Impact of the fermentation parameters pH and temperature on stress resilience of Lactobacillus reuteri DSM 17938

Non-inhibitory levels of oxygen during cultivation increase freeze-drying stress tolerance in Limosilactobacillus reuteri DSM 17938

The physiological effects of oxygen on Limosilactobacillus reuteri DSM 17938 during cultivation and the ensuing properties of the freeze-dried probiotic product was investigated. On-line flow cytometry and k-means clustering gating was used to follow growth and viability in real time during cultivation. The bacterium tolerated aeration at 500 mL/min, with a growth rate of 0.74 ± 0.13 h^-1 which demonstrated that low levels of oxygen did not influence the growth kinetics of the bacterium. Modulation of the redox metabolism was, however, seen already at non-inhibitory oxygen levels by 1.5-fold higher production of acetate and 1.5-fold lower ethanol production. A significantly higher survival rate in the freeze-dried product was observed for cells cultivated in presence of oxygen compared to absence of oxygen (61.8% ± 2.4% vs. 11.5% ± 4.3%), coinciding with a higher degree of unsaturated fatty acids (UFA:SFA ratio of 10 for air sparged vs. 3.59 for N₂ sparged conditions.). Oxygen also resulted in improved bile tolerance and boosted 5'nucleotidase activity (370 U/L vs. 240 U/L in N₂ sparged conditions) but lower tolerance to acidic conditions compared bacteria grown under complete anaerobic conditions which survived up to 90 min of exposure at pH 2. Overall, our results indicate the controlled supply of oxygen during production may be used as means for probiotic activity optimization of L. reuteri DSM 17938.

Improvement of the Lyophilization Survival Rate of Lactobacillus casei via Regulation of Its Surface Substances

The influence of surface substance production on the freeze-drying survival of Lactobacillus casei and methods to control the surface substances during fermentation were studied. The bacteria were treated with hypertonicity combined with ultrasound, and the survival rate was determined. The optimal conditions for removing surface substance without harming the bacteria were 81 w/18 min. The surface substances provided a protective effect on the lyophilization of the bacteria without protectants. However, in the presence of protectants, excessive surface substances reduced the protective effect of the optimum protectant alginate to 39.69 ± 1.27%. Finally, the amount of surface substances and lyophilized survival rate of collected bacteria were determined by adding EDTA during fermentation and regulating fermentation conditions, such as the carbon source, carbon-to-nitrogen ratio, and pH. The highest survival rate was 85.79 ± 3.29%, which was achieved when the amount of surface substances was (2.82 ± 0.55) × 10−11 mg/CFU. Therefore, the production of surface substances by the bacteria could be reduced by modifying the fermentation stage, which has significance in the improvement of the lyophilization survival rate of L. casei and the number of live bacteria per unit mass of L. casei in the lyophilized preparation.

Current Trends in the Production of Probiotic Formulations

Preparations containing probiotic strains of bacteria have a beneficial effect on human and animal health. The benefits of probiotics translate into an increased interest in techniques for the preservation of microorganisms. This review compares different drying methods and their improvements, with specific reference to processing conditions, microorganisms, and protective substances. It also highlights some factors that may influence the quality and stability of the final probiotic preparations, including thermal, osmotic, oxidative, and acidic stresses, as well as dehydration and shear forces. Processing and storage result in the loss of viability and stability in probiotic formulations. Herein, the addition of protective substances, the optimization of process parameters, and the adaptation of cells to stress factors before drying are described as countermeasures to these challenges. The latest trends and developments in the fields of drying technologies and probiotic production are also discussed. These developments include novel application methods, controlled release, the use of food matrices, and the use of analytical methods to determine the viability of probiotic bacteria.

Assessing Viability and Stress Tolerance of Probiotics—A Review

The interest in probiotics has increased rapidly the latest years together with the global market for probiotic products. Consequently, establishing reliable microbiological methods for assuring the presence of a certain number of viable microorganisms in probiotic products has become increasingly important. To assure adequate numbers of viable cells, authorities are enquiring for information on viability rates within a certain shelf-life in colony forming units (CFU). This information is obtained from plate count enumeration, a method that enables detection of bacterial cells based on their ability to replicate. Although performing plate count enumeration is one manner of assessing viability, cells can still be viable without possessing the ability to replicate. Thus, to properly assess probiotic viability, further analysis of a broader group of characteristics using several types of methods is proposed. In addition to viability, it is crucial to identify how well the cells in a probiotic product can survive in the gastrointestinal tract (GIT) and thus be able to mediate the desired health benefit while passing through the human body. A broad spectrum of different assay designs for assessing probiotic gastric tolerance have been used in research and quality control. However, the absence of any consensus on how to assess these qualities makes it difficult to compare between laboratories and to translate the results into in vivo tolerance. This review presents and discusses the complexity of assuring that a probiotic is suitable for beneficial consumption. It summarizes the information that can be subtracted from the currently available methods for assessment of viability and stress tolerance of a probiotic, hereby altogether defined as “activity.” Strengths and limitations of the different methods are presented together with favorable method combinations. Finally, the importance of choosing a set of analyses that reveals the necessary aspects of probiotic activity for a certain product or application is emphasized.

Flow cytometric analysis reveals culture condition dependent variations in phenotypic heterogeneity of Limosilactobacillus reuteri

Optimisation of cultivation conditions in the industrial production of probiotics is crucial to reach a high-quality product with retained probiotic functionality. Flow cytometry-based descriptors of bacterial morphology may be used as markers to estimate physiological fitness during cultivation, and can be applied for online monitoring to avoid suboptimal growth. In the current study, the effects of temperature, initial pH and oxygen levels on cell growth and cell size distributions of Limosilactobacillus reuteri DSM 17938 were measured using multivariate flow cytometry. A pleomorphic behaviour was evident from the measurements of light scatter and pulse width distributions. A pattern of high growth yielding smaller cells and less heterogeneous populations could be observed. Analysis of pulse width distributions revealed significant morphological heterogeneities within the bacterial cell population under non-optimal growth conditions, and pointed towards low temperature, high initial pH, and high oxygen levels all being triggers for changes in morphology towards cell chain formation. However, cell size did not correlate to survivability after freeze-thaw or freeze-drying stress, indicating that it is not a key determinant for physical stress tolerance. The fact that L. reuteri morphology varies depending on cultivation conditions suggests that it can be used as marker for estimating physiological fitness and responses to its environment.

Functional Foods as a formulation ingredients in beverages: Technological Advancements and Constraints

As a consequence of expanded science and technical research, the market perception of consumers has shifted from standard traditional to valuable foods, which are furthermore nutritional as well as healthier in today’s world. This food concept, precisely referred to as functional, focuses on including probiotics, which enhance immune system activity, cognitive response, and overall health. This review primarily focuses on functional foods as functional additives in beverages and other food items that can regulate the human immune system and avert any possibility of contracting the infection. Many safety concerns must be resolved during their administration. Functional foods must have an adequate amount of specific probiotic strain(s) during their use and storage, as good viability is needed for optimum functionality of the probiotic. Thus, when developing novel functional food-based formulations, choosing a strain with strong technological properties is crucial. The present review focused on probiotics as an active ingredient in different beverage formulations and the exerting mechanism of action and fate of probiotics in the human body. Moreover, a comprehensive overview of the regulative and safety issues of probiotics-based foods and beverages formulations.

Turbidimetric definition of growth limits in probiotic Lactobacillus strains from the perspective of an adaptation strategy

The application of an adaptation strategy for probiotics, which may improve their stress tolerance, requires the identification of the growth range for each parameter tested. In this study, 4 probiotics (Lactobacillus acidophilus, Lacticaseibacillus casei, Lacticaseibacillus rhamnosus, and Lactiplantibacillus plantarum) were grown under different pH, NaCl, and sucrose concentrations at 25°C, 30°C, and 37°C. Turbidimetric growth curves were carried out and lag phase duration, maximum growth rate, and amplitude (i.e., the difference between initial and stationary phase optical density) were estimated. Moreover, cell morphology was observed, and cell length measured. The growth response, as well as the morphological changes, were quite different within the 4 species. The L. acidophilus was the most sensitive strain, whereas L. plantarum was shown to better tolerate a wide range of stressful conditions. Frequently, morphological changes occurred when the growth curve was delayed. Based on the results, ranges of environmental parameters are proposed that can be considered suboptimal for each strain, and therefore could be tested. The quantitative evaluation of the growth kinetics as well as the morphological observation of the cells can constitute useful support to the choice of the parameters to be used in an adaptation strategy, notwithstanding the need to verify the effect on viability both in model systems and in foods.

Probiotic Potential of a Novel Vitamin B2-Overproducing Lactobacillus plantarum Strain, HY7715, Isolated from Kimchi

Vitamin B2, also known as riboflavin, is essential for maintaining human health. The purpose of this study was to isolate novel lactic acid bacteria that overproduce vitamin B2 and to validate their potential as probiotics. In this study, Lactobacillus plantarum HY7715 (HY7715) was selected among lactic acid bacteria isolated from Kimchi. HY7715 showed a very high riboflavin-producing ability compared to the control strain due to the high expression of ribA, ribB, ribC, ribH, and ribG genes. HY7715 produced 34.5 ± 2.41 mg/L of riboflavin for 24 h without consuming riboflavin in the medium under optimal growth conditions. It was able to produce riboflavin in an in vitro model of the intestinal environment. In addition, when riboflavin deficiency was induced in mice through nutritional restriction, higher levels of riboflavin were detected in plasma and urine in the HY7715 administration group than in the control group. HY7715 showed high survival rate in simulated gastrointestinal conditions and had antibiotic resistance below the cutoff MIC value suggested by the European Food Safety Authority; moreover, it did not cause hemolysis. In conclusion, HY7715 could be considered a beneficial probiotic strain for human and animal applications, suggesting that it could be a new alternative to address riboflavin deficiency.

Fermentation Strategies to Improve Soil Bio-Inoculant Production and Quality

The application of plant beneficial microorganisms has been widely accepted as an efficient alternative to chemical fertilizers and pesticides. Isolation and selection of efficient microorganisms, their characterization and testing in soil-plant systems are well studied. However, the production stage and formulation of the final products are not in the focus of the research, which affects the achievement of stable and consistent results in the field. Recent analysis of the field of plant beneficial microorganisms suggests a more integrated view on soil inoculants with a special emphasis on the inoculant production process, including fermentation, formulation, processes, and additives. This mini-review describes the different groups of fermentation processes and their characteristics, bearing in mind different factors, both nutritional and operational, which affect the biomass/spores yield and microbial metabolite activity. The characteristics of the final products of fermentation process optimization strategies determine further steps of development of the microbial inoculants. Submerged liquid and solid-state fermentation processes, fed-batch operations, immobilized cell systems, and production of arbuscular mycorrhiza are presented and their advantages and disadvantages are discussed. Recommendations for further development of the fermentation strategies for biofertilizer production are also considered.

Autolysis and Cell Death Is Affected by pH in L. reuteri DSM 20016 Cells

A key obstacle to the successful delivery of a probiotic to the consumer is maintaining viability of the live cells during storage, a challenge for the beneficial Lactibacillus reuteri. Three processes play a role in the reduction of viability: autolysis, cell death, and cell weakening. Using a phosphate induction model of autolysis, the initial aim of this project was to discover novel molecular determinants of autolysis in L. reuteri, with the long -term goal of elucidating new strategies for increasing viability. We employed a 2D Native/SDS-Page method to monitor changes in protein expression over time; however, the result was that excess phosphate did not induce noticeable changes in expression patterns. On the other hand, we found that pH affects both the rate of total viability and autolysis, as seen with other species of LAB. In addition, we found that the phosphate model of autolysis may not be sufficient to explain how autolysis is triggered in L. reuteri. Two parameters appear to modulate the pH in media containing L. reuteri cells: overall buffering capacity and the presence of a carbon source. Ultimately, phosphate sources appear to facilitate autolysis by maintaining pH in the media via a higher buffering capacity. In addition, the alkaline sugar free almond drink appears to be a promising possible preservative for L. reuteri.

Culture conditions affect Lactobacillus reuteri DSM 17938 ability to perform glycerol bioconversion into 3-hydroxypropionic acid

The platform molecule 3-hydroxypropionic acid (3-HP) can be produced using Lactobacillus reuteri through a two-step bioprocess that involves a growth phase followed by a bioconversion phase. The bioproduction is performed by resting cells that convert glycerol into 3-HP and 1,3-propanediol in fed-batch mode. This work aimed at studying the effect of the growth conditions of L. reuteri DSM 17938 during the first step, on the glycerol bioconversion into 3-HP during the second step. A Plackett and Burman design was carried out to test, in controlled bioreactors, the effect of 11 growth conditions simultaneously, at fixed bioconversion conditions. The supplementation of the growth medium with vitamin B12 and cysteine displayed a negative effect on the 3-HP bioproduction. The addition of glucose, phytone peptone, Tween 80, 1,2-propanediol and betaine in the growth medium, together with a low temperature and an optimal pH of 6.0 during the growth phase increased the bioconversion duration from 56 h to 89 h at a glycerol feeding rate of 0.5 g·h^-1. A validating experiment displayed that the 3-HP titer, 3-HP production yield and 3-HP specific production rate were significantly improved by 25 %, 150 % and 61 %, respectively.

Growth Kinetics of Probiotic Lactobacillus Strains in the Alternative, Cost-Efficient Semi-Solid Fermentation Medium

The growing need for Lactobacillus bacteria usage in industry and the expending probiotic market led to a search for new cost-efficient fermentation media from which a high yield of these bacteria could be obtained. The following study aimed to elaborate cultivation medium, for Lactobacillus spp. growth, which main components would be wheat, maize, barley, and rye flours. The optimal temperature for Lactobacillus growth in new semi-solid fermentation (SSF) medium, water content, and pH of the medium were analyzed by the plate count method. It was established, that the highest bacteria counts were obtained from cultures conducted in the SSF medium with flours to water ratio of 1:1.5 with a natural pH of 6.0 at 37 °C. Subsequently, the growth kinetics of analyzed strains, in both MRS and the SSF media, were studied. The newly designed media contributed to the increased duration of selected Lactobacillus strains lag phase, which varied from 1.98 to 5.64; nevertheless, the maximum growth rate of the strains was two times higher in the SSF medium rather than in MRS, which also resulted in shorter generation time. The developed medium has the potential to become a new cost-efficient fermentation medium for Lactobacillus spp.

Antimicrobial and Antibiofilm Activities of Probiotic Lactobacilli on Antibiotic-Resistant Proteus mirabilis

The emergence of biofilm-forming, multi-drug-resistant (MDR) Proteus mirabilis infections is a serious threat that necessitates non-antibiotic therapies. Antibiotic susceptibility and biofilm-forming activity of P. mirabilis isolates from urine samples were assessed by disc diffusion and crystal violet assays, respectively. Antimicrobial activities of probiotic Lactobacilli were evaluated by agar diffusion. Antibiofilm and anti-adherence activities were evaluated by crystal violet assays. While most P. mirabilis isolates were antibiotic-resistant to varying degrees, isolate P14 was MDR (resistant to ceftazidime, cefotaxime, amoxicillin-clavulanic acid, imipenem, ciprofloxacin, and amikacin) and formed strong biofilms. Cultures and cell-free supernatants of Lactobacillus casei and Lactobacillus reuteri exhibited antimicrobial and antibiofilm activities. The 1/16 concentration of untreated supernatants of L. casei and L. reuteri significantly reduced mature biofilm formation and adherence of P14 by 60% and 72%, respectively (for L. casei), and by 73% each (for L. reuteri). The 1/8 concentration of pH-adjusted supernatants of L. casei and L. reuteri significantly reduced mature biofilm formation and adherence of P14 by 39% and 75%, respectively (for L. casei), and by 73% each (for L. reuteri). Scanning electron microscopy (SEM) confirmed eradication of P14’s biofilm by L. casei. L. casei and L. reuteri could be utilized to combat Proteus-associated urinary tract infections.

Probiotic potential and safety assessment of Lactobacillus isolated from yaks

Current problem of antibiotic resistance and the high incidence of bacterial diseases has brought huge losses to the yak breeding industry in Tibet. Therefore, the purpose of this study was to isolate Lactobacillus with safety and beneficial probiotic potential for the prophylaxis of intestinal diseases in yaks. After 16S rDNA sequence, four strains i.e. Lactobacillus sakei (named L4), Enterococcus hirae (named E5), Pediococcus acidilactici (named P7), Weissella confusa (named W8) were isolated from feces of yaks. The results of tolerance to acid, bile salt, enzyme and temperature showed that P7 was highly tolerant to acid, bile salt and digestive enzyme, while E5 was more resistant to temperature. The antibacterial assay showed L4 had a strong inhibitory effect against Staphylococcus aureus (BNCC186335), and E5, P7, W8 had effective antibacterial ability against Escherichia coli (C83902). In addition, L4, E5, P7 and W8 mainly produced organic acids and bacteriocin production to inhibit common intestinal pathogens. The results of antibiotic susceptibility assay indicated that L4, E5, P7 and W8 were highly sensitive to most clinically used antibiotics and didn't contain the VanA and VanB genes on the basis of PCR amplification, and L4, E5, P7 and W8 didn't exhibit hemolytic activity. The animal toxicity experiment results showed that no obvious pathological change was found in intestinal tissue sections, and L4, E5 and W8 strains also promoted the growth performance of mice, consequently, the L4, E5, P7 and W8 had no toxic effect on mice. In conclusion, lactobacillus isolated from feces of yaks not only have potential probiotics and strong antibacterial ability in vitro, but also are safe. Therefore, they have the potential to reduce the occurrence of bacterial diseases as new feed additives.

Production of Probiotic Passion Fruit (Passiflora edulis Sims f. flavicarpa Deg.) Drink Using Lactobacillus reuteri and Microencapsulation via Spray Drying

Probiotic foods offer many benefits to human health, causing increased interest in the development of new food products that exploit such benefits. However, traditional dairy foods are being replaced by other non-dairy foods to provide additional sources of benefits provided by bioactive molecules. Therefore, the objective of the present work was to study the production process of a probiotic fruit drink and then microencapsulate the probiotic pulp to stabilize the drink further. Passion fruit pulp (Passiflora edulis Sims f. flavicarpa Deg.) was fermented with Lactobacillus reuteri under different temperature conditions in combination with different pHs to find the best fermentation conditions. Different from dairy sources, the optimal conditions for the growth of Lactobacillus reuteri in the passion fruit pulp were found to be 30 °C at pH 3.18, where phenolic compounds could also be used as a secondary metabolic pathway. Spray-drying was performed using different conditions for microencapsulation. Process yields and Lactobacillus reuteri survival showed the dependency of droplet sizes, whereas phenolic compound retention was increased when higher amounts of gelatin were used. Therefore, the development of a new food product comprising a powdered fruit pulp rich in probiotic and phenolic compounds was possible.