Use of alginate and cryo-protective sugars to improve the viability of lactic acid bacteria after freezing and freeze-drying

Sodium carboxymethyl celluloses as a cryoprotectant for survival improvement of lactic acid bacterial strains subjected to freeze-drying

This study investigated the possibility of sodium carboxymethyl celluloses (Na-CMC) in protecting the viability of lactic acid bacteria (LAB) against freeze-drying stress. 1 % concentration of Na-CMC with a 0.7 substitution degree and viscosity of 1500 to 3100 (MPa.s) was found to protect Lactobacillus delbrueckii subsp. bulgaricus CICC 6098 best, giving a high survival rate of 23.19 ± 0.88 %, high key enzymatic activities, and 28-day storage stability. Additionally, Na-CMC as cryoprotectant provided good protection for other 7 lactic acid bacterial strains subjected to freeze-drying. The highest survival rate was 48.79 ± 0.20 U/mg for β-GAL, 2.75 ± 0.15 U/mg for Na+-K+-ATPase, and 2.73 ± 0.41 U/mg for Ca2+-Mg2+-ATPase as 48.48 ± 0.46 % for freeze-dried Pediococcus pentosaceus CICC 22228. It was Interesting to note that the presence of Na-CMC reduced the freezable water content of the lyophilized powders containing the tested strains through its hydroxyl group, and supplied micro-holes and fibers for protecting the integrated structure of LAB cell membrane and wall against the freezing damage. It is clear that addition of Na-CMC should be promising as a new cryoprotective agent available for processing the lyophilized stater cultures of LAB strains.

Usage of ectoine as a cryoprotectant for cryopreservation of lactic acid bacteria

Streptococcus thermophilus, the only Streptococcus species considered "Generally Recognized Safe", has been used widely in the food industry. This bacterium is one of the most valuable industrial lactic acid bacterial species. Due to the importance of this bacterium in industrial applications, it should be stored for a long time without losing its metabolic properties. The present study aimed to investigate the cryoprotectant effect of three compatible solutes (ectoine, trehalose, and sucrose) on bacterial cells stored at different temperatures (frozen at -80 °C or freeze-dried and subsequently stored at +4, -20, and -80 °C) for three months. The bacterial cells were tested for cell viability, bile salt tolerance, and lactic acid production before and after processing. The highest cell viability, bile salt tolerance, and lactic acid production were obtained with ectoine and under frozen (storage at -80 °C) conditions. In freeze-dried and subsequently stored at various temperatures, the best preservation was obtained at -80 °C, followed by -20 °C and +4 °C. Moreover, when ectoine's preservation potential was compared to other cryoprotectants, ectoine showed the highest preservation, followed by trehalose and sucrose. Although ectoine has a variety of qualities that have been proven, in the current work, we have shown for the first time that ectoine has cryoprotectant potential in yogurt starter cultures (S. thermophilus).

Comparison of Electrostatic Spray Drying, Spray Drying, and Freeze Drying for Lacticaseibacillus rhamnosus GG Dehydration

Spray drying (SD) is extensively used to encapsulate lactic acid bacteria in large-scale industrial applications; however, bacteria combat several harms that reduce their viability. In this study, a novel technique called electrostatic spray drying (ESD) was used to explore the benefits and disadvantages of using electrostatic charge and lower temperatures in the system. Freeze drying (FD) was used as a reference. The effect of different encapsulation agents, like maltodextrin, arabic gum, and skim milk, on the viability of Lacticaseibacillus rhamnosus GG (LGG) was investigated. The initial cell concentration, particle size distribution, aspect ratio, sphericity, scanning-electron-microscopy images, moisture content, water activity, glass transition, rehydration abilities, and survival during storage were compared. Skim milk was proven to be the best protectant for LGG, regardless of the drying process or storage time. A huge reduction in cell numbers (4.49 ± 0.06 log CFU/g) was observed with maltodextrin using SD; meanwhile, it was protected with minimum loss (8.64 ± 0.62 log CFU/g) with ESD. In general, ESD preserved more LGG cells during processing compared to SD, and provided better stability than FD and SD during storage, regardless of the applied voltage. The ESD product analysis demonstrated an efficient LGG preservation, close to FD; therefore, ESD presented to be a promising and scalable substitute for SD and FD.

Understanding the Probiotic Bacterial Responses Against Various Stresses in Food Matrix and Gastrointestinal Tract: A Review

Probiotic bacteria are known to have ability to tolerate inhospitable conditions experienced during food preparation, food storage, and gastrointestinal tract of consumer. As probiotics are living cells, they are adversely affected by the harsh environment of the carrier matrix as well as low pH, bile salts, oxidative stress, osmotic pressure, and commensal microflora of the host. To overcome the unfavorable environments, many probiotics switch on the cell-mediated protection mechanisms, which helps them to survive, acclimatize and remain operational in the harsh circumstances. In this review, we provide comprehensive understanding on the different stresses experienced by the probiotic when added in carrier food as well as during human gastrointestinal tract transit. Under such situation how these health beneficial bacteria protect themselves by activation of several defense systems and get adapted to the lethal environments.

Determining the Role of UTP-Glucose-1-Phosphate Uridylyltransferase (GalU) in Improving the Resistance of Lactobacillus acidophilus NCFM to Freeze-Drying

Lactobacillus acidophilus NCFM is widely used in the fermentation industry; using it as a freeze-dried powder can greatly reduce the costs associated with packaging and transportation, and even prolong the storage period. Previously published research has reported that the expression of galU (EC: 2.7.7.9) is significantly increased as a result of freezing and drying. Herein, we aimed to explore how galU plays an important role in improving the resistance of Lactobacillus acidophilus NCFM to freeze-drying. For this study, galU was first knocked out and then re-expressed in L. acidophilus NCFM to functionally characterize its role in the pertinent metabolic pathways. The knockout strain ΔgalU showed lactose/galactose deficiency and displayed irregular cell morphology, shortened cell length, thin and rough capsules, and abnormal cell division, and the progeny could not be separated. In the re-expression strain pgalU, these inhibited pathways were restored; moreover, the pgalU cells showed a strengthened cell wall and capsule, which enhanced their resistance to adverse environments. The pgalU cells showed GalU activity that was 229% higher than that shown by the wild-type strain, and the freeze-drying survival rate was 84%, this being 4.7 times higher than that of the wild-type strain. To summarize, expression of the galU gene can significantly enhance gene expression in galactose metabolic pathway and make the strain form a stronger cell wall and cell capsule and enhance the resistance of the bacteria to an adverse external environment, to improve the freeze-drying survival rate of L. acidophilus NCFM.

Design of a new lyoprotectant increasing freeze-dried Lactobacillus strain survival to long-term storage

Background

Stabilization of freeze-dried lactic acid bacteria during long-term storage is challenging for the food industry. Water activity of the lyophilizates is clearly related to the water availability and maintaining a low a_w during storage allows to increase bacteria viability. The aim of this study was to achieve a low water activity after freeze-drying and subsequently during long-term storage through the design of a lyoprotectant. Indeed, for the same water content as sucrose (commonly used lyoprotectant), water activity is lower for some components such as whey, micellar casein or inulin. We hypothesized that the addition of these components in a lyoprotectant, with a higher bound water content than sucrose would improve lactobacilli strains survival to long-term storage. Therefore, in this study, 5% whey (w/v), 5% micellar casein (w/v) or 5% inulin (w/v) were added to a 5% sucrose solution (w/v) and compared with a lyoprotectant only composed of 5% sucrose (w/v). Protective effect of the four lyoprotectants was assessed measuring Lactiplantibacillus plantarum CNCM I-4459 survival and water activity after freeze-drying and during 9 months storage at 25 °C.

Results

The addition whey and inulin were not effective in increasing Lactiplantibacillus plantarum CNCM I-4459 survival to long-term-storage (4 log reduction at 9 months storage). However, the addition of micellar casein to sucrose increased drastically the protective effect of the lyoprotectant (3.6 log i.e. 0.4 log reduction at 9 months storage). Comparing to a lyoprotectant containing whey or inulin, a lyoprotectant containing micellar casein resulted in a lower water activity after freeze-drying and its maintenance during storage (0.13 ± 0.05).

Conclusions

The addition of micellar casein to a sucrose solution, contrary to the addition of whey and inulin, resulted in a higher bacterial viability to long-term storage. Indeed, for the same water content as the others lyoprotectants, a significant lower water activity was obtained with micellar casein during storage. Probably due to high bound water content of micellar casein, less water could be available for chemical degradation reactions, responsible for bacterial damages during long-term storage. Therefore, the addition of this component to a sucrose solution could be an effective strategy for dried bacteria stabilization during long-term storage.

Experimental Whisky Fermentations: Influence of Wort Pretreatments

In addition to ethanol yield, the production of flavour congeners during fermentation is a major consideration for Scotch whisky producers. Experimental whisky fermentations can provide useful information to the industry, and this is the focus of this paper. This study investigated the impact of wort pretreatments (boiled, autoclaved, filtered) on fermentation performance and flavour development in Scotch whisky distillates as an alternative to freezing wort for storage. Our study showed that no significant sensorial differences were detected in low wines (first distillates), while the chemical compositions showed clear changes in increased levels of esters and higher alcohols in boiled and autoclaved wort. In contrast, filtered wort comprised overall lower levels of congeners. Regarding alcohol yield, all three pretreatments resulted in decreased yields. In practice, the pretreatment of wort prior to fermentation requires additional process operations, while freezing requires large storage units. The pretreatments adopted in this study significantly influence the composition of the malt wort used for experimental whisky fermentations, and this results in a poorer fermentation performance compared with untreated wort. We recommend the use of fresh or frozen wort as the best options for small-scale fermentation trials.

Distribution of Sulfate-Reducing Bacteria in the Environment: Cryopreservation Techniques and Their Potential Storage Application

Sulfate-reducing bacteria (SRB) are a heterogeneous group of anaerobic microorganisms that play an important role in producing hydrogen sulfide not only in the natural environment, but also in the gastrointestinal tract and oral cavity of animals and humans. The present review was written with the inclusion of 110 references including the time period from 1951 to 2021. The following databases were evaluated: Web of Science, Scopus and Google Scholar. The articles chosen to be included in the review were written mainly in the English and Czech languages. The molecular mechanisms of microbial cryoprotection differ depending on the environment where microorganisms were initially isolated. It was observed that the viability of microorganisms after cryopreservation is dependent on a number of factors, primarily colony age, amount of inoculum, cell size or rate of cooling, and their molecular inventory. Therefore, this paper is devoted to assessing the performance and suitability of various cryopreservation methods of intestinal bacteria, including molecular mechanisms of their protection. In order to successfully complete the cryopreservation process, selecting the correct laboratory equipment and cryopreservation methodology is important. Our analysis revealed that SRB should be stored in glass vials to help mitigate the corrosive nature of hydrogen sulfide, which can affect their physiology on a molecular level. Furthermore, it is recommended that their storage be performed in distilled water or in a suspension with a low salt concentration. From a molecular biological and bioengineering perspective, this contribution emphasizes the need to consider the potential impact associated with SRB in the medical, construction, and environmental sectors.

Uranium removal from complex mining waters by alginate beads doped with cells of Stenotrophomonas sp. Br8: Novel perspectives for metal bioremediation

Uranium-containing effluents generated by nuclear energy industry must be efficiently remediated before release to the environment. Currently, numerous microbial-based strategies are being developed for this purpose. In particular, the bacterial strain Stenotrophomonas sp. Br8, isolated from U mill tailings porewaters, has been already shown to efficiently precipitate U(VI) as stable U phosphates mediated by phosphatase activity. However, the upscaling of this strategy should overcome some constraints regarding cell exposure to harsh environmental conditions. In the present study, the immobilization of Br8 biomass in an inorganic matrix was optimized to provide protection to the cells as well as to make the process more convenient for real-scale utilization. The use of biocompatible, highly porous alginate beads for Br8 cells immobilization resulted the best alternative when investigating by a multidisciplinary approach (High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM), Environmental Scanning Electron Microscopy (ESEM), Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance, etc.) several consolidated entrapment methods. This biomaterial was applied to complex real U mining porewaters (containing 47 mg/L U) in presence of an organic phosphate source (glycerol-2-phosphate) to produce reactive free orthophosphates through Br8 phosphatase activity. Uranium immobilization rates around 98 % were observed after one cycle of 72 h. In terms of U removal ability as a function of biomass, Br8-doped alginate beads were determined to remove up to 1199.5 mg U/g dry biomass over two treatment cycles. Additionally, optimized conditions for storing Br8-doped beads and for a correct application were assessed. Results for U accumulation kinetics and HAADF-STEM/ESEM analyses revealed that U removal by the immobilized cells is a biphasic process combining a first passive U sorption onto bead and/or cell surfaces and a second slow active biomineralization. This work provides new practical insights into the biological and physico-chemical parameters governing a high-efficient U bioremediation process based on the phosphatase activity of immobilized bacterial cells when applied to complex mining waters under laboratory conditions.

Survivability of Collagen-Peptide Microencapsulated Lactic Acid Bacteria during Storage and Simulated Gastrointestinal Conditions

The intracellular homeostasis of lyophilized lactic acid bacteria (LAB) is destroyed by extreme cold stress, resulting in decreased stability. This study aimed to verify the validity of collagen as a potential protective agent for improving microbial stability deteriorated by freezing. The collagen types used in this study were low molecular weight collagen (LC) of less than 1000 Da and low molecular weight collagen-peptide (LCP) of less than 300 Da. By the accelerated stability test according to the addition of each collagen type, a 3% LCP displaying a protective effect on the viability of various LAB strains (Lactoplantibacillus plantarum MG989, Lactococcus lactis MG5125, Enterococcus faecium MG5232, Bifidobacterium animalis ssp. lactis MG741, and Streptococcus thermophilus MG5140) was finally selected. It was evaluated whether LCP enhances bacterial stability, survivability in the gastrointestinal (GI) tract, and heat resistance. LCP significantly improved the viability of all strains in the GI tract compared to sucrose and skim milk, which are conventional protective agents. Based on morphological observations, LCP was uniformly coated on the cell surface, resulting in protective effects against multiple external stress stimuli. Such findings indicate the applicability of LCP as an unprecedented protective agent, which can improve the stability of various probiotics with antifreeze effects.

Solid-State Fermentation of Arthrospira platensis to Implement New Food Products: Evaluation of Stabilization Treatments and Bacterial Growth on the Volatile Fraction

Arthrospira platensis is a cyanobacterium widely used in food formulation and mainly consumed as a food supplement because of its high amount of proteins, vitamins and minerals. Different probiotic food supplements are present in the market, and a lactic acid fermented food product like dried spirulina could be useful not only to introduce lactic acid bacteria (LAB) with beneficial effects to the diet of consumers, but also to improve or change the aromatic profile of the substrate. Therefore, the aim of this study was the evaluation of lactic acid fermentation of A. platensis biomass, focusing on the consequent changes in the aromatic profile. For this purpose, two different stabilization treatments (UV light treatment and sterilization) were applied prior to fermentation with two LAB strains, Lacticaseibacillus casei 2240 and Lacticaseibacillus rhamnosus GG. The biomass proved to be a suitable matrix for solid-state fermentation, showing a LAB growth of more than 2 log CFU/g in 48 h. The fermentation process was also useful for off-flavor reduction. In particular, the fermentation process significantly influenced the concentration of those compounds responsible for aldehydic/ethereal, buttery/waxy (acetoin and diacetyl), alkane and fermented aromatic notes (isoamyl alcohol). The heat treatment of the matrix, in addition to guaranteed safety for consumers, led to an improved aroma after fermentation. In conclusion, a fermented spirulina powder with a different aromatic profile was obtained with the applied heat treatment. Fermentation with lactic acid bacteria can be an interesting tool to obtain cyanobacterial biomasses with more pleasant sensory properties for potential use in food formulations.

Enhanced Viability of Probiotics against Gastric Acid by One-Step Coating Process with Poly-L-Lysine: In Vitro and In Vivo Evaluation

Due to their low acid tolerance, a majority of probiotics face difficulties with regard to surviving in the gastric environment long enough to reach the intestinal surfaces where they colonize and provide health benefits. We prepared a probiotic delivery system that can enhance their viability in acidic conditions by developing a one-step poly-L-lysine (PLL) coating process. We determined whether the coating process was successful by measuring the zeta potential and observing it with confocal scanning microscopy. PLL-coated L. plantarum (PLL-LP), incubated in a solution of pH 2 for 2 h, exhibited a higher viability (6.86 ± 0.12 log CFU/mL of viable cells) than non-coated L. plantarum (non-coated LP), which exhibited only 2.7 ± 1.23 log CFU/mL of viable cells. In addition, a higher amount of L. plantarum was detected in the feces of mice orally administered PLL-LP (6.2 ± 0.4 log CFU/g of feces) than in the feces of the control groups. In addition to enhancing probiotic viability in pH 2 solution, the PLL coating showed no effect on the probiotic growth pattern and the viability of either freeze-dried L. plantarum or L. plantarum, stored at −20 °C and 4 °C, respectively. Overall, these results indicated that the PLL coating is a promising potential probiotic delivery system.

Propionibacterium freudenreichii CIRM-BIA 129 Osmoadaptation Coupled to Acid-Adaptation Increases Its Viability During Freeze-Drying

Propionibacterium freudenreichii is a beneficial bacterium with documented effects on the gut microbiota and on inflammation. Its presence within the animal and human intestinal microbiota was correlated with immunomodulatory effects, mediated by both propionibacterial surface components and by secreted metabolites. It is widely implemented, both in the manufacture of fermented dairy products such as Swiss-type cheeses, and in the production of probiotic food complements, under the form of freeze-dried powders. The bottleneck of this drying process consists in the limited survival of bacteria during drying and storage. Protective pre-treatments have been applied to other bacteria and may, in a strain-dependent manner, confer enhanced resistance. However, very little information was yet published on P. freudenreichii adaptation to freeze-drying. In this report, an immunomodulatory strain of this probiotic bacterium was cultured under hyperosmotic constraint in order to trigger osmoadaptation. This adaptation was then combined with acid or thermal pre-treatment. Such combination led to accumulation of key stress proteins, of intracellular compatible solute glycine betaine, to modulation of the propionibacterial membrane composition, and to enhanced survival upon freeze-drying. This work opens new perspectives for efficient production of live and active probiotic propionibacteria.

Optimization of Production Parameters for Probiotic Lactobacillus Strains as Feed Additive

In animal nutrition, probiotics are considered as desirable alternatives to antibiotic growth promoters. The beneficial effects of probiotics primarily depend on their viability in feed, which demands technical optimization of biomass production, since processing and storage capacities are often strain-specific. In this study, we optimized the production parameters for two broiler-derived probiotic lactobacilli (L. salivarius and L. agilis). Carbohydrate utilization of both strains was determined and preferred substrates that boosted biomass production in lab-scale fermentations were selected. The strains showed good aerobic tolerance, which resulted in easier scale-up production. For the freeze-drying process, the response surface methodology was applied to optimize the composition of cryoprotective media. A quadratic polynomial model was built to study three protective factors (skim milk, sucrose, and trehalose) and to predict the optimal working conditions for maximum viability. The optimal combination of protectants was 0.14g/mL skim milk/ 0.08 g/mL sucrose/ 0.09 g/mL trehalose (L. salivarius) and 0.15g/mL skim milk/ 0.08 g/mL sucrose/ 0.07 g/mL (L. agilis), respectively. Furthermore, the in-feed stabilities of the probiotic strains were evaluated under different conditions. Our results indicate that the chosen protectants exerted an extensive protection on strains during the storage. Although only storage of the strains at 4 °C retained the maximum stability of both Lactobacillus strains, the employed protectant matrix showed promising results at room temperature.

The Effect of Eight Thermal Protectants on the Survival Rate and the Viable Counts of Lactobacillus casei After Heat Treatment in Fermented Goat Milk

In order to improve the survival rate of probiotics and produce probiotic goat milk from fermented goat milk of Lactobacillus casei L61 by spray drying. Spray drying has been applied to large-scale industrial production of milk powder due to its high efficiency and low cost. However, high temperatures in spray drying can result in the loss of large numbers of probiotic.The purpose of this paper is to study the effects of eight thermal protectants including skim milk, sucrose, glucose, β-cyclodextrin, gelatin, maltodextrin, glycerol, trehalose on the survival rate and viable counts of L.casei L61 after heat treatment by the single factor experiment. All protective agents have a positive effect on increasing the survival rate of L.casei L61 (p<0.05). The results indicated that the survival rates of L.casei L61 were up to the maximum of 10.94%, 1.13%, 3.04%, 0.21%, 6.97%, 0.075, 4.71% and 0.29%, while the additions of skim milk, sucrose, glucose, β-cyclodextrin, gelatin, maltodextrin, glycerol, trehalose were 20mg/L, 10%, 7%, 15%, 1.5%, 3%, 8mL/L, 10%, respectively; the viable counts after heat treatment are 19.69, 0.81, 1.78, 0.455, 12.2, 0.12, 2.75, 0.435(×106CFU/mL), respectively. This paper provides technical a reference for the development of probiotic goat milk powder.

Review: Adaptation of Beneficial Propionibacteria, Lactobacilli, and Bifidobacteria Improves Tolerance Toward Technological and Digestive Stresses

This review deals with beneficial bacteria, with a focus on lactobacilli, propionibacteria, and bifidobacteria. As being recognized as beneficial bacteria, they are consumed as probiotics in various food products. Some may also be used as starters in food fermentation. In either case, these bacteria may be exposed to various environmental stresses during industrial production steps, including drying and storage, and during the digestion process. In accordance with their adaptation to harsh environmental conditions, they possess adaptation mechanisms, which can be induced by pretreatments. Adaptive mechanisms include accumulation of compatible solutes and of energy storage compounds, which can be largely modulated by the culture conditions. They also include the regulation of energy production pathways, as well as the modulation of the cell envelop, i.e., membrane, cell wall, surface layers, and exopolysaccharides. They finally lead to the overexpression of molecular chaperones and of stress-responsive proteases. Triggering these adaptive mechanisms can improve the resistance of beneficial bacteria toward technological and digestive stresses. This opens new perspectives for the improvement of industrial processes efficiency with regard to the survival of beneficial bacteria. However, this bibliographical survey evidenced that adaptive responses are strain-dependent, so that growth and adaptation should be optimized case-by-case.

Assessment of Ready-to-Use Freeze-dried Immobilized Biocatalysts as Innovative Starter Cultures in Sourdough Bread Making

In the present study the effect of innovative biocatalysts as starter cultures in sourdough bread making was explored. The biocatalysts consisted of Lactobacillus paracasei K5 and Lactobacillus bulgaricus ATCC 11842 (in single and mixed form), immobilized on delignified wheat bran (DWB), and freeze dried without cryoprotectants. The parameters monitored were physicochemical characteristics, mold and rope spoilage appearance, volatile composition, and organoleptic characteristics. Results obtained showed that both biocatalysts exhibit good fermentative activity. However, the best results were achieved when freeze-dried immobilized L. paracasei K5 was applied as a single culture. In particular, the produced bread had a higher acidity (8.67 mL 0.1 N NaOH) and higher organic load (2.90 g/kg lactic acid and 1.11 g/kg acetic acid). This outcome was the main reason why this bread was preserved more regarding mold spoilage (14 days) and rope spoilage (12 days), respectively. In addition, the employment of freeze-dried immobilized L. paracasei K5 led to bread with better aromatic profile in terms of concentrations and number of volatile compounds produced as gas chromatography/mass spectrometry (GC/MS) analysis proved. Finally, no significant differences were observed through sensorial tests. Last but not least, it should be highlighted that the used microorganisms were cultured in cheese whey, minimizing the cost of the proposed biotechnological procedure.

Development of Freeze-Thaw Tolerant Lactobacillus rhamnosus GG by Adaptive Laboratory Evolution

The industrial application of microorganisms as starters or probiotics requires their preservation to assure viability and metabolic activity. Freezing is routinely used for this purpose, but the cold damage caused by ice crystal formation may result in severe decrease in microbial activity. In this study, adaptive laboratory evolution (ALE) technique was applied to a lactic acid bacterium to select tolerant strains against freezing and thawing stresses. Lactobacillus rhamnosus GG was subjected to freeze-thaw-growth (FTG) for 150 cycles with four replicates. After 150 cycles, FTG-evolved mutants showed improved fitness (survival rates), faster growth rate, and shortened lag phase than those of the ancestor. Genome sequencing analysis of two evolved mutants showed genetic variants at distant loci in six genes and one intergenic space. Loss-of-function mutations were thought to alter the structure of the microbial cell membrane (one insertion in cls), peptidoglycan (two missense mutations in dacA and murQ), and capsular polysaccharides (one missense mutation in wze), resulting in an increase in cellular fluidity. Consequently, L. rhamnosus GG was successfully evolved into stress-tolerant mutants using FTG-ALE in a concerted mode at distal loci of DNA. This study reports for the first time the functioning of dacA and murQ in freeze-thaw sensitivity of cells and demonstrates that simple treatment of ALE designed appropriately can lead to an intelligent genetic changes at multiple target genes in the host microbial cell.

The performance of five fruit-derived and freeze-dried potentially probiotic Lactobacillus strains in apple, orange, and grape juices

BACKGROUND

This study assessed the survival of the fruit-derived and freeze-dried L. plantarum 49, L. brevis 59, L. paracasei 108, L. fermentum 111 and L. pentosus 129 strains during frozen storage and when incorporated into apple, orange, and grape juice stored under refrigeration. Physicochemical parameters of juices containing the freeze-dried Lactobacillus strains and the survival of the test strains in the fruit juices during in vitro digestion were also evaluated.

RESULTS

No decreases in survival rates (log N/log N0) of the freeze-dried cells were observed in up to 1 month of storage. The survival rates of the freeze-dried strains L. plantarum 49 and L. paracasei 108 were > 0.75 in up to 4 months of storage. All freeze-dried strains exhibited survival rates of >0.75 in up to 2 weeks of storage in apple juice; only L. plantarum 49 and L. paracasei 108 showed similar survival rates in orange and grape juices in up to 2 weeks of storage. The contents of the monitored organic acids or sugars during storage varied depending on the added strain and the type of fruit juice. At the end of in vitro digestion, L. brevis 59, L. paracasei 108 and L. fermentum 111 showed survival rates of >0.80 in apple juice.

CONCLUSION

Apple juice was the best substrate for the survival of the tested freeze-dried Lactobacillus strains over time. L. paracasei 108 and L. plantarum 49 were the strains presenting the best performance for incorporation in potentially probiotic fruit juices. © 2018 Society of Chemical Industry.

Evaluation of Streptococcus thermophilus IFFI 6038 Microcapsules Prepared Using an Ultra-fine Particle Processing System

Microencapsulation technology has the potential to protect probiotics and to deliver them to the gut, and extrusion is one of the most commonly used methods. However, the rather large diameters of 1~5 mm produced tend to cause oral grittiness and result in low compliance. In this article, Streptococcus thermophilus IFFI 6038 (IFFI 6038) microcapsules were prepared using an ultra-fine particle processing system (UPPS) previously developed by this research group. IFFI 6038 suspension was pumped by a peristaltic pump to the feeding inlet nozzle and then dispersed into micro-droplets by a rotating disk, followed by solidification. Trehalose (16%) was used as a cryoprotectant to protect IFFI 6038 from damage by lyophilization used in the process. Alginate (3%) resulted in IFFI 6038 microcapsules with a median particle diameter (d ₅₀) of 29.32 ± 0.12 μm and a span value of 1.00 ± 0.02, indicating uniform particle size distribution. To evaluate the potential of microencapsulation in protecting IFFI 6038 from the gastric conditions, the viable counts of IFFI 6038 following incubation of IFFI 6038 microcapsules in simulated gastric juices for 120 min were determined and compared with those of free IFFI 6038. The stability of microencapsulated IFFI 6038 upon storage for 3 months at 4°C and 25°C, respectively, was also determined. The results showed that microcapsules prepared by UPPS protected IFFI 6038 from gastric conditions. The results from a rat diarrhea model showed that microcapsules prepared by the UPPS method were able to effectively improve the diarrhea conditions in rats.

Preparation of Acid-Resistant Microcapsules with Shell-Matrix Structure to Enhance Stability of Streptococcus Thermophilus IFFI 6038

Microencapsulation is an effective technology used to protect probiotics against harsh conditions. Extrusion is a commonly used microencapsulation method utilized to prepare probiotics microcapsules that is regarded as economical and simple to operate. This research aims to prepare acid-resistant probiotic microcapsules with high viability after freeze-drying and optimized storage stability. Streptococcus thermophilus IFFI 6038 (IFFI 6038) cells were mixed with trehalose and alginate to fabricate microcapsules using extrusion. These capsules were subsequently coated with chitosan to obtain chitosan-trehalose-alginate microcapsules with shell-matrix structure. Chitosan-alginate microcapsules (without trehalose) were also prepared using the same method. The characteristics of the microcapsules were observed by measuring the freeze-dried viability, acid resistance, and long-term storage stability of the cells. The viable count of IFFI 6038 in the chitosan-trehalose-alginate microcapsules was 8.34 ± 0.30 log CFU g^-1 after freeze-drying (lyophilization), which was nearly 1 log units g^-1 greater than the chitosan-alginate microcapsules. The viability of IFFI 6038 in the chitosan-trehalose-alginate microcapsules was 6.45 ± 0.09 log CFU g^-1 after 120 min of treatment in simulated gastric juices, while the chitosan-alginate microcapsules only measured 4.82 ± 0.22 log CFU g^-1 . The results of the long-term storage stability assay indicated that the viability of IFFI 6038 in chitosan-trehalose-alginate microcapsules was higher than in chitosan-alginate microcapsules after storage at 25 °C. Trehalose played an important role in the stability of IFFI 6038 during storage. The novel shell-matrix chitosan-trehalose-alginate microcapsules showed optimal stability and acid resistance, demonstrating their potential as a delivery vehicle to transport probiotics.

A technique for lyopreservation of Clostridium ljungdahlii in a biocomposite matrix for CO absorption

A system capable of biocatalytic conversion of distributed sources of single carbon gases such as carbon monoxide into hydrocarbons can be highly beneficial for developing commercially viable biotechnology applications in alternative energy. Several anaerobic bacterial strains can be used for such conversion. The anaerobic carbon monoxide-fixing bacteria Clostridium ljungdahlii OTA1 is a model CO assimilating microorganism that currently requires cryogenic temperature for storage of the viable strains. If these organisms can be stabilized and concentrated in thin films in advanced porous materials, it will enable development of high gas fraction, biocomposite absorbers with elevated carbon monoxide (CO) mass transfer rate, that require minimal power input and liquid, and demonstrate elevated substrate consumption rate compared to conventional suspended cell bioreactors. We report development of a technique for dry-stabilization of C. ljungdahlii OTA1 on a paper biocomposite. Bacterial samples coated onto paper were desiccated in the presence of trehalose using convective drying and stored at 4°C. Optimal dryness was ~1g H₂O per gram of dry weight (g_DW). CO uptake directly following biocomposite rehydration steadily increases over time indicating immediate cellular metabolic recovery. A high-resolution Raman microspectroscopic hyperspectral imaging technique was employed to spatially quantify the residual moisture content. We have demonstrated for the first time that convectively dried and stored C. ljungdahlii strains were stabilized in a desiccated state for over 38 days without a loss in CO absorbing reactivity. The Raman hyperspectral imaging technique described here is a non-invasive characterization tool to support development of dry-stabilization techniques for microorganisms on inexpensive porous support materials. The present study successfully extends and implements the principles of dry-stabilization for preservation of strictly anaerobic bacteria as an alternative to lyophilization or spray drying that could enable centralized biocomposite biocatalyst fabrication and decentralized bioprocessing of CO to liquid fuels or chemicals.

Stabilization of freeze-dried Lactobacillus paracasei subsp. paracasei JCM 8130T with the addition of disaccharides, polymers, and their mixtures

Although freeze-drying is a widely used dehydration technique for the stabilizing of unstable lactic acid bacteria, Lactobacillus paracasei subsp. paracasei JCM 8130^T (L. paracasei) is destabilized after freeze-drying and subsequent storage. In order to improve the stability of freeze-dried L. paracasei, effects of disaccharides (sucrose and trehalose), polymers (maltodextrin; MD and bovine serum albumin; BSA), and their mixtures on the survival rate of freeze-dried L. paracasei were investigated. The survival rate of non-additive sample decreased slightly after freeze-drying but decreased drastically after subsequent storage at 37 °C for 4 weeks. The reduction was diminished by the addition of disaccharides and polymers. The stabilizing effect of disaccharides was not affected by the co-addition of MD. In contrast, the disaccharide-BSA mixtures had a synergistic stabilizing effect, and the survival rates were largely maintained even after storage. It is suggested that the synergistic effect originates from the conformational stabilization of the dehydrated bacteria.

Genetic Selection of Peptide Aptamers That Interact and Inhibit Both Small Protein B and Alternative Ribosome-Rescue Factor A of Aeromonas veronii C4

Aeromonas veronii is a pathogenic gram-negative bacterium, which infects a variety of animals and results in mass mortality. The stalled-ribosome rescues are reported to ensure viability and virulence under stress conditions, of which primarily include trans-translation and alternative ribosome-rescue factor A (ArfA) in A. veronii. For identification of specific peptides that interact and inhibit the stalled-ribosome rescues, peptide aptamer library (pTRG-SN-peptides) was constructed using pTRG as vector and Staphylococcus aureus nuclease (SN) as scaffold protein, in which 16 random amino acids were introduced to form an exposed surface loop. In the meantime both Small Protein B (SmpB) which acts as one of the key components in trans-translation, and ArfA were inserted to pBT to constitute pBT-SmpB and pBT-ArfA, respectively. The peptide aptamer PA-2 was selected from pTRG-SN-peptides by bacterial two-hybrid system (B2H) employing pBT-SmpB or pBT-ArfA as baits. The conserved sites G₁₃₃K₁₃₄ and D₁₃₈K₁₃₉R₁₄₀ of C-terminal SmpB were identified by interacting with N-terminal SN, and concurrently the residue K₆₂ of ArfA was recognized by interacting with the surface loop of the specific peptide aptamer PA-2. The expression plasmids pN-SN or pN-PA-2, which combined the duplication origin of pRE112 with the neokanamycin promoter expressing SN or PA-2, were created and transformed into A. veronii C4, separately. The engineered A. veronii C4 which endowing SN or PA-2 expression impaired growth capabilities under stress conditions including temperatures, sucrose, glucose, potassium chloride (KCl) and antibiotics, and the stress-related genes rpoS and nhaP were down-regulated significantly by Quantitative Real-time PCR (qRT-PCR) when treating in 2.0% KCl. Thus, the engineered A. veronii C4 conferring PA-2 expression might be potentially attenuated vaccine, and also the peptide aptamer PA-2 could develop as anti-microbial drugs targeted to the ribosome rescued factors in A. veronii.

Improved viability of Lactobacillus acidophilus NRRL-B 4495 during freeze-drying in whey protein-pullulan microcapsules

In this research, pullulan was incorporated in protein-based encapsulation matrix in order to assess its cryoprotective effect on the viability of freeze-dried (FD) probiotic Lactobacillus acidophilus NRRL-B 4495. This study demonstrated that pullulan in encapsulation matrix resulted in a 90.4% survival rate as compared to 88.1% for whey protein (WPI) encapsulated cells. The protective effects of pullulan on the survival of FD-encapsulated cells in gastrointestinal conditions were compared. FD WPI-pullulan capsules retained higher survived cell numbers (7.10 log CFU/g) than those of FD WPI capsules (6.03 log CFU/g) after simulated gastric juice exposure. Additionally, use of pullulan resulted in an increased viability after bile exposure. FD-free bacteria exhibited 2.18 log CFU/g reduction, while FD WPI and FD WPI-pullulan encapsulated bacteria showed 0.95 and 0.49 log CFU/g reduction after 24 h exposure to bile solution, respectively. Morphology of the FD microcapsules was visualized by scanning electron microscopy.

Effect of different calcium salts and methods for triggering gelation on the characteristics of microencapsulated Lactobacillus plantarum LIP-1

Probiotic Lactobacillus plantarum isolate LIP-1 was microencapsulated in milk protein matrices by means of rennet-induced gelation combined with an emulsification technique.

Eruca sativa might influence the growth, survival under simulated gastrointestinal conditions and some biological features of Lactobacillus acidophilus, Lactobacillus plantarum and Lactobacillus rhamnosus strains

The growth and viability of three Lactobacillus strains, Lactobacillus acidophilus, Lactobacillus plantarum and Lactobacillus rhamnosus, after their passage through simulated gastric and pancreatic juices were studied as a function of their presence in the growth medium of rocket salad (Eruca sativa). The presence of E. sativa affected some of the biological properties of the strains. For example, L. acidophilus and L. plantarum worked more efficiently in the presence of E. sativa, increasing not only the antioxidant activity of the medium, but also their own antioxidant power and antimicrobial activity; L. rhamnosus was not affected in the same manner. Overall, the presence of vegetables might help to boost, in specific cases, some of the characteristics of lactobacilli, including antioxidant and antimicrobial power.

Ability of synbiotic encapsulated Saccharomyces cerevisiae boulardii to grow in berry juice and to survive under simulated gastrointestinal conditions

The probiotic yeast, Saccharomyces cerevisiae boulardii, was microencapsulated in a mixture of alginate-inulin-xanthan gum, and its ability to grow in berry juice and survive 4 weeks of storage at 4 °C was determined. Exposure of the yeast in these forms to artificial gastrointestinal conditions was also assessed. Encapsulation significantly enhanced cell viability after fermentation and storage compared with the free yeast (7.59 log10 colony forming units/ml versus 6.98 log10 colony forming units/ml, respectively) and protected it from exposure to a simulated gastrointestinal transit after 4 weeks of storage. Conversely, a dramatic loss of viability was exhibited by free yeast after 4 weeks of storage, and viability values closer to zero (0.23 log10 cfu/ml) were found after the simulated gastrointestinal treatment. Microcapsules were capable of absorbing a certain amount of polyphenols and anthocyanins. This work, based on use of microencapsulated probiotic yeasts, might represent the starting point for the development of new functional foods or functional ingredients. Microcapsules were capable to absorb, from berry juice, a certain amount of anthocyanins which, maintaining their native form after the in vitro gastrointestinal transit, might in vivo therein be transformed into other, simpler molecules, with beneficial effect on microflora and human health too.