Galacto-oligosaccharides as protective molecules in the preservation of Lactobacillus delbrueckii subsp. bulgaricus

Improvement of rheological and sensory properties of Lactobacillus helveticus fermented milk by prebiotics

The fermentation characteristics and aroma-producing properties of Lactobacilli could influence the flavour quality of fermented milk, an important influencing factor of consumers' preference. In this study, fermented milk was prepared using Lactobacillus helveticus and the dynamic changes in the sensory quality of fermented milk throught fermentation were to assess the dynamic changes in sensory quality of fermented milks throughout the fermentation process, including rheological properties and flavour profiles. Styrene, linalool, octanoic acid, and 1-nonanol were considered as the key flavour components during fermentation. The quality of the fermented milk tends to be stabilized after 24-h, showing the minimal off-flavour at 48-h and optimal fermented aroma at 72-h. Three prebiotics (inulin, Galactooligosaccharides and inulin mixed with Galactooligosaccharides) were added to Lactobacillus spiralis fermented milk separately, and the results showed that inulin mixed with Galactooligosaccharides was the most effective group in improving the organoleptic quality of the fermented milk. Overall, the experimental results provide deeper insights into the release and retention of aroma compounds during fermentation and scientific reference for broadening the application of prebiotics and flavour-producing Lactobacilli in fermented milk processing.

Commercial probiotic products in public health: current status and potential limitations

Consumption of commercial probiotics for health improvement and disease treatment has increased in popularity among the public in recent years. The local shops and pharmacies are brimming with various probiotic products such as probiotic food, dietary supplement and pharmaceuticals that herald a range of health benefits, from nutraceutical benefits to pharmaceutical effects. However, although the probiotic market is expanding rapidly, there is increasing evidence challenging it. Emerging insights from microbiome research and public health demonstrate several potential limitations of the natural properties, regulatory frameworks, and market consequences of commercial probiotics. In this review, we highlight the potential safety and performance issues of the natural properties of commercial probiotics, from the genetic level to trait characteristics and probiotic properties and further to the probiotic-host interaction. Besides, the diverse regulatory frameworks and confusing probiotic guidelines worldwide have led to product consequences such as pathogenic contamination, overstated claims, inaccurate labeling and counterfeit trademarks for probiotic products. Here, we propose a plethora of available methods and strategies related to strain selection and modification, safety and efficacy assessment, and some recommendations for regulatory agencies to address these limitations to guarantee sustainability and progress in the probiotic industry and improve long-term public health and development.

Effects of sucrose, carnosine, and their mixture on the glass transition behavior and storage stability of freeze-dried lactic acid bacteria at various water activities

Effects of sucrose, carnosine, and their mixture on the glass transition behavior and storage stability of freeze-dried Lactobacillus reuteri at various water activities (a_w) were investigated. At a_w = 0.328, the control (non-additive sample) showed viable cells as uncountable after storage at 25 °C for 4 weeks. The sucrose and sucrose-carnosine samples showed clear glass transition at a slightly lower temperature than the storage temperature, and maintained a large number of viable cells after storage. The carnosine sample crystalized during the storage, and a large reduction in viable cells was observed. At a_w = 0.576, the samples showed a small endothermic shift due to glass transition, suggesting partial crystallization. The T_g decreased with increases in a_w because of the water plasticizing effect. After storage, the sucrose-carnosine sample showed much higher viable cell numbers than the other samples. At a_w = 0.753, the sucrose and sucrose-carnosine samples showed clear glass transition. The carnosine sample showed freeze-concentrated glass transition and subsequent ice melting. After storage, the sucrose and carnosine samples showed an uncountable and a low number of viable cells, respectively, but sucrose-carnosine maintained relatively high viable cell numbers. In addition, carnosine strongly supported the stabilizing effect of sucrose (even at low additive levels) depending on the a_w. These results suggest that sucrose-carnosine shows a synergistic stabilizing effect.

Valorization of renewable resources to functional oligosaccharides: Recent trends and future prospective

Lignocellulosic wastes have the ability to be transformed into oligosaccharides and other value-added products. The synthesis of oligosaccharides from renewable sources bestow to growing bioeconomies. Oligosaccharides are synthesized chemically or biologically from agricultural residues. These oligosaccharides are functional food supplements that have a positive impact on humans and livestock. Non-digestible oligosaccharides, refered as prebiotics are beneficial for the colonic microbiota inhabiting the f the digestive system. These microbiota plays a crucial role in stimulating the host immune system and other physiological responses. The commonly known prebiotics, galactooligosaccharides (GOS), xylooligosaccharides (XOS), fructooligosaccharides (FOS), mannanooligosaccharides (MOS), and isomaltooligosaccharides (IOS) are synthesized either through enzymatic or whole cell-mediated approaches using natural or agricultural waste substrates. This review focusses on recent advancements in biological processes, for the synthesis of oligosaccharides using renewable resources (lignocellulosic substrates) for sustainable circular bioeconomy. The work also addresses the limitations associated with the processes and commercialization of the products.

Review on development of assigned value microbiological reference materials used in food testing

Evolving testing methods in food Microbiology have resulted in the need for different types of microbiological reference materials. Based on the research articles available in this area, it is evident that development has been quite substantial in chemical testing compared to Microbiology. The primary reason could be the ease of spiking, and recovery in chemical RM as compared to microbiological RM. A significant challenge faced in recovery and stability during the development of quantitative microbiological RM depends on temperature, type of microbiological media used, method of analysis including reconstitution method, interference due to antimicrobial agents in food matrices, and competitor microorganisms present in higher numbers then the target microorganisms. Most of the research papers published on microbiological reference materials are contributed by developed economies were in the information related to complex food matrices are limited. Further analysis of different International Depository Agencies under the Budapest treaty indicates that there are only three institutes based in Europe providing quantitative or assigned value RM. This, in turn, highlights the scarcity in the availability of quantitative RM in Microbiology. This article provides a global overview of the availability of microbiological RM, microbial preservation techniques, protective agents, and elaboration on developing different formats of microbiological RM used in food testing.

Fructose derived oligosaccharides prevent lipid membrane destabilization and DNA conformational alterations during vacuum-drying of Lactobacillus delbrueckii subsp. bulgaricus

Dehydration of lactic acid bacteria for technological purposes conducts to multilevel damage of bacterial cells. The goal of this work was to determine at which molecular level fructose-oligosaccharides (FOS) and sucrose protect Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 during the vacuum-drying process. To achieve this aim, the cultivability and metabolic activity of vacuum-dried bacteria were firstly determined (plate counting and absorbance kinetics). Then, the membrane integrity and fluidity were assessed using propidium iodide and Laurdan probes (general polarization -GP-), respectively. Finally, bacterial structural alterations were determined using high throughput methods (fluorescence confocal microscopy and Raman spectroscopy coupled to Multivariate Curve Resolution analysis -MCR-). The vacuum-drying process directly affected the microorganism's cultivability and membrane integrity. Non-dehydrated cells and sugar protected bacteria (both with FOS or sucrose) presented high GP values typical from the gel state, as well as phospholipids microdomains laterally organized along the cytoplasmic membrane. On the contrary, bacteria dehydrated without protectants presented low GP values and greater water penetration, associated with membrane destabilization. Raman spectroscopy of vacuum-dried cells revealed DNA conformational changes, B-DNA conformations being associated to non-dehydrated or sugar protected bacteria, and A-DNA conformations being higher in bacteria vacuum-dried without protectants. These results support the role of FOS and sucrose as protective compounds, not only acting at the membrane organizational level but also preventing conformational alterations of intracellular structures, like DNA.

Protective Effects of Tropical Fruit Processing Coproducts on Probiotic Lactobacillus Strains during Freeze-Drying and Storage

This study evaluated the protective effects of coproducts from agroindustrial processing of the tropical fruits acerola (Malpighia glabra L., ACE), cashew (Anacardium occidentale L., CAS), and guava (Psidium guayaba L., GUA) on the probiotics Lactobacillus paracasei L-10, Lactobacillus casei L-26, and Lactobacillus acidophilus LA-05 during freeze-drying and storage. The occurrence of damage to membrane integrity, membrane potential, and efflux activity of Lactobacillus cells after freeze-drying was evaluated by flow cytometry, and viable counts were measured immediately after freeze-drying and during 90 days of storage under refrigerated or room temperature conditions. Probiotic strains freeze-dried without substrate had the overall highest count reductions (0.5 ± 0.1 to 2.9 ± 0.3 log cycles) after freeze-drying. Probiotics freeze-dried with fruit processing coproducts had small cell subpopulations with damaged efflux activity and membrane potential. Average counts of probiotics freeze-dried with ACE, CAS, or GUA after 90 days of storage under refrigerated or room temperature were in the range of 4.2 ± 0.1 to 5.3 ± 0.2 and 2.6 ± 0.3 to 4.9 ± 0.2 log CFU/g, respectively, which were higher than those observed for strains freeze-dried without substrate. The greatest protective effects on freeze-dried probiotics were overall presented by ACE. These results revealed that ACE, CAS, and GUA can exert protective effects and increase the stability of probiotic lactobacilli during freeze-drying and storage, in addition to supporting a possible added-value destination for these agroindustrial coproducts as vehicles for probiotics and for the development of novel functional foods.

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.

Inclusion of prebiotics on the viability of a commercial Lactobacillus casei subsp. rhamnosus culture in a tropical fruit beverage

The viability of probiotics in the development of functional tropical fruit beverages is a technological challenge that may benefit from the addition of prebiotics, due to the synergistic (synbiotic) interaction. This study evaluated the viability of a commercial probiotic (Lactobacillus casei) in a blended red fruit beverage (RFB; 20% strawberry, 10% blackberry and 5% papaya), enriched with three separate prebiotics: inulin (IN), fructooligosaccharides (FOS) and galactooligosaccharides, added at 1 and 5%. The consumer preference for the beverages was also examined. The inoculum was produced in MRS broth supplemented with 10% RFB, which reached the exponential phase (9.96 log CFU mL^-1) after incubation at 37 °C for 24 h. In search of the probiotic strain's adaptation and viability in the presence of the different prebiotics (measured by optical density, OD_{600 nm}), the prebiotics were added to MRS broth at 1 and 5%. Since 1% IN (OD = 3.99 ± 0.36) and 1% FOS (OD = 3.48 ± 0.28) were the most significant, these treatments, without inoculation of probiotics, were assessed by the sensory panel. Although neither RFB was significantly preferred the RFB with 1% IN received the greatest number of responses (n = 33/60). Its effect on the viability of L. casei inoculated in the RFB was monitored by the growth kinetics at 37 °C for 50 h. The findings indicated that fortification with 1% IN could have a possible protective effect on the stability of L. casei in RFBs, highlighting the use of tropical fruits as potential carriers of probiotics.

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.

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

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

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.

Use of whey permeate containing in situ synthesised galacto-oligosaccharides for the growth and preservation of Lactobacillus plantarum

Galacto-oligosaccharides (GOS) are prebiotics that have a beneficial effect on human health by promoting the growth of probiotic bacteria in the gut. GOS are commonly produced from lactose in an enzymatic reaction catalysed by β-galactosidase, named transglycosylation. Lactose is the main constituent of whey permeate (WP), normally wasted output from the cheese industry. Therefore, the main goal of this work was to optimise the synthesis of GOS in WP using β-galatosidase from Aspergillus oryzaea. WP and whey permeate enzymatically treated (WP-GOS) were used as culture media of Lactobacillus plantarum 299v. Lb. plantarum 299v attained the stationary phase in approximately 16 h, reaching 3·6 and 4·1×108 CFU/ml in WP and WP-GOS, respectively. The in situ synthesised GOS were not consumed during growth. No significant differences were observed in the growth kinetics of microorganisms in both media. After fermentation, microorganisms were dehydrated by freeze-drying and spray-drying and stored. The recovery of microorganisms after fermentation, dehydration and storage at 4 °C for at least 120 d was above 108 CFU/g. These studies demonstrated that WP is an appropriate substrate for the synthesis of GOS and the obtained product is also adequate as culture medium of Lb. plantarum 299v. The coexistence of GOS and dehydrated viable probiotic microorganisms, prepared using an effluent as raw material, represents the main achievement of this work, with potential impact in the development of functional foods.

Effect of physical properties on the stability of Lactobacillus bulgaricus in a freeze-dried galacto-oligosaccharides matrix

The ability of galacto-oligosaccharides (GOS) to protect Lactobacillus delbrueckii subsp. bulgaricus upon freeze drying was analyzed on the basis of their capacity to form glassy structures. Glass transition temperatures (T(g)) of a GOS matrix at various relative humidities (RH) were determined by DSC. Survival of L. bulgaricus in a glassy GOS matrix was investigated after freezing, freeze drying, equilibration at different RHs and storage at different temperatures. At 32 °C, a drastic viability loss was observed. At 20 °C, the survival was affected by the water content, having the samples stored at lower RHs, the highest survival percentages. At 4°C, no decay in the cells count was observed after 45 days of storage. The correlation between molecular mobility [as measured by Proton nuclear magnetic resonance (¹H NMR)] and loss of viability explained the efficiency of GOS as cryoprotectants. The preservation of microorganisms was improved at low molecular mobility and this condition was obtained at low water contents and low storage temperatures. These results are important in the developing of new functional foods containing pre and probiotics.