Comparative survival rates of human-derived probiotic Lactobacillus paracasei and L. salivarius strains during heat treatment and spray drying

Presence of two Lactobacillus and Bifidobacterium probiotic strains in the neonatal ileum

The overall purpose of this study was to examine the lactobacilli and bifidobacteria microbiota in the human ileum at a very early stage of life. Ileostomy effluents from two infants, taken at different time points, were plated on Lactobacillus selective agar and cys-MRS containing mupirocin to select for bifidobacteria. In one case, a stool sample following ileostomy reversal was subsequently analyzed microbiologically. Pulse-field gel electrophoresis and 16S rRNA sequencing was used to investigate the cultivable population of bifidobacteria and lactobacilli and denaturing gradient gel electrophoresis (DGGE) to examine the non-cultivable population. The probiotic strain, Lactobacillus paracasei NFBC 338, was recovered at both time points from one of the infants and dominated in the small intestine for a period of over 3 weeks. Moreover, the probiotic strain, B. animalis subsp. lactis Bb12, was obtained from the other infant. This study shows the presence of two known probiotic strains in the upper intestinal tract at an early stage of human life and thus provides some evidence for their ability to colonize the infant small intestine.

Evaluation of the thermally dried immobilized cells of Lactobacillus delbrueckii subsp. bulgaricus on apple pieces as a potent starter culture

The aim of the present study was to evaluate the impact of thermal drying of immobilized Lactobacillus delbrueckii subsp. bulgaricus on apple pieces on the use of the derived biocatalyst in whey fermentation. The thermally dried immobilized biocatalyst was compared to wet and freeze-dried immobilized cells, in respect to maintenance of cell viability and fermentation efficiency. The thermal drying process appeared to be more efficient on survival rate as an 84% of the cells used for immobilization survived the process, while the freeze-drying process led to a 78% rate. The thermally dried immobilized biocatalyst was used in 12 repeated batch fermentations of synthetic lactose medium and whey at 37, 45, and 50 degrees C in order to evaluate its metabolic activity. The high number of repeated batch fermentations showed a tendency for high operational stability. Fermentations continued for up to 2 months without any significant loss of metabolic activity. SPME GC/MS analysis of aroma-related compounds revealed the distinctive character of fermented whey produced by the thermally dried immobilized bacterium cells. The effect of storage at 4-6 degrees C for up to 165 days of the biocatalyst, held directly after drying and after repeated batch fermentations, on fermentation activity was also studied. After storage, reactivation in whey was immediate, and the immobilized biocatalyst was able to produce up to 51.7 g/L lactic acid at 37 degrees C. The potential of thermally dried immobilized L. delbrueckii as a starter culture for food production was subsequently evaluated.

Dry stress and survival time of Enterobacter sakazakii and other Enterobacteriaceae in dehydrated powdered infant formula

Powdered infant formula is not a sterile product, and opportunistic pathogens could multiply in the reconstituted product, resulting in neonatal infections. In this study, the generation of sublethally injured Enterobacteriaceae during desiccation and their persistence in dehydrated powdered infant formula was assessed during a 2.5-year period. The study included 27 strains of Enterobacter sakazakii, Enterobacter cloacae, Salmonella Enteritidis, Citrobacter koseri, Citrobacter freundii, Escherichia coli, Escherichia vulneris, Pantoea spp., Klebsiella oxytoca, and Klebsiella pneumoniae. The number of sublethally injured cells generated during desiccation was lower for K. oxytoca, Pantoea spp., Salmonella Enteritidis, and capsulated strains of E. sakazakii than for the other Enterobacteriaceae. The Enterobacteriaceae could be divided into three groups with respect to their long-term survival in the desiccated state. C. freundii, C. koseri, and E. cloacae were no longer recoverable after 6 months, and Salmonella Enteritidis, K. pneumoniae, and E. coli could not be recovered after 15 months. Pantoea spp., K. oxytoca, and E. vulneris persisted over 2 years, and some capsulated strains of E. sakazakii were still recoverable after 2.5 years.

Culture and spray-drying of Tsukamurella paurometabola C-924: stability of formulated powders

The nematocidal agent, Tsukamurella paurometabola C-924, was cultured in a 300 l bioreactor. Spray-dried formulations of this microorganism were prepared using sucrose. At an outlet temperature 62 degrees C, survival rates between 12 and 85% were reached with sucrose up to 10% (w/w). The stability study of the powders showed that the best storage condition was at 4 degrees C under vacuum. A new method for the calculation of cell death order for bacteria stored at low temperatures was developed. Powders stored under vacuum showed an Arrhenius behavior in relation to cell death kinetics.

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.

Sensitive quantitative detection of commensal bacteria by rRNA-targeted reverse transcription-PCR

A sensitive rRNA-targeted reverse transcription-quantitative PCR (RT-qPCR) method was developed for exact and sensitive enumeration of subdominant bacterial populations. Using group- or species-specific primers for 16S or 23S rRNA, analytical curves were constructed for Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, Clostridium perfringens, and Pseudomonas aeruginosa, and the threshold cycle value was found to be linear up to an RNA amount of 10(-3) cell per RT-PCR. The number of bacteria in culture was determined by RT-qPCR, and the results correlated well with the CFU count over the range from 10(0) to 10(5) CFU. The bacterial counts obtained by RT-qPCR were the same as the CFU counts irrespective of the growth phase in vitro, except for C. perfringens during starvation periods; the viable cell counts obtained by using a combination of 4',6-diamidino-2-phenylindole (DAPI) staining and SYTO9-propidium iodide double staining were in good agreement with the RT-qPCR counts rather than with the CFU counts. The RT-qPCR method could detect endogenous Enterobacteriaceae and P. aeruginosa in feces of hospitalized patients (n = 38) at a level of 10(3) cells per g of feces, and for enumeration of S. aureus or P. aeruginosa spiked into human peripheral blood, the lower detection limit for RT-qPCR quantification of the bacteria was 2 cells per ml of blood, suggesting that this method was equivalent to the conventional culture method. As only 5 h was needed for RT-qPCR quantification, we suggest that rRNA-targeted RT-qPCR assays provide a sensitive and convenient system for quantification of commensal bacteria and for examining their possible invasion of a host.

Enhanced survival of GroESL-overproducing Lactobacillus paracasei NFBC 338 under stressful conditions induced by drying

GroESL-overproducing Lactobacillus paracasei NFBC 338 was dried, and its viability was compared with that of controls. Spray- and freeze-dried cultures overproducing GroESL exhibited approximately 10-fold and 2-fold better survival, respectively, demonstrating the importance of GroESL in stress tolerance, which can be exploited to enhance the technological performance of sensitive probiotic cultures.

Preservation of micro-organisms by drying; A review

The preservation of micro-organisms by different drying methodologies has been used for decades. Freeze drying in particular is the preferred method for transporting and storing vast culture collections of micro-organism strain types. The literature on drying and preserving micro-organisms is extensive, but is often specific to one particular strain. This review attempts to draw some similar concepts and findings together in one paper, to compare different drying techniques, with specific reference to microorganisms. The main topics covered are cell growth phases and concentration, inducing drying tolerance in microbial cells, drying methods, rehydration of dried cells and packaging and storage conditions. Also, particular attention has been paid to the use of freeze drying and the protective matrices used to improve microbial cell viability after drying.

Selection of potential probiotic lactobacilli from pig feces to be used as additives in pelleted feeding

Thirty-five isolates from pig feces were identified as Lactobacillus reuteri (12 strains), Lactobacillus mucosae (7), Lactobacillus plantarum (6), Lactobacillus kitasatonis (3), Lactobacillus rossiae (2), Lactobacillus ultunensis (2), Lactobacillus crispatus (2), and Lactobacillus intestinalis (1) by partial sequence analysis of the 16S rRNA. All isolates were detected at 8-9 log CFU g(-1). Preliminarily, strains were selected based on resistance to heat treatments (ca. 70 degrees C for 10 s). The decrease in viability for some L. reuteri, L. mucosae, L. plantarum, L. kitasatonis, and L. rossiae strains was lower than 1 log cycle. Selected strains were further characterized for acid and bile salt resistance, and antibacterial activity. Except for L. kitasatonis, tolerance to simulated gastric and intestinal conditions was enhanced for all strains by addition of reconstituted skimmed milk. Antibacterial activity was found against Gram-positive and -negative potential pathogens. L. reuteri 8.1, 3S7, 6.2, and 1.2, L. mucosae 1.1R, L. plantarum 4.1, and L. rossiae 4.4 were freeze-dried and mixed (1%, w/w) into pig feed before pelleting. After pelleting, pig feed contained 10-9 log CFU kg(-1) of lactobacilli. L. plantarum 4.1, and L. reuteri 3S7 were selected based on their bile salt resistance, pH tolerance, antimicrobial activity and heat resistance. The findings in this study provide a strong basis for exploring the potential of porcine lactobacilli isolates to be used in pelleted feeding as probiotic additives.

Heterologous expression of BetL, a betaine uptake system, enhances the stress tolerance of Lactobacillus salivarius UCC118

Given the increasing commercial and clinical relevance of probiotic cultures, improving the technological robustness of what are often process-sensitive cultures is an important biological goal. The nisin-controlled expression system was used to direct the heterologous expression of the listerial betaine uptake system BetL in the probiotic strain Lactobacillus salivarius UCC118. Following nisin induction, strains expressing betL exhibited a significant increase in resistance to several stresses, including elevated osmo-, cryo-, baro-, and chill tolerance, as well as increased resistance to spray- and freeze-drying. The ability to confer additional stress tolerance on a probiotic culture may be an important step in delivering viable cultures for maximal efficacy.

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

AIMS

To assess four carbohydrates for the protective effect against Lactobacillus helveticus cells inactivation during vacuum drying, and to study the effect of selected carbohydrate on changes of inactivation kinetics.

METHODS AND RESULTS

Early stationary phase L. helveticus cells grown in MRS media were recovered from fermentation broth, washed with PBS buffer (pH 7.0), and then mixed with different concentrations of four carbohydrates, namely lactose, sorbitol, inulin, and xanthan gum. Cells were dried in a vacuum drier at 100 mbar, 43 degrees C for 12 h. Only cells with 1% sorbitol addition showed higher survival (18%) over cells without added carbohydrate (8%). Using in situ microbalance technique whereby cell weight during vacuum drying was continuously monitored via precision balances integrated into the vacuum chamber, drying and inactivation kinetics of cells and cells mixed with sorbitol were established.

CONCLUSION

Survival of L. helveticus during the vacuum drying could be improved by the addition of optimal concentration of 1% sorbitol. Addition of sorbitol did not cause drastic changes in drying rate, water content and water activity of samples. The protection mechanisms of sorbitol seemed not to be due to a direct physical effect, which could be related to drying rate.

SIGNIFICANCE AND IMPACT OF THE STUDY

The increase in survival of cells after vacuum drying by the addition of a protective carbohydrate may provide an alternative mean to preserve starter cultures at a higher level of activity.

Altering Renneting pH Changes Microstructure, Cell Distribution, and Lysis of Lactococcus lactis AM2 in Cheese Made from Ultrafiltered Milk

The objective of this study was to investigate the lysis of a highly autolytic strain of Lactococcus lactis ssp. cremoris AM2 in a model cheese made from concentrated ultrafiltered milk. From the same initial ultrafiltered retentate inoculated with L. lactis AM2, 5 cheeses were made by the addition of rennet at different pH values (6.6, 6.2, 5.8, 5.4, and 5.2). Lysis was monitored by measurement of the release of lactate dehydrogenase, an intracellular marker enzyme, and by immunodetection of intracellular proteins with species-specific antibodies. Confocal scanning laser microscopy (CSLM) was used to investigate the cheese microstructure by staining for protein and fat. Dual staining with a bacterial viability kit with CSLM was performed to reveal the integrity and localization of the bacterial cells. Levels of soluble calcium significantly increased when the pH at which the rennet was added decreased. In cheese renneted at pH 6.6, CSLM revealed an open porous structure containing a dense protein network with fat globules of different sizes distributed in the aqueous phase. In cheese renneted at pH 5.2, the protein network was homogeneous, with a less dense protein network, and an even distribution of fat globules. On d 1, bacterial cells were organized into colonies in cheese renneted at pH 6.6, whereas in cheeses renneted at pH 5.2, bacteria were evenly dispersed as single cells throughout the protein network. Lysis was detected on d 1 in cheeses renneted at high pH values and continued to increase throughout ripening, whereas induction of lysis was delayed in cheeses renneted at lower pH values until the end of ripening. This study demonstrates that alterations in the microstructure of the cheese and the distribution of cells play a role in lysis induction of L. lactis AM2.

Intrinsic tolerance of Bifidobacterium species to heat and oxygen and survival following spray drying and storage

AIMS

This study examined the tolerance of various species of the genus Bifidobacterium to heat and oxygen and evaluated the survival of selected strains following spray drying and during storage.

METHODS AND RESULTS

Nine Bifidobacterium species were considered to be relatively tolerant to both heat and oxygen and mostly segregated into two clusters within the 16S rDNA phylogenetic tree. Four species were tolerant to oxygen and 12 species were considered sensitive to oxygen and heat. Using a skimmed milk-based carrier good survival following spray drying and storage at 4 degrees C correlated with tolerance to heat and oxygen. Viability was inversely related to storage temperature and at 15 degrees C and 25 degrees C, a significant decline was observed for all species. The inclusion of gum acacia had no significant affect on survival or viability. However, using a fluidized-bed spray dryer viability was greatly improved.

CONCLUSIONS

A group of closely related species tolerant to heat and oxygen had high survival following spray drying and maintained viability during prolonged storage at 4 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

Spray drying is a suitable method for the production of skimmed milk powder enriched with high numbers of viable bifidobacteria.

Enumeration and identification of pediococci in powder-based products using selective media and rapid PFGE

In this study, pediococci selective medium (PSM) was evaluated for the enumeration of Pediococcus acidilactici and Pediococcus pentosaceus from probiotic animal feed and silage inoculants. PSM is based on the complex basal medium MRS supplemented with cysteine hydrochloride, novobiocin, vancomycin, and nystatin. No significant change in electivity was observed when pediococci where recovered from culture or powder-based products following incubation at 37 degrees C under anaerobic conditions for 24 h. The medium was suitable for the enumeration of pediococci in samples also containing bacilli, bifidobacteria, enterococci, lactobacilli, lactococci, propionibacteria, streptococci, and yeast components. However, to inhibit Lactobacillus plantarum and Lactobacillus casei, ampicillin was added and the revised medium, termed PSM+A, was also considered to be suitably elective for pediococci recovered from powder. In addition, a rapid PFGE protocol is presented, which allows Pediococcus species and strain verification from colonies in less than 3 days.

Application of a direct fluorescence-based live/dead staining combined with fluorescence in situ hybridization for assessment of survival rate of Bacteroides spp. in drinking water

To evaluate the viability and survival ability of fecal Bacteroides spp. in environmental waters, a fluorescence-based live/dead staining method using ViaGram Red+ Bacterial gram stain and viability kit was combined with fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probe (referred as LDS-FISH). The proposed LDS-FISH was a direct and reliable method to detect fecal Bacteroides cells and their viability at single-cell level in complex microbial communities. The pure culture of Bacteroides fragilis and whole human feces were dispersed in aerobic drinking water and incubated at different water temperatures (4 degrees C, 13 degrees C, 18 degrees C, and 24 degrees C), and then the viability of B. fragilis and fecal Bacteroides spp. were determined by applying the LDS-FISH. The results revealed that temperature and the presence of oxygen have significant effects on the survival ability. Increasing the temperature resulted in a rapid decrease in the viability of both pure cultured B. fragilis cells and fecal Bacteroides spp. The live pure cultured B. fragilis cells could be found at the level of detection in drinking water for 48 h of incubation at 24 degrees C, whereas live fecal Bacteroides spp. could be detected for only 4 h of incubation at 24 degrees C. The proposed LDS-FISH method should provide useful quantitative information on the presence and viability of Bacteroides spp., a potential alternative fecal indicator, in environmental waters.

Inhibition of bacteriophage K proliferation on Staphylococcus aureus in raw bovine milk

AIMS

To assess the ability of staphylococcal bacteriophage K to inhibit Staphylococcus aureus in raw milk.

METHODS AND RESULTS

The ability of bacteriophage (phage) to replicate in milk is important in situations where phage might be used as a therapeutic for bovine mastitis. Phage K was able to replicate normally, leading to elimination of the host culture in milk, which had been previously heat-treated. When raw milk was used under identical conditions, the phages were unable to replicate. Phage adsorption assays were performed and these demonstrated that adsorption of phage was significantly reduced in the raw milk while it was restored in the heat-treated sample (86.50% compared with 99.96% adsorption respectively). When confocal microscopy with a Live/Dead Bac light staining system was employed, it was observed that in raw milk S. aureus formed clusters associated with fat globules, while in heat-treated milk, bacterial agglutination had not occurred.

CONCLUSIONS

Raw milk inhibits staphylococcal phage K proliferation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This observation has implications for the exploitation of staphylococcal therapeutic phage in milk.

Sequence analysis of the plasmid genome of the probiotic strain Lactobacillus paracasei NFBC338 which includes the plasmids pCD01 and pCD02

Lactobacillus paracasei NFBC338 is a probiotic strain that was isolated from the human gastrointestinal tract (GIT) and contains a plasmid genome of 80kb. Using a shotgun sequencing approach, two of the plasmids, pCD01 (19,882bp) and pCD02 (8554bp) have been completely sequenced, and four contiguous sequences (Contigs) have been assembled. Bioinformatic analysis of pCD01 revealed that it contains 23 putative open reading frames (ORFs) and that it contains regions characterised by potential replication functions and multidrug resistance (MDR). In contrast, the content of pCD02 is mainly cryptic, although, it does contain two insertion sequence (IS) elements. Indeed, up to 17% of the entire plasmid genome encodes putative transposable elements. In addition, there are a number of interesting ORFs distributed over the four Contigs that show significant homology to genes such as those involved in adherence and biotin metabolism, which may prove beneficial to Lb. paracasei NFBC338 under certain environmental conditions. This study provides a novel insight into the rich plasmid complement of this probiotic Lactobacillus strain, which may potentially be exploited as the basis for development of improved genetic tools for probiotic lactobacilli.

Air drying optimization of Saccharomyces cerevisiae through its water-glycerol dehydration properties

AIMS

This study describes the different stages of optimization in an original drying process for yeasts, which allows the retrieval of dried samples of Saccharomyces cerevisiae CBS 1171 with maximum viability.

METHODS AND RESULTS

The process involves the addition of wheat flour to yeast pellets, followed by mixing and then air-drying in a fluidized bed dryer. The sensitivity to the osmotic stress was first studied in a water-glycerol solution and the observed results were then applied to the drying process. This study have shown that the yeast was quite resistant to osmotic stress and pointed out the existence of zones of sensitivity where viability dramatically decrease as function of final osmotic pressure and temperature of the treatment. Thus, for dehydration until low osmotic pressure (133 MPa, i.e. a(w) = 0.38) results have shown that viability was better when temperature of the treatment was less than 8 degrees C or higher than 25 degrees C. Moreover, kinetic of dehydration was found to greatly influence cells recovery.

CONCLUSIONS

These observations allowed the choice of parameters of dehydration of yeasts with an original drying process which involve the mix of the yeasts with wheat flour and then drying in a fluidized bed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This process dried rapidly the yeasts to less than 220 MPa (aw < or = 0.2) with whole cell recovery and good fermentative capabilities.

Survival of Lactobacillus sakei during heating, drying and storage in the dried state when growth has occurred in the presence of sucrose or monosodium glutamate

Spray-dried cells of Lactobacillus sakei CTC 494 survived ca. 60% longer in the spray dried state when cells were grown in the presence of 20 g sucrose l(-1) or 12.5 g monosodium glutamate l(-1). No significant differences were observed in viability during storage in the freeze dried state with the addition of these compounds to the growth medium, nor in survival during a heat treatment (55 degrees C). Both sucrose and glutamate in the growth medium suppressed intracellular accumulation of total amino acids and changed the overall pattern of the individual amino acids. Glutamate in the growth medium enhanced intracellular glutamate by ca. 38%.

Survival of Lactobacillus plantarum 44a after spraying and drying in feed and during exposure to gastrointestinal tract fluids in vitro

A good probiotic strain should be able to survive the conditions of handling and storage to be delivered in high concentration to the host. That is especially important when stressful conditions are prevalent in the carrier, for instance in low water content foods like animal feed. The aim of this research was to study the survival of the probiotic candidate Lactobacillus plantarum 44a after spraying and drying in feed, and during storage and exposure to gastrointestinal tract fluids in vitro. In addition, the viability of the strain during exposure to distilled water and 2% NaCl was studied. Feed was sprayed with a suspension of asymptotically equal to 2 x 10(10) CFU of L. plantarum 44a in 10, 15, 20, 25 and 30% v/w of the feed and dried to constant weight (6% moisture) in a convective oven at 25 degrees C. L. plantarum 44a survived 14.67, 36, 51.86, 78.9 and 105.3% respectively in relation to the original % v/w of the feed. After 3 weeks of storage at 25 degrees C, survival was similarly low in all the treatments. L. plantarum 44a stored in feed containing 13% moisture, vacuum-packaged and stored in refrigeration, maintained high viability (approximately 100%) after 1 year of storage. Survival was not affected after feed-containing lactobacilli was exposed to gastrointestinal fluids in a simulation model. Viability of L. plantarum 44a as a cell suspension in PBS added directly to distilled water or distilled water with 2% NaCl was maintained up to 48 h; after 72 h, viability started to decline. It is concluded that L. plantarum 44a maintained high viability after being dried and stored in feed even after exposure to gastric and intestinal fluids in vitro.

Improved stress tolerance of GroESL-overproducing Lactococcus lactis and probiotic Lactobacillus paracasei NFBC 338

The bacterial heat shock response is characterized by the elevated expression of a number of chaperone complexes. Two-dimensional polyacrylamide gel electrophoresis revealed that GroEL expression in probiotic Lactobacillus paracasei NFBC 338 was increased under heat adaptation conditions (52 degrees C for 15 min). Subsequently, the groESL operon of L. paracasei NFBC 338 was PCR amplified, and by using the nisin-inducible expression system, two plasmids, pGRO1 and pGRO2, were constructed on the basis of vectors pNZ8048 and pMSP3535, respectively. These vectors were transferred into Lactococcus lactis(pGRO1) and L. paracasei(pGRO2), and after induction with nisin, overexpressed GroEL represented 15 and 20% of the total cellular protein in each strain, respectively. Following heat shock treatment of lactococci (at 54 degrees C) and lactobacilli (at 60 degrees C), the heat-adapted cultures maintained the highest level of viability (5-log-unit increase, approximately) in each case, while it was found that the GroESL-overproducing strains performed only moderately better (1-log-unit increase) than the controls. On the other hand, the salt tolerance of both GroESL-overproducing strains (in 5 M NaCl) was similar to that of the parent cultures. Interestingly, both strains overproducing GroESL exhibited increased solvent tolerance, most notably, the ability to grow in the presence of butanol (0.5% [vol/vol]) for 5 h, while the viability of the parent strain declined. These results confirm the integral role of GroESL in solvent tolerance, and to a lesser extent, thermotolerance of lactic acid bacteria. Furthermore, this study demonstrates that technologically sensitive cultures, including certain probiotic lactobacilli, can potentially be manipulated to become more robust for survival under harsh conditions, such as food product development and gastrointestinal transit.

Comparative survival of probiotic lactobacilli spray-dried in the presence of prebiotic substances

AIMS

Probiotic milk-based formulations were spray-dried with various combinations of prebiotic substances in an effort to generate synbiotic powder products.

METHODS AND RESULTS

To examine the effect of growth phase and inclusion of a prebiotic substance in the feed media on probiotic viability during spray-drying, Lactobacillus rhamnosus GG was spray-dried in lag, early log and stationary phases of growth in reconstituted skim milk (RSM) (20% w/v) or RSM (10% w/v), polydextrose (PD) (10% w/v) mixture at an outlet temperature of 85-90 degrees C. Stationary phase cultures survived best (31-50%) in both feed media and were the most stable during powder storage at 4-37 degrees C over 8 weeks, with 30-140-fold reductions in cell viability at 37 degrees C in RSM and PD/RSM powders, respectively. Stationary phase Lact. rhamnosus GG was subsequently spray-dried in the presence of the prebiotic inulin in the feed media, composed of RSM (10% w/v) and inulin (10% w/v), and survival following spray-drying was of the order 7.1-43%, while viability losses of 20,000-90,000-fold occurred in these powders after 8 weeks' storage at 37 degrees C. Survival of the Lactobacillus culture after spray-drying in powders produced using PD (20% w/v) or inulin (20% w/v) as the feed media was only 0.011-0.45%. To compare different probiotic lactobacilli during spray-drying, stationary phase Lact. rhamnosus E800 and Lact. salivarius UCC 500 were spray-dried using the same parameters as for Lact. rhamnosus GG in either RSM (20% w/v) or RSM (10% w/v) and PD (10% w/v). Lact. rhamnosus E800 experienced approx. 25-41% survival, yielding powders containing approximately 10(9) CFU g(-1), while Lact. salivarius UCC 500 performed poorly, experiencing over 99% loss in viability during spray-drying in both feed media. In addition to the superior survival of Lact. rhamnosus GG after spray-drying, both strains experienced higher viability losses (570-700-fold) during storage at 37 degrees C over 8 weeks compared with Lact. rhamnosus GG.

CONCLUSIONS

Stationary phase cultures were most suitable for the spray-drying process, while lag phase was most susceptible. The presence of the prebiotics PD and inulin did not enhance viability during spray-drying or powder storage.

SIGNIFICANCE AND IMPACT OF THE STUDY

High viability (approximately 10(9) CFU g(-1)) powders containing probiotic lactobacilli in combination with prebiotics were developed, which may be useful as functional food ingredients for the manufacture of probiotic foods.

Stationary-phase acid and heat treatments for improvement of the viability of probiotic lactobacilli and bifidobacteria

AIMS

To investigate whether sublethal treatments of stationary-phase probiotic cultures enhance their survival during lethal treatments and to adapt these treatments to the fermenter-scale production of probiotic cultures.

METHODS AND RESULTS

Conditions for acid and heat pretreatments were screened for three Lactobacillus and two Bifidobacterium strains. Strains were sublethally treated both at laboratory scale and at fermenter scale in a strain-specific manner and exposed to a subsequent lethal treatment. At laboratory scale viability improvement was detected in each strain. However, improvement was more pronounced in the Lactobacillus than in the Bifidobacterium strains. At fermenter scale three strains were tested: for the two Lactobacillus strains a marked improvement in viability was obtained whereas for the Bifidobacterium strain the improvement was either minor or not detected.

CONCLUSIONS

Development of treatments for viability enhancement of probiotic strains is feasible, but strain-specific optimization is necessary to obtain notable improvements.

SIGNIFICANCE AND IMPACT OF THE STUDY

Strain-specific treatments were developed for the viability enhancement of stationary-phase probiotic cells both at laboratory and fermenter scale. These results can be utilised in the production of probiotic cultures with improved viability.

Heat shock response in Lactobacillus plantarum

Heat stress resistance and response were studied in strains of Lactobacillus plantarum. Stationary-phase cells of L. plantarum DPC2739 had decimal reduction times (D values) (D value was the time that it took to reduce the number of cells by 1 log cycle) in sterile milk of 32.9, 14.7, and 7.14 s at 60, 72, and 75 degrees C, respectively. When mid-exponential-phase cells were used, the D values decreased. The temperature increases which caused a 10-fold reduction in the D value ranged from 9 to 20 degrees C, depending on the strain. Part of the cell population treated at 72 degrees C for 90 s recovered viability during incubation at 7 degrees C in sterile milk for 20 days. When mid-exponential- or stationary-phase cells of L. plantarum DPC2739 were adapted to 42 degrees C for 1 h, the heat resistance at 72 degrees C for 90 s increased ca. 3 and 2 log cycles, respectively. Heat-adapted cells also showed increased growth at pH 5 and in the presence of 6% NaCl. Two-dimensional gel electrophoresis of proteins expressed by control and heat-adapted cells revealed changes in the levels of expression of 31 and 18 proteins in mid-exponential- and stationary-phase cells, respectively. Twelve proteins were commonly induced. Nine proteins induced in the heat-adapted mid-exponential- and/or stationary-phase cells of L. plantarum DPC2739 were subjected to N-terminal sequencing. These proteins were identified as DnaK, GroEL, trigger factor, ribosomal proteins L1, L11, L31, and S6, DNA-binding protein II HlbA, and CspC. All of these proteins have been found to play a role in the mechanisms of stress adaptation in other bacteria. Antibodies against GroES detected a protein which was induced moderately, while antibodies against DnaJ and GrpE reacted with proteins whose level of expression did not vary after heat adaptation. This study showed that the heat resistance of L. plantarum is a complex process involving proteins with various roles in cell physiology, including chaperone activity, ribosome stability, stringent response mediation, temperature sensing, and control of ribosomal function. The physiological mechanisms of response to pasteurization in L. plantarum are fundamental for survival in cheese during manufacture.

New drying process for lactic bacteria based on their dehydration behavior in liquid medium

This study describes the different stages of optimization in an original drying process for lactic acid bacteria that allows the retrieval of dried samples of Lactobacillus plantarum with maximum viability. The process involves the addition of casein powder to bacterial pellets, followed by mixing and then air-drying in a fluidized bed dryer. The effects on bacterial viability of the a(w) of the casein powder and the kinetics of a(w) variation in the fluidized bed dryer are considered. These parameters were first studied in a water-glycerol solution and the results were then applied to the drying process. Data from the study in liquid medium were reliable in the fluidized drying stage, insofar as optimal viability was achieved for similar dehydration times (16-50 min in liquid medium, and 30 min in the fluidized bed dryer). However, when the powder was mixed rapidly with bacteria, the level of destruction differed from that observed in liquid medium. Viability was up to 70% when the a(w) of water-glycerol was 0.55, whereas it was only 2.1% when the a(w) of the casein-bacterial mix was 0.64. The predictive capacity of dehydration in liquid medium is discussed with regard to the permeability of cells to external solutes. The new process allowed 100% survival of L. plantarum after complete drying (final a(w) < 0.2). However, when used for the desiccation of L. bulgaricus, these parameters achieved a viability of less than 10%.

Action of trehalose on the preservation of Lactobacillus delbrueckii ssp. bulgaricus by heat and osmotic dehydration

AIM

This work determines the efficiency of trehalose on the preservation by heat or osmotic drying of a strain of Lactobacillus delbrueckii ssp. bulgaricus. Cell recovery at different trehalose concentrations during drying correlated with the surface properties and osmotic response of cells after rehydration.

METHODS AND RESULTS

Bacteria were dried in the presence of glycerol, trehalose, sucrose at 70 degrees C and at 20 degrees C. Trehalose attenuates the loss of viability at 0.25 m. At this concentration, the osmotic response and zeta potential of the bacteria were comparable with the nondried ones.

CONCLUSIONS

Trehalose diminishes significantly the damage produced by dehydration both when the bacteria are dried by heating or subjected to osmotic dehydration. This effect appears related to the preservation of the permeability to water and the surface potential of the bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dehydration occurring during heating or during osmosis appears to have similar effects. As dehydration-induced damage is in correlation with osmotic response recovery and is hindered or buffered by the presence of trehalose, it may be related to water eliminated from biological structures involved in water permeation.

Improved survival of Lactobacillus paracasei NFBC 338 in spray-dried powders containing gum acacia

AIMS

To assess the protective effect of gum acacia (GA) on the performance of Lactobacillus paracasei NFBC 338 during spray-drying, subsequent storage and exposure of the culture to porcine gastric juice.

METHODS AND RESULTS

For these studies, Lact. paracasei NFBC 338 was grown in a mixture of reconstituted skim milk (10% w/v) and GA (10% w/v) to mid log phase and spray-dried at outlet temperatures between 95 and 105 degrees C. On spray drying at the higher air outlet temperature of 100-105 degrees C, the GA-treated culture displayed 10-fold greater survival than control cells. Probiotic lactobacilli in GA-containing powders also survived dramatically better than untreated cultures during storage at 4-30 degrees C for 4 weeks. A 20-fold better survival of the probiotic culture in GA-containing powders was obtained during storage at 4 degrees C while, at 15 and 30 degrees C, greater than 1000-fold higher survival was obtained. Furthermore, the viability of probiotic lactobacilli in GA-containing powders was 100-fold higher when exposed to porcine gastric juice over 120 min compared with the control spray-dried culture.

CONCLUSIONS

The data indicate that GA has applications in the protection of probiotic cultures during drying, storage and gastric transit.

SIGNIFICANCE AND IMPACT OF THE STUDY

Gum acacia treatment for the manufacture of probiotic-containing powders should result in more efficient probiotic delivery to the host gastrointestinal tract.

Effect of raw-milk cheese consumption on the enterococcal flora of human feces

Enterococci are one of the major facultative anaerobic bacterial groups that reside in the human gastrointestinal tract. In the present study, the composition of the enterococcal fecal flora in three healthy humans was analyzed before, during, and after the daily consumption of approximately 125 g of a raw-milk Cheddar-type cheese containing 3.2 x 10(4) enterococci/g of cheese. Enterococcal counts ranged between 1.4 x 10(2) and 2.5 x 10(8) CFU/g of feces and differed from subject to subject and from week to week. The cheese contained mainly Enterococcus casseliflavus and a small population of Enterococcus faecalis. Clonal relationships were determined by pulsed-field gel electrophoresis. Before and after consumption of the cheese, samples from humans contained mainly Enterococcus faecium, with some of the clones being resident. During consumption of the cheese, one particular transient clone of E. faecalis, clone Fs2, which was present in small numbers in the cheese, largely dominated the feces. Two clones of E. casseliflavus from the cheese were also found in the feces of one of the subjects during cheese consumption. These results suggest that a clone need not be present in a food in high numbers to establish itself in the intestine.

Bacteriocin production by spray-dried lactic acid bacteria

AIMS

Cell survival and antagonistic activity against Listeria innocua, Listeria monocytogenes and Staphylococcus aureus were investigated after spray-drying three bacteriocin-producing strains of lactic acid bacteria: Carnobacterium divergens, Lactobacillus salivarius and Lactobacillus sakei.

METHODS AND RESULTS

Bacterial cell concentrates were spray-dried and stored at 4 degrees C and 18 degrees C and 0.3% ERH (equilibrium relative humidity). Enumeration and antagonistic activity were evaluated before and after spray-drying and at regular intervals during storage.

CONCLUSIONS

A higher survival rate was obtained when survival was performed at 4 degrees C. With the exception of Carnobacterium divergens which lost the inhibitory activity against Staph. aureus after drying, antagonistic production was not affected by the process nor by the storage. Of the three species studied, Lact. salivarius showed the highest resistance to the spray-drying and storage processes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Spray-drying is a potentially useful process for large scale production of dried powders containing viable organisms with antagonistic activity against pathogens.

Role of probiotics in the treatment of intestinal infections and inflammation

Despite the relative success of analogous approaches in soil, aquatic, and animal environments, the enhancement of human health through probiotic consumption has not been generally endorsed in modern medicine. Laboratory-based studies are elucidating the mechanisms that mediate the properties attributed to beneficial lactic acid bacteria and Saccharomyces species in vivo. This research is now providing fundamental evidence to support observations of adhesion of probiotic species to intestinal tissue, antimicrobial activities, and immunomodulation. Probiotics appear to have a promising future in the treatment of certain disorders. Rigorously performed, controlled, double-blinded trials will overcome doubts relating to efficacy in vivo and open avenues along which probiotic-based therapies will rapidly progress. As a result of our emerging understanding of microbial activities and gene expression in situ, novel strategies will combine complementary probiotic functionalities in the form of microbial consortia or genetically enhanced organisms. As scientific knowledge and biotechnologic proficiency advance at an accelerating pace, the requirement for informed legislation and for mechanisms of effectively delivering these therapies to the sites of their intended function may limit the applications of probiotics.

Evaluation of microencapsulation of a Bifidobacterium strain with starch as an approach to prolonging viability during storage

AIMS

To optimize a spray coating process for the production of encapsulated microspheres containing viable Bifidobacterium cells and to determine whether the readily gelatinized modified starch coating used in this study improved bacterial survival in foods or under acid conditions.

METHODS AND RESULTS

An air inlet temperature of 100 degrees C was demonstrated to be optimal for the spray drying process, as it afforded good drying, low outlet temperatures (45 degrees C) and resulted in less than 1 log reduction in bifidobacteria numbers during drying. Maximum recovery yields of 30% were obtained after optimizing the air aspiration conditions. The average size of the Bifidobacterium PL1-containing starch microparticles was determined by scanning electron microscopy to be of the order of 5 microm. The starch-coated cells did not display any enhanced viability compared with free PL1 cells when exposed to acid conditions for 6 h or in two dry food preparations over 20 d storage at ambient temperature (19-24 degrees C). Determination of 1491 nucleotides of the 16S rRNA gene from PL1 indicated that it shared 97% homology with a previously sequenced Bifidobacterium ruminantium strain.

CONCLUSIONS

Our data demonstrated that, although spray drying is a valuable process for encapsulating bifidobacteria, further work is required to ascertain a more appropriate coating material that will protect this strain against adverse environmental conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The production of small, uniformly coated microspheres containing viable bifidobacteria using an affordable and industrially convenient process, such as spray drying, has commercial implications for the production of probiotic products. Although popular for use as a coating polymer by the food industry, this study indicated that modified starches might not be suitable for use as an encapsulating material for probiotic strains.