertz-inspired function with the Bigelow secondary model was used to describe the death phase of the E. coli and S. aureus isolates. The prediction ability of the growth of the H-GD tertiary model for co-cultures was cross-validated within the isolates and datasets in milk and milk medium with 1% NaCl. The study can be used as knowledge support for the hygiene guidelines of short-ripened raw milk cheeses, as was our case in Slovakia.

Selection of lactic acid bacteria as biopreservation agents and optimization of their mode of application for the control of Listeria monocytogenes in ready-to-eat cooked meat products

In order to meet consumers´ demands for more natural foods and to find new methods to control foodborne pathogens in them, research is currently being focused on alternative preservation approaches, such as biopreservation with lactic acid bacteria (LAB). Here, a collection of lactic acid bacteria (LAB) isolates was characterized to identify potential biopreservative agents. Six isolates (one Lactococcus lactis, one Lacticaseibacillus paracasei and four Lactiplantibacillus plantarum) were selected based on their antimicrobial activity in in vitro assays. Whole genome sequencing showed that none of the six LAB isolates carried known virulence factors or acquired antimicrobial resistance genes, and that the L. lactis isolate was potentially a nisin Z producer. Growth of L. monocytogenes was successfully limited by L. lactis ULE383, L. paracasei ULE721 and L. plantarum ULE1599 throughout the shelf-life of cooked ham, meatloaf and roasted pork shoulder. These LAB isolates were also applied individually or as a cocktail at different inoculum concentrations (4, 6 and 8 log10 CFU/g) in challenge test studies involving cooked ham, showing a stronger anti-Listerial activity when a cocktail was used at 8 log10 CFU/g. Thus, a reduction of up to ~5.0 log10 CFU/g in L. monocytogenes growth potential was attained in cooked ham packaged under vacuum, modified atmosphere packaging or vacuum followed by high pressure processing (HPP). Only minor changes in color and texture were induced, although there was a significant acidification of the product when the LAB cultures were applied. Remarkably, this acidification was delayed when HPP was applied to the LAB inoculated batches. Metataxonomic analyses showed that the LAB cocktail was able to grow in the cooked ham and outcompete the indigenous microbiota, including spoilage microorganisms such as Brochothrix. Moreover, none of the batches were considered unacceptable in a sensory evaluation.Overall, this study shows the favourable antilisterial activity of the cocktail of LAB employed, with the combination of HPP and LAB achieving a complete inhibition of the pathogen with no detrimental effects in physico-chemical or sensorial evaluations, highlighting the usefulness of biopreservation approaches involving LAB for enhancing the safety of cooked meat products.

Exploring the correlation of metabolites changes and microbial succession in solid-state fermentation of Sichuan Sun-dried vinegar

BackgroundThe traditional Sichuan Sun-dried vinegar (SSV) with unique flavor and taste is believed to be generated by the solid-state fermentation craft. However, how microorganisms and their metabolites change along with fermentation has not yet been explored.ResultsIn this study, our results demonstrated that the middle and late stages of SSV fermentation were the periods showing the largest accumulation of organic acids and amino acids. Furthermore, in the bacterial community, the highest average relative abundance was Lactobacillus (ranging from 37.55 to 92.50%) in all fermentation stages, while Acetobacters ranked second position (ranging from 20.15 to 0.55%). The number of culturable lactic acid bacteria is also increased during fermentation process (ranging from 3.93 to 8.31 CFU/g). In fungal community, Alternaria (29.42%), Issatchenkia (37.56%) and Zygosaccharomyces (69.24%) were most abundant in different fermentation stages, respectively. Interestingly, Zygosaccharomyces, Schwanniomyces and Issatchenkia were first noticed as the dominant yeast genera in vinegar fermentation process. Additionally, spearman correlation coefficients exhibited that Lactobacillus, Zygosaccharomyces and Schwanniomyces were significant correlation with most metabolites during the fermentation, implying that these microorganisms might make a significant contribution to the flavor formation of SSV.ConclusionThe unique flavor of SSV is mainly produced by the core microorganisms (Lactobacillus, Zygosaccharomyces and Schwanniomyces) during fermentation. This study will provide detailed information related to the structure of microorganism and correlation between changes in metabolites and microbial succession in SSV. And it will be very helpful for proposing a potential approach to monitor the traditional fermentation process.