Effect of freeze drying and protectants on viability of the biocontrol yeast Candida sake

Optimization of cryoprotectant formulation to enhance the viability of Lactiplantibacillus plantarum NBC99 isolated from human origin

Freeze drying has been well applied in the preparation of high-efficiency viability probiotic powders. However, the process is generally accompanied by probiotic viability deficiency, which poses a problem for further application. In this study, various kinds of cryoprotectant formulations (skim milk, maltodextrin, and sucrose) were tested to enhance the survival of Lactiplantibacillus plantarum NBC99 after freezing and freeze-drying. An I-optimal experimental design-oriented optimization model was presented to optimize the cryoprotective medium, and the highest cell survival was observed with 25% skim milk, 8.71% maltodextrin, and 1.13% sucrose cryoprotectant as the optimum condition. L. plantarum NBC99 has been a good potential strain for the manufacture of an industrial probiotic, and this research has aimed to investigate the long-term protective effects of optimum cryoprotectant formulations on the viability of bacteria. The results showed the potential value of freeze-dried probiotic L. plantarum NBC99 culture for commercialization.

The Effect of Lactiplantibacillus plantarum x3-2b Bacterial Powder on the Physicochemical Quality and Biogenic Amines of Fermented Lamb Jerky

In this study, a protective agent was added to prepare a high-activity Lactiplantibacillus plantarum x3-2b bacterial powder as a fermentation agent and explore its effect on the physicochemical quality, biogenic amines, and flavor of fermented lamb jerky. A composite protective agent, composed of 15% skim milk powder and 10% trehalose, was used, and bacterial mud was mixed with the protective agent at a 1:1.2 mass ratio. The resulting freeze-dried bacterial powder achieved a viable count of 5.1 lg CFU/g with a lyophilization survival rate of 87.58%. Scanning electron microscopy revealed enhanced cell coverage by the composite protective agent, maintaining the cell membrane's integrity. Inoculation with x3-2b bacterial powder increased the pH and the reduction in aw, enhanced the appearance and texture of fermented lamb jerky, increased the variety and quantity of flavor compounds, and reduced the accumulation of biogenic amines (phenethylamine, histamine, and putrescine). This research provides a theoretical basis for improving and regulating the quality of lamb jerky and establishes a foundation for the development of bacterial powder for the commercial fermentation of meat products.

CodY: An Essential Transcriptional Regulator Involved in Environmental Stress Tolerance in Foodborne Staphylococcus aureus RMSA24

Staphylococcus aureus (S. aureus), as the main pathogen in milk and dairy products, usually causes intoxication with vomiting and various kinds of inflammation after entering the human body. CodY, an important transcriptional regulator in S. aureus, plays an important role in regulating metabolism, growth, and virulence. However, little is known about the role of CodY on environmental stress tolerance. In this research, we revealed the role of CodY in environmental stress tolerance in foodborne S. aureus RMSA24. codY mutation significantly reduced the tolerance of S. aureus to desiccation and oxidative, salt, and high-temperature stresses. However, S. aureus was more tolerant to low temperature stress due to mutation of codY. We found that the expressions of two important heat shock proteins-GroEL and DanJ-were significantly down-regulated in the mutant codY. This suggests that CodY may indirectly regulate the high- and low-temperature tolerance of S. aureus by regulating the expressions of groEL and danJ. This study reveals a new mechanism of environmental stress tolerance in S. aureus and provides new insights into controlling the contamination and harm caused by S. aureus in the food industry.

Assessment of drying conditions for storage of a yeast-based decolorization solution for application in textile industrial wastewater treatment plants

The textile industry produces harmful effluents that are discharged into the environment, damaging the aquatic and other ecosystems. A yeast-based solution for decolorization of textile industrial wastewater was produced and evaluated. Three yeast strains, Candida parapsilosis (HOMOGS20B), Yarrowia lipolytica (HOMOGST27AB) and Candida pseudoglaebosa (LIIIS36B), isolated from a textile wastewater treatment plant and previously selected for their dye decolorization capacity, were freeze-dried. Additionally, Yarrowia lipolytica (HOMOGST27AB) was also spray-dried. Skim milk powder and maltodextrin were used as cell protectors, and the freeze-dried products were stored at cold (4 °C) and room temperature for 210 days. The viability of the yeast cells and their decolorization capacity over time were assessed. Dried yeast cells maintained their viability, and decolorization capacity for at least 90 days of storage after spray- and freeze-drying with both cell-protecting agents. The dried yeast-based solution for decolorizing textile industrial wastewater combines stability, efficiency, and convenience of production for application in real industrial facilities.

Selection of Autochthonous Yeasts Isolated from the Intestinal Tracts of Cobia Fish (Rachycentron canadum) with Probiotic Potential

Some yeast strains have been proposed as probiotics to improve the health of cultured fish. Cobia is a tropical benthopelagic fish species with potential for marine aquaculture; however, one of the main limitations to its large-scale production is the high mortality of fish larvae. In this study, we evaluated the probiotic potential of autochthonous yeasts from the intestines of cobia. Thirty-nine yeast isolates were recovered from the intestinal mucosa of 37 adult healthy cobia by culture methods. Yeasts were identified by sequencing of the ITS and D1/D2 regions of the 28S rRNA gene and typed by RAPD-PCR using the M13 primer. Yeast strains with unique RAPD patterns were characterized in terms of their cell biomass production ability; anti-Vibrio, enzymatic, and hemolytic activity; biofilm production; hydrophobicity; autoaggregation; polyamine production; safety; and protection of cobia larvae against saline stress. Candida haemuloni C27 and Debaryomyces hansenii C10 and C28 were selected as potential probiotics. They did not affect the survival of larvae and showed biomass production >1 g L^-1, hydrophobicity >41.47%, hemolytic activity γ, and activity in more than 8 hydrolytic enzymes. The results suggest that the selected yeast strains could be considered as potential probiotic candidates and should be evaluated in cobia larvae.

Selection of Yarrowia lipolytica Strains as Possible Solution to Valorize Untreated Cheese Whey

Cheese whey management and disposal is a major issue for dairy industries due to its high level of chemical and biochemical oxygen demand. However, it can still represent a source of nutrients (i.e., sugars, proteins and lipids) that can be applied, among other options, as substrate for microbial growth. Yarrowia lipolytica can grow in different environments, consuming both hydrophilic and hydrophobic substrates, and tolerates high salt concentrations. In this work, the lipolytic and proteolytic profile of 20 strains of Y. lipolytica were tested on caseins and butter. Then, their growth potential was evaluated in four types of whey (caciotta, ricotta, squacquerone and their mix). Y. lipolytica showed a very strain-dependent behavior for both hydrolytic profiles and growth capabilities on the different substrates. The best growers for all the types of whey tested were PO1, PO2, and RO2, with the first one reaching up to 8.77 log cfu/mL in caciotta whey after 72 h. The volatile molecule profile of the samples incubated with the best growers were characterized by higher amounts of esters, acids, ketones and alcohols. In this way, cheese whey can become a source of microbial cultures exploitable in the dairy sector.

Enhancing cell resistance for production of mixed microbiological reference materials with Salmonella and coliforms by freeze-drying

The reference material (RM) is a technical requirement for the quality assurance of analytical results and proficiency tests or interlaboratory comparisons. Microbiological RMs are most available in the dehydrated form, mainly by freeze-drying, and maintaining bacterial survival after preparation is a challenge. Thus, obtaining the most resistant cells is essential. Considering that bacteria present cross-response to dehydration after being submitted to an array of stress conditions, this study aimed to evaluate the influence of growth conditions on enterobacteria for the production of mixed microbiological RMs by freeze-drying in skim milk powder. Salmonella enterica serovar Enteritidis, Cronobacter sakazakii, Escherichia coli, and Citrobacter freundii were grown in a minimal medium with 0.5 M NaCl and 0 to 5.0 mM of manganese sulfate (MnSO4) until stationary phase. Salmonella Enteritidis presented an increased resistance to dehydration in the presence of Mn, while C. sakazakii was the most resistant to freeze-drying and further storage for 90 days. Mixed microbiological RMs were produced by freeze-drying and containing Salmonella Enteritidis and coliforms in skim milk powder with 100 mM of trehalose and the Salmonella survival rate was 91.2 to 93.6%. The mixed RM was stable after 30 days at -20 °C, and Salmonella and coliforms were detected by different methods being, the Rambach Agar the best for the bacterial differentiation. The results showed that the culture conditions applied in this study resulted in bacterial cells being more resistant to dehydration, freeze-drying, and stabilization for the production of mixed microbiological RMs more stable and homogeneous.

Insight into a Successful Development of Biocontrol Agents: Production, Formulation, Packaging, and Shelf Life as Key Aspects

Biocontrol agents (BCAs) have been proposed and studied over recent decades as a suitable alternative to diminish or substitute synthetic fungicides used to control pre- and postharvest diseases. However, the development of BCAs has many constraints and obstacles that would have to be overcome before they could be successfully implemented in the market. For the BCA commercial development, the microorganism should be mass-produced on a large-scale, and, independently of the method used for the production, a particular plan regarding the formulation of BCAs by multidisciplinary approaches (liquid or solid) is required to optimize the yield, efficacy, and shelf life of the developed product. Unfortunately, not all BCAs can survive the conditions imposed during the formulation process. Improved stability can be achieved by either using special conditions during growing or by adding protective substances to the formulation medium. Finally, BCAs should be formulated in such a way as to guarantee long-term stability and ease of application of the product. Therefore, an accurate range of the packaging conditions should be considered to extend the shelf life of the formulated product, preferably up to two years. Herein, we discussed the main aspects regarding the production, formulation, packaging, and shelf life of BCAs.

Impact of the Inoculation Method of Geotrichum candidum, Used as Biocontrol Agent, on T-2 Toxin Produced by Fusarium sporotrichioides and F. langsethiae during the Malting Process

In malt production, steeping and germination steps offer favorable environmental conditions for fungal proliferation when barley is already contaminated by Fusarium species, T-2 toxin producers. However, the use of G. candidum as a biocontrol agent can prevent this proliferation. Indeed, in previous work, a correlation between phenyllactic acid (PLA) production by G. candidum and the reduction in Fusarium sporotrichioides and F. langsethiae growth and T-2 toxin concentration was demonstrated. In the present study, to improve the efficiency of G. candidum, the effects of the inoculum concentration and the inoculation method of G. candidum on PLA and T-2 toxin concentrations were evaluated. First, co-culture experiments with Fusarium species and G. candidum were conducted in a liquid synthetic medium. The results showed that inoculation of G. candidum in the freeze-dried form at 0.4 g/L allowed the production of PLA from the second day of incubation associated with a reduction in T-2 toxin concentration of 82% and 69% produced by F. sporotrichioides and F. langsethiae, respectively. Moreover, the activated form of G. candidum at 0.4 g/L enhanced PLA concentration leading to better T-2 toxin reduction. Second, experiments were conducted on artificially infected barley kernels with both Fusarium species under conditions mimicking the malting step. As for co-culture experiments, the use of the activated form of G. candidum was established as the best condition for T-2 toxin concentration reduction for a 3 day malting period.

Optimization of compatible solutes for improving survival of freeze-dried Lactobacillus delbrueckii subsp. bulgaricus using Box-Behnken design

Lactobacillus delbrueckii subsp. bulgaricus is widely used in yogurt as a starter. The freeze-drying process may cause bacteria death. In the present work, the effect of three solutes (NaCl, sorbitol, and sodium glutamate) in MRS on viability of L.bulgaricus during freeze-drying was investigated. The optimal combination of adequate solutes was chosen by Box-Behnken Design. The survival rate and viable counts in freeze-dried powder, as well as the viable counts in broth, were used as responses. The results revealed that the optimum combination of solutes in MRS broth were 0.50% NaCl, 0.19% sorbitol, and 0.06% sodium glutamate. Under these optimal conditions, the survival rate was 53.2±0.14%, the viable counts in freeze-dried powder was 8.51±0.23×1010 CFU/g, and the viable counts in broth was 6.05±0.19 ×108 CFU/mL, which were increased by 17.18%, 15.94%, and 17.31%, respectively, compared to the control. This research demonstrated the possibility of viability improvement of L.bulgaricus, which may provide a feasible reference for industrial development.

Effect of two preservation methods on the viability and enzyme production of a recombinant Komagataella phaffii (Pichia pastoris) strain

The methylotrophic yeast Komagataella phaffii, previously known as Pichia pastoris, has been reported as a host for producing human recombinant lysosomal enzymes intended for enzyme replacement therapy. K. phaffii has advantages such as easy genetic handling, rapid growth, cost-effective mediums, and the ability to develop mammalian-like post-translational modifications. To maintain cell viability and enzyme activity over time, it is important to consider the bioprocess optimization and the proper selection and preservation of clones. In this study, we evaluated the effect of glycerol and skim milk in cryopreservation at -80 °C, as well as the use of skim milk or its combination with NaCl, disaccharides or sorbitol in freeze-drying on the cell viability and activity of a recombinant lysosomal enzyme (i.e., human β-hexosaminidase-A) produced in K. phaffii GS115 strain. The results showed that cryopreservation with glycerol and skim milk, as well as freeze-drying using disaccharides and sorbitol with skim milk, maintained the viability above 80%. Although variations in enzyme activity among treatments were found, the use of disaccharides had a positive effect on the enzymatic activity levels. This is the first report of the evaluation of two suitable methods to preserve a recombinant K. phaffii strain, preventing the loss of viability and maintaining the activity of the recombinant protein.

Comparison of the Fermentation Activities and Volatile Flavor Profiles of Chinese Rice Wine Fermented Using an Artificial Starter, a Traditional JIUYAO and a Commercial Starter

In this study, an artificial starter culture was prepared using the core microbial species of JIUYAO to produce Chinese rice wine (CRW). The fermentation activity and flavor profiles of CRW samples fermented with traditional JIUYAO, a commercial starter culture, and our artificial starter culture were compared. The optimal protectant combination for lyophilization of the artificial starter was established as 15.09% skim milk, 4.45% polyethylene glycol, 1.96% sodium glutamate, and 11.81% maltodextrin. A comparative analysis revealed that the ethanol content of the three CRW samples was similar. The total acid content of the CRW sample fermented with the artificial starter (7.10 g/L) was close to that of the sample fermented with JIUYAO (7.35 g/L), but higher than that of the sample fermented with the commercial starter (5.40 g/L). An electronic nose analysis revealed that the olfactory fingerprints of the CRW samples fermented with JIUYAO and the artificial starter resembled each other. For both above mentioned samples, the flavor profiles determined by gas chromatography–mass spectrometry indicated some differences in the variety and content of the aroma compounds, but the key odorants (odor activity values ≥1), such as isoamyl acetate, ethyl acetate, phenyl alcohol, and isoamyl alcohol, were similar.

Sodium glutamate as a booster: Inducing Rhodosporidium paludigenum to enhance the inhibition of Penicillium expansum on pears

AIMS

This research sought to improve the ability of biocontrol yeast to suppress postharvest fungal disease and explore possible mechanisms of action.

METHODS AND RESULTS

The addition of 2% sodium glutamate (SG), which is edible and recognized as safe, enhances the inhibitory effect of Rhodosporidium paludigenum Fell & Tallman on Penicillium expansum in vivo and in vitro. Rhodosporidium paludigenum cells grown in medium with a final concentration of 2% SG, displayed viability under a variety of stress conditions, including sodium chloride (NaCl), calcofluor white (CFW), Congo red (CR) and sodium dodecyl sulphate (SDS). Activity and relative gene expression levels of antioxidant-related enzymes in R. paludigenum, including peroxisomal catalase (CAT), thioredoxin reductase (TrxR), glutathione peroxidase (GSH-PX), glutathione reductase (GR) and superoxide dismutase (SOD) were altered in the presence of SG. Levels of reactive oxygen species (ROS) increased in cells grown in the presence of SG as well as the content of several amino acids.

CONCLUSIONS

In the presence of 2% SG R. paludigenum inhibited P. expansum and exhibited tolerance to a number of stressful conditions which may involve the upregulation of antioxidant enzymes and amino acids.

SIGNIFICANCE AND IMPACT OF THE STUDY

The ability of culture conditions to enhance the fungal suppressive abilities of yeast has the potential to enhance the management of postharvest disease in fruit.

Preservation of non-Saccharomyces yeasts: Current technologies and challenges

There is a recent and growing interest in the study and application of non-Saccharomyces yeasts, mainly in fermented foods. Numerous publications and patents show the importance of these yeasts. However, a fundamental issue in studying and applying them is to ensure an appropriate preservation scheme that allows to the non-Saccharomyces yeasts conserve their characteristics and fermentative capabilities by long periods of time. The main objective of this review is to present and analyze the techniques available to preserve these yeasts (by conventional and non-conventional methods), in small or large quantities for laboratory or industrial applications, respectively. Wine fermentation is one of the few industrial applications of non-Saccharomyces yeasts, but the preservation stage has been a major obstacle to achieve a wider application of these yeasts. This review considers the preservation techniques, and clearly defines parameters such as culturability, viability, vitality and robustness. Several conservation strategies published in research articles as well as patents are analyzed, and the advantages and disadvantages of each technique used are discussed. Another important issue during conservation processes is the stress to which yeasts are subjected at the time of preservation (mainly oxidative stress). There is little published information on the subject for non-Saccharomyces yeast, but it is a fundamental point to consider when designing a preservation strategy.

Studies on the Catalytic Properties of Crude Freeze-Dried Preparations of Yarrowia lipolytica Extracellular Lipases for Geranyl Ester Derivative Synthesis

The study aimed to evaluate the impact of selected factors of the freeze-drying process on the hydrolytic and synthetic activity of the extracellular lipases of Y. lipolytica KKP 379 and to attempt the use of the crude enzyme preparation as a biocatalyst in the synthesis of geranyl 4-hydroxyphenylpropanoate. Antioxidant and antibacterial properties of the geranyl ester derivative were also investigated in order to evaluate their usefulness as a novel food additive. The studies confirmed that freeze-drying was an effective method of dehydrating yeast supernatant and allowed for obtaining lyophilizates with low water activity from 0.055 to 0.160. The type and concentration of the additive (2-6% whey protein hydrolyzate, 0.5% and 1% ammonium sulphate) had a significant effect on the hydrolytic activity of enzyme preparations, while the selected variants of drying temperature during the freeze-drying process were not significant (10 °C and 50 °C). Low yield of geranyl 4-hydroxyphenylopropionate was shown when the lyophilized supernatant was used (5.3%), but the yield of ester synthesis increased when the freeze-dried Y. lipolytica yeast biomass was applied (47.9%). The study confirmed the antioxidant properties of the synthesized ester by the DPPH• and CUPRAC methods, as well as higher antibacterial activity against tested bacteria than its precursor with 0.125 mM MIC (minimal inhibitory concentration) against L. monocytogenes.

Current Approaches of Preservation of Cells During (freeze-) Drying

The widespread application of therapeutic cells requires a successful stabilization of cells for the duration of transport and storage. Cryopreservation is currently considered the gold standard for the storage of active cells; however, (freeze-) drying cells could enable higher shelf life stability at ambient temperatures and facilitate easier transport and storage. During (freeze-) drying, freezing, (primary and secondary) drying and also the reconstitution step pose the risk of potential cell damage. To prevent these damaging processes, a wide range of protecting excipients has emerged, which can be classified, according to their chemical affiliation, into sugars, macromolecules, polyols, antioxidants and chelating agents. As many excipients cannot easily permeate the cell membrane, researchers have established various techniques to introduce especially trehalose intracellularly, prior to drying. This review aims to summarize the main damaging mechanisms during (freeze-) drying and to introduce the most common excipients with further details on their stabilizing properties and process approaches for the intracellular loading of excipients. Additionally, we would like to briefly explain recently discovered advantages of drying microorganisms, sperm, platelets, red blood cells, and eukaryotic cells, paying particular attention to the drying technique and residual moisture content.

Combinatorial Effects of Protective Agents on Survival Rate of the Yeast Starter, Saccharomyces cerevisiae 88-4, after Freeze-Drying

A yeast starter is formulated for commercial practices, including storage and distribution. The cell viability of the yeast starter is one of the most important factors for manufacturing alcoholic beverages to ensure their properties during the fermentation and formulation processes. In this study, 64 potential protective agents were evaluated to enhance the survival rate of the brewing yeast Saccharomyces cerevisiae 88-4 after freeze-drying. In addition, the optimized combination of protective agents was assessed for long-term storage. Finally, response surface methodology was applied to investigate the optimal concentration of each protectant. Twenty of the 64 additives led to an increase in the survival rate of freeze-dried S. cerevisiae 88-4. Among the various combinations of protectants, four had a survival rate >95%. The combination of skim milk, maltose, and maltitol exhibited the best survival rate of 61% after 42 weeks in refrigerated storage, and the composition of protectants optimized by response surface methodology was 6.5–10% skim milk, 1.8–4.5% maltose, and 16.5–18.2% maltitol. These results demonstrated that the combination of multiple protectants could alleviate damage to yeasts during freeze-drying and could be applied to the manufacturing starters for fermented foods.

Impact of a Novel Nano-Protectant on the Viability of Probiotic Bacterium Lactobacillus casei K17

Probiotics are considered as desirable alternatives to antibiotics because of their beneficial effects on the safety and economy of farm animals. The protectant can ensure the viability of probiotics, which is the prerequisite of the beneficial effects. The objective of this study was to evaluate the effects of a novel nano-protectant containing trehalose, skim milk powder, phytoglycogen nanoparticles, and nano-phytoglycogen Pickering emulsions on the viability of Lactobacillus casei K17 under different conditions. The results indicated that the optimal concentration of the carbohydrate substrate was determined to be 10% skim milk powder (w/w) instead of trehalose. The combination of 10% skim milk powder (w/w), 1% phytoglycogen nanoparticles (w/w), and 10% Pickering emulsions (w/w) was selected as the optimal component of the protectant. Trilayer protectants with an optimal component had a more significant protective effect on the bacteria than that of the monolayer and bilayer protectants, or the control in feed storage, freeze-drying, and simulated gastrointestinal environment. A scanning electron microscope was used to monitor the morphological characteristics of the protectants for different layers on L. casei. In conclusion, the trilayer protectant exhibited a substantial effect on L. casei during storage and consumption, which could be used in the feed and functional food.

High engraftment capacity of frozen ready-to-use human fecal microbiota transplants assessed in germ-free mice

The number of indications for fecal microbiota transplantation is expected to rise, thus increasing the needs for production of readily available frozen or freeze-dried transplants. Using shotgun metagenomics, we investigated the capacity of two novel human fecal microbiota transplants prepared in maltodextrin-trehalose solutions (abbreviated MD and TR for maltodextrin:trehalose, 3:1, w/w, and trehalose:maltodextrin 3:1, w/w, respectively), to colonize a germ-free born mouse model. Gavage with frozen-thawed MD or TR suspensions gave the taxonomic profiles of mouse feces that best resembled those obtained with the fresh inoculum (Spearman correlations based on relative abundances of metagenomic species around 0.80 and 0.75 for MD and TR respectively), while engraftment capacity of defrosted NaCl transplants most diverged (Spearman correlations around 0.63). Engraftment of members of the family Lachnospiraceae and Ruminoccocaceae was the most challenging in all groups of mice, being improved with MD and TR transplants compared to NaCl, but still lower than with the fresh preparation. Improvement of engraftment of this important group in maintaining health represents a challenge that could benefit from further research on fecal microbiota transplant manufacturing.

Genotypic and Phenotypic Stability of Mixed Primary Isolates of Cryptococcus gattii and Cryptococcus neoformans: A Comparative Analysis of Four Preservation Methods

The choice of a suitable preservation method is critical for long-term microorganisms' viability. The strains should be preserved for long periods using reliable and reproducible methods that minimize genotypic and phenotypic variations and viability losses. The methodologies are usually designed for a better performance in isolated microorganisms. However, atypical primary isolates of Cryptococcus neoformans or Cryptococcus gattii, such as mixed species or even different species of a species complex, are a challenge for long-term preservation and taxonomic review studies. The aim of this study was to evaluate which of the four preservation methods tested presented better performance in the preservation of simulated coexistence strains of C. neoformans and C. gattii. Two environmental strains, one C. gattii and one C. neoformans, were mixed in vitro to test four different preservation methods (freezing at -20°C, -80°C, -196°C, and freeze-drying). The colony-forming units from each preservation method were evaluated, and colonies were randomly selected and cultivated in canavanine glycine bromothymol blue (CGB) agar to evaluate the amounts of CGB-positive (C. gattii) and CGB-negative (C. neoformans) colonies resulting from each preservation method after 1 week, 15 days, 1 month, 6 months, and 1 year. According to our results, cryopreservation at -20°C demonstrated was preferable for C. neoformans species, and further studies after long-term storage are necessary. Recovery of yeast cells after freeze-dried preservation in skim milk is better for both species. Ultrafreezing methods evaluated (-80°C and -196°C) also showed better results in the maintenance of C. gattii. Freeze-drying should be preferred for the maintenance of multilineage isolates from the C. neoformans and C. gattii species complexes.

A new protectant medium preserving bacterial viability after freeze drying

Freeze-drying technology has been widely considered for decades as a suitable technique to preserve microorganisms. However, protective agents must be added prior to freeze drying to improve the survival and storage stability of the bacteria. The objective of our study was to evaluate the effect of a new protectant medium containing sucrose (10 %), trehalose (10 %), skimmed milk (10 %) and antioxidants on the viability of gut bacteria under different storage conditions. Two strains were tested, Escherichia coli and Akkermansia muciniphila, as examples of facultative aerobic and anaerobic bacteria, respectively. We studied the cell viability and bacterial morphology in 5 fecal samples in the presence and absence of this protectant medium using plating technique, flow cytometry and scanning electron microscopy. The results of bacterial viability assessed by plating method showed that the protectant medium yielded higher survival rates for both strains whatever the storage conditions (85-93 %) compared to normal saline solution (0.36-37.50 %). It also showed its effectiveness on fecal samples, where bacterial viability after freeze-drying was 89.47 ± 7.63 % and 84.01 ± 7.44 %, as evidenced by flow cytometry analysis and plating method. However unprotected samples showed the lowest cell viability at 19.01 ± 12.88 % and 13.23 ± 9.56 %, as measured by flow cytometry and plating method. In addition, bacterial size and shape were conserved in the protectant medium. In contrast, storage without protectant medium severely damaged bacterial morphology. In conclusion, our study is the first to use morphological features as well as culture-dependant and culture-independent tests to evaluate the effectiveness of a new protectant medium.

Along the Process Chain to Probiotic Tablets: Evaluation of Mechanical Impacts on Microbial Viability

Today, probiotics are predominantly used in liquid or semi-solid functionalized foods, showing a rapid loss of cell viability. Due to the increasing spread of antibiotic resistance, probiotics are promising in pharmaceutical development because of their antimicrobial effects. This increases the formulation requirements, e.g., the need for an enhanced shelf life that is achieved by drying, mainly by lyophilization. For oral administration, the process chain for production of tablets containing microorganisms is of high interest and, thus, was investigated in this study. Lyophilization as an initial process step showed low cell survival of only 12.8%. However, the addition of cryoprotectants enabled survival rates up to 42.9%. Subsequently, the dried cells were gently milled. This powder was tableted directly or after mixing with excipients microcrystalline cellulose, dicalcium phosphate or lactose. Survival rates during tableting varied between 1.4% and 24.1%, depending on the formulation and the applied compaction stress. More detailed analysis of the tablet properties showed advantages of excipients in respect of cell survival and tablet mechanical strength. Maximum overall survival rate along the complete manufacturing process was >5%, enabling doses of 6 × 108 colony forming units per gram (CFU gtotal−1), including cryoprotectants and excipients.

Biocontrol yeasts: mechanisms and applications

Yeasts occur in all environments and have been described as potent antagonists of various plant pathogens. Due to their antagonistic ability, undemanding cultivation requirements, and limited biosafety concerns, many of these unicellular fungi have been considered for biocontrol applications. Here, we review the fundamental research on the mechanisms (e.g., competition, enzyme secretion, toxin production, volatiles, mycoparasitism, induction of resistance) by which biocontrol yeasts exert their activity as plant protection agents. In a second part, we focus on five yeast species (Candida oleophila, Aureobasidium pullulans, Metschnikowia fructicola, Cryptococcus albidus, Saccharomyces cerevisiae) that are or have been registered for the application as biocontrol products. These examples demonstrate the potential of yeasts for commercial biocontrol usage, but this review also highlights the scarcity of fundamental studies on yeast biocontrol mechanisms and of registered yeast-based biocontrol products. Yeast biocontrol mechanisms thus represent a largely unexplored field of research and plentiful opportunities for the development of commercial, yeast-based applications for plant protection exist.

Survival of Spray-Dried Rhodotorula mucilaginosa Isolated from Natural Microbiota of Murta Berries and Antagonistic Effect on Botrytis cinerea

The aim of this study is to evaluate the survival rate and effective antagonistic activity against Botrytis cinerea, responsible for grey mould on harvested fruits and vegetables, of yeast Rhodotorula mucilaginosa, isolated and identified from the natural microbiota of murta (Chilean guava) berries, after spray drying at different inlet air temperatures, mass per volume ratio of encapsulating agent (maltodextrin) and feed flow rates. The 100% survival of the yeast was obtained after spray drying with 18% maltodextrin at 130 °C inlet temperature and a feed flow rate of 9.25 mL/min. The dried yeast obtained under such conditions had the highest antagonistic activity in vitro and in vivo on apples, which showed that spray drying is a valid method to produce active dried cells of R. mucilaginosa that can be used for biocontrol of grey mould spoilage. It was also found that the encapsulating agent maltodextrin improved the in vitro antagonistic activity of R. mucilaginosa.

Encapsulation of Lactobacillus plantarum ATCC 8014 and Pediococcus acidilactici ATCC 8042 in a freeze-dried alginate-gum arabic system and its in vitro testing under gastrointestinal conditions

The aim of this study was to investigate the viability of Pediococcus acidilactici ATCC 8042 and Lactobacillus plantarum ATCC 8014 in a freeze-dried capsules system prepared with sodium alginate and gum arabic using the extrusion technique. The capsules made with alginate 2% (w/v)/gum arabic 2% (w/v) showed higher hardness (7.12 ± 0.71 N), with highly cohesive (0.81 ± 0.02) and elastic (0.99 ± 0.00) features on the Texture Profile Analysis (TPA), as well as higher sphericity with 1.75 ± 0.12 mm y 1.73 ± 0.13 mm diameter axes and regularity in their surface by Scanning Electron Microscopy (SEM). The use of skimmed milk at 10% as a cryoprotector in the freeze-drying process allowed the obtention of high viability percentages (88% a 96%) for both strains. Best results of viability for P. acidilactici encapsulated was with the use of alginate 2% (w/v)/gum arabic 2% (w/v) (92%±2.65), and L. plantarum with the use of alginate 2% (w/v) (84.71%±10.33) during the gastrointestinal environment challenge.

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.

Comprehensive optimization of composite cryoprotectant for Saccharomyces boulardii during freeze-drying and evaluation of its storage stability

Saccharomyces boulardii (S. boulardii) is widely adopted in the diarrhea treatment for humans or livestock, so guaranteeing the survival rate of S. boulardii is the critical issue during freeze-drying process. In this study, the survival rate of S. boulardii with composite cryoprotectants during freeze-drying procedure and the subsequent storage were investigated. With the aid of response surface method, the composite cryoprotectants were comprehensively optimized to be lactose of 21.24%, trehalose of 22.00%, and sodium glutamate of 4.00%, contributing to the supreme survival rate of S. boulardii of 64.22 ± 1.35% with the viable cell number of 9.5 ± 0.07 × 10⁹ CFU/g, which was very close to the expected rate of 65.55% with a number of 9.6 × 10⁹ CFU/g. The accelerated storage test demonstrated that the inactivation rate constant of the freeze-dried S. boulardii powder was k_-18 = 8.04 × 10^-6. In addition, the freeze-dried goat milk powder results exhibited that the inactivation rate constants were k₄ = 4.48 × 10^-4 and k₂₅ = 9.72 × 10^-3 under 4 and 25 °C, respectively. This work provides a composite cryoprotectant formulation that has a good protective effect for the probiotic S. boulardii during freeze-drying process, possessing the potential application prospect in food, medicine, and even feed industry.

A Guide for Ex Vivo Handling and Storage of Stool Samples Intended for Fecal Microbiota Transplantation

Owing to the growing recognition of the gut microbiota as a main partner of human health, we are expecting that the number of indications for fecal microbiota transplantation (FMT) will increase. Thus, there is an urgent need for standardization of the entire process of fecal transplant production. This study provides a complete standardized procedure to prepare and store live and ready-to-use transplants that meet the standard requirements of good practices to applied use in pharmaceutical industry. We show that, if time before transformation to transplants would exceed 24 hours, fresh samples should not be exposed to temperatures above 20 °C, and refrigeration at 4 °C can be a safe solution. Oxygen-free atmosphere was not necessary and simply removing air above collected samples was sufficient to preserve viability. Transplants prepared in maltodextrin-trehalose solutions, stored in a -80 °C standard freezer and then rapidly thawed at 37 °C, retained the best revivification potential as  proven by 16S rRNA profiles, metabolomic fingerprints, and flow cytometry assays over a 3-month observation period. Maltodextrin-trehalose containing cryoprotectants were also efficient in preserving viability of lyophilized transplants, either in their crude or purified form, an option that can be attractive for fecal transplant biobanking and oral formulation.

Effect of the Freeze-Drying Process on the Physicochemical and Microbiological Properties of Mexican Kefir Grains

The purpose of this study was to investigate how the properties of Mexican kefir grains (MKG) are affected by the operating parameters used in the freeze-drying process. The factors investigated were the freezing time (3–9 h), freezing temperature (−20 to −80 °C), pressure (0.2–0.8 mbar), and lyophilization time (5–20 h). The maximum range of change and one-way analysis of variance showed that lyophilization time and freezing time significant affects (p < 0.05) the response variables, residual moisture content and water activity, and pressure had a significant effect on the color difference and survival rate of probiotic microorganisms. The best drying conditions were a freezing time of 3 h, a freezing temperature of −20 °C, a pressure of 0.6 mbar, and a lyophilization time of 15 h. Under these conditions, we obtained a product with residual moisture content below 6%, water activity below 0.2, and survival rates above 8.5 log cfu per gram of lactic acid bacteria and above 8.6 log for yeast.

Sugar Protectants Improve the Thermotolerance and Biocontrol Efficacy of the Biocontrol Yeast, Candida oleophila

A variety of sugar compounds have been used as additives to protect various biocontrol yeasts from adverse environmental stresses. However, studies on maltose and lactose as sugar protectants are limited, and their protective effect is not clear. In the present study, exposure of the biocontrol yeast Candida oleophila cells to 45°C for 10 min, while immersed in either 5 or 10% (w/v) maltose or lactose, provided a significant protective effect. The addition of maltose and lactose significantly enhanced enzyme activity and gene expression of catalase, thioredoxin reductase, and glutathione reductase, relative to cells that have been immersed in sterile distilled water (controls) exposed to 45°C. In addition, C. oleophila cells suspended in maltose and lactose solutions also exhibited higher viability and ATP levels, relative to control cells. Notably, the biocontrol efficacy of C. oleophila against postharvest diseases of apple fruit was maintained after the yeast was exposed to the high temperature treatment while immersed in maltose and lactose solutions. These results demonstrate the potential of maltose and lactose as sugar protectants for biocontrol agent against heat stress.

Isolation and Selection of Potential Probiotic Bacteria from the Pig Gastrointestinal Tract

The present study aimed to isolate bacterial strains from the pig gastrointestinal tract that have antagonistic activity against potential pathogens and are able to produce antimicrobial compounds. That ability would be a first requirement for the strains' possible use as probiotics. Samples obtained from pig intestinal mucosa and contents were screened for the presence of antagonistic activity against pathogenic indicator strains of Escherichia coli, Salmonella, and Listeria by means of the double-layer technique. Samples displaying the largest inhibitory halos were further studied for the production of inhibitory substances using the agar diffusion and microtitration methods. The three most promising isolates were identified by sequencing of the 16S rRNA gene and showed highest affiliation to Lactobacillus salivarius. Optimal growth conditions and bacteriocin production were recorded in de Man, Rogosa, and Sharpe broth under anaerobic conditions at 37 °C. The antimicrobial substances were found to be sensitive to proteolytic enzymes but showed good stability at pH values below 6. Our findings suggest that these three intestinal strains are able to produce antimicrobial substances capable of inhibiting the growth of potential enteric pathogens and might have potential as probiotic feed additives for the prevention of gastrointestinal diseases.

Effects of Carbohydrates, Prebiotics and Salts on Survival of Saccharomyces boulardii During Freeze-Drying

Saccharomyces boulardii, as a probiotic yeast, had been commonly used in food, medicine and feed to treat diarrhea in humans or livestock. However, there are few researches focusing on the preparation of its freeze-drying S.boulardii powder. In this study, the effect of carbohydrates (glucose, sucrose, maltose, fructose, lactose, mannose and trehalose), prebiotics (isomalto-oligosaccharide, xylo-oligosaccharide, raffinose, stachyose, inulin, galacto-oligosaccharide and fructo-oligosaccharide) and salts (NaHCO3, MgSO4, sodium glutamate, sodium ascorbate, and phosphate buffer) on the freeze-dried survival of S. boulardii were investigated to screen the cryoprotectant by using single factor experiments. As the result, trehalose and XOS had better protective effect, the survival rate was 23.72% and 20.70% respectively, the number of viable cells reached 0.91×1010 CFU/g and 0.85×1010 CFU/g respectively; the addition amount of NaHCO3 was 0.3%, the freeze-dried survival rate reached the maximum value of 12.92%. The phosphate buffer additive amount and the bacterial sludge weight were 0.8:1, the freeze-dried survival rate reached a maximum of 14.14%, the freeze-dried survival rate of sodium glutamate, sodium ascorbate and MgSO4 groups was increasing, reaching a maximum of 20.26%, 16.47% and 6.29% when the addition amount was 2%, 10%, 0.5%.

Effect of Cation Influx on the Viability of Freeze-Dried Lactobacillus brevis WiKim0069

Extension of the storage stability of freeze-dried lactic acid bacteria is important for industrialization. In this study, the effect of cation influx from soy powder, which contains high amounts of cations, as a cryoprotective agent on the viability of freeze-dried Lactobacillus brevis WiKim0069 was tested. Compared to that in the absence of the soy powder, bacterial viability was significantly higher in the presence of soy powder. Approximately 4.7% of L. brevis WiKim0069 survived in the absence of the protective agent, whereas 92.8% viability was observed in the presence of soy powder. However, when cations were removed from the soy powder by using ethylenediaminetetraacetic acid (EDTA) and a cationic resin filter, the viability of L. brevis WiKim0069 decreased to 22.9–24.7%. When the soy powder was treated with ethylene glycol tetraacetic acid, the viability was higher than when it was pretreated with EDTA and a cationic resin filter, suggesting that Mg2+ had a role in enhancing the viability of L. brevis WiKim0069. Cold adaptation at 10 °C prior to freeze-drying had a positive effect on the storage stability of freeze-dried L. brevis WiKim0069, with 60.6% viability after 56 days of storage. A decrease in the fluorescence polarization value indicated an increase in membrane fluidity, which regulates the activity of ion channels present in the cell membrane. Cold adaptation caused activation of the cation channels, resulting in increased intracellular influx of cations, i.e., Ca2+ and Mg2+. These results suggest that cold adaptation can be used to improve the storage stability of L. brevis WiKim0069.

Enhancement of viability, acid, and bile tolerance and accelerated stability in lyophilized Weissella cibaria JW15 with protective agents

Dietary supplementation with lactic acid bacteria to maintain or improve intestinal health is advocated. Weissella spp. are present in different fermented vegetable-based foods like kimchi, as well as in the normal gastrointestinal (GI) tract of humans. Weissella cibaria strains have been proposed as potential probiotics. Freeze-drying is a promising treatment method for these strains for industrial applications and to increase the accessibility of their health-promoting benefits. Moreover, probiotic strains need to be able to survive in the host GI tract, and acid and bile are both environmental stressors that can reduce strain survival. Therefore, this study evaluated the effect of the combination of protective agents on the acid and bile resistance of W. cibaria JW15 after freeze-drying. A protective agent combination with a 1:1 ratio of 5 g + 5 g/100 ml w/v soy flour + yeast extract (SFY) retained nearly 100% viability after freeze-drying and was resistant to artificial bile acids. Remarkably, skim milk + soy flour (SSF) was resistant to an acidic solution, and the viability of W. cibaria JW15 in artificial gastric acid was enhanced when treated with this mixture. Furthermore, SFY and SSF were found to maintain high numbers of viable cells with a low specific rate of cell death (k) after storage at 50°C, 60°C, and 70°C. These results support an effective probiotic formulation system with a high number of viable cells, and its protective effects can be leveraged in the development of probiotic products with health benefits.

Effect of cryopreservation and lyophilization on viability and growth of strict anaerobic human gut microbes

Strict anaerobic gut microbes have been suggested as ‘next‐generation probiotics’ for treating several intestinal disorders. The development of preservation techniques is of major importance for therapeutic application. This study investigated cryopreservation (−80°C) and lyophilization survival and storage stability (4°C for 3 months) of the strict anaerobic gut microbes Bacteroides thetaiotaomicron, Faecalibacterium prausnitzii, Roseburia intestinalis, Anaerostipes caccae, Eubacterium hallii and Blautia obeum. To improve preservation survival, protectants sucrose and inulin (both 5% w/v) were added for lyophilization and were also combined with glycerol (15% v/v) for cryopreservation. Bacterial fitness, evaluated by maximum growth rate and lag phase, viability and membrane integrity were determined using a standardized growth assay and by flow cytometry as markers for preservation resistance. Lyophilization was more detrimental to viability and fitness than cryopreservation, but led to better storage stability. Adding sucrose and inulin enhanced viability and the proportion of intact cells during lyophilization of all strains. Viability of protectant‐free B. thetaiotaomicron, A. caccae and F. prausnitzii was above 50% after cryopreservation and storage and increased to above 80% if protectants were present. The addition of glycerol, sucrose and inulin strongly enhanced the viability of B. obeum, E. hallii and R. intestinalis from 0.03–2% in protectant‐free cultures to 11–37%. This is the first study that quantitatively compared the effect of cryopreservation and lyophilization and the addition of selected protectants on viability and fitness of six strict anaerobic gut microbes. Our results suggest that efficiency of protectants is process‐ and species‐specific.

Improved stability of live attenuated vaccine gdhA derivative Pasteurella multocida B:2 by freeze drying method for use as animal vaccine

The efficacy of attenuated strain of gdhA derivative Pasteurella multocida B:2 mutant as a live vaccine to control haemorrhagic septicaemia (HS) disease in cattle and buffaloes has been demonstrated. In order to use P. multocida B:2 mutant as a commercial product, it is essential to optimise its formulation for high viability and stability of the live cells. The effectiveness of freeze-drying process using different protective agent formulations for improving cells viability was explored. Sugar and nitrogen compounds were used as protective agents in freeze-drying and the capability of these compounds in maintaining the viability of mutant P. multocida B:2 during subsequent storage was investigated. A complete loss in viability of freeze-dried mutant P. multocida B:2 was monthly observed until 6-12 months of storage at -30 °C, 4 °C and 27 °C when nitrogen compound or no protective agent was added. Trehalose and sucrose showed significantly high survival rate of 93-95% immediately after freeze-drying and the viability was retained during the subsequent storage at -30 °C and 4 °C. A smooth cell surface without any cell-wall damage was observed for the cells formulated with trehalose under scanning electron micrograph. This study presented a freeze-drying process generating a dried live attenuated vaccine formulation with high stability for commercial applications.

Freeze-drying of mammalian cells using trehalose: preservation of DNA integrity

The aim of this study was to investigate preservation of biomolecular structures, particularly DNA, in freeze-dried fibroblasts, after loading with trehalose via freezing-induced uptake. Cells were freeze-dried with trehalose alone or in a mixture of albumin and trehalose. Albumin was added to increase the glass transition temperature and storage stability. No viable cells were recovered after freeze-drying and rehydration. FTIR studies showed that membrane phase behavior of freeze-dried cells resembles that of fresh cells. However, one day after rehydration membrane phase separation was observed, irrespective of the presence or absence of trehalose during freeze-drying. Freeze-drying did not affect the overall protein secondary structure. Analysis of DNA damage via single cell gel electrophoresis (‘comet assay’) showed that DNA damage progressively increased with storage duration and temperature. DNA damage was prevented during storage at 4 °C. It is shown that trehalose reduces DNA damage during storage, whereas addition of albumin did not seem to have an additional protective effect on storage stability (i.e. DNA integrity) despite the fact that albumin increased the glass transition temperature. Taken together, DNA in freeze-dried somatic cells can be preserved using trehalose as protectant and storage at or below 4 °C.