Fermentation of beet juice by beneficial lactic acid bacteria

Red beets were evaluated as a potential substrate for the production of probiotic beet juice by four species of lactic acid bacteria (Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus plantarum). All the lactic cultures were found capable of rapidly utilizing beet juice for cell synthesis and lactic acid production. However, L. acidophilus and L. plantarum produced a greater amount of lactic acid than other cultures and reduced the pH of fermented beet juice from an initial value of 6.3 to below 4.5 after 48 h of fermentation at 30°C. Although the lactic cultures in fermented beet juice gradually lost their viability during cold storage, the viable cell counts of these lactic acid bacteria except for L. acidophilus in the fermented beet juice still remained at 10⁶–10⁸ CFU/ml after 4 weeks of cold storage at 4°C.     

Effect of cryoprotectants,prebiotics and microencapsulation on survival of probiotic organisms in yoghurt and freeze-dried yoghurt

The survival of probiotic microorganisms including Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus and Bifidobacterium spp. was evaluated in yoghurt and freeze-dried yoghurt after processing and storage. The effectiveness of microencapsulating probiotic organisms as well as adding cryoprotectants and prebiotics in improving their viability was also investigated. The viability of Bifidobacterium infantis 17930 and L. rhamnosus GG was reduced by 0.07 log, while that of L. casei 1520 and Bifidobacterium longum 1941 was reduced by 0.28 and 0.39 log, respectively. There was a 7% improvement in the viability of L. casei 1520 when cryoprotectant ‘Unipectine™ RS 150’ was added at 2.5% (w/v). The prebiotic ‘Raftilose^®P95’ when added at 1.5% w/v to yoghurt improved the viability of the combined selected probiotic organisms by 1.42 log during four weeks of storage at 4 °C. Microencapsulation with alginate improved viability of combined selected probiotic organisms by 0.31 log in freeze-dried yoghurt stored at 21 °C.     

The influence of multi stage alginate coating on survivability of potential probiotic bacteria in simulated gastric and intestinal juice

The probiotics, Lactobacillus acidophilus PTCC1643 and Lactobacillus rhamnosus PTCC1637, were encapsulated into uncoated calcium alginate beads and the same beads were coated with one or two layers of sodium alginate with the objective of enhancing survival during exposure to the adverse conditions of the gastro-intestinal tract. The survivability of the strains, was expressed as the destructive value (decimal reduction time). Particle size distribution was measured using laser diffraction technique. The thickness of the alginate beads increased with the addition of coating layers. No differences were detectable in the bead appearance by scanning electron microscopy (SEM). The alginate coat prevented acid-induced reduction of the strains in simulated gastric juice (pH 1.5, 2 h), resulting in significantly (P < 0.05) higher numbers of survivors. After incubation in simulated gastric (60 min) and intestinal juices (pH 7.25, 2 h), number of surviving cells were 6.5 log cfu mL^?1 for L. acidophilus and 7.6 log cfu mL^?1 for L. rhamnosus by double layer coated alginate microspheres, respectively, while 2.3 and 2.0 log cfu mL^?1 were obtained for free cells, respectively.     

Development of probiotic beads similar to fish eggs

Probiotic foods are mainly restricted to dairy and soy products. This study aimed to develop a new probiotic beads similar to fish eggs, commonly used in oriental cuisine. Beads were produced by the extrusion encapsulation technique with calcium alginate, added to one of the following cultures: Lactobacillus rhamnosus GG ATCC 53103 and Bifidobacterium animalis DN-173 010 and stored for 30 days at 4 °C. The beads were characterized by the size, weight, morphology and viability of the probiotic strains in different storage temperatures and in simulated gastric juice adjusted to different pH values. The beads were also evaluated by a sensorial affective hedonic scale. The beads present a 2.8 mm diameter and a weight of 0.01 g (p > 0.05). Free and encapsulated cells were tolerant to pH 3.0. At pH 2.5 only of the encapsulated cells presented counts above 6 Log colony-forming units per gram (CFU/g). Beads containing L. rhamnosus showed higher viability 10⁷ CFU/g in storage for 30 days under refrigeration. The beads may be stored at abusive temperature for 5 h without loss of viability cells. The probiotic product developed showed an 82.2% acceptability index of overall characteristics and good market potential as a new probiotic product.     

Transglutaminase-induced caseinate gelation for the microencapsulation of probiotic cells

A novel method for the encapsulation of probiotic cells in foodgrade casein microcapsules was developed. The process is based on a transglutaminase-catalysed gelation of casein suspensions containing probiotic cells. Water insoluble, spherical capsules with a volume-based median diameter of 165 ± 23 μm resulted from the process. Encapsulation yields of 70 ± 15% and 93 ± 22% were achieved for Lactobacillus paracasei ssp. paracasei F19 and Bifidobacterium lactis Bb12, respectively. Analysis of living cell numbers after incubation of free and encapsulated probiotics in simulated gastric juice without pepsin at pH 2.5 and pH 3.6 (37 °C, 90 min) showed a protective effect due to microencapsulation under all conditions tested. The study indicates that transglutaminase-induced caseinate gelation can be applied to the microencapsulation of probiotics. Furthermore, it could be shown that an entrapment in a dense casein matrix can protect these microorganisms from damage due to pH-levels similar to those in the human stomach.     

Effect of acidification on the activity of probiotics in yoghurt during cold storage

The viability of Lactobacillus acidophilus LAFTI^® L10, Bifidobacterium lactis LAFTI^® B94, and L. paracasei LAFTI^® L26 and their proteolytic activities were assessed in yoghurt at different termination pH of 4.45, 4.50, 4.55, and 4.60 in the presence of L. delbrueckii ssp. bulgaricus Lb1466 and Streptococcus thermophilus St1342 during 28 days of storage at 4 °C. All strains achieved the recommended level of 6.00 log cfu g⁻¹ of the product with L. acidophilus LAFTI^® L10 and L. paracasei LAFTI^® L26 exceeding the number to 8.00 and 7.00 log cfu g⁻¹, respectively. Lactobacilli strains showed a good cellular stability maintaining constant concentration throughout storage period regardless of termination pH. On the other hand, the cell counts of B. lactis LAFTI^® B94 decreased by one log cycle at the end of storage. The presence of probiotic organisms enhanced proteolysis significantly in comparison with the control batch containing L. delbrueckii ssp. bulgaricus Lb1466 and S. thermophilus St1342 only. The proteolytic activity varied due to termination pH, but also appeared to be strain related. The increased proteolysis improved survival of L. delbrueckii ssp. bulgaricus Lb1466 during storage resulting in lowering of pH and production of higher levels of organic acids, which might have caused the low cell counts for B. lactis LAFTI^® B94.     

Milk enhances intestinal absorption of green tea catechins in in vitro digestion/Caco-2 cells model

The effect of milk on the absorption of polyphenols is still controversial so far. In order to determine the impact of milk addition on green tea catechins bioaccessibility and intestinal absorption an in vitro digestion/Caco-2 cell model was applied. Green tea extract (GTE) was solubilized in distilled water at 23 °C and 100 °C, combined with skimmed milk (GTE + 10% milk and GTE + 25% milk) and subjected to simulated gastric and intestinal digestion, followed by transepithelial absorption in Caco-2 cells monolayers. In the mixture with milk, gallated catechins: ECG and EGCG showed binding to milk proteins while EC and EGC seemed to have weaker affinity. Catechins were stable during gastric incubation and very sensitive to intestinal digestion. Bioaccessibility of green tea catechins brewed at 100 °C was higher than brewed at 23 °C. Catechins from digested GTE with 10% and 25% milk exhibited enhanced intestinal permeability in Caco-2 model in comparison to non-digested GTE and digested GTE without milk. Apparent permeability coefficients (P_app) of EGCG and ECG in digested GTE with 25% milk were significantly higher compared to those in GTE with 10% milk, and amounted to 2.41 × 10^− 6 cm/s and 1.39 × 10^− 6 cm/s. The recoveries of all catechins in GTE with milk in Caco-2 cells after 2 h incubation were significantly higher than that without milk. To summarize, these data suggest that milk addition may increase catechin bioavailability by enhancing their transepithelial absorption and uptake from green tea extract.     

Growth-inhibition of hiochi bacteria in namazake (raw sake) by bacteriocins from lactic acid bacteria

The bacteriocins produced by Lactococcus lactis subsp. lactis C101910 (C101910) and NBRC 12007 (NBRC 12007) were used to prevent the growth of sake spoiling hiochi bacteria (Lactobacillus hilgardii, Lactobacillus fructivorans, and Lactobacillus paracasei) in namazake, which is raw (unpasteurized) sake. The bacteriocin concentrations required for decreasing the viable cell concentrations of L. hilgardii and L. fructivorans below the detection limit (1.0 × 10² cells/ml) in 24 h from the initial concentration of 4.0–9.5 × 10⁵ cells/ml in the namazake at pH 4.5 and at 4°C, were 18–35 U/ml and 5.6 U/ml for the bacteriocin from C101910 and NBRC 12007, respectively. To decrease the viable cell concentration of L. paracasei from the initial concentration of 7.5 × 10⁵ cells/ml to below the detection limit (1.0 × 10² cells/ml) in 24 h, 350 U/ml bacteriocin from C101910 and 140 U/ml bacteriocin from NBRC 12007 were required. In experiments using McIlvaine buffer (pH 4.5) with 15% ethanol instead of namazake as the medium, the viable cell concentrations of L. hilgardii and L. paracasei decreased to less than 1.0 × 10² cells/ml, whereas those of L. fructivorans decreased to less than 1.0 × 10³ cells/ml, when bacteriocins were added at the concentrations that had proven effective in namazake. The membrane depolarization assay using a fluorescent probe showed that the presence of ethanol stimulated the collapse of the membrane potential induced by bacteriocins. The ethanol induced collapse of the membrane potential suggests that the application of bacteriocins at the storage stage of namazake is more beneficial than when used in other stages of the sake brewing process.     

Stability of microencapsulated Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris during storage at room temperature at low aw

The effect of freeze drying or spray drying, the use of desiccants to maintain the low a_w and the period of storage (at 25 °C) of Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris on survival, acid tolerance, bile tolerance, retention of surface hydrophobicity and retention of β-galactosidase was studied; an estimation of the maximum storage period was also carried out. Sodium caseinate, vegetable oil, glucose, mannitol and fructooligosaccharides were used as protectant of L. acidophilus and L. cremoris during freeze drying or spray drying and during subsequent storage. NaOH, LiCl and silica gel were used as desiccants during 10 weeks of storage of microencapsulated L. acidophilus and L. cremoris kept in an aluminum foil pouch. The results showed that mainly freeze dried L. acidophilus and L. cremoris kept in foil pouch containing NaOH (a_w 0.07) or LiCl (a_w 0.1) showed higher survival (89–94%) than spray dried bacteria kept under the same conditions (86–90%) after 10 weeks of storage (P = 0.0005). Similar results were also showed by acid tolerance, bile tolerance and surface hydrophobicity of freeze-dried or spray-dried L. acidophilus and L. cremoris. Silica gel was less effective in protecting the functional properties of microencapsulated L. acidophilus or L. cremoris with percentage of survival between 81 and 87% at week 10 of the storage. However, retention of β-galactosidase was only influenced by a_w adjusted by desiccators (P < 0.05). Based on forecasting using linear regression, the predicted storage period for freeze dried L. acidophilus, spray dried L. acidophilus and freeze dried L. cremoris kept in foil pouch containing NaOH would be 46, 42 and 42 weeks, respectively; while spray dried L. cremoris under LiCl desiccant would require 39 weeks to achieve minimum required bacterial population of 10⁷ CFU/g.     

HPLC of proteose peptones for evaluating ageing of packaged pasteurized milk

The proteolysis of casein (CN) occurring in packaged pasteurized milk (PM) during refrigerated storage was studied with relation to hygienic and microbiological characteristics of starting raw milk. Six batches of raw milk having standard plate count (SPC) from 1.5×10⁴ to 2.5×10⁵ cfu mL⁻¹ and somatic cell count (SCC) from 1.6×10⁵ to 4.4×10⁵ units mL⁻¹ were pasteurized (73 °C for 15 s), packaged and stored at 4 °C for 12 days. Capillary zone electrophoresis of CN showed breakdown of β-CN in all PM samples during storage. An HPLC method for monitoring proteose peptones (PP) formation was developed. Level of PP in PM samples increased, with keeping time from 667–789 to 947–1383 mg L⁻¹ and PP formation was significantly (P<0.05) related to SCC of starting raw milk. Electrospray ionization–mass spectrometry showed that PP were mainly represented by PP-5 from either A¹ or A² variants of β-CN. Five commercial samples of PM were analysed for PP formation during 14-day storage at 4 °C. Commercial samples prepared by microfiltration process or bactofugation combined with pasteurization showed the slowest formation of PP. The effect of storage temperature on PP formation was evaluated by keeping a conventional PM sample at either 8 or 12 °C for 12 days. Proteolysis of all major CNs upon action of plasmin and bacterial proteinases was observed under these conditions. PP level thus proves to be a reliable analytical index for evaluating the ageing of packaged PM during refrigerated storage.     

Conjugated linoleic acid production by immobilized cells of Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus acidophilus

Lactobacillus delbrueckii ssp. bulgaricus (CCRC14009) and L. acidophilus (CCRC14079), immobilized with chitosan and polyacrylamide, were tested for CLA production. A 10-ml aliquot of L. delbrueckii ssp. bulgaricus cell suspension (3.59 × 10⁷ CFU/ml) was adsorbed to 0.5 g chitosan and polyacrylamide, mixed with 0.2 ml linoleic acid (0.9 g/ml), and incubated at 37 °C for 24 h at pH 5, 6, 7, and 8 for CLA production. CLA levels, produced by immobilized cells of L. delbrueckii ssp. bulgaricus and L. acidophilus with increasing cell counts to 1.08 and 1.28 × 10¹⁰ CFU/ml, respectively, at optimal reaction pHs were evaluated. More CLA was formed at pH 8 of chitosan and pH 7 of polyacrylamide-immobilized L. delbrueckii ssp. bulgaricus cell treatments. Increase in cell count resulted in higher CLA production. The adsorption of L. delbrueckii ssp. bulgaricus cells onto polyacrylamide at pH 7 showed significant improvement in total CLA level. Results demonstrated a potential for enhancing CLA production through immobilization.     

Comparative Studies of Ginger (Zingiber officinale) and West African Black Pepper (Piper guineense) Extracts at Different Concentrations on the Microbial Quality of Soymilk and Kunun-zaki

Extracts of two spices, namely ginger (Zingiber officinale) and black pepper (Piper guineense) were prepared in 0.4%, 1.2%, 2.4% and 3.6% concentrations. Soymilk and kunun-zaki were treated respectively with the different concentrations and stored at ambient temperature for 5 days. The microbial load and identification were determined every day of storage until samples were adjudged spoilt.On the first day, 0.4% ginger extract in soymilk and kunun-zaki had a microbial load of 7.77 × 10^6b and 5.17 × 10^6b respectively. 3.6% ginger extract in soymilk and kunun-zaki recorded 3.73 × 10^6b and 3.30 × 106 each. 0.4% black pepper extract in soymilk had 6.273 × 10^6b and recorded 4.63 × 10^6b in kunun-zaki. 3.6% black pepper extract in soymilk and kunun-zaki had a microbial load of 3.20 × 10^6d and 2.90 × 10^6c respectively. On the third day the microbial load increased for both ginger and black pepper extract. Ginger extract recorded 9.13 × 10^6b in soymilk and 5.60 × 10^6b in kunun-zaki at 0.4% concentration. Black pepper extracts recorded 7.43 × 10^6b in soymilk and 3.27 × 10^6b in kunun-zaki also at 0.4% extract. 3.6% black pepper extract recorded 4.10 × 10^6a in soymilk and 2.20 × 106c in kunun-zaki.There was linear reduction of microbial load as spice concentration increased. Black pepper recorded lower microbial load, thus having more antimicrobial activity and may be preferred to be used as natural antimicrobial preservatives to extend the shelf-life of food.     

Apple,grape or orange juice: Which one offers the best substrate for lactobacilli growth? — A screening study on bacteria viability,superoxide dismutase activity,folates production and hedonic characteristics

Fermentation can contribute to improve functional aspects of foods. The first goal of this study was to determine amongst apple, grape and orange juices, the one with the best bacterial growth performance during fermentation by Lactobacillus strains from commercial and artisanal food origins, at 40 °C for 48 h. The juice with the highest bacterial growth was evaluated for bacteria viability during 4 weeks of cold storage, superoxide dismutase (SOD) activity and folates production analyzed through HPLC/fluorimetry. Acceptability of fermented juice was appraised through hedonic analysis. Lactobacilli counts were the highest in apple and the lowest in orange juices at t = 48 h. In most cases, bacteria counts were higher in fermented (5.5 to 9.5 log CFU/ml) than in supplemented apple juices (4.2 to 5.7 log CFU/ml), at the 4th week of cold storage. SOD activity was significantly increased in all apple juices fermented by commercial Lactobacilli strains. Folates were produced in apple juices fermented by Lactobacillus plantarum and Lactobacillus rhamnosus. Apple juice was the best substrate for Lactobacillus growth and, considering bacterial viability and overall acceptance by the panelists, Lactobacillus acidophilus L10 was the most suitable strain for apple juice fermentation.     

Stability of probiotic Lactobacillus plantarum in dry microcapsules under accelerated storage conditions

This study investigated the stability of freeze dried and fluid bed dried alginate microcapsules coated with chitosan containing model probiotic bacteria, Lactobacillus plantarum, during storage for up to 45 days at different water activities (0.11, 0.23, 0.40 and 0.70) and temperatures (4, 30 and 37 °C). The loss in cell viability was around 0.8 log in the case of fluid bed drying and around 1.3 in the case of freeze drying, with the former method resulting in dried capsules of smaller size (~ 1 mm vs 1.3 mm), more irregular shape, and with a rougher surface. In both cases, the water activity and water content were less than 0.25 and 10% w/w, respectively, which favours high storage stability. The storage stability studies demonstrated that as the water activity and temperature decreased the survival of the dried encapsulated cells increased. Considerably better survival was observed for fluid bed dried encapsulated cells compared to freeze dried encapsulated cells and freeze dried free cells with 10% sucrose (control), and in some cases, e.g. at 4 and 30 °C at water activities of 0.11, 0.23 and 0.40, there was more than 1 log difference after 45 days, with concentrations higher than 10⁸ CFU/g after 45 days of storage. The results indicate that fluid bed drying is an effective and efficient manufacturing method to produce probiotic containing capsules with enhanced storage stability.     

Synergistic effect of sonication and high osmotic pressure enhances membrane damage and viability loss of Salmonella in orange juice

The efficacy of using sonication (50 ± 0.2 W, 20 kHz), combined with subsequent concentration and storage at high osmotic pressure, has been evaluated to reduce levels of Salmonella bacteria in different solutions (PBS, sucrose and orange juice) at varying concentrations. To visualize the impact on cell membranes, we used a staining protocol (propidium iodide [PI] and 4′,6′-diamidino-2-phenylindole [DAPI]). Sonication alone did not cause significant membrane damage. Storage alone, for 48 h and at high osmotic pressure (10.9 MPa), affected membrane permeability in 20% of cells. However, sonication, combined with storage, considerably increased loss of membrane integrity, resulting in a significant logarithmic reduction of microorganisms. When the combination was applied to contaminated orange juice, a 5 log₁₀ cfu ml^?1 reduction of Salmonella spp. was obtained. “Osmosonication”—the synergistic combination of sonication and subsequent storage at high osmotic pressure—is an innovative alternative for the non-thermal decontamination of liquid foods.     

The protective effect of monosodium glutamate on survival of Lactobacillus rhamnosus GG and Lactobacillus rhamnosus E-97800 (E800) strains during spray-drying and storage in trehalose-containing powders

The use of trehalose as a means of preserving Lactobacillus rhamnosus GG (LGG) and L. rhamnosus E-97800 (E800) during spray-drying and the effects of incorporated monosodium glutamate (MSG) in the carrier medium on the survival rates during drying and storage were examined. E800 was more resistant to heat than LGG in 20%, w/w, trehalose; the d-values at 65 °C were 14 s and 5.1 s, respectively. An air outlet temperature of 65–70 °C was taken as optimal for the drying process, as the resultant moisture levels in trehalose containing these bacteria were 4.1% (w/w) and 3.79% (w/w) with corresponding viable counts of 3.65 × 10⁸ cfu mL^?1 and 1.80 × 10⁹ cfu mL^?1, respectively. The presence of MSG increased the final viable counts of LGG and E800 to 3.05 × 10⁹ cfu mL^?1 and 1.30 × 10⁹ cfu mL^?1, respectively. Survival of LGG and E800 remained constant at a minimum level of ～10⁸ cfu mL^?1 during storage at 25 °C in trehalose–MSG medium.     

Survival and activity of selected probiotic organisms in set-type yoghurt during cold storage

The growth and metabolism of two probiotic organisms (L. acidophilus LAFTI^® L10 and Lactobacillus casei LAFTI^® L26) and a regular yoghurt culture (L. delbrueckii ssp. bulgaricus Lb1466 and Streptococcus thermophilus St1342) were studied in yoghurt containing 0.5%, 1.0%, and 1.5% (w/v) of high amylose corn starch powder (Hi-maize^®) or inulin. Viable cell counts of probiotic organisms, their metabolites and proteolytic activities, and viscosity of the yoghurts were determined during refrigerated storage for 28 d at 4 ^oC. In the presence of inulin, cultures showed better retention of viability (8.0 log cfu g⁻¹) in comparison with that of Hi-maize, which had a reduction by one log cycle. Lower concentrations of 0.5–1.0% Hi-maize improved (P<0.05) the production of propionic acid and also increased proteolytic activity of probiotic organisms substantially. A greater release of free amino acids may have sustained better growth of the organisms in yoghurts. Supplementation with either Hi-maize or inulin increased the viscosity of probiotic yoghurts significantly (P<0.05).     

Inactivation of Escherichia coli O157:H7 by cinnamic aldehyde purified from Cinnamomum cassia shoot

Escherichia coli O157:H7 is a pathogen, which causes the hemorrhagic colitis, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura in humans. Control of the bacterial cells in foods is an important factor to reduce outbreaks of the foodborne diseases. In this study, cinnamic aldehyde possessing antimicrobial activity against the bacterial cells was purified from the extract of cinnamon (Cinnamomum cassia Blume) shoot by sequential fractionation with various solvents and silica gel column chromatography. When E. coli O157:H7 cells were incubated at 37°C for 12 h in the presence of 500 μg ml⁻¹ of the purified from cinnamic aldehyde, the viable counts decreased dramatically (from 4.9×10⁶ to 1.0×10² cfu ml⁻¹). In the presence of 1000 μg ml⁻¹ of the substance, most of the cells were killed after 2 h of incubation suggesting that the antimicrobial activity of cinnamic aldehyde is bacteriocidal in E. coli. Scanning electron microscopic observations revealed that the bacterial cells treated with the cinnamic aldehyde suffered from severe damages in their surface structure. Minimal inhibitory concentration of the cinnamic aldehyde was determined to be 250 μg ml⁻¹ against E. coli strains O157:H7 and O26 or 500 μg ml⁻¹ against strains ATCC11105 and O111.     

Kinetic parameters of Escherichia coli O157:H7 survival during fermentation of milk and refrigeration of home-made yoghurt

The survival parameters of Escherichia coli O157:H7 during milk fermentation (carried out by the LIM or “longer incubation method” at 30 °C, or by the SIM or “short incubation method” at 43 °C) and storage of home-made yoghurt at refrigeration temperatures (2, 4, or 8 °C) were studied. The E. coli O157:H7 counts increased slightly during fermentation by the LIM, from 5.1 to 5.4 log cfu mL⁻¹, and it was not found after 21 d of storage at 2 or 4 °C, and after 10 d at 8 °C. The microorganism counts increased from 4.8 to 5.4 log cfu mL⁻¹ during the SIM, and it was not detected after 7 d stored at 8 °C. The microorganism grew faster at 43 °C (generation time=0.93 h) than at 30 °C (4.12 h) during the fermentation period. The death time decreased with the increase of the storage temperature (from 38.1 h at 2 °C to 30.1 h at 8 °C) in the yoghurt produced by fermentation at 30 °C; however, a clear relationship between death time and storage temperature was not evident at 43 °C. The pH values of the yoghurt ranged from 4.0 to 4.7.     

Kefir yeasts enhance probiotic potentials of Lactobacillus paracasei H9: The positive effects of coaggregation between the two strains

This study investigated pure Lactobacillus paracasei H9 tolerance to simulated gastrointestinal juices and adhesion to intestinal mucosa cells without yeasts, with viable yeasts (VY) and with different pretreated yeasts. Three models including gastric secretion tolerance (GST), intestinal juice tolerance (IJT) and sequential gastrointestinal tolerance (SGT) were respectively employed to assay the tolerance of L. paracasei H9, whilst Caco-2 cell line was used to investigate the bacterial adhesion. Particularly, the co-aggregation ability of the two strains at pH values of 2.0, 8.0 and 7.2 was originally carried out to study relations to the bacterial probiotic potentials. Results showed that yeast counts in the range from 3.0 to 5.0 log CFU mL^? 1 could gradually increase the viability of L. paracasei H9 in SGT. The bacterial viability in the three tolerance models and the adherent number to Caco-2 cells were significantly improved with addition of VY (P < 0.05). The L. paracasei H9 with VY in gastric juice at pH 2.0 and intestinal juice at pH 8.0, respectively, exhibited higher aggregation percentage compared with that of single L. paracasei H9 at 37 °C (P < 0.05). The aggregation ability of L. paracasei H9 with VY at pH 7.2, which might contribute to increase the adhesion of the bacteria, also excelled that of L. paracasei H9 (P < 0.05). It is deduced that proteins of the bacterial cell surface and polysaccharides in yeast cell walls play important roles in co-aggregation of the two strains and the microbial adhesion specificity to Caco-2 cells. The co-aggregation of the two strains also contributes to enhancing probiotic potentials of L. paracasei H9.