Effect of protective solutes on leakage from and survival of immobilized Lactobacillus subjected to drying, storage and rehydration

When lactic acid bacteria are used industrially as fermentation starters it is important to obtain stable and highly viable bacterial cultures. Six strains of Lactobacillus encapsulated in Ca-alginate gel beads were investigated to determine whether dehydration, storage and rehydration may inflict injury. A negative relationship between leakage of lactate dehydrogenase and survival rates was found. Mesophilic lactobacilli showed only negligible leakage compared with thermophilic strains when dehydrated at 30 °C to a level of 0·11 g H₂0 (g dry wt)⁻¹. The choice of an appropriate suspending medium to be introduced before drying was therefore very important for thermophilic lactobacilli in order to increase the survival rates during dehydration, storage and rehydration. The osmoregulatory solutes tested were adonitol, betaine, glycerol and reconstituted non-fat milk solids (NFMS). Less injury was inflected during dehydration for Lactobacillus helveticus with adonitol, glycerol and NFMS. Survival rates for the strains subjected to immobilization, dehydration, storage and rehydration varied with the strain and the protective solute when fluidized-bed drying was used at 5 °C to a level as high as 0·34 g H₂0 (g dry wt)⁻¹. Non-fat milk solids gave the best protection for thermophilic lactobacilli, while adonitol and NFMS were best for mesophilic lactobacilli.     

Effect of water activity adjusted with different solutes on growth and lactic acid production byLactobacillus helveticus

Effect of water activity (a _w) adjusted with NaCl or glycerol on the growth and metabolism ofLactobacillus helveticus var.pragensis at 40°C was demonstrated by growth curves (generation time) and changes in the degree of acidity of a milk medium expressed as lactic acid content. NaCl-regulateda _w of 0.970 inhibited growth and acid production completely. The same, glycerol-regulateda _w of 0.970 increased the generation time only from 33 min (a _w=0.994) to 67 min which was less than the generation time at the highera _w of 0.982 adjusted with NaCl (103 min). Glycerol-regulateda _w of 0.970 did not decrease the acid production (2.6% lactic acid). Ata _w of 0.951, the acid production was decreased by 39% compared with the values found in milk media with the original, unadjusteda _w of 0.994, after the same time of incubation. Media witha _w adjusted to the same values with NaCl or glycerol do not influence the growth and acid production ofL. helveticus in the same way. In contrast to glycerol, NaCl has a strong effect.     

The effects of temperature,water activity and pH on the growth of Aeromonas hydrophila and on its subsequent survival in microcosm water

AIMS: The influence of temperature, water activity and pH on the growth of Aeromonas hydrophila, and on its survival after transfer in nutrient-poor water were assessed. METHODS AND RESULTS: Experiments were carried out according to a Box-Behnken matrix at 10-30 degrees C, 0.95-0.99 water activity (aw) and pH 5-9. The effect of each factor on the kinetic parameters of growth (i.e. the maximal specific growth rate, mumax, and the lag time, lambda) and on the decline of the bacteria in microcosm water (time to obtain a reduction of 5 log, T5 log) were studied by applying central composite design. CONCLUSIONS: The major effect of temperature and water activity on the growth of A. hydrophila was highlighted, whereas the effect of pH in these experimental conditions was not significant. Models describing the effect of environmental parameters on the growth of A. hydrophila were proposed. The effect of the growth environment, and particularly the incubation temperature, have an influence on the survival ability of the bacteria in nutrient-poor water. SIGNIFICANCE AND IMPACT OF THE STUDY: The Box-Behnken design was well suited to determine the influence of environmental factors on the growth of A. hydrophila and to investigate the effect of previous growth conditions on its survival in microcosm water.     

Associative growth behavior of dahi and yoghurt starter cultures with Bifidobacterium bifidum and Lactobacillus acidophilus in buffalo skim milk

We report here for the first time variations in the viability and biochemical activity of dahi and yoghurt cultures, when grown together with therapeutic cultures, such as Lactobacillus acidophilus I and Bifidobacterium bifidum R, in buffalo skim milk. Nearly one log reduction in mesophilic lactic count was observed in dahi supplemented with probiotic cultures after 18 h of incubation at 30 °C. Associative growth increased the titratable acidity (TA) of dahi marginally (from 0.93 to 1.18 % lactic acid) but reduced the TA in yoghurt (from 1.68 to 1.44 % lactic acid). Probiotic culture supplementation reduced volatile acidity (VA) (from 36.0 to 15.8 ml) and diacetyl (from 4.05 to 2.80 ppm) and tyrosine (from 0.46 to 0.36 μg tyrosine/g curd ) content in dahi, whereas it increased VA (from 8.2 to 8.6 ml of 0.01 % NaoH/50 g) and acetaldehyde (from 28.4 to 34.6 ppm) production in yoghurt. Based on these results, the associative growth had no effect on proteolytic activity of probiotic yoghurt.     

The effect of water activity on Legionella spp. growth and survival

Growth and survival of Legionella spp. at various water activity (aw) levels were determined. Compared with Escherichia coli, the growth of Legionella spp. was limited to a high aw environment (greater than or equal to 0.98).     

The effect of water activity on Legionella spp. growth and survival

Growth and survival of Legionella spp. at various water activity (a_w) levels were determined. Compared with Escherichia coli , the growth of Legionella spp. was limited to a high a_w environment (≥0.98).     

Effect of aerosolization on subsequent bacterial survival

To determine whether aerosolization could impair bacterial survival, Pseudomonas syringae and Erwinia herbicola were aerosolized in a greenhouse, the aerosol was sampled at various distances from the site of release by using all-glass impingers, and bacterial survival was followed in the impingers for 6 h. Bacterial survival subsequent to aerosolization of P. syringae and E. herbicola was not impaired 1 m from the site of release. P. syringae aerosolized at 3 to 15 m from the site of release at a temperature of 12 degrees C and a relative humidity of 80% survived 35- to 65-fold better than P. syringae released at 27 degrees C and a relative humidity of 40%. No difference was observed in the survival of P. syringae and E. herbicola following aerosolization at the same temperature and relative humidity. Bacteria sprayed directly onto bean and oat plants established stable populations at comparable numbers on both plants over an 8-day period following inoculation. Bacteria that inoculated adjacent plants by drifting downwind up to 5 m were detectable at an initial population of 10(2) CFU/g on oats and 10(5) CFU/g on beans 2 h after the spray. However, bacterial populations on both plants were undetectable within 48 h.     

Malt sprout extract medium for cultivation of Lactobacillus plantarum protective cultures

AIMS: The aim was to develop a cheap cereal-based alternative medium for the large-scale production of biopreservative Lactobacillus plantarum VTT E-79098. We examined the effect of growth medium and pH control on the cell yield of Lact. plantarum E-79098 and the antimicrobial activity of the cell-free extracts. METHODS: Fermentations using a novel Malt Sprout Extract Medium (MSE) were performed with different pH regimes. The antimicrobial activity of the cell-free extracts against Pantoea agglomerans VTT E-90396 and Fusarium avenaceum VTT D-80147 was assessed with automated turbidometry. SIGNIFICANCE AND IMPACT OF THE STUDY: When compared with MRS, the MSE medium cultures produced equal growth yields of Lact. plantarum VTT E-79098 and enhanced antimicrobial potential against the Gram-negative bacterium P. agglomerans and a Fusarium fungus. The MSE medium can be used as a low-cost alternative to MRS for producing high cell yields and good antimicrobial activity of Lact. plantarum.     

Effect of aerosolization on subsequent bacterial survival.

To determine whether aerosolization could impair bacterial survival, Pseudomonas syringae and Erwinia herbicola were aerosolized in a greenhouse, the aerosol was sampled at various distances from the site of release by using all-glass impingers, and bacterial survival was followed in the impingers for 6 h. Bacterial survival subsequent to aerosolization of P. syringae and E. herbicola was not impaired 1 m from the site of release. P. syringae aerosolized at 3 to 15 m from the site of release at a temperature of 12 degrees C and a relative humidity of 80% survived 35- to 65-fold better than P. syringae released at 27 degrees C and a relative humidity of 40%. No difference was observed in the survival of P. syringae and E. herbicola following aerosolization at the same temperature and relative humidity. Bacteria sprayed directly onto bean and oat plants established stable populations at comparable numbers on both plants over an 8-day period following inoculation. Bacteria that inoculated adjacent plants by drifting downwind up to 5 m were detectable at an initial population of 10(2) CFU/g on oats and 10(5) CFU/g on beans 2 h after the spray. However, bacterial populations on both plants were undetectable within 48 h.     

Effects of Lactobacillus amylovorus and Bifidobacterium breve on cholesterol

To determine the validity of the hypothesis of assimilation and/or precipitation of cholesterol by Lactobacillus and Bifidobacterium species, culture were undertaken in TPY medium containing oxgall or taurocholic acid. In the case of growing cells, both strains were able to remove cholesterol in the presence of bile salts. Nevertheless, the behaviour was different according to the kind of bile salt. In the presence of taurocholic acid, the removal of cholesterol was due to both bacterial uptake and precipitation. In the presence of Oxgall, bacterial uptake and precipitation were observed for Lactobacillus but only precipitation occurred for Bifidobacterium.     

Effect of growth parameters on the residual activity of Lactobacillus plantarum after drying

In order to select optimal conditions for the production of dry and active starter cultures it is important to determine the influence of growth conditions on the residual activity of dried bacteria. The influence of medium composition, pH during growth, continuous vs batch reactor and growth phase was studied on the residual activity of Lactobacillus plantarum after drying. The effect of high sodium chloride concentrations during growth on the residual activity of Lact. plantarum after drying was measured. The samples were dried by convection and in a fluidized bed. Bacteria with the highest residual activity after drying were produced in batch or chemostat with pH-controlled growth using enriched or diluted MRS medium. The presence of 1 or 1·25 mol l⁻¹ NaCl during growth resulted in a decreased residual activity after drying. Variations in growth conditions (application of stress) generally did not result in higher residual activities after drying.     

Effect of water and salt stresses on growth, chlorophyll, mineral ions and organic solutes contents, and enzymes activity in mung bean seedlings

The experiment was made by using different concentrations of polyethylene glycol (PEG) or salt solutions to decrease the osmotic potential of the growth medium to reveal the response of mung bean (Vigna radiata) to water and salt stresses. No germination (emergence of the seedling) occurred at medium osmotic potential lower than -1.0 MPa in all treatments. It was found that the activity of α-amylase and protease, and contents of proline, saccharides and the soluble proteins decreased in the germinating seeds during 3-d stress. However, after 10-d stress, the contents of organic solutes and the activity of the hydrolytic enzymes increased. Growth, chlorophyll content and mineral uptake were also significantly reduced under stress. The seedlings under water stress induced by PEG were affected much more than under salinity. This may be due to the maintenance of a higher succulence under salt stress than under PEG-induced water stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modelling the acidifying activity profile of Lactobacillus bulgaricus cultures

A model that fully describes the typical pH(t) profile representing the lactic acid production kinetics of Lactobacillus bulgaricus cultures is reported. The model, a four-parameter function [pH = (A–D)/(1 + (t/C)^B) + D], is able to fit any change on the experimental pH-time curves, due to variations on the inoculum cell concentration of the culture. The four fitting parameters(A, B, C and D) of this model are closely related to the lactic acid fermentation and they have a physical meaning. Parameters A and D represent the initial and final pH of the culture, respectively. Parameter B is related to the slope of the linear decreasing region from the pH-time curve and C represents the time at which half of the total decrement of pH is achieved. The proposed model can be used not only for evaluating and comparing the acidifying capacity of homolactic cultures but also for predictions of final fermentation times.     

Effect of moderate electric field frequency on growth kinetics and metabolic activity of Lactobacillus acidophilus

Moderate electric fields (MEF) have been previously shown to alter the metabolic activity of microbial cells; thus, the effect of frequency and electric field would be of considerable interest. We investigated herein the effects of MEF frequency on microbial growth kinetics and bacteriocin (Lacidin A) production of Lactobacillus acidophilus OSU 133 during fermentation. The following fermentation treatments were compared: conventional (for 40 h), MEF (1 V cm(-1), for 40 h), combination of MEF (1 V cm(-1), for the first 5 h) and conventional (for 35 h) at various frequency levels (45, 60, and 90 Hz) all at 30 degrees C, and control (conventional) fermentation at 37 degrees C. MEF treatments with purely sinusoidal waveforms at all frequencies at 30 degrees C produced a shorter lag phase than conventional fermentation. However, no lag phase reduction was found for a 60 Hz waveform that contained high-frequency harmonics. There was, however, a significant increase in the bacteriocin production under early MEF treatment at 60 Hz with high-frequency harmonics. On the basis of these observations, the fermentation process is accelerated by applying pure sinusoidal MEF at the early stage of growth while a significant increase in the bacteriocin production occurs when sinusoidal field at 60 Hz with harmonics is applied at the early stage of the growth.     

Effect of medium on growth and subsequent survival,after freeze-drying,ofLactobacillus delbrueckii subsp.bulgaricus

Summary Growth ofLactobacillus delbrueckii subsp.bulgaricus, grown at a constant pH (5.7) in papain-or pepsin-treated whey was superior to that in whey or whey permeate, but inferior to growth in milk; it was not significantly different from that found in a 1:1 whey: milk medium. When 2% sodium citrate was added to the fermented medium, the cell recovery levels (59–75%) upon centrifugation were not significantly different in papain-treated media compared to untreated substrates. Cultures obtained from papain-treated milk or whey showed similar mortality levels following freeze-drying (99%) to those grown on untreated milk or whey. Addition of Tween 80 to the growth medium improved survival rate by a factor of ten.     

Effect of moderate electric field on the metabolic activity and growth kinetics of Lactobacillus acidophilus

Moderate electric fields (MEF), applied across microbial growth media may potentially affect the permeability of cell membranes. We investigated the effects of MEF on bacteriocin (lacidin A) production during fermentation and on microbial growth kinetics of Lactobacillus acidophilus OSU 133. We comparatively investigated the following treatments: conventional, MEF (1 V/cm, 60 Hz, for 40 h), combinations of MEF (1 V/cm, 60 Hz, for the first 5 h) and conventional fermentation (for 35 h), and discrete MEF (1 V/cm, 2 min on and off, for 40 h). In all treatments, except as noted below, temperature was set at 30 degrees C. The two exceptions were control (conventional) and discrete MEF treatment, which were conducted both at 30 and 37 degrees C. MEF treatments at the early stage of fermentation at 30 degrees C showed the maximum bacteriocin activity. Minimum bacteriocin production was observed under conventional fermentation at 37 degrees C. A mathematical model based on Monod growth kinetics was used to predict bacteriocin production and showed results consistent with conventional treatment data. MEF did not have a significant effect on the lag time, maximum specific growth rate, biomass production and pH change under the different experimental conditions at each specific temperature. Based on the observations, bacteriocin activity under the presence of MEF at the early stage of fermentation increased without significant change in the final biomass.     

Effect of the pH of growth on the survival of Lactobacillus delbrueckii subsp. bulgaricus to stress conditions during spray-drying

AIMS: The aim of this study was to optimize survival of Lactobacillus delbrueckii subsp. bulgaricus during spray-drying and subsequent storage through optimizing the pH of growth conditions. METHODS AND RESULTS: Cell concentrates previously grown without or with pH controlled were spray-dried and stored at 20 degrees C and heat treated at 57 degrees C. Cells grown under noncontrolled pH were more resistant to both drying and heating than cells grown under controlled pH but no significant differences were observed during storage. The intracellular proteins profile of cells grown under both conditions was studied by two-dimensional SDS-polyacrylamide gel electrophoresis. Eight proteins were identified using automated mass spectrometry (MS) and tandem mass spectrometry (MS/MS) data acquisition. Of the identified proteins, only cochaperonin GroES corresponded to a known heat shock protein (HSP). The other proteins identified are proteins involved in glycolysis. For cells grown under noncontrolled pH the expression of the Hsp70, GroES and GroEL, measured by Western blotting, was enhanced. CONCLUSIONS: The higher resistance of cells grown under noncontrolled pH correlates with the enhanced production of heat shock proteins. SIGNIFICANCE AND IMPACT OF THE STUDY: Growth of L. bulgaricus under controlled pH (commonly used by the starter cultures production industry) results in cells more sensitive to stresses frequently encountered by the cells during starter cultures preparation/storage/utilization.     

酸性水对淡水螺类存活,生长与繁殖的影响

研究了酸性水对椭圆萝卜螺和铜锈环棱螺等淡水螺类存活、生长及繁殖的影响。结果表明,椭圆萝卜螺对低pH值的耐受能力,96小时LC_(50)值为pH3.96。pH值低于5.0时,淡水肺螺类产的卵袋数量较少,卵孵化时间较长,幼螺生长较缓慢。铜锈环棱螺仔螺在低pH(对照组)下生长到第35和45天时,其体长生长率分别为1.21和1.07％,而pH5.0组则仅有0.18和0.29％。pH5.5对淡水肺螺类无明显影响,pH3.0则不能生存。     

Effect of apoplastic solutes on water potential in elongating sugarcane leaves

Solute concentration in the apoplast of growing sugarcane (Saccharum spp. hybrid) leaves was measured using one direct and several indirect methods. The osmotic potential of apoplast solution collected directly by centrifugation of noninfiltrated tissue segments ranged from −0.25 megapascal in mature tissue to −0.35 megapascal in tissue just outside the elongation zone. The presence of these solutes in the apoplast manifested itself as a tissue water potential equal to the apoplast osmotic potential. Since the tissue was not elongating, the measurements were not influenced by growth-induced water uptake and no significant tension was detected with the pressure chamber. Further evidence for a significant apoplast solute concentration was obtained from pressure exudation experiments and comparison of methods for estimating tissue apoplast water fraction. For elongating leaf tissue the centrifugation method could not be used to obtain direct measurements of apoplast solute concentration. However, several other observations suggested that the apoplast water potential of −0.35 to −0.45 megapascal in elongating tissue had a significant osmotic component and small, but significant tension component. Results of experiments in which exudate was collected from pressurized tissue segments of different ages suggested that a tissue age-dependent dynamic equilibrium existed between intra- and extracellular solutes.