Man, Rogosa And Sharpe Medium Research Articles

Characterization of lipases and preliminary purification of tributyrinesterases from lactic acid bacteria strains belonging to the Enterococcus and Lactococcus genera

The objective of this study is to characterize and attempt to purify lipolytic enzymes derived from strains of Enterococcus and Lactococcus genera isolated from various environments. For this purpose, ten strains of lactic acid bacteria were studied for their lipolytic and esterasic activities on an MRS (Man, Rogosa, and Sharpe) medium containing natural and/or artificial lipid substrates. Among them, two strains: Lactococcus lactis subsp lactis and Lactococcus lactis subsp cremoris showed maximum extracellular lipolytic activity in the presence of 1% olive oil. It was observed that both strains exhibited higher lipolytic activity at pH 7 and 8, with an optimal temperature of 30 °C and 37 °C, respectively. Glucose was found to be the best carbon source for both tested strains. The study of growth kinetics and fatty acid production over time revealed that fatty acid production begins during the exponential phase and reaches its maximum during the stationary phase. The purification of tributyrinesterases was carried out on two strains of Enterococcus genus: Enterococcus feacium and Enterococcus durans through ammonium sulfate precipitation and Sephadex G-100 gel filtration chromatography allowed the estimation of the molecular weight of the tributyrinesterases as 32.09 kDa and 38.49 kDa for both strains, respectively.

Microbial conversion of agro-wastes for lactic acid production

Lactic acid (LA) is an organic compound produced via fermentation by microorganisms that can utilize a wide range of carbohydrate sources and has gained relevance in food industries for preservation, pharmaceutical industries as additives, textile industries as mordants and production of cosmetics and bioplastics. In spite of the various applications of lactic acid, its availability is a challenge, especially in developing countries like Nigeria and therefore has to be imported, making it very expensive. One of the core substrates for lactic acid production is glucose. This study focused on the production of lactic acid using reducing sugar from locally sourced agro-wastes (corncob, sugarcane bagasse, plantain peduncle and groundnut shell). Bacteria were isolated from the agro-wastes dumpsite and screened for lactic acid production using De Man Rogosa and Sharpe (MRS) agar. The agro-wastes were pretreated using NaOH and hydrolyzed using cellulase produced from Aspergillus niger. The lactic acid bacteria (LAB) were identified based on their cultural, morphological, biochemical and molecular characteristics. The screened isolates were used for the production of lactic acid in an MRS medium containing the agro-waste hydrolysates as the sole carbon source. The LAB isolate with the best ability for lactic acid production was ascertained using the spectrophotometric method. Eleven (11) isolates were obtained from the agro-wastes dumpsites. Lactiplantibacillus plantarum (accession number OM510300) from plantain peduncle dumpsites had the highest potential for lactic acid production (1.9558 g/L). The study revealed that Nigerian-locally sourced agro-wastes can be developed as an alternative source of reducing sugar for lactic acid production and thus leads to agro-wastes management in the environment.

Sangyod rice bran extract enhances Lacticaseibacillus paracasei growth during the exponential phase and antibacterial activity of L. paracasei supernatant against zoonotic and foodborne pathogens

Prebiotics are a group of nutrients or compounds that are degraded by the gut microbiota, including Lacticaseibacillus paracasei. The probiotic plays an important role in adhesion to the gut and is able to produce antimicrobial substances to inhibit pathogens. This study aimed to investigate the effects of Sangyod rice bran extract on the growth promotion of L. paracasei. Furthermore, antibacterial activity of the extract and L. paracasei supernatants cultured in De Man, Rogosa and Sharpe (MRS) medium plus the extract against zoonotic and foodborne pathogens was investigated. Antibacterial activity of the crude extract and the oil from Sangyod rice bran against the pathogens, including Bacillus cereus, Staphylococcus aureus, Escherichia coli, Avian pathogenic E. coli, and Pseudomonas aeruginosa was investigated using broth microdilution assay. The effects of the crude extract and the oil on the growth and adhesion of L. paracasei were further determined. The antibacterial activity of L. paracasei supernatant cultured in the medium supplemented with the extract and the oil against the pathogens was determined by agar well diffusion assay, followed by the broth microdilution assay. Finally, the chemical constituents and antioxidant activity of the crude extract and the oil from Sangyod rice bran were investigated. The crude extract and the oil from Sangyod rice bran enhanced L. paracasei growth during the exponential phase. Furthermore, the crude extract at 0.25 mg/mL significantly enhanced the adhesion of L. paracasei to the surface compared with the control. Both minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of the crude extract against B. cereus and S. aureus were 0.5 and 1.0 mg/mL, respectively. All pathogens were sensitive to the supernatant of L. paracasei with similar MIC and MBC ranging from 12.5% v/v to 50% v/v. However, the MIC and MBC values of L. paracasei supernatant grown in MRS medium plus the crude extract and oil were not significantly different compared to the supernatant obtained from MRS alone. The crude extract had free radical scavenging activities with IC50 values at 0.61 mg/mL. The results suggested the potential benefits of the crude extract from Sangyod rice bran for inducing the growth and the adhesion of L. paracasei and inhibiting zoonotic and foodborne pathogens.

Optimizatiaon of MRS (De Man, Rogosa and Sharpe) Media with an organic waste substitute to assess the potential of Lactobacillus in Ink degradation

Lactobacillus species are normally found in human digestive and urinary tracts. In this study, the capability of probiotic strains to grow in media using banana peel waste as an alternative carbohydrate source was investigated. Lactic acid bacteria were isolated using homemade curd, banana peel powder was made using an alternate drum drier technique and used as a fermentation media on which strain of probiotic, Lactobacillus sp. were grown. The result showed that bacterial growth using banana peel powder obtained at 370C under anaerobic condition (2- 3 days), was comparable to growth seen in MRS medium. It can be concluded that the banana peel powder can be utilized to produce culture medium for cultivation of probiotic bacteria as a substitute to MRS medium which is expensive for cultivating probiotics. This will not only result in cost reduction of probiotic from cheap, inexpensive Agro-waste material, but also helps in solving the environmental pollution problem caused by their extensive disposal. The capability of Lactobacillus sp. to degrade dye was also investigated. Lactobacilli was incorporated under anaerobic condition in the M9 media containing the dye. The dye degrading capability of Lactobacillus sp was estimated colorimetrically at 520nm. The result showed a decrease in the dye concentration obtained at 37oC under anaerobic condition. So, it can be concluded that the Lactobacillus strain can be used for the bioremediation of dyes.

Growth Optimization of Lactobacillus acidophilus for Production of Antimicrobial Peptide Acidocin 4356: Scale up from Flask to Lab-Scale Fermenter.

Background: Antibiotic-resistant bacteria are a major threat to global health. Older antibiotics have become more or less ineffective as a result of widespread microbial resistance and an urgent need has emerged for the development of new antimicrobial strategies. Acidocin 4356 is a novel antimicrobial bacteriocin peptide produced by Lactobacillus acidophilus ATCC 4356 and capable of confronting the Pseudomonas aeruginosa ATCC 27853 infection challenges. According to our previous studies, the production of Acidocin 4356 is in parallel with cellular biomass production.Objectives: Given the costly production of Acidocin 4356, the development of a beneficial approach for increasing productivity of the cellular biomass has been targeted in the lab-scale fermenter for scale-up production of this bacteriocin. Therefore, in this study, we developed an inexpensive optimal culture medium based on the whey feedstock, evaluating this medium for scaling-up of the bacteriocin production from flask to fermenter.Material and Methods: In the first step, the optimization of the process parameters and medium components was carried out using the Plackett-Burman (PB) design and Response surface methodology (RSM) in flask culture. After optimization of the medium, bacteriocin production in the optimum culture medium was compared with de Man, Rogosa and Sharpe (MRS) medium by analyzing the intensity of the peptide band. Intensity analysis has been conducted on the PAGE band of the peptide using Image J software. Finally, the scale- up of bacteriocin production in the optimum culture medium was evaluated by batch fermentation in a 3-liter fermenter.Results: In this study, a medium containing whey (40 g.L-1) and sodium acetate (5 g.L-1) was used as basal medium, and the effect of other factors were then evaluated. According to the PB design, three factors of peptone concentration, yeast extract concentrations and cultivation temperature were selected as the most effective factors which improve the growth of L. acidophilus. The condition providing the highest growth capacity for bacteriocin production were predicted based on the results of RSM as following: temperature 40 ° C, yeast (4 g.L-1), and peptone (8 g.L-1). Finally, the dry cell weight was obtained after incubation for 12 h as 2.25 g.L-1. Comparison of cell growth and bacteriocin production between MRS medium and optimized medium confirmed the efficacy of these optimal conditions for the cost-effective production of Acidocin 4356 in the flask. Besides, the scale- up of bacteriocin production has made under optimal condition in the 3-L fermenter.Conclusions: In this study, for the first time, scale- up production of Acidocin 4356 was presented by using a low-cost method based on whey feedstock to tackle P. aeruginosa infections.

Co-production of gamma amino butyric acid (GABA) and lactic acid using Lactobacillus plantarum LP-9 from agro-residues

Microbial conversion of agro-residues into valuable products such as GABA and lactic acid is of considerable environmental and biotechnological significance. In this study, twenty-nine lactic acid bacteria were isolated from traditional fermented milk and screened for lactic acid and GABA production. Among these, one strain LP-9, identified as Lactobacillus plantarum demonstrated co-production of GABA (0.86 g/L) and lactic acid (19.81 g/L) in De Man, Rogosa and Sharpe (MRS) broth supplemented with 1% monosodium glutamate (MSG). Under RSM optimized conditions, cumulative effect of factors influencing microbial product formation led to a two-fold increase in production of GABA (1.53 g/L) as compared to unoptimized conditions along with substantial production of lactic acid (21.87 g/L). Further, to develop an economical bioprocess on these lines, L. plantarum LP-9 was tested for its capability to utilize agro residues (wheat bran, rice bran and corn bran) and cassava (starchy food crop as control) in form of carbon source for GABA and lactic acid production using conditions optimized in RSM. The substrates were saccharified with enzyme cocktail containing α-amylase, amyloglucosidase, and cellulase followed by fermentation with L. plantarum LP-9 in MRS medium supplemented with 1% MSG but without sugar. The results showed that the saccharified agroresidues tested gave significant and comparable production of GABA (1.14–1.30 g/L) and lactic acid (22.83–29.82 g/L) as that obtained with cassava (1.39 g/L GABA and 31.76 g/L LA). This study illustrated the potential of isolate L. plantarum LP-9 to co-produce GABA and lactic acid from agro residues via biorefinery approach. The developed bioprocess will also help in safe, efficient and ecofriendly disposal of agriwastes.

Comparing the Performance of Lactobacillus delbrueckii and Lactobacillus rhamnosus on The Formation of Lactic Acid from Glucose

For producing lactic acid, it may use pure glucose. Lactic acid is a category in organic compounds, and it has a high sales value since being used in the food processing industry is quite diverse. Lactic acid has also has used in numerous manufacturing fields and that same food industry, including pharmaceuticals, cosmetics, chemicals, and textiles. We can make lactic acid from refined starch and cellulose fermentation materials; lactic acid is a monomer of poly-lactic acid (PLA), the primary ingredient manufacturer of environmentally friendly biodegradable plastic. Variables used in this research include up to 10-60 percent for medium BHM (Bushnell Haas Medium), 40-60 percent for medium MRS (de Man Rogosa and Sharpe), and Lactobacillus delbrueckii and Lactobacillus rhamnosus for glucose concentration. After the fermentation process, we took lactic acid, and absorbance, lactic acid, and glucose levels have measured. The study shows that best-operating conditions are 21 hours of fermentation time. Lactobacillus delbrueckii develops more vital lactic acid from both the media used, BHM, and MRS media.

Effects of maltogenic amylase from Lactobacillus plantarum on retrogradation of bread

Maltogenic amylase originated from Lactobacillus plantarum (LpMA) was studied to investigate its applicability as an antistaling enzyme. The differential scanning calorimetry (DSC) results demonstrated that the bread treated with purified LpMA exhibited a retrogradation peak that was 65% that of the control bread. Then, for the purpose of practically using L. plantarum as an antistaling agent, the expression of LpMA in L. plantarum was enhanced by growth on a modified medium; the LpMA expression of L. plantarum grown on De Man, Rogosa and Sharpe (MRS) medium supplemented with an additional 6% glucose was 54 times higher than that of L. plantarum grown on the original MRS medium. The side chain length distribution analysis showed that the cell extract of L. plantarum (CELP) tended to prefer to hydrolyzes the long side chains of amylopectin (>30). During storage for 9 days at 4 °C, the bread treated with CELP exhibited a 25% slower retrogradation rate and 63% lower hardness relative to the control bread, indicating that the CELP is a potential candidate for use as an antistaling agent.

Optimization of Streptococcus macedonicus MBF10-2 Lysate Production in Plant-based Medium by Using Response Surface Methodology

Bacterial lysates have become a common ingredient for natural health care. Lactic acid bacteria (LAB) could serve as potential candidates for lysate production: the lactic acids produced by LAB have been utilized for their moisturizing, antimicrobial, and rejuvenating effects, while other substances provide topical benefits and health effects for the skin. Our study aimed to obtain lysate from a LAB S. macedonicus MBF 10-2 through an optimized fermentation using the Response Surface Methodology. Strain MBF10-2 was cultivated in a 2L fermenter tank in de Man Rogosa and Sharpe (MRS) medium and in plant-based peptone modified MRS, i.e. Soy-peptone and Vegitone. The duration and the medium composition (dextrose and soy peptone or proteose peptone) were adjusted to obtain an optimum production of cell lysate. Central Composite Design was employed for Design Expert 7.0.0 by adjusting 3 factors: dextrose (1%, 1.5%, 2%, 2.5%, 3%), soy or proteose peptone (0.5%, 0.75%, 1%, 1.25% and 1.5%), and duration of fermentation (8, 10, 12 14, and 16 h for MRS-Soy peptone and 15, 17, 19, 21, and 23 h for MRS Vegitone). Bacteriocin-Like Inhibitor Substance activity of lysate and pH were used as indicators. The optimum condition for lysate production using MRS Soy Peptone and Vegitone are as follows: dextrose concentration 2.5%, plant-based peptone 1.25%, while optimum fermentation duration were 11.18 h (MRS Soy Peptone) and 17 h (MRS Vegitone) with a starter concentration of 10% at OD600nm 0.2 ± 0.05. However, the standard MRS medium produced better quality lysate compared to MRS plant-based peptones.

Incubation of Aquilaria subintegra with Microbial Culture Supernatants Enhances Production of Volatile Compounds and Improves Quality of Agarwood Oil

Incubation with microbial culture supernatants improved essential oil yield from Aquilaria subintegra woodchips. The harvested woodchips were incubated with de man, rogosa and sharpe (MRS) agar, yeast mold (YM) agar medium and six different microbial culture supernatants obtained from Lactobacillus bulgaricus, L. acidophilus, Streptococcus thermophilus, Lactococcus lactis, Saccharomyces carlsbergensis and S. cerevisiae prior to hydrodistillation. Incubation with lactic acid bacteria supernatants provided higher yield of agarwood oil (0.45% w/w) than that obtained from yeast (0.25% w/w), agar media (0.23% w/w) and water (0.22% w/w). The composition of agarwood oil from all media and microbial supernatant incubations was investigated by using gas chromatography-mass spectrometry. Overall, three major volatile profiles were obtained, which corresponded to water soaking (control), as well as, both YM and MRS media, lactic acid bacteria, and yeast supernatant incubations. Sesquiterpenes and their oxygenated derivatives were key components of agarwood oil. Fifty-two volatile components were tentatively identified in all samples. Beta-agarofuran, α-eudesmol, karanone, α-agarofuran and agarospirol were major components present in most of the incubated samples, while S. cerevisiae-incubated A. subintegra provided higher amount of phenyl acetaldehyde. Microbial culture supernatant incubation numerically provided the highest yield of agarwood oil compared to water soaking traditional method, possibly resulting from activity of extracellular enzymes produced by the microbes. Incubation of agarwood with lactic acid bacteria supernatant significantly enhanced oil yields without changing volatile profile/composition of agarwood essential oil, thus this is a promising method for future use.

Production of Antimicrobial Substances by <i>Lactobacillus plantarum</i> Immobilized in Calcium Alginate Gel Beads

Production of anti-microbial substances by Lactobacillus plantarum , immobilized in calcium alginate gel beads was investigated. The beads were very unstable in De man Rogosa and Sharpe (MRS) medium but the stability of the beads improved by removing potassium and phosphate from the MRS medium. The highest stability of the beads was achieved by addition of calcium chloride to the medium. When 5% calcium chloride was added to the medium, the stability of the beads increased from 24h (when no calcium chloride was added) to 500 h, without adverse effects on the growth and antimicrobial substance production by the immobilized cells. Although the produced antimicrobial substances inhibited the growth of Bacillus cereus, B. subtilis, Listeria monocytogenes, and Escherichia coli, B. subtilis was the most susceptible. Under all the conditions investigated, immobilization of L. plantarum significantly increased the organism’s ability to produce antimicrobial substances. Although suspended cells produced higher antimicrobial substances under anaerobic condition, aerobic condition improved antimicrobial substance production by the immobilized cells. This implies that microaerophilic condition is the best for antimicrobial substance production by L. plantarum . Keywords: Bio-insecticide, anti-microbial substances, Bacillus thuringiensis , endotoxin

Overexpression and optimization of glutamate decarboxylase in Lactobacillus plantarum Taj-Apis362 for high gamma-aminobutyric acid production.

Gamma-aminobutyric acid (GABA) is an important bioactive compound biosynthesized by microorganisms through decarboxylation of glutamate by glutamate decarboxylase (GAD). In this study, a full-length GAD gene was obtained by cloning the template deoxyribonucleic acid to pTZ57R/T vector. The open reading frame of the GAD gene showed the cloned gene was composed of 1410 nucleotides and encoded a 469 amino acids protein. To improve the GABA-production, the GAD gene was cloned into pMG36e-LbGAD, and then expressed in Lactobacillus plantarum Taj-Apis362 cells. The overexpression was confirmed by SDS-PAGE and GAD activity, showing a 53 KDa protein with the enzyme activity increased by sevenfold compared with the original GAD activity. The optimal fermentation conditions for GABA production established using response surface methodology were at glutamic acid concentration of 497.973 mM, temperature 36°C, pH 5.31 and time 60 h. Under the conditions, maximum GABA concentration obtained (11.09 mM) was comparable with the predicted value by the model at 11.23 mM. To our knowledge, this is the first report of successful cloning (clone-back) and overexpression of the LbGAD gene from L. plantarum to L. plantarum cells. The recombinant Lactobacillus could be used as a starter culture for direct incorporation into a food system during fermentation for production of GABA-rich products.

Characterization of nitrite degradation by Lactobacillus casei subsp. rhamnosus LCR 6013.

Nitrites are potential carcinogens. Therefore, limiting nitrites in food is critically important for food safety. The nitrite degradation capacity of Lactobacillus casei subsp. rhamnosus LCR 6013 was investigated in pickle fermentation. After LCR 6013 fermentation for 120 h at 37°C, the nitrite concentration in the fermentation system was significantly lower than that in the control sample without the LCR 6013 strain. The effects of NaCl and Vc on nitrite degradation by LCR 6013 in the De Man, Rogosa and Sharpe (MRS) medium were also investigated. The highest nitrite degradations, 9.29 mg/L and 9.89 mg/L, were observed when NaCl and Vc concentrations were 0.75% and 0.02%, respectively in the MRS medium, which was significantly higher than the control group (p ≤ 0.01). Electron capture/gas chromatography and indophenol blue staining were used to study the nitrite degradation pathway of LCR 6013. The nitrite degradation products contained N2O, but no NH4 +The LCR 6013 strain completely degraded all NaNO2 (50.00 mg/L) after 16 h of fermentation. The enzyme activity of NiR in the periplasmic space was 2.5 times of that in the cytoplasm. Our results demonstrated that L. casei subsp. rhamnosus LCR 6013 can effectively degrade nitrites in both the pickle fermentation system and in MRS medium by NiR. Nitrites are degraded by the LCR 6013 strain, likely via the nitrate respiration pathway (NO2 −>NO−>N2O−>N2), rather than the aammonium formation pathway (dissimilatory nitrate reduction to ammonium, DNRA), because the degradation products contain N2O, but not NH4 +.

Orthogonal array deciphering MRS medium requirements for isolated Lactobacillus rhamnosus ZY with cell properties characterization

Lactobacillus rhamnosus is a well-known lactic acid bacterium (LAB), but a new ZY strain was isolated for the first time from commercial probiotic powder recently. Although many studies have focused on developing cost-effective media for the production of LAB, the de Man, Rogosa and Sharpe (MRS) medium is still the most common medium for bioprocesses. The aim of the current study is to decipher the composition of MRS based on a statistical approach, which will allow a higher biomass of Lactobacillus to be obtained. In Taguchi's approach, an L27 orthogonal array was adopted to evaluate the significance of 10 ingredients in MRS, in which the effects of the components were ranked according to their effect on biomass at OD600 as dextrose > MnSO4·H2O > beef extract > CH3COONa > MgSO4 > yeast extract > proteose peptone > K2HPO4 > ammonium citrate > Tween 80. Although the individual trace elements of ammonium citrate, K2HPO4, CH3COONa and MgSO4 in MRS had an insignificant influence on the biomass after statistical analysis, the total elimination of trace elements would predominantly affect the cell growth of Lactobacillus. Further characterization of the cell properties through attenuated total reflectance of Fourier transform infrared (ATR-FTIR) spectroscopy and protein identification via SDS-PAGE coupled with tandem mass spectrometry implied that dextrose as major carbon source in MRS played the most crucial role for L. rhamnosus production.

Differential cultivation and enumeration of Lactobacillus plantarum (PTCC 1058) in the presence of yogurt starter bacteria

This study was aimed at assessing the different selective media and incubation conditions for achieving an appropriate method in the isolation and enumeration of Lactobacillusplantarum PTCC 1058, Lactobacillus delbrueckii ssp. bulgaricus and Streptococcusthermophilus in probiotic yogurt. The yogurt samples containing 1% of L. plantarum PTCC 1058 were prepared using YoFlex Express cultures (containing L. delbrueckii ssp.bulgaricus and S. thermophilus) and stored at 4°C. After 24 h, they were cultivated in seven different agar media including: de Man, Rogosa and Sharpe (MRS) agar, MRS-Bile agar, acidified MRS agar (pH = 5.2), yogurt-lactic-agar (YL), Elliker’s lactic-agar (EL), M17 medium and S. thermophilus (ST) agar as pour plate and surface plate culture, and were incubated in aerobic and anaerobic conditions at three different incubation temperatures: 15, 37 and 45°C, for 48 to 72 h. For more practical examination, L. plantarum PTCC 1058and yogurt bacteria were enumerated every week over 6 weeks. Also, the ability of L. plantarum PTCC 1058 and yogurt bacteria to grow in concentration of 0.5 to 5% of bile salts were investigated. The results indicated that both L. plantarum PTCC 1058 and L. bulgaricus could grow in low concentration (≤ 2%) of bile salts. So, MRS-Bile-agar medium was not suitable for differentiation of L. plantarum PTCC 1058 and yogurt bacteria. The best condition for differentiation of L. plantarum PTCC 1058 from yogurt bacteria was cultivation on MRS medium and incubation at 15°C for 72 h. YL and EL media and aerobic incubation at 37°C for 48 h were suitable for enumeration of L. bulgaricus, and surface plate culture in YL, M17 and ST media and aerobic incubation at 45°C for 48 h was useful for enumeration of S. thermophilus in yogurt. Key words: Lactobacillus plantarum PTCC 1058, probiotic yogurt, differential culture, yogurt starter bacteria.

Effect of Bile and Nalidixic Acid on Growth of Selected Probiotics

Effect of bile and nalidixic acid on growth of Lactobacillus acidophilus, Bifidobacterium bifidum, Lactobacillus bulgaricus, Lactobacillus casei and Lactobacillus rhamnosus was studied by measuring the optical density at 600nm (OD600) and pH using De Man, Rogosa and Sharpe (MRS ) broth as the control. The addition of bile (%, w/v) was 0.03%, 0.06%, 0.09%, 0.12% and 0.15% and the addition of nalidixic acid (%, w/v) was 0.003%, 0.009%, 0.015%, 0.045% and 0.075%. Results were as follows: addition of bile at the concentration above 0.06% has a significant inhibition on the growth of L. bulgaricus and B. bifidum at incubation 24h. The optimum selective concentration of bile in MRS media was 0.06% for L. bulgaricus and B. bifidum. Addition of nalidixic acid has no effect on the growth of the five selected probiotics at incubation 24h. Addition of nalidixic acid in MRS can not use to realize selective enumeration in yogurt product containing probiotics.

Enhancement of enterocin A production by Enterococcus faecium MMRA and determination of its stability to temperature and pH

The growth, nutrient (total sugars, phosphorous, nitrogen and proteins) consumption and product formation by Enterococcus faecium MMRA in de Man, Rogosa and Sharpe (MRS) broth was followed in non-realkalized batch, realkalized batch and realkalized fed-batch cultures. In the latter fermentation, the growing culture was fed with a mixture of MRS medium (20 g of glucose/L) and a 400 g/L concentrated glucose. In the three cultures, a typically homolactic fermentation (only lactic acid was produced) was observed. The realkalized fed-batch culture was mainly characterized with higher biomass (2.4 g/L), lactic acid (32.5 g/L) and enterocin A (35.9 AU/mL) concentrations compared with the two batch processes. Mathematical models were developed to describe the productions of biomass, enterocin A and lactic acid in the two realkalized cultures. The growth and lactic acid production were successfully modelled with the Monod and the Luedeking and Piret models, respectively. Enterocin A was modelled by using a modified form of the Luedeking and Piret model, which includes a term for the effect of the pH drop rate on bacteriocin synthesis. Furthermore, the maximum enterocin A stability was obtained at temperatures below 100 °C, at acidic pH values and short incubation times.

Pediocin PA-1 production during repeated-cycle batch culture of immobilized Pediococcus acidilactici UL5 cells

Pediocin PA-1 production by Pediococcus acidilactici UL5 cells immobilized in kappa-carrageenan/locust bean gum gel beads was studied during repeated-cycle batch (RCB) culture with pH control in Man Rogosa and Sharpe (MRS) broth supplemented with 1% glucose and whey permeate (SWP) medium. The pediocin PA-1 production by free P. acidilactici cells pH-controlled batch culture has reached 2048 and 4096 AU ml(-1) after 11 and 12 h of incubation, with volumetric productivities of 187 and 342 AU ml(-1) h(-1) in SWP and MRS media, respectively. In RCB culture, immobilized cells reached a maximum concentration of 7.3+/-0.2 x 10(10) and 4.3+/-0.9 x 10(10) cfu g(-1) of beads in MRS and SWP media, respectively. The maximum pediocin PA-1 activity obtained during RCB fermentation was 4096 AU ml(-1); it was attained after only 0.75 and 2 h of incubation in MRS and SWP media, respectively. The corresponding volumetric productivities were 5461 and 2048 AU ml(-1) h(-1). Pediocin PA-1 production in the RCB culture was highly stable over 12 fermentation cycles carried out over 3 d in SWP media.

Productions and monomer compositions of exopolysaccharides by Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains isolated from traditional home‐made yoghurts and raw milk

SummaryIn this study, a total of forty‐five strains of lactobacilli and streptococci were determined exopolysaccharide (EPS) production in skim milk and Man Rogosa and Sharpe (MRS)/M17 medium, viscosity and proteolytic activity. The exopolysaccharide production by lactobacilli strains during growth in MRS medium was twenty‐one to 211 mg L−1, while in skim milk was to thirty‐six to 315 mg L−1. The EPS production by streptococci strains during growth in M17 medium was sixteen to 114 mg L−1, while in skim milk was to twenty‐four to 140 mg L−1. The EPS production of strains was lower in MRS/M17 medium than skim milk. Results showed that it was not clear correlation between the viscosity and EPS production of some strains. All strains were shown proteolytic activity. Positive correlations between exopolysaccharide production and proteolytic activity in skim milk were found some strains of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. These results indicated that the high exocellular protease‐producing strains can produce high EPS in skim milk. The monomer compositions of the EPSs formed by selected five strains were analysed. Mannose dominated (99–100%) on the EPS produced by L. delbrueckii subsp. bulgaricus and S. thermophilusstrains (except L. delbrueckii subsp. bulgaricus 22) in skim milk and MRS/M17 medium. Besides, the EPSs of strains in skim milk contained small amount of lactose.

Hydrolysis of soybean isoflavone glucosides by lactic acid bacteria

Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047, grown in de Man, Rogosa and Sharpe (MRS) or soymilk media, completely hydrolyzed the isoflavone glucosides, genistin and daidzin at 50 μg ml−1, into their respective aglycones, genistein and daidzein within 30 min. Other lactic acid bacteria did not produce β-glucosidase, the enzyme responsible for the hydrolysis of isoflavone glucosides, when cultured in MRS medium. Glucoside-hydrolyzing activity was induced in some lactic acid bacteria when cultured in soymilk medium. These strains hydrolyzed 70–80% of genistin into genistein and 25–40% of daidzin into daidzein.