Effect of carbohydrates on the survival of Lactobacillus helveticus during vacuum drying

The Effect of Decreased Ca++/Mg++ ATPase Activity on Lactobacillus delbrueckii subsp. bulgaricus sp1.1 Survival during Spray Drying

Compared with the commonly used technique of freeze-drying, spray drying has lower energy costs. However, spray drying also has a fatal disadvantage: a lower survival rate. In this study, the survival of bacteria in a spray-drying tower decreased as the water content was reduced. The water content of 21.10% was the critical point for spray drying Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) sp1.1 based on sampling in the tower. Based on the relationship between the moisture content of spray drying and the survival rate, the water content of 21.10% was also the critical point for the change in the survival rate during spray drying. Proteomic analysis was used to investigate the reasons for L. bulgaricus sp1.1 inactivation during and after spray drying. Gene Ontology (GO) enrichment revealed that differentially expressed proteins were mainly associated with the cell membrane and transport. In particular, proteins related to metal ion transport included those involved in the transport of potassium, calcium and magnesium ions. The protein-protein interaction (PPI) network revealed that Ca⁺⁺/Mg⁺⁺ adenosine triphosphatase (ATPase) may be a key protein. Ca⁺⁺/Mg⁺⁺ ATPase activity decreased substantially during spray drying (p < 0.05). Supplementation with Ca⁺⁺ and Mg⁺⁺ significantly increased the expression of ATPase-related genes and enzyme activity (p < 0.05). The Ca⁺⁺/Mg⁺⁺ ATPase activity of L. bulgaricus sp1.1 was enhanced by increasing the intracellular Ca⁺⁺ or Mg⁺⁺ concentration, thus increasing the survival of spray-dried LAB. Bacterial survival rates were increased to 43.06% with the addition of Ca⁺⁺ and to 42.64% with the addition of Mg⁺⁺, respectively. Ca⁺⁺/Mg⁺⁺ ATPase may be the key to the damage observed in spray-dried bacteria. Furthermore, the addition of Ca⁺⁺ or Mg⁺⁺ also reduced bacterial injury during spray drying by enhancing the activity of Ca⁺⁺/Mg⁺⁺ ATPase.

Effect of protective agents on the storage stability of freeze-dried Ligilactobacillus salivarius CECT5713

Ligilactobacillus salivarius is a lactic acid bacterium exhibiting several health benefits but remains commercially underexploited due to its inability to survive during long-term storage in the dried state. Our objective was to study the effect of various protective molecules (maltodextrin, trehalose, antioxidants, and fructooligosaccharides), being efficient on other bacteria, on the freeze-dried stability of L. salivarius CECT5713. The culturability was evaluated after freezing, freeze-drying, and subsequent storage at 37 °C, as well as the biochemical composition of cells in an aqueous environment using Fourier transform infrared (FTIR) micro-spectroscopy. The assignment of principal absorption bands to cellular components was performed using data from the literature on bacteria. The membrane fatty acid composition was determined after freeze-drying and storage. Glass transition temperature of the liquid and freeze-dried bacterial suspensions and water activity of the freeze-dried samples were measured. The best storage stability was observed for the formulations involving maltodextrin and antioxidants. The analysis of the FTIR spectra of freeze-thawed cells and rehydrated cells after freeze-drying and storage revealed that freeze-drying induced damage to proteins, peptidoglycans of the cell wall and nucleic acids. Storage stability appeared to be dependent on the ability of the protective molecules to limit damage during freeze-drying. The inactivation rates of bacteria during storage were analyzed as a function of the temperature difference between the product temperature during sublimation or during storage and the glass transition temperature, allowing a better insight into the stabilization mechanisms of freeze-dried bacteria. Maintaining during the process a product temperature well below the glass transition temperature, especially during storage, appeared essential for L. salivarius CECT5713 storage stability. KEY POINTS: • L. salivarius CECT5713 highly resisted freezing but was sensitive to freeze-drying and storage. • Freeze-drying and storage mainly altered cell proteins, peptidoglycans, and nucleic acids. • A glassy matrix containing maltodextrin and an antioxidant ensured the highest storage stability.

Current Trends in the Production of Probiotic Formulations

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

Emerging Technologies and Coating Materials for Improved Probiotication in Food Products: a Review

From the past few decades, consumers' demand for probiotic-based functional and healthy food products is rising exponentially. Encapsulation is an emerging field to protect probiotics from unfavorable conditions and to deliver probiotics at the target place while maintaining the controlled release in the colon. Probiotics have been encapsulated for decades using different encapsulation methods to maintain their viability during processing, storage, and digestion and to give health benefits. This review focuses on novel microencapsulation techniques of probiotic bacteria including vacuum drying, microwave drying, spray freeze drying, fluidized bed drying, impinging aerosol technology, hybridization system, ultrasonication with their recent advancement, and characteristics of the commonly used polymers have been briefly discussed. Other than novel techniques, characterization of microcapsules along with their mechanism of release and stability have shown great interest recently in developing novel functional food products with synergetic effects, especially in COVID-19 outbreak. A thorough discussion of novel processing technologies and applications in food products with the incorporation of recent research works is the novelty and highlight of this review paper.

Metabolic Pathway Profiling in Intracellular and Extracellular Environments of Streptococcus thermophilus During pH-Controlled Batch Fermentations

Elucidating the metabolite profiles during the growth of Streptococcus thermophilus is beneficial for understanding its growth characteristics. The changes in the intracellular and extracellular concentrations of carbohydrates, nucleotides, amino sugars, nucleoside sugars, fatty acids, and amino acids, as well as their metabolites over time, were investigated by metabolomics technology. Most metabolites of nucleotides were highly accumulated in the intracellular environment after the mid-exponential phase. Increases in the intracellular unsaturated fatty acids and N-acetyl-glucosamine and N-acetyl-muramoate recycling provided potential evidence that cell envelope remodeling occurred after the mid-exponential phase. At the later fermentation stages, potentially functional metabolite produced by glycine was highly accumulated in the intracellular environment. Additionally, potential toxic metabolites produced by phenylalanine and tyrosine could not be excreted into the extracellular environment in a timely basis. The accumulation of large amounts of these metabolites might be the primary cause of the overconsumption of amino acids and influence the growth of S. thermophilus.

Probiotics in Food Systems: Significance and Emerging Strategies Towards Improved Viability and Delivery of Enhanced Beneficial Value

Preserving the efficacy of probiotic bacteria exhibits paramount challenges that need to be addressed during the development of functional food products. Several factors have been claimed to be responsible for reducing the viability of probiotics including matrix acidity, level of oxygen in products, presence of other lactic acid bacteria, and sensitivity to metabolites produced by other competing bacteria. Several approaches are undertaken to improve and sustain microbial cell viability, like strain selection, immobilization technologies, synbiotics development etc. Among them, cell immobilization in various carriers, including composite carrier matrix systems has recently attracted interest targeting to protect probiotics from different types of environmental stress (e.g., pH and heat treatments). Likewise, to successfully deliver the probiotics in the large intestine, cells must survive food processing and storage, and withstand the stress conditions encountered in the upper gastrointestinal tract. Hence, the appropriate selection of probiotics and their effective delivery remains a technological challenge with special focus on sustaining the viability of the probiotic culture in the formulated product. Development of synbiotic combinations exhibits another approach of functional food to stimulate the growth of probiotics. The aim of the current review is to summarize the strategies and the novel techniques adopted to enhance the viability of probiotics.

Importance of intact secondary protein structures of cell envelopes and glass transition temperature of the stabilization matrix on the storage stability of probiotics

Lactobacillus reuteri LR6 cells were stabilized using a novel combination of wet granulation and fluidized-bed-drying techniques. The stabilized cells were stored at 37 °C and at two water activity (a_w) levels (0.11 & 0.30). Superior storage stability was recorded in the lower a_w environment, supported by a stronger glassy matrix when skim milk powder was used as the excipient. The initial viable cell populations of the samples stabilized in different matrices ranged from 8.3 to 9.1 log CFU/g. At the end of the storage period, the viable cell populations were reduced to 6.7 to 7.3 log CFU/g at a_w 0.11 and to 6.1 to 6.6 CFU/g when the a_w was maintained at 0.30. Fourier transform infrared spectroscopic examination of the cell envelopes revealed substantial dissimilarities between samples at the beginning and at the end of the storage period, which indicated alteration in the secondary protein structures of the cell envelope and also correlated well with the loss in cell viability. In milk-powder-based matrices, adjusting the a_w to 0.30 resulted in a weaker or no glassy state whereas the same matrices had a high glass transition temperature at a_w 0.11. This strong glassy matrix and low a_w combination was found to enhance the bacterial stability at the storage temperature of 37 °C. Scanning electron microscopy revealed the formation of corrugated surfaces and blister-type deformations on the cell envelopes during the stabilization process.

Raman spectroscopic analysis of Lactobacillus rhamnosus GG in response to dehydration reveals DNA conformation changes

Dehydration of bacterial cells elicits cellular stress responses in bacteria. Microencapsulation has been used to protect cells against the environmental stress. In this study, Confocal Raman Spectroscopy was used to examine DNA changes in the chemical composition of non-encapsulated and microencapsulated Lactobacillus rhamnosus GG and the reversibility of these changes upon freeze drying and rehydration. The viability of cells upon freeze drying was also enumerated using culture methods and membrane integrity was measured using BacLight Live/Dead staining. Raman analyses show changes in the spectral features associated with various biochemical compounds, which are interpreted as the result of detrimental freeze drying effects on the bacterial cells. Specifically, analyses based on Principal Components Analysis (PCA) of Raman spectra, confirm that microencapsulation protects cells from environmental stress. The results also reveal a B- to A-like DNA conformation change in dormant cells that provided insights into the extent of reversibility of this transition upon rehydration. The extent of this reversibility is less in non-encapsulated than in microencapsulated cells. These findings indicate the potential application of Raman spectroscopy in rapid sensing of microbial dehydration stress responses.

Effect of Drying Methods on Protein and DNA Conformation Changes in Lactobacillus rhamnosus GG Cells by Fourier Transform Infrared Spectroscopy

Microencapsulation protects cells against environmental stress encountered during the production of probiotics, which are used as live microbial food ingredients. Freeze-drying and spray-drying are used in the preparation of powdered microencapsulated probiotics. This study examines the ability of Fourier transform infrared (FTIR) spectroscopy to detect differences in cells exposed to freeze-drying and spray-drying of encapsulated Lactobacillus rhamnosus GG cells. The FTIR analysis clearly demonstrated there were more significant molecular changes in lipid, fatty acid content, protein, and DNA conformation of nonencapsulated compared to encapsulated bacterial cells. The technique was also able to differentiate between spray-dried and freeze-dried cells. The results also revealed the extent of protection from a protein-carbohydrate-based encapsulant matrix on the cells depending on the type drying process. The extent of this protection to the dehydration stress was shown to be less in spray-dried cells than in freeze-dried cells. This suggests that FTIR could be used as a rapid, noninvasive, and real-time measurement technique to detect detrimental drying effects on cells.

Technology and potential applications of probiotic encapsulation in fermented milk products

Fermented milk products containing probiotics and prebiotics can be used in management, prevention and treatment of some important diseases (e.g., intestinal- and immune-associated diseases). Microencapsulation has been used as an efficient method for improving the viability of probiotics in fermented milks and gastrointestinal tract. Microencapsulation of probiotic bacterial cells provides shelter against adverse conditions during processing, storage and gastrointestinal passage. Important challenges in the field include survival of probiotics during microencapsulation, stability of microencapsulated probiotics in fermented milks, sensory quality of fermented milks with microencapsulated probiotics, and efficacy of microencapsulation to deliver probiotics and their controlled or targeted release in the gastrointestinal tract. This study reviews the current knowledge, and the future prospects and challenges of microencapsulation of probiotics used in fermented milk products. In addition, the influence of microencapsulation on probiotics viability and survival is reviewed.

Agent selection and protective effects during single droplet drying of bacteria

The protective mechanisms of whey protein isolate (WPI), trehalose, lactose, and skim milk on Lactobacillus plantarum A17 during convective droplet drying has been explored. A single droplet drying technique was used to monitor cell survival, droplet temperature and corresponding changes in mass. WPI and skim milk provided the highest protection amongst the materials tested. In situ analysis of the intermediate stage of drying revealed that for WPI and skim milk, crust formation reduces the rate of sudden temperature increase thereby imparting less stress on the cells. Irreversible denaturation of the WPI components might have also contributed to the protection of the cells. Skim milk, however, 'loses' the protective behaviour towards the latter stages of drying. This indicates that the concentration of the WPI components could be another possible factor determining the sustained protective behaviour during the later stages of drying when the moisture content is low.

Production of monodisperse epigallocatechin gallate (EGCG) microparticles by spray drying for high antioxidant activity retention

Epigallocatechin gallate (EGCG) originated from green tea is well-known for its pharmaceutical potential and antiproliferating effect on carcinoma cells. For drug delivery, EGCG in a micro-/nanoparticle form is desirable for their optimized chemopreventive effect. In this study, first time reports that EGCG microparticles produced by low temperature spray drying can maintain high antioxidant activity. A monodisperse droplet generation system was used to realize the production of EGCG microparticles. EGCG microparticles were obtained with narrow size distribution and diameter of 30.24 ± 1.88 μM and 43.39 ± 0.69 μM for pure EGCG and lactose-added EGCG, respectively. The EC50 value (the amount of EGCG necessary to scavenge 50% of free radical in the medium) of spray dried pure EGCG particles obtained from different temperature is in the range of 3.029-3.075 μM compared to untreated EGCG with EC50 value of 3.028 μM. Varying the drying temperatures from 70°C and 130°C showed little detrimental effect on EGCG antioxidant activity. NMR spectrum demonstrated the EGCG did not undergo chemical structural change after spray drying. The major protective mechanism was considered to be: (1) the use of low temperature and (2) the heat loss from water evaporation that kept the particle temperature at low level. With further drier optimization, this monodisperse spray drying technique can be used as an efficient and economic approach to produce EGCG micro-/nanoparticles.

Reconstitution conditions for dried probiotic powders represent a critical step in determining cell viability

AIMS

Resuscitation of dried cultures represents a critical control point in obtaining active and effective probiotic strains. This study examined the effects of various rehydration conditions on the viability of Bifidobacterium longum NCC3001 and Lactobacillus johnsonii La1.

METHODS AND RESULTS

Reconstitution conditions for these strains were optimized using a multivariate experimental design approach. Furthermore, using flow cytometry, the cell integrity was followed during reconstitution. By adjusting the pH, availability of a metabolizable sugar, reconstitution duration, powder matrix and ratio of powder to reconstitution solution, the recovery of Bif. longum NCC3001 and Lact. johnsonii La1 following reconstitution was increased eight- and two-fold, respectively, over standard reconstitution in maximum recovery diluent. It was shown that pH had a significant effect on the recovery of Bif. longum NCC3001 and Lact. johnsonii La1.

CONCLUSIONS

The recovery of dried probiotic cultures is greatly dependent on the reconstitution conditions. The maximum recovery of 11.7 (10)log CFU g(-1) Bif. longum NCC3001 was achieved at 30-min reconstitution at pH 8, in the presence of 2% L-arabinose and a ratio of 1:100 of powder to diluent. Lact. johnsonii La1 showed highest recovery (9.3 (10)log CFU g(-1)) after reconstitution, when mixed with maltodextrin at pH 4.

SIGNIFICANCE AND IMPACT OF THE STUDY

To achieve accurate viable probiotic numbers from dried probiotic cultures, the reconstitution conditions should be optimized for the strain used.

Proteomic insights into adaptive responses of Saccharomyces cerevisiae to the repeated vacuum fermentation

The responses and adaptation mechanisms of the industrial Saccharomyces cerevisiae to vacuum fermentation were explored using proteomic approach. After qualitative and quantitative analyses, a total of 106 spots corresponding to 68 different proteins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The differentially expressed proteins were involved in amino acid and carbohydrate metabolisms, various signal pathways (Ras/MAPK, Ras-cyclic adenosine monophosphate, and HOG pathway), and heat shock and oxidative responses. Among them, alternations in levels of 17 proteins associated with carbohydrate metabolisms, in particular, the upregulations of proteins involved in glycolysis, trehalose biosynthesis, and the pentose phosphate pathway, suggested vacuum-induced redistribution of the metabolic fluxes. The upregulation of 17 heat stress and oxidative response proteins indicated that multifactors contributed to oxidative stresses by affecting cell redox homeostasis. Taken together with upregulation in 14-3-3 proteins levels, 22 proteins were detected in multispots, respectively, indicating that vacuum might have promoted posttranslational modifications of some proteins in S. cerevisiae. Further investigation revealed that the elevations of the differentially expressed proteins were mainly derived from vacuum stress rather than the absence of oxygen. These findings provide new molecular mechanisms for understanding of adaptation and tolerance of yeast to vacuum fermentation.

Damage of cell envelope of Lactobacillus helveticus during vacuum drying

AIMS

The aim of this study was to gain insight into the inactivation mechanisms of Lactobacillus helveticus during vacuum drying.

METHODS AND RESULTS

Early stationary phase cells of L. helveticus were dried in a vacuum drier. Viability, cell integrity and metabolic activity of cells were assessed over time by plate counts on de Man Rogosa and Sharpe broth agar medium and cytological methods employing fluorescent reagents and nucleic acid stains. The cell envelope damage was visualized by atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FT-IR) was used to indirectly observe changes in cell components during drying. Viability, metabolic activity and cell integrity decreased during vacuum drying, and different inactivation curves, characterized by the loss of ability to resume growth, and cell injuries were found. AFM images showed cracks on the surface of dried cells. Main changes in FT-IR spectra were attributed to the damage in cell envelope.

CONCLUSION

The cell envelope was the main site of damage in L. helveticus during vacuum drying.

SIGNIFICANCE AND IMPACT OF THE STUDY

Inactivation mechanisms of L. helveticus during vacuum drying were partly elucidated. This information is useful for the improvement of the viability of vacuum-dried starter cultures.