Stability of freeze-dried Lactobacillus delbrueckii subsp. bulgaricus in the presence of galacto-oligosaccharides and lactulose as determined by near infrared spectroscopy

Yacon juice as culture and cryoprotectant medium for Latilactobacillus sakei and Staphylococcus vitulinus autochthonous strains

Abstract Yacon is mainly constituted of water and carbohydrates [single sugars and fructooligosaccharides (FOS)], thus being an excellent alternative for the growth and preservation of bacterial culture. Latilactobacillus sakei ACU-2 and Staphylococcus vitulinus ACU-10 comprised the autochthonous starter culture SAS-1 designed for the manufacture of dry sausages. This study evaluated the use of yacon juice as a potential growth medium and cryoprotectant for these bacteria. The growth medium was prepared with yacon juice supplemented with peptone and dipotassium phosphate. After growing, cells were resuspended in yacon juice (5, 10 and 25 mL/100 mL) and lyophilized. Viable cells were count before, immediately after lyophilization, and along 6 months of refrigerated storage. Both bacteria grew in every yacon concentration tested; however, juice concentration affected their growth. Latilactobacillus sakei grew at μ = 0.256 ± 0.01 giving the highest bacterial density at 10 mL/100 mL (Log DOmax 0.33 ± 0.01). While 5 mL/100 mL yacon juice provided the best conditions for S. vitulinus growth (μ = 0.215 ± 0.016; Log DOmax 0.32 ± 0.01). After lyophilization, the survival rate was 91.1% for L. sakei and 65.8% for S. vitulinus. Throughout storage, high cell counts suggested good stability of both bacteria. Results revealed that yacon juice comprises a nutritive substrate for the growth and cryopreservation of tested strains from the genus Latilactobacillus and Staphylococcus.

Solid inoculants as a practice for bioaugmentation to enhance bioremediation of hydrocarbon contaminated areas

Vacuum freeze-drying is a scientifically advanced method to prepare solid inoculants from oil degrading bacterium. The introduction of oil-degrading microbes or bioaugmentation can be an efficient way to bioremediate oil spills in marine areas, where oil-degrading bacteria are deficient. The purpose of this study is to evaluate the potential use of solid inoculants of LZ-2 bacteria to enhance the degradation rate of crude oil. In this study, response surface methodology (RSM) was incorporated into the experimental design to optimize a response, which is influenced by different protectants. Our results showed that five factors have interactive and synergistic protective effects on the growth of LZ-2. Optimal growth of freeze-dried LZ-2 (63.8%) was observed with a 10.5% solution of skim milk supplemented with 14.3% sucrose, 14.4% of trehalose, 4.9% of glycerin and 14.7% of β-cyclodextrin. The culture grew in medium containing crude oil (3 g L^-1) at 37 °C at 150 rpm for 30 d, GC and GC-MS analysis showed biodegradation of 44.2 and 21.6% for total saturate and aromatic hydrocarbons respectively. These results indicated that the solid inoculants of LZ-2 bacteria had the potential to be used for ex-situ bioremediation of hydrocarbon pollutants associated with crude oil.

A Recent Overview of Microbes and Microbiome Preservation

Microbes are mediators in almost all ecosystem processes and act as a pivotal game changer in various ecological activities, globally. Therefore, understanding of microbial community structure and related functions in different environmental and micro-environmental niches is not only critical, but also a matter of greatest importance. Due to our inability to cultivate and preserve all sorts of microorganisms, we are losing some ecologically and industrially relevant components of microbial community, due to extinction caused by environmental and climatic variations with time. Intact sample and microbiome preservation are crucial for future cultivation as well as to study the effects of ecological and climatic variations on community functionality and shift with time, using OMICS. Although, methods for pure culture preservation are almost optimized, the techniques of microbiome preservation still remain as an unsolved challenge for microbiologists due to technical and physiological constraints. Present article discusses, recent approaches of microbial preservation with special reference to intact sample, mixed culture and microbiome preservation. It also incorporates recent practices used to achieve the highest viability and metabolic activities in long-term preserved microbiome.

Impact of protectants on the storage stability of freeze-dried probiotic Lactobacillus plantarum

The ability of rice protein supplemented with various prebiotics to protect probiotic Lactobacillus plantarum TISTR 2075 upon freeze-drying and subsequent storage was determined. A combination of rice protein-fructooligosaccharide (RF) provided the best storage stability with the lowest specific rate of cell death (k) of 1.20 × 10-2 and 5.79 × 10-2 1/day during subsequent storage at 4 °C for 180 days and 30 °C for 90 days, respectively. Glass transition temperatures (T g) of freeze-dried probiotic in various protectants were 14.2-25.4 and 42.9-50.1 °C after storage at 4 and 30 °C, respectively. The functional properties of freeze-dried probiotic with protectants remained stable. The presence of RF could effectively protect and enhance the probiotic functionality during exposure to gastrointestinal tract conditions. The pathogenic inhibition of freeze-dried probiotic against foodborne pathogens was not different from the active cells. Protective agents were able to maintain high degrees of cell surface hydrophobicity.

Pectin-decorated magnetite nanoparticles as both iron delivery systems and protective matrices for probiotic bacteria

The goal of this work was to investigate biophysical stability of iron-pectin nanoparticles and analyze the feasibility of using them as delivery systems for the probiotic strain Lactobacillus plantarum CIDCA 83114. Iron oxide (Fe₃O₄) nanoparticles were synthesized from 0.25M FeCl₂/0.5 M FeCl₃.6H₂O, and coated with citrus pectins. Their physico-chemical properties [FTIR, X-ray diffraction (XRD), ζ-potential, particle size, SEM, TEM] and their effect on bacterial stabilization (viability after freeze-drying/storage, stability when exposed to simulated gastro-intestinal conditions) were assessed. XRD indicated the almost exclusive presence of magnetite crystalline phases. FTIR spectra confirmed the adsorption of pectin on magnetite nanoparticles surface. SEM and TEM images evidenced agglomerated nanoparticles, and a morphological surface change after adsorption of pectin. DLS and ζ-potential results proved the solvation of the ionizable groups in the hydrophilic network which induced chain expansion and agglomeration. Iron from nanoparticles demonstrated to be non-toxic for microorganisms up to 1.00 mg/mL. Simulated saliva and gastric solutions prevented nanoparticles from dissolution. The higher pH of the intestinal conditions (solvated -COO- and Fe-O- groups) facilitated the dispersion and partial dissolution of nanoparticles. Pectins adsorption on magnetite nanoparticles significantly enhanced electrostatic repulsion, which aided the solvation of ionized iron forms. The soluble species diffused out from the aggregates, being detected in the simulated intestinal fluid. Regarding bacterial viability, no decays were observed neither when pectin-decorated nanoparticles were exposed to simulated fluids nor when stored at 4 °C for 60 days. The composites engineered in this work appear as adequate delivery systems for probiotic bacteria, whose target is the gut.

Flour from mature Prosopis nigra pods as suitable substrate for the synthesis of prebiotic fructo-oligosaccharides and stabilization of dehydrated Lactobacillus delbrueckii subsp. bulgaricus

Prosopis nigra, a sucrose-rich crop, was used to enzymatically synthesize fructo-oligosaccharides (FOS). The obtained products were used as stabilizing matrices during freeze-drying and storage of Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333. The centesimal composition of P. nigra flour was firstly determined. FOS were synthesized using Viscozyme L as biocatalyst. The progress of the enzymatic reaction was monitored by HPLC and compared with a reaction carried out using equivalent concentrations of pure sucrose as substrate (control). Then, P. nigra containing or not the obtained FOS (P. nigra + FOS or P. nigra) were used as matrices for freeze-drying and storage of L. delbrueckii subsp. bulgaricus CIDCA 333. P. nigra flour was rich in simple sugars (sucrose and fructose), total dietary fiber, and polyphenols. The main products of synthesis were FOS with degrees of polymerization (DP) within 3 and 5, and these results were comparable with those of the controls. DP3 was the first product obtained, attaining the maximal production after 1.29 hours of synthesis. The maximal production of total FOS (DP3 + DP4 + DP5) was achieved after 2.57 hours, indicating that larger FOS (DP4, DP5) were produced from DP3. Glucose was obtained as secondary product, but with significantly lower V_max and K_f (maximal velocity for the production and constant for the formation) than DP3. Both P. nigra + FOS or P. nigra matrices stabilized the highly sensitive L. delbrueckii subsp. bulgaricus CIDCA 333 strain during freeze-drying and storage for up to 140 days at 4 °C, and were significantly better protectants than the controls of sucrose (p <0.05). The concomitant presence of prebiotics (FOS), antioxidants (polypyhenols) and lactic acid bacteria in the matrices provides a smart strategy to increase the value of this underutilized regional crop, turning it in an interesting ingredient potentially useful in the food industry.

Valorization of okara oil for the encapsulation of Lactobacillus plantarum

Oil-in-water (O/W) emulsions of okara oil-caseinate (1:2; 1:3 and 1:4 O/W ratios) were used to encapsulate Lactobacillus plantarum CIDCA 83114. Once encapsulated, microorganisms were freeze-dried or spray-dried, and observed by scanning electronic and confocal microscopies. A physical characterization of the dehydrated capsules was carried out by determining their moisture content, water activity, particle size, polydispersity index and zeta potential. Determining the induction times and peroxide values provided information about their susceptibility to oxidation. In turn, bacterial stability was analyzed by plate counting before and after freeze-drying and spray-drying, and during storage at 4°C. Spray-dried emulsions had lower Z-sizes and polydispersity indexes, higher induction times and lower peroxide values than the freeze-dried ones, thus resulting better systems to protect L. plantarum CIDCA 83114. In addition, the culturability of spray-dried bacteria did not decrease neither after spray-drying nor up to 60days of storage at 4°C. The results showed that the better physical-chemical stability of spray-dried capsules determined the greater stability of microorganisms. This demonstrates the importance of defining adequate emulsions' formulations for an efficient encapsulation of microorganisms, with promising applications in the development of novel functional foods.

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus ND02 derived from 2 propagation procedures was determined. The subpopulations consisted of 3 categories (physiological states): viable cells capable of forming colonies on agar plates (VC+), viable cells incapable of forming colonies on agar plates (VC-), widely referred to as viable but nonculturable (VBNC) cells, and nonviable or dead cells (NVC). Counts of VC+ were recorded using a conventional plate count procedure. A fluorescent vital staining procedure that discriminates between viable (VC+ and VC-) and NVC cells was used to determine the number of viable and nonviable cells. Both propagation procedures had 2 variables: in procedure (P)1, the propagation medium was rich in yeast extract (4.0%) and the pH was maintained at 5.7; in P2, the medium was devoid of yeast extract and the pH was maintained at 5.1. The results showed that post-propagation operations-concentration of cells by centrifugation and subsequent freezing or lyophilization of cell concentrate-induced different degrees of transience from VC+ to VC- states in cells derived from P1 and P2. Compared with cells derived from P2, cells from P1 were more labile to stress associated with centrifugation, freezing, and lyophilization, as revealed by differential counting.

Okara: A Nutritionally Valuable By-product Able to Stabilize Lactobacillus plantarum during Freeze-drying, Spray-drying, and Storage

Okara is a nutritionally valuable by-product produced in large quantities as result of soymilk elaboration. This work proposes its use as both culture and dehydration medium during freeze-drying, spray-drying, and storage of Lactobacillus plantarum CIDCA 83114. Whole and defatted okara were employed as culture media for L. plantarum CIDCA 83114. The growth kinetics were followed by plate counting and compared with those of bacteria grown in MRS broth (control). No significant differences in plate counting were observed in the three media. The fatty acid composition of bacteria grown in whole and defatted okara showed a noticeable increase in the unsaturated/saturated (U/S) fatty acid ratio, with regard to bacteria grown in MRS. This change was mainly due to the increase in polyunsaturated fatty acids, namely C18:2. For dehydration assays, cultures in the stationary phase were neutralized and freeze-dried (with or without the addition of 250 mM sucrose) or spray-dried. Bacteria were plate counted immediately after freeze-drying or spray-drying and during storage at 4°C for 90 days. Freeze-drying in whole okara conducted to the highest bacterial recovery. Regarding storage, spray-dried bacteria previously grown in whole and defatted okara showed higher plate counts than those grown in MRS. On the contrary, freeze-dried bacteria previously grown in all the three culture media were those with the lowest plate counts. The addition of sucrose to the dehydration media improved their recovery. The higher recovery of microorganisms grown in okara after freeze-drying and spray-drying processes and during storage was ascribed to both the presence of fiber and proteins in the dehydration media, and the increase in U/S fatty acids ratio in bacterial membranes. The obtained results support for the first time the use of okara as an innovative matrix to deliver L. plantarum. Considering that okara is an agro-waste obtained in large quantities, these results represent an innovative strategy to add it value, providing a symbiotic ingredient with promising industrial applications in the development of novel functional foods and feeds.

Interaction of galacto-oligosaccharides and lactulose with dipalmitoylphosphatidilcholine lipid membranes as determined by infrared spectroscopy

Galacto-oligosaccharides and lactulose interact with DPPC lipid membranes by modifying theirT_m, and this effect is dependent on their degree of polymerization.

Effect of Galacto-Oligosaccharides: Maltodextrin Matrices on the Recovery of Lactobacillus plantarum after Spray-Drying

In this work maltodextrins were added to commercial galacto-oligosaccharides (GOS) in a 1:1 ratio and their thermophysical characteristics were analyzed. GOS:MD solutions were then used as matrices during spray-drying of Lactobacillus plantarum CIDCA 83114. The obtained powders were equilibrated at different relative humidities (RH) and stored at 5 and 20°C for 12 weeks, or at 30°C for 6 weeks. The Tgs of GOS:MD matrices were about 20-30°C higher than those of GOS at RH within 11 and 52%. A linear relation between the spin-spin relaxation time (T2) and T-Tg parameter was observed for GOS:MD matrices equilibrated at 11, 22, 33, and 44% RH at 5, 20, and 30°C. Spray-drying of L. plantarum CIDCA 83114 in GOS:MD matrices allowed the recovery of 93% microorganisms. In contrast, only 64% microorganisms were recovered when no GOS were included in the dehydration medium. Survival of L. plantarum CIDCA 83114 during storage showed the best performance for bacteria stored at 5°C. In a further step, the slopes of the linear regressions provided information about the rate of microbial inactivation for each storage condition (k values). This information can be useful to calculate the shelf-life of spray-dried starters stored at different temperatures and RH. Using GOS:MD matrices as a dehydration medium enhanced the recovery of L. plantarum CIDCA 83114 after spray-drying. This strategy allowed for the first time the spray-drying stabilization of a potentially probiotic strain in the presence of GOS.

Applications of Infrared and Raman Spectroscopies to Probiotic Investigation

In this review, we overview the most important contributions of vibrational spectroscopy based techniques in the study of probiotics and lactic acid bacteria. First, we briefly introduce the fundamentals of these techniques, together with the main multivariate analytical tools used for spectral interpretation. Then, four main groups of applications are reported: (a) bacterial taxonomy (Subsection 4.1); (b) bacterial preservation (Subsection 4.2); (c) monitoring processes involving lactic acid bacteria and probiotics (Subsection 4.3); (d) imaging-based applications (Subsection 4.4). A final conclusion, underlying the potentialities of these techniques, is presented.

Galacto-oligosaccharides and lactulose as protectants against desiccation of Lactobacillus delbrueckii subsp. bulcaricus

Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 was dehydrated on desiccators containing silica gel in the presence of 20% w/w of two types of galacto-oligosaccharides (GOS Biotempo and GOS Cup Oligo H-70®) and lactulose, until no changes in water desorption were detected. After rehydration, bacterial growth was monitored at 37°C by determining: (a) the absorbance at 600 nm and (b) the near infrared spectra (NIR). Principal component analysis (PCA) was then performed on the NIR spectra of samples dehydrated in all conditions. A multiparametric flow cytometry assay was carried out using carboxyfluorescein diacetate and propidium iodide probes to determine the relative composition of damaged, viable, and dead bacteria throughout the growth kinetics. The absorbance at 600 nm and the position of the second derivative band at ∼1370 nm were plotted against the time of incubation. The efficiency of the protectants was GOS Biotempo > GOS Cup Oligo H-70®  > lactulose. The better protectant capacity of GOS Biotempo was explained on the basis of the lower contribution of damaged cells immediately after rehydration (t = 0). PCA showed three groups along PC1, corresponding to the lag, exponential and stationary phases of growth, which explained 99% of the total variance. Along PC2, two groups were observed, corresponding to damaged or viable cells. The results obtained support the use of NIR to monitor the recovery of desiccated microorganisms in real time and without the need of chemical reagents. The use of GOS and lactulose as protectants in dehydration/rehydration processes was also supported.

Determination of amorphous/rubbery states in freeze-dried prebiotic sugars using a combined approach of near-infrared spectroscopy and multivariate analysis

Galacto-oligosaccharides (GOS) and lactulose are well-recognized prebiotics widely used in functional food and pharmaceutical products, but there is still a lack of knowledge regarding their physical-chemical properties. In this study, a physical-chemical approach on two GOS of different composition (GOS Cup Oligo H-70® and GOS Biotempo) and lactulose was assessed. Mid infrared and Raman spectra of the freeze-dried sugars allowed their structural characterization in the amorphous state, lactulose, showing the main spectral differences. Freeze-dried sugars were then equilibrated at 4°C at relative humidity (RH) ranging from 11% to 80%. Near-infrared reflectance spectra were registered in each condition in the 900- to 1700-nm region. A principal component analysis (PCA) was performed on the three sugars equilibrated at different RH. In all the three sugars, the groups observed explained more than 95% of the variance and were related with the RH of the samples. According to the loading plots of PC1, the main differences related with RH were observed in the 1380- to 1500-nm region. As the amorphous states are very sensitive to changes in temperature and moisture content, and the moisture content is related with the parameter T-Tg (T: storage temperature; Tg: vitreous transition temperature), an effort was made to determine this parameter directly from the NIR spectra. To this aim, a partial least square model (PLS) was defined. Tg values obtained by differential scanning calorimetry (DSC) were used to calculate the T-Tg values of reference. The model was validated with an independent set of data. The mean of predicted values fitted nicely T-Tg obtained from DSC (correlation=0.966; R²=0.934), thus supporting the use of the PLS model to investigate unknown samples. The stability of amorphous sugars in foods and pharmaceuticals is of practical and economical importance because it affects different quality attributes of foods, including texture, aroma retention and shelf life. Therefore, predicting T-Tg, a parameter that is independent on the sugar investigated, directly from their NIR spectra is of utmost importance to determine the shelf life of food and food-related products and up to our knowledge has never been determined hereto.