Resistance of functional Lactobacillus plantarum strains against food stress conditions

Recent Advances in the Understanding of Stress Resistance Mechanisms in Probiotics: Relevance for the Design of Functional Food Systems

In recent years, more and more scientific community, food producers, and food industry show increased interest in functional foods containing probiotics, which is a big challenge. The consumption of probiotics in the context of a balanced diet through the consumption of functional foods or through the intake of pharmaceutical preparations has proven to contribute to the improvement of human health, even contributing to the prevention of diseases. In order for probiotics to be considered suitable for consumption, they must contain a minimum concentration of viable cells, namely, at least 107 colony forming units of beneficial microbes per gram. Ensuring the viability of bacterial cells until the moment of consumption is the overriding priority of functional probiotic food manufacturers. Probiotic bacteria are subject to stress conditions not only during food manufacturing but also during gastrointestinal passage, which limit or even compromise their functionality. This paper first examines all the stressful conditions faced by probiotic cells in their production stages and related to the conditions present in the bioreactor fermentation and drying processes as well as factors related to the food matrix and storage. The stress situations faced by probiotic microorganisms during the gastrointestinal transit especially during stomach and intestinal residence are also analyzed. In order to understand the adaptation mechanisms of probiotic bacteria to gastrointestinal stress, intrinsic and adaptive mechanisms identified in probiotic strains in response to acid stress and to bile and bile acid stress are analyzed. In addition, improvement strategies for multiple stress tolerance of lactic acid bacteria through directions dealing with stress, accumulation of metabolites, use of protectants, and regulation of technological parameters are examined. Finally, the definition of postbiotics, inanimate microorganisms and/or their components conferring health benefits, is also introduced. Postbiotics include cell lysates, enzymes, and cell wall fragments derived from probiotic bacteria and may represent an alternative to the use of probiotics, when they do not tolerate stressful conditions.

Exploiting the beneficial effects of Salvia officinalis L. extracts in human health and assessing their activity as potent functional regulators of food microbiota

Salvia officinalis L. has attracted scientific and industrial interest due to its pharmacological properties. However, its detailed phytochemical profile and its correlation with beneficial effects in the human microbiome and oxidative stress remained elusive. To unveil this, S. officinalis was collected from the region of Epirus and its molecular identity was verified with DNA barcoding. Phytochemical profile for both aqueous and ethanol-based extracts was determined by high-pressure liquid chromatography-tandem mass spectrometry and 103 phytochemicals were determined. The effect of S. officinalis extracts as functional regulators of food microbiota by stimulating the growth of Lacticaseibacillus rhamnosus strains and by suppressing evolution of pathogenic bacteria was verified. Furthermore, we recorded that both extracts exhibited a significant cellular protection against H2O2-induced DNA damage. Finally, both extracts exhibited strong inhibitory effect towards LDL oxidation. This study provides a comprehensive characterization of S. officinalis on its phytochemical components as also its potential impact in human microbiome and oxidative stress.

B-vitamins and heat processed fermented starchy and vegetable foods in sub-Saharan Africa: A review

Micronutrient deficiency still occurs in sub-Saharan Africa (SSA) despite the availability of several food resources, particularly fermented foods and vegetables, with high nutritional potential. Fermentation enhances the quality of food in several aspects. Organoleptically, certain taste, aroma, and textures are developed. Health and safety are improved by inhibiting the growth of several foodborne pathogens and removing harmful toxic compounds. Furthermore, nutrition is enhanced by improving micronutrient contents and bioavailability from the food, especially vitamin B content. However, during processing and before final consumption, many fermented foods are heat treated (drying, pasteurization, cooking, etc.) to make the food digestible and safe for consumption. Heat treatment improves the bioavailability of B-vitamins in some foods. In other foods, heating decreases the nutritional value because some B-vitamins are degraded. In SSA, cooked starchy foods are often associated with vegetables in household meals. This paper reviews studies that have focused fermented starchy foods and vegetable foods in SSA with the potential to provide B-vitamins to consumers. The review also describes the process of the preparation of these foods for final consumption, and techniques that can prevent or lessen B-vitamin loss, or enrich B-vitamins prior to consumption.

Application of pre-adaptation strategies to improve the growth of probiotic lactobacilli under food-relevant stressful conditions

While formulating a probiotic food, it is mandatory to make sure that the viability of probiotics is adequate at the point of consumption, which can be strongly compromised by stressful conditions due to low pH and high osmolarity. In this study, three probiotic lactobacilli were subjected to different pre-adaptation conditions, and the turbidimetric growth kinetics in challenging conditions (pH 4.0-6.5, NaCl 1-7%, sucrose 0.1-0.7 M) were evaluated. Different effects were observed for Lactobacillus acidophilus, Lacticaseibacillus casei, and Lactiplantibacillus plantarum. Indeed, pre-exposition to sub-optimal conditions in terms of pH and % NaCl significantly improved the ability of L. acidophilus and L. casei to overcome the osmotic stress due to salt or sucrose, and similar effects were observed for acidic stress. L. plantarum showed to be more tolerant to the challenging conditions applied in this study. Anyway, the pre-adaptation at conditions SUB_1 (pH 4.5 and NaCl 4%) and SUB_2 (pH 5 and NaCl 2%) speeded-up its growth kinetics by reducing the length of the lag phase under sucrose stress and enhancing the maximum growth rate at the highest pH tested. Moreover, an improvement in biomass amount was observed under sucrose stress. The whole data evidenced that the application of the appropriate pre-adaptation condition could contribute to making probiotics more robust towards challenging conditions due to food matrix, processing, and storage as well as gastrointestinal transit. Further studies will be necessary to gain insight into the proteomics and metabolomics responsible for increased tolerance to stressful conditions.

A comprehensive review on the development of probiotic supplemented confectioneries

Probiotics are living organisms that have beneficial effects on host by regulating the microbial balance of the intestinal system. While probiotics are naturally found in yogurt and other fermented foods, they can also be added to many products. Although mostly in dairy products, it is possible to see examples of food products supplemented by probiotics in bakeries, chocolates and confectioneries. Nowadays, the COVID-19 pandemic that the world suffers increased the demand for such functional food products including probiotics. Due to probiotics having potential effects on strengthening the immune system, confectioneries supplemented by probiotics were comprehensively discussed in this review together with the suggestion of a novel gelly composition. The suggested formulation of the product is a gel-like snack contains natural ingredients such as carrot, lemon juice and sugar provided from apples. This research review article provided a guide together with the recommendations for potential probiotic research in candy and confectionery industry.

Complete Genome Sequence of the Newly Developed Lactobacillus acidophilus Strain With Improved Thermal Adaptability

Lactobacillus acidophilus (L. acidophilus) is a representative probiotic and is widely used in many industrial products for its beneficial effects on human and animal health. This bacterium is exposed to harsh environments such as high temperatures for manufacturing industrial products, but cell yield under high temperatures is relatively low. To resolve this issue, we developed a new L. acidophilus strain with improved heat resistance while retaining the existing beneficial properties through the adaptive laboratory evolution (ALE) method. The newly developed strain, L. acidophilus EG008, has improved the existing limit of thermal resistance from 65°C to 75°C. Furthermore, we performed whole-genome sequencing and comparative genome analysis of wild-type and EG008 strains to unravel the molecular mechanism of improved heat resistance. Interestingly, only two single-nucleotide polymorphisms (SNPs) were different compared to the L. acidophilus wild-type. We identified that one of these SNPs is a non-synonymous SNP capable of altering the structure of MurD protein through the 435th amino acid change from serine to threonine. We believe that these results will directly contribute to any industrial field where L. acidophilus is applied. In addition, these results make a step forward in understanding the molecular mechanisms of lactic acid bacteria evolution under extreme conditions.

Turbidimetric definition of growth limits in probiotic Lactobacillus strains from the perspective of an adaptation strategy

The application of an adaptation strategy for probiotics, which may improve their stress tolerance, requires the identification of the growth range for each parameter tested. In this study, 4 probiotics (Lactobacillus acidophilus, Lacticaseibacillus casei, Lacticaseibacillus rhamnosus, and Lactiplantibacillus plantarum) were grown under different pH, NaCl, and sucrose concentrations at 25°C, 30°C, and 37°C. Turbidimetric growth curves were carried out and lag phase duration, maximum growth rate, and amplitude (i.e., the difference between initial and stationary phase optical density) were estimated. Moreover, cell morphology was observed, and cell length measured. The growth response, as well as the morphological changes, were quite different within the 4 species. The L. acidophilus was the most sensitive strain, whereas L. plantarum was shown to better tolerate a wide range of stressful conditions. Frequently, morphological changes occurred when the growth curve was delayed. Based on the results, ranges of environmental parameters are proposed that can be considered suboptimal for each strain, and therefore could be tested. The quantitative evaluation of the growth kinetics as well as the morphological observation of the cells can constitute useful support to the choice of the parameters to be used in an adaptation strategy, notwithstanding the need to verify the effect on viability both in model systems and in foods.

Strain diversity of plant-associated Lactiplantibacillus plantarum

Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a lactic acid bacteria species found on plants that is essential for many plant food fermentations. In this study, we investigated the intraspecific phenotypic and genetic diversity of 13 L. plantarum strains isolated from different plant foods, including fermented olives and tomatoes, cactus fruit, teff injera, wheat boza and wheat sourdough starter. We found that strains from the same or similar plant food types frequently exhibited similar carbohydrate metabolism and stress tolerance responses. The isolates from acidic, brine‐containing ferments (olives and tomatoes) were more resistant to MRS adjusted to pH 3.5 or containing 4% w/v NaCl, than those recovered from grain fermentations. Strains from fermented olives grew robustly on raffinose as the sole carbon source and were better able to grow in the presence of ethanol (8% v/v or sequential exposure of 8% (v/v) and then 12% (v/v) ethanol) than most isolates from other plant types and the reference strain NCIMB8826R. Cell free culture supernatants from the olive‐associated strains were also more effective at inhibiting growth of an olive spoilage strain of Saccharomyces cerevisiae. Multi‐locus sequence typing and comparative genomics indicated that isolates from the same source tended to be genetically related. However, despite these similarities, other traits were highly variable between strains from the same plant source, including the capacity for biofilm formation and survival at pH 2 or 50°C. Genomic comparisons were unable to resolve strain differences, with the exception of the most phenotypically impaired and robust isolates, highlighting the importance of utilizing phenotypic studies to investigate differences between strains of L. plantarum. The findings show that L. plantarum is adapted for growth on specific plants or plant food types, but that intraspecific variation may be important for ecological fitness and strain coexistence within individual habitats.

Physiological, Morphological and Antioxidant Responses of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 Isolated from Harbin Dry Sausages to Oxidative Stress

As functional starter cultures and potential probiotics, the ability of lactic acid bacteria to resist oxidative stress is essential to maintain viability and functional properties. This study investigates the effects of H₂O₂ at different concentrations (0, 1, 2, and 3 mM) on the physiological, morphological, and antioxidant properties of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 isolated from Harbin dry sausages. The increase in H₂O₂ concentration induced a significant increase in reactive oxygen species and a decrease in intracellular ATP levels (p < 0.05). Based on scanning electron microscopy, transmission electron microscopy, and electric conductivity analysis, H₂O₂ stress caused cell deformation, the destruction of cell membrane integrity, partial loss of the cytoplasm, and an increase in the cell conductivity of both strains. H₂O₂ stress with 1 mM or 2 mM concentrations could effectively improve the scavenging rates of free radicals, the activities of superoxide dismutase and glutathione peroxide, and the total antioxidant capacity of both strains (p < 0.05). In conclusion, an appropriate oxidative stress contributed to the activation of the antioxidant defense system of both strains, conferred strains a better effect in inhibiting the oxidation of fermented foods, and improved the health of the host.

Screening of autochthonous vaginal beneficial lactobacilli strains by their growth at high temperatures for technological applications

The pharmaceutical industry shows an emerging interest in formulas that contain live and beneficial microorganisms, also known as probiotics or pharmabiotics, which in many cases, are host-specific. The resistance to higher temperature is an essential feature of these microorganisms when working on the design of products for vaginal formula. In order to obtain a high number of viable cells and a prolonged shelf life in the designed product, it is required to apply technological procedures using high temperatures or abrupt changes of them, which result in conditions that are different from the optimal growth temperature and can affect the metabolic capabilities of the bacteria when administered to the host in order to reestablish the ecological mucosa. The aim of this work was to evaluate the behavior of 30 different species and strains of autochthonous beneficial vaginal lactobacilli (BVL) when exposed to high temperatures, determine their survival capabilities and analyze their pre-adaptation to those temperatures, in order that they still maintain their viability after technological processes and further conservation. BVL were exhibited to temperatures higher than optimal, with the purpose of evaluating their growth kinetics and parameters. Later, they were exposed to higher temperatures, and then, returned to their optimal, to determine if they were able to grow again. The strains that showed higher resistance were selected, and their viability and beneficial properties studied further. The growth kinetics of strains exposed to higher temperatures showed different patterns, which provided evidence that the thermal adaptation is strain-dependent and is not related to any particular species and/or metabolic group in which the strains were taxonomically classified. The pre-adaptive step allowed the growth of some of the strains, preserving their viability and probiotic properties after the high temperatures were applied. The results shows that BVL can be exposed to high temperatures used in different technological processes that are applied for pharmabiotic formulations, such as spray dried or vacuum rotary evaporation, and/or during the conservation period. The results obtained indicate that some specific BVL strains resist high temperatures and grow afterwards at optimal conditions.

Heat Adaptation Improved Cell Viability of Probiotic Enterococcus faecium HL7 upon Various Environmental Stresses

The production of viable functional probiotics presupposes stability of strain features in the final product. In previous studies, Enterococcus faecium HL7 was found to have relatively higher cell viability after freeze-drying and the long-lasting resistance to heat (60 °C) as well as higher antimicrobial activities against some of fish and human pathogens among isolated strains. For heat adaptation, E. faecium HL7 cells were exposed to 52 °C for 15 min. After adaption, slight decreases of unsaturated membrane fatty acid ratios were confirmed through fatty acid analysis. Upon subsequent exposure to various stress conditions such as H₂O₂ (0.01%), ethanol (20%), acid (pH 3), and alkali (pH 12), the survival rate of heat-adapted HL7 was 10³-10⁵-fold higher than that of non-adapted one. These results highlight the potential of preconditioning treatments for maximizing survival of probiotic bacteria during development of probiotic functional foods. The cross-protection afforded by acid against thermal stress may indicate that certain common protective mechanisms are induced by both heat and acid stress. These results can be applied to enhancing the cell viability during live cell formulation of E. faecium HL7 to be used as a potential probiotics in aquaculture.

Virulence of Leuconostoc phages: Influence of stress conditions associated to dairy processes on their host-phage interactions

In this work, we assessed the impact of technological cell stress conditions, commonly present in industrial dairy processes, on the host strain-phage interactions in Leuconostoc. Adsorption and burst size of LDG (Leuconostoc pseudomesenteroides) and Ln-9 (Leuconostoc mesenteroides) phages were evaluated under the following conditions: i) MRS broth, 30 °C; ii) MRS broth at pH 5.5, 30 °C (acidic stress); iii) MRS broth added of NaCl at 4% w/v, 30 °C (osmotic stress) and iv) MRS broth, 10 °C (cold stress). Experiences were performed with the host strains growing both in MRS broth (30 °C) and under stress conditions. On the other hand, the effect of diverse levels of NaCl, KCl, saccharose and glucose on the adsorption for LDG phage was evaluated. Acidic and cold conditions did not significantly affect the adsorption rates for any phage. However, adsorption rate of phage LDG was highly reduced under osmotic stress (NaCl), except when the host strain previously grew in presence of the salt. LDG phage adsorption was not modified by addition of saccharides, but it drastically decreased in presence of salts. Acidic conditions did not affect the burst size for LDG phage, but Ln-9 phage diminished this parameter (61 phage particles/infected cell). Latency time showed a lengthening of 10 min for both phages, while the burst time remained unaltered for LDG and it was delayed 10 min for Ln-9. LDG phage did not propagate under osmotic conditions, but Ln-9 phage released phage particles with an important increase of its latent period and burst time. No phage particles were released within 90 min after the adsorption step under cold stress. This is the first report about this subject. Under certain conditions of technological stress (osmotic and cold) associated to dairy processes, phage infections on the two systems studied in this work could be delayed/inhibited.

The Phenotypic Analysis of Lactobacillus plantarum shsp Mutants Reveals a Potential Role for hsp1 in Cryotolerance

Small heat shock proteins (sHSPs) are ubiquitous, low molecular weight (MW) proteins that share a conserved alpha-crystallin domain. sHSPs oligomers exhibit chaperon-like activities by interacting with unfolded substrates, thereby preventing their aggregation and precipitation. Unlike most lactobacilli, which have single shsp genes, three different sHSP-encoding genes, i.e., hsp1, hsp2, and hsp3, were previously identified in the probiotic Lactobacillus plantarum WCFS1. Early studies, including the characterization of the knock out (KO) mutant for hsp2, indicated a different organization and transcriptional regulation of these genes and suggested that the three L. plantarum sHSPs might accomplish different tasks in stress response. To unravel the role of sHSPs, KO mutants of hsp1 and hsp3 were generated using a Cre-lox based system. Mutation of either genes resulted in impaired growth capacity under normal conditions, heat-stress and stresses typically found during host interactions and food technological process. However, survival to heat shock and the level of thermal stabilization of cytoplasmic proteins were similar between mutants and parental strain. Transcriptional analysis revealed that in the mutant genetic backgrounds there is an upregulated basal expression of the un-mutated mate hsps and other stress-related genes, which may compensate for the loss of HSP function, hence possibly accounting for the lack of a remarkable susceptibility to heat challenge. HSP3 seemed relevant for the induction of thermotolerance, while HSP1 was required for improved cryotolerance. Cell surface properties and plasma membrane fluidity were investigated to ascertain the possible membrane association of sHSP. Intriguingly, the loss of hsp1 was associated to a lower level of maximal membrane fluidity upon heat stress. A role for HSP1 in controlling and improving membrane fluidity is suggested which may pertains its cryoprotective function.

Survival of probiotic Lactobacillus plantarum and Enterococcus faecium in alginate beads during stress treatments

Purpose

This study aims to protect Lactobacillus plantarum and Enterococcus faecium encapsulated in alginate beads during stress treatments, such as high temperatures and concentrations of sodium chloride (NaCl) and sodium nitrite (NaNO2).

Design/methodology/approach

Free and encapsulated probiotics were subjected to 70 and 80°C during 5, 10, 20 and 30 min. In addition, the probiotics were subjected to concentrations of 0.5, 1.0, 2.5 and 5.0 per cent NaCl and 0.5 and 1.0per cent of NaNO2.

Findings

Free Lactobacillus plantarum was more resistant to heat than free Enterococcus faecium. Alginate-encapsulated Lactobacillus plantarum (ALP) also was more resistant to heat treatments than alginate-encapsulated Enterococcus faecium (AEF). After 30 min at 70°C, ALP showed levels about 6.9 log CFU/g while AEF presented 4.3 log CFU/g (p = 0.005). However, at 80°C, ALP maintained levels higher than 6 log CFU/g for up to 10 min, while AEF was able to maintain those levels only for approximately 5 min (p = 0.003). Encapsulation process provided adequate protection for both probiotics against NaCl. In relation to NaNO2 concentrations, 0.5 and 1.0 per cent reduced viability of both probiotics (p = 0.014), either as free cells or as alginate-encapsulated forms.

Practical implications

Alginate beads containing probiotics is an interesting alternative for application in foods such as cooked meat products.

Originality/value

Alginate beads elaborated with milk powder, inulin and trehalose were effective to protect probiotics in stress situations similar to those can be found in the processing of foods, such as cooked meat products.

Characterization and adsorption of a Lactobacillus plantarum virulent phage

Bacteriophage infection of lactic acid bacteria is considered one of the biggest worldwide problems in the food industry. Bacteriophages may cause negative effects on the fermentation of various dairy-based products. A virulent bacteriophage was isolated from an abnormal fermentation liquid of Lactobacillus plantarum IMAU10120. The characterization and influence of temperature, pH, divalent cations, and chloramphenicol on the adsorption ability of this phage were evaluated. The results showed that this phage belonged to the Siphoviridae family. It exhibited a burst time of 135 min and a burst size of approximately 215 counts expressed per milliliter per infective center. No significant effect was shown to influence its viability and adsorption at 10 to 37°C. More than 90% of phages exhibited infectivity from pH 5 to 9. Divalent ions and chloramphenicol did not have a significant influence on the adsorption of this phage. The information obtained in this study will enrich the database of lactobacilli virulent phages and provide a basis of information for the control of phages in the food fermentation industry.

Soy extract and maltodextrin as microencapsulating agents for Lactobacillus acidophilus: a model approach

The present study aimed to optimise the microencapsulation of Lactobacillus acidophilus La-05 by spray drying, using soy extract and maltodextrin as encapsulants. Air inlet temperature, maltodextrin/soy extract ratio and feed flow rate were investigated through Central Composite Rotational Design (CCRD). Probiotic viability increased with increasing the proportion of soy extract. Temperature and feed flow rate had a negative effect. Particle diameter ranged from 4.97 to 8.82 μm, water activity from 0.25 to 0.52 and moisture from 2.30 to 7.01 g.100g-1 Particles produced following the optimised conditions (air temperature of 87 °C, maltodextrin/soy extract ratio of 2:3 w.w-1, feed flow rate of 0.54 L.h-1) reached Encapsulation yield (EY) of 83%. Thermogravimetry and FTIR analysis suggested that microcapsules could protect L. acidophilus cells against dehydration and heating. During storage, microencapsulated probiotic had high cell viability (reductions ranged between 0.12 and 1.72 log cycles). Soy extract/maltodextrin presented well-encapsulating properties of Lactobacillus acidophilus La-05.

Proteomic analysis of Lactobacillus casei GCRL163 cell-free extracts reveals a SecB homolog and other biomarkers of prolonged heat stress

Prolonged heat stress is one of the harsh conditions Lactobacillus casei strains encounter as non-starter lactic acid bacteria in dairy product manufacture. To understand the physiological and molecular mechanisms through which Lb. casei GCRL163 adapts to persistent elevated temperature, label-free quantitative proteomics of cell-free extracts was used to characterize the global responses of the strain cultured anaerobically in bioreactors at 30 to 45°C, pH 6.5, together with GC-MS for fatty acid methyl ester analysis at different growth phases. At higher growth temperatures, repression of energy-consuming metabolic pathways, such as fatty acid, nucleotide and amino acid biosynthesis, was observed, while PTS- and ABC-type transporter systems associated with uptake of nitrogen and carbon sources were up-regulated. Alkaline shock protein Asp23_2 was only detected at 45°C, expressed at high abundance, and presumptive α-L-fucosidase only at 40 and 45°C, with highly increased abundance (log2-fold change of 7) at 45°C. We identified a novel SecB homolog as a protein export chaperone putatively involved in posttranslational translocation systems, which was down-regulated as growth temperature increased and where the modelled 3D-structure shared architectural similarities with the Escherichia coli SecB protein. Membrane lipid analyses revealed temporal changes in fatty acid composition, cyclization of oleic acid to cyclopropane and novel cyclopentenyl moieties, and reduced synthesis of vaccenic acid, at higher temperatures. An 18kDa α-crystallin domain, Hsp20 family heat shock protein was more highly up-regulated in response to heat stress compared to other molecular chaperones, suggesting this protein could be a useful biomarker of prolonged heat stress in Lb. casei GCRL163.

In situ riboflavin fortification of different kefir-like cereal-based beverages using selected Andean LAB strains

Cereal-based functional beverages represent social, economic, and environmental sustainable opportunities to cope with emerging trends in food consumption and global nutrition. Here we report, for the first time, the polyphasic characterization of three cereal-based kefir-like riboflavin-enriched beverages, obtained from oat, maize and barley flours, and their comparison with classical milk-based kefir. The four matrices were successfully fermented with commercial starters: i) milk-kefir and ii) water-kefir, proving the potential of cereal ingredients in the formulation of dairy-like fermented beverages with milk-kefir starter behavior better in these matrices. In the light of their potentiality, seven riboflavin-producing Andean Lactic Acid Bacteria (LAB) were tested for tolerance to food stresses commonly encountered during food fermentation. Moreover, the LAB strains investigated were screened for spontaneous riboflavin overproducing derivatives. Lactobacillus plantarum M5MA1-B2 with outstanding response to stress, was selected to improve riboflavin content in an in situ fortification approach. The combination of L. plantarum M5MA1-B2 riboflavin overproducing strain with milk kefir starter in oat, lead to cover, for one serving of 100 g, 11.4% of Recommended Dietary Allowance (RDA). Besides, addition of L. plantarum M5MA1-B2 improved performance of water kefir in oat and maize matrices. Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) analysis provided the on-line Volatile Organic Compounds profiles supporting the best combination of starter, LAB and cereal matrix for novel functional foods development.

Enhancing water stress tolerance improves fitness in biological control strains of Lactobacillus plantarum in plant environments

Lactobacillus plantarum strains PM411 and TC92 can efficiently control bacterial plant diseases, but their fitness on the plant surface is limited under unfavourable low relative humidity (RH) conditions. To increase tolerance of these strains to water stress, an adaptive strategy was used consisting of hyperosmotic and acidic conditions during growth. Adapted cells had higher survival rates under desiccation than non-adapted cells. Transcript levels and patterns of general stress-related genes increased immediately after the combined-stress adaptation treatment, and remained unaltered or repressed during the desiccation challenge. However, there were differences between strains in the transcription patterns that were in agreement with a better performance of adapted cells of PM411 than TC92 in plant surfaces under low RH environmental conditions. The combined-stress adaptation treatment increased the survival of PM411 cells consistently in different plant hosts in the greenhouse and under field conditions. Stress-adapted cells of PM411 had similar biocontrol potential against bacterial plant pathogens than non-adapted cells, but with less variability within experiments.

Leuconostoc strains isolated from dairy products: Response against food stress conditions

A systematic study about the intrinsic resistance of 29 strains (26 autochthonous and 3 commercial ones), belonging to Leuconostoc genus, against diverse stress factors (thermal, acidic, alkaline, osmotic and oxidative) commonly present at industrial or conservation processes were evaluated. Exhaustive result processing was made by applying one-way ANOVA, Student's test (t), multivariate analysis by Principal Component Analysis (PCA) and Matrix Hierarchical Cluster Analysis. In addition, heat adaptation on 4 strains carefully selected based on previous data analysis was assayed. The strains revealed wide diversity of resistance to stress factors and, in general, a clear relationship between resistance and Leuconostoc species was established. In this sense, the highest resistance was shown by Leuconostoc lactis followed by Leuconostoc mesenteroides strains, while Leuconostoc pseudomesenteroides and Leuconostoc citreum strains revealed the lowest resistance to the stress factors applied. Heat adaptation improved thermal cell survival and resulted in a cross-resistance against the acidic factor. However, all adapted cells showed diminished their oxidative resistance. According to our knowledge, this is the first study regarding response of Leuconostoc strains against technological stress factors and could establish the basis for the selection of "more robust" strains and propose the possibility of improving their performance during industrial processes.

Characteristics and Application in Food Preservatives of Lactobacillus plantarum TK9 Isolated from Naturally Fermented Congee

In the present research, a strain of Lactobacillus plantarum TK9 was isolated from the Chinese naturally fermented congee and its characteristics for probiotic and food preservation were investigated. In terms of probiotic, the strain not only survives bile salts and simulated gastric juice but grows well under hypertonic conditions. Besides, the L. plantarum TK9 exhibited a broad antifungal spectrum, including most of the species closely related to food spoilage, like Penicillium roqueforti, Penicillium citrinum, Penicillium oxalicum, Aspergillus fumigatus, Aspergillus flavus and Rhizopus nigricans. But no evident inhibition effect was found on Aspergillus niger. To further evaluate its potential as bio-preservative, L. plantarum TK9 was inoculated into citrus, apples and yogurt prior to the addition of moulds. The results indicated that L. plantarum TK9 could obviously prolong shelf life of the test food for 72–96 h and represent an excellent candidate for food-related bio-preservative.

Phage adsorption and lytic propagation in Lactobacillus plantarum: could host cell starvation affect them?

Background

Bacteriophages constitute a great threat to the activity of lactic acid bacteria used in industrial processes. Several factors can influence the infection cycle of bacteriophages. That is the case of the physiological state of host cells, which could produce inhibition or delay of the phage infection process. In the present work, the influence of Lactobacillus plantarum host cell starvation on phage B1 adsorption and propagation was investigated.

Result

First, cell growth kinetics of L. plantarum ATCC 8014 were determined in MRS, limiting carbon (S-N), limiting nitrogen (S-C) and limiting carbon/nitrogen (S) broth. L. plantarum ATCC 8014 strain showed reduced growth rate under starvation conditions in comparison to the one obtained in MRS broth. Adsorption efficiencies of > 99 % were observed on the starved L. plantarum ATCC 8014 cells. Finally, the influence of cell starvation conditions in phage propagation was investigated through one-step growth curves. In this regard, production of phage progeny was studied when phage infection began before or after cell starvation. When bacterial cells were starved after phage infection, phage B1 was able to propagate in L. plantarum ATCC 8014 strain in a medium devoid of carbon source (S-N) but not when nitrogen (S-C broth) or nitrogen/carbon (S broth) sources were removed. However, addition of nitrogen and carbon/nitrogen compounds to starved infected cells caused the restoration of phage production. When bacterial cells were starved before phage infection, phage B1 propagated in either nitrogen or nitrogen/carbon starved cells only when the favorable conditions of culture (MRS) were used as a propagation medium. Regarding carbon starved cells, phage propagation in either MRS or S-N broth was evidenced.

Conclusions

These results demonstrated that phage B1 could propagate in host cells even in unfavorable culture conditions, becoming a hazardous source of phages that could disseminate to industrial environments.