Bacteriocinogenic Lactobacillus plantarum ST16Pa isolated from papaya (Carica papaya) — From isolation to application: Characterization of a bacteriocin

Strain ST16PA, isolated from papaya was identified as Lactobacillus plantarum based on biochemical tests, PCR with species-specific primers and 16S rDNA sequencing. L. plantarum ST16PA produces a 6.5 kDa bacteriocin, active against different species from genera Enterobacter, Enterococcus, Lactobacillus, Pseudomonas, Streptococcus and Staphylococcus and different serotypes of Listeria spp. The peptide is inactivated by proteolytic enzymes, but not when treated with ??-amylase, catalase, lipase, Triton X-100, SDS, Tween 20, Tween 80, urea, NaCl and EDTA. However, presence of 1% Triton X-114 deactivates the bacteriocin. No change in activity was recorded after 2 h at pH values between 2.0 and 12.0, and after treatment at 100 °C for 120 min or 121 °C for 20 min. The mode of activity against Lactobacillus sakei ATCC 15521, Enterococcus faecalis ATCC 19443 and Listeria innocua 2030C was bactericidal, resulting in cell lysis and enzyme-leakage. No significant differences in cell growth and bacteriocin production were observed when strain ST16Pa was cultured in MRS broth at 26 °C and 30 °C for 24 h (25 600 AU/ml). However, even though strain ST16PA grows well in MRS broth at 15 °C and 37 °C, a reduction of bacteriocin production was observed (400 AU/ml and 1600 AU/ml, respectively). In addition, effect of MRS medium components, different initial pH and additions of glycerol or vitamins to the media on bacteriocin ST16Pa production was studied.Peptide ST16PA adsorbs (400 AU/ml) to producer cells. However, bacteriocin ST16Pa was adsorbed at 50% to cells of L. innocua 2030C and at 75% to L. sakei ATCC 15521 and E. faecalis ATCC 19433 when experiments were conducted at 30 °C and pH 6.5. Adsorption of bacteriocin ST16Pa to target cells at different temperatures, pH and in presence of potassium sorbate, sodium nitrate, sodium chloride, ascorbic acid, Tween 80 and Tween 20 were also studied. To the best of our knowledge, this is the first report on detection of L. plantarum in papaya.     

Antibacterial activity and mechanism of a novel bacteriocin produced by Lactiplantibacillus plantarum against Escherichia coli and Staphylococcus aureus

The purpose of the study was to explore the antibacterial effect and mechanism of a novel bacteriocin of Lactiplantibacillus plantarum (L. plantarum) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial activity was determined by the Oxford cup method, and the dynamic growth curves were conducted with continuous shaking incubation. The result showed that the bacteriocin was a protein or protein-like antibacterial substance susceptible to pepsin and trypsin. And it had good antibacterial activity, pH stability, thermostability and enzyme treatment stability against E. coli and S. aureus. The SEM, flow cytometry and nucleic acid leakage showed that the bacteriocin disrupted the cell structures of the two bacteria by damaging cell walls and cell membranes. An agarose gel electrophoresis and SDS-PAGE analysis showed that the bacteriocin inhibited DNA replication and interfered with the protein formation, which resulted in the inhibition of the two bacteria's growth. Therefore, the use of the L. plantarum bacteriocin might be a promising biocontrol strategy to inhibit the pollution of E. coli and S. aureus simultaneously in foods.     

Antiviral activities of cell-free supernatants of yogurts metabolites against some RNA viruses

The antiviral activity of the cell-free supernatants (CFS) containing the metabolites of five yogurts fermented under anaerobic conditions with Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus plantarum, Streptococcus thermophilus and Bifidobacterium bifidum, respectively, was initially evaluated against seven RNA viruses using virus-induced cytopathic effects reduction method, while comparing that of De Man, Rogosa, and Sharpe (MRS) broths containing metabolites fermented with the same bacteria. All the CFS of yogurt showed high antiviral activity against seven RNA viruses, while the CFS of MRS broth exhibited similar or lower antiviral activity. Each CFS of yogurt and MRS broth showed no cytotoxicity with normal morphology in Vero or MDCK cells. Furthermore, CFS of each yogurt was more effective than that of MRS broth against the three enteroviruses and CFS of yogurt containing metabolites fermented with L. plantarum exhibited strong anti-influenza virus activity among that of the other yogurt and MRS broth. Therefore, CFS of the yogurt containing metabolites fermented with probiotic bacteria showed high potential to be used for developing fermented milk-based foods or drugs.     

Synergy effects by combination with lactic acid bacteria and frutooligosaccharides on the cell growth and antimicrobial activity

The aim of this study was to identify probiotic possibility of lactic acid bacteria (LAB) from mustard leaf kimchi and investigate synergy effects of combination with LAB and fructooligosaccharide (FOS) on antimicrobial activity. Lactobacillus acidophilus GK20, L. paracasei GK74, and L. plantarum GK81 have high survival ratio under gastric and intestinal fluids and were resistant to ampicillin, streptomycin, or tetracycline. The pH of LAB gradually decreased but the titratable acidity increased owing to organic acids production. Especially, L. acidophilus GK20 and L. paracasei GK74 produced hydrogen peroxide and bacteriocin. When LAB was co-cultured with Listeria monocytogenes or Staphylococcus aureus in broth without FOS, the inhibition ratio of L. monocytogenes and S. aureus by L. acidophilus GK20 was 36 and 57%, but L. paracasei GK74 showed higher inhibitory effect against L. monocytogenes than S. aureus. Meanwhile, the cell growth, culture pH, titratable acidity, and bacteriocin activity of L. acidophilus GK20 and L. paracasei GK74 were significantly (p<0.05) increased in MRS with FOS than without prebiotic. In conclusion, L. acidophilus GK20 and L. paracasei GK74 could be potentially used as novel probiotic strains, moreover, the combination between L. acidophilus GK20 or L. paracasei GK74 and FOS has great potential as a synbiotic.     

Antilisterial Activity of Hops Beta Acids in Broth with or Without Other Antimicrobials

ABSTRACT: Hops beta acids (HBA) are parts of hops flowers used to preserve wort and provide flavor in beer, and are reported as having antimicrobial properties. This study evaluated the antilisterial activity of HBA alone or in combination with other known antimicrobials in a culture broth medium. Listeria monocytogenes (10‐strain mixture) was inoculated (2.6 to 2.8 log CFU/mL) into tryptic soy broth supplemented with 0.6% yeast extract (TSBYE) without (control) or with HBA (0.5 to 5.0 μg/mL), potassium lactate (1.0%), sodium diacetate (0.25%), or acetic acid (0.1%), alone or in combination with HBA (0.5 to 3.0 μg/mL). Survival/growth of the pathogen during storage at 4 °C (35 d), 10 °C (20 d), or 25 °C (2 d) was periodically monitored by spiral plating onto tryptic soy agar plus 0.6% yeast extract. As expected, TSBYE without antimicrobials (control) supported rapid pathogen growth with growth rates of 0.40, 2.88, and 9.58 log CFU/mL/d at 4, 10, and 25 °C, respectively; corresponding Y_end values exceeded 9.0 log CFU/mL at 35, 20, and 2 d storage. HBA used alone (1.0 to 5.0 μg/mL) inhibited growth of L. monocytogenes at all 3 temperatures, with inhibition being more pronounced at higher concentrations and at the lower storage temperature (4 °C). The antilisterial activity of HBA (0.5 to 3.0 μg/mL) was enhanced when combined with sodium diacetate, acetic acid, or potassium lactate, achieving complete inhibition at 4 °C when 3.0 μg/mL HBA were used in combination with each of the above antimicrobials. Overall, HBA exhibited promising antilisterial activity in a broth medium and further studies are needed to investigate its potential antilisterial effects in food products.     

Antiviral activity of yogurt against enterovirus 71 in vero cells

Five yogurts were fermented with each bacteria strain. The viability and pH of each yogurt during fermentation or storage were evaluated, and then the cytotoxicity and antiviral activity against enterovirus (EV) 71 of cell-free supernatants (CFS) of the metabolites of each yogurt were compared with those of de Man, Rogosa, and Sharpe (MRS) broth fermented with the same bacteria. As the results, the number of viable bacteria for each yogurt after fermentation or during storage always remained higher than 5 log CFU/mL and the pH of those ranged from 4 to 6. The CFS of all yogurts showed antiviral activity over 45% against EV71, while it didn’t exhibit cytotoxicity in Vero cells. Specially, the CFS of yogurt fermented with Lactobacillus plantarum and Bifidobacterium bifidum exhibited high anti-EV71 activity of 92.74 and 90.44%, respectively. In contrast, the CFS of each MRS broth fermented with the same bacteria showed low antiviral activity of less than 30%.     

Modeling of growth and bacteriocin production by Leuconostoc mesenteroides E131

Leuconostoc mesenteroides E131, isolated from dry fermented sausages, produces an antimicrobial agent, characterized as bacteriocin. The effect of pH and temperature on growth and bacteriocin production, using MRS broth as growth medium, was studied in a fermentor. The pH value at which the best cell growth was observed (6.5) did not coincided with the value at which the maximum bacteriocin activity was attained (5.5). In contrast, the maximum bacteriocin activity was attained at temperature (25 °C) close to the optimum temperature for cell growth (25–30 °C). Notably, the range of pH and temperature for good bacteriocin production was within the range used for sausage fermentation. An empirical model was developed to describe the growth and bacteriocin production in different pH and temperature conditions. The model was able to describe growth and bacteriocin production and it could be used to predict the kinetic parameters of growth and bacteriocin production within the pH and temperature range examined.     

Assessment of probiotic characteristics of lactic acid bacteria isolated from fermented yak milk products of Sikkim,India: Chhurpi,Shyow, and Khachu

The present study documents the probiotic attributes of indigenous lactic acid bacteria (LAB) isolated from local fermented Yak milk products namely Chhurpi, Shyow and Khachu prepared in the northern and eastern region of Sikkim in the Himalayas. Samples were collected aseptically and a total of 170 LAB was isolated and screened for putative probiotic properties like hypocholesteromic effect, acid tolerance, bile tolerance, bile salt hydrolase (BSH) activity and cell surface hydrophobicity. It was observed that 70 LAB isolates showed cholesterol lowering activity, out of which 35 isolates were selected that showed 50% and less cholesterol reducing effect in vitro. Acid tolerance test revealed good tolerance of 12 isolates at pH 2.5 and pH 2.0 for up to 2 hours. The tolerance to 0.5% and 1% of three bile salts acid revealed more growth in MRS broth containing taurocholic acid with the isolates revealing good BSH activity leading to bile acid deconjugation. The cell surface hydrophobicity ranged from 20–95%. Furthermore, 16S rRNA gene sequencing revealed Lactobacillus plantarum YD5S and YD9S, L. pentosus YD8S, L. paraplantarum YD11S, Enterococcus lactis YHC20 and E. faecium YY1 as the best isolates with technological properties. The isolates may serve as potential probiotic candidates with potential for hypocholesteromic benefits in the future.     

Effect of inulin on growth and bacteriocin production by Lactobacillus plantarum in stationary and shaken cultures

The prebiotic effect of inulin added to MRS medium on growth and bacteriocin production by L. plantarum ST16 Pa was investigated in stationary cultures in anaerobic jars with medium containing 0.025% sodium thioglycolate or in flasks shaken at 100 rpm. In the presence of 1% inulin in anaerobic stationary cultures, this strain produced lactic acid at a level that was 36.5% higher than in the absence of the polysaccharide. In shaken cultures without inulin, cell count was 54% higher than in the stationary ones. Under stationary conditions in anaerobic jars, the addition of inulin increased the maximum specific growth rate from 0.37 to 0.49 h^?1 and reduced the generation time from 1.85 h to 1.40 h. Consequently, the exponential phase was shortened from 12 to 9 h when the cells were grown in stationary cultures with the oxygen scavenger. Despite this effect of inulin on growth rate, stationary cultures without inulin displayed higher antimicrobial activity against Listeria monocytogenes L104 (3200 AU/mL) than cultures with inulin (1600 AU/mL); therefore, inulin behaved as a compound able to accelerate growth rather than to stimulate bacteriocin production. The results presented in this study are very promising, as L. monocytogenes is a well‐known foodborne pathogenic microorganism. Moreover, L. plantarum ST16 Pa has proven to be a potential producer of a natural food preservative at an industrial level.     

Characterization of bacteriocin ST8KF produced by a kefir isolate Lactobacillus plantarum ST8KF

Lactobacillus plantarum ST8KF, isolated from kefir, produced a 3.5 kDa bacteriocin (bacST8KF) active against Lb. casei, Lb. salivarius, Lb. curvatus and Listeria innocua. BacST8KF was sensitive to proteolytic enzymes, but stable between pH 2.0 and 10.0, and heat resistant (20 min at 121 °C). BacST8KF did not adsorb to the surface of the producer cell. Maximum activity (25,600 AU mL⁻¹) was recorded in MRS broth with glucose, in MRS broth with glucose replaced by sucrose, and in MRS broth with glucose, supplemented with KH₂PO₄ after 24 h at 30 °C. Tri-ammonium citrate and glycerol in excess of 5.0 g L⁻¹ repressed bacST8KF production. Production of bacST8KF increased from 800 AU mL⁻¹ after 3 h of fermentation in MRS broth at 30 °C to 12,800 AU mL⁻¹ after 9 h and to 51,200 AU mL⁻¹ after 27 h. These results suggest that bacST8KF may be a secondary metabolite and shows that its mode of activity is bacteriostatic.     

Effect of Extrinsic Parameters on the Production of a Bacteriocin by Lactobacillus buchneri,Isolated from Mexican Raw Sausages

Bacteriocins are antimicrobial peptides acting on certain pathogens and spoilage microorganisms. They have recently been considered as natural alternative to food preservatives. The objective of this work was to study the inhibition spectrum of a bacteriocin produced by Lactobacillus buchneri, isolated from a Mexican sausage, against Listeria monocytogenes and several lactic acid bacteria, and the influence of several extrinsic parameters on bacteriocin activity. Culture media (MRS or APT) had no significant effect on bacteriocin production (p < 0.060) although higher activity was observed in MRS (220 AU/mL). Conversely, temperature significant affected production (p > 0.001). Bacteriocin activity was also increased by 100% nitrogen atmosphere (180 AU/mL) as compared to N₂/CO₂ (50:50) (150 AU/mL) and 100% CO₂ (60 AU/mL). Maximum activity occurred at the end of the exponential growth phase. This bacteriocin inhibited some Listeria monocytogens strains and several lactic acid bacteria, mainly Lactobacillus sp.     

Isolation and characterisation of the bacteriocin-producing Leuconostoc citreum HW02 from malts

Herein, a lactic acid bacterium which produces bacteriocin was isolated from malted barley. The isolated strain was identified by 16 S rRNA analysis and designated Leuconostoc citreum HW02. Bacteriocin HW02 was shown to have growth inhibition against health-threatening Gram-positive microorganisms such as Staphylococcus aureus, Listeria monocytogenes, and Latilactobacillus curvatus. Bacteriocin HW02 was reported to be incapable of inhibiting the growth of health-threatening microorganisms after treatment with proteolytic enzymes; thus, it was indicated that bacteriocin is proteinaceous in nature. Bacteriocin HW02 showed stability against a broad range of temperatures (60–121 °C), pH (2–10), various detergents, or organic solvents. Its antimicrobial activity against the indicator strain, Lactiplantibacillus plantarum NCDO 955, was maximised (320 AU mL⁻¹) midway through the stationary phase at 12 h. The crude bacteriocin HW02 molecular weight was estimated to be about 7.7 kDa. After the treatment of the indicator strain with bacteriocin, the maintenance of the optical density of the culture, the morphological analysis of cell-structure abnormalities, and cell shrinkage implied that bacteriocin showed bactericidal activity.     

Effect of growing bacteria isolated from food on staphylococcal growth and thermonuclease activity

The effect of growing Bacillus subtilis, Streptococcus faecalis var. liquefaciens, Escherichia coli and Lactobacillus plantarum on staphylococcal growth and thermonuclease (TNase) activity was investigated in liquid media and in foods. Growth of S. aureus at 37°C for 24 h under aerobic conditions was not inhibited by the four test strains. However, staphylococcal TNase activity decreased by 70 and 80% in the presence of B. subtilis and S. faecalis var. liquefaciens respectively. Staphylococcal growth and TNase activity were strongly inhibited by L. plantarum under anaerobic conditions at pH 5.5 but not at pH 7.0. Furthermore, optimal TNase production by S. aureus occurred in cooked meat medium containing 0.5 to 5.0% NaCl. TNase production significantly decreased at higher concentrations of NaCl. In the presence of B. subtilis and S. faecalis var. liquefaciens. TNase activity decreased at NaCl levels of 0.5 to 5.0% but not at NaCl concentrations>5.0%. TNase activity was also inhibited by growing B. subtilis and S. faecalis var. Liquefaciens at pH 5.0 to 7.0. The rate of inhibition increased with increasing pH. TNase activity was not inhibited after 48 h incubation at 20° in the presence of B. subtilis and S. faecalis var. liquefaciens but significant inactivation could be demonstrated at 25° to 37°C. The results obtained with artificially contaminated, sterile food samples were similar to those obtained with brain-heart infusion broth, but the degree of decrease in TNase activity in food was much lower than that in brain-heart infusion broth.     

Comparison of the performances of different fermentation strategies on cell growth and bacteriocin production by Lactobacillus curvatus CWBI‐B28

The dynamics of cell growth and bacteriocin production by Lactobacillus curvatus CWBI‐B28 in modified De Man/Rogosa/Sharp (mMRS) broth with various concentrations of glucose and complex nitrogen source (CNS; peptone, yeast extract and meat extract) was investigated in flask fermentations and in a laboratory fermentor using batch and fed‐batch cultivations. In fed‐batch fermentation the rate of feeding of the reactor with the substrates was either maintained constant (0.12 L h^?1) or varied exponentially as a function of time. The results showed that both cell growth and bacteriocin activity were influenced by changes in the concentrations of glucose and CNS. Optimal growth and bacteriocin activity were obtained in mMRS broth containing 40 g L^?1 glucose and 40 g L^?1 CNS (mMRS_40/40). A bacteriocin titre of 4266 AU mL^?1 and a cell count of 8.7 log colony‐forming units (cfu) mL^?1 were recorded when this medium was used for cultivation. In batch fermentation using the same medium, a higher cell count (9.5 log cfu mL^?1) and twice as much bacteriocin as in flask fermentation were produced. The highest bacteriocin titre (8533 AU mL^?1) was obtained with fed‐batch fermentation at an exponentially varying rate of feeding. Bacteriocin activity and cell dry mass did not always correlate. Copyright © 2007 Society of Chemical Industry     

Inhibition of Shigella sonnei and Shigella flexneri in Hummus Using Citric Acid and Garlic Extract

Hummus (chickpea dip) is a ready‐to‐eat product that may pose a significant risk to human if pathogens are present. Several organisms including Shigella spp. have been isolated from hummus. However, studies on the survival and inhibition of Shigella spp. in food are scarce. This study investigated the growth pattern of Sh. sonnei and Sh. flexneri in hummus at different temperatures (4, 10, and 24 °C). Additionally, the inhibitory activity of different concentrations of citric acid (CA) (0.5%, 1.0%, and 2.0%) and garlic extract (GE) (1.0%, 2.0%, and 3.0%) against Sh. sonnei and Sh. flexneri inoculated into hummus and stored at 4 and 10 °C was investigated. Both Shigella spp. survived well at 4 °C, while both grew to >7.0 log₁₀ after 4 d at 10 °C or 1 d at 24 °C. At 4 °C, CA at 0.5% and 1.0% resulted in a slight reduction in the count (approximately 1.0 log₁₀); a complete elimination of Sh. sonnei was attained by using 2.0% CA. However, approximately 3.0 log₁₀ reduction in Sh. sonnei was obtained at 10 °C. For Sh. flexneri, CA at 0.5% and 1.0% resulted in a bacteriostatic inhibition. GE at 1.0% and 2.0% resulted in approximately 1.0 to 2.0 log₁₀ reduction in Sh. sonnei count at 4 °C, while at 3.0% GE, approximately 4.0 and 3.0 log₁₀ reductions were obtained at 4 and 10 °C, respectively. In comparison, the 2.0% and 3.0% GE resulted in a bacteriostatic effect against Sh. flexneri at 4 and 10 °C.     

Metabolism of ferulic acid during growth of Lactobacillus plantarum and Lactobacillus collinoides

BACKGROUND: Food‐isolated lactic acid bacteria can transform ferulic acid (FA) into several products. Since quantification of these metabolites during the different bacterial growth phases is lacking, the aim of this study was to identify and quantify conversion products of FA and to follow the kinetics of FA metabolism during growth of Lactobacillus plantarum and Lactobacillus collinoides. RESULTS: Lactobacillus plantarum and Lactobacillus collinoides were incubated in MRS broth, to which different amounts of FA were added (final concentrations of 0, 0.5, 1.5 and 3 mmol L^?1), at 30 °C until the late stationary phase. Lactobacillus plantarum metabolised FA into 4‐vinylguaiacol (4‐VG) and hydroferulic acid (HFA). Conversion to 4‐VG started simultaneously with the degradation of FA, while formation of HFA started in the mid‐exponential phase. Lactobacillus collinoides only formed 4‐VG, mainly in the stationary phase. No significant effect of the different amounts of FA was seen on the growth and fermentation characteristics of both bacteria. CONCLUSION: The results demonstrate that both bacteria are able to convert FA. However, start of conversion differs between the two strains. The different amounts of FA had no influence on the growth and fermentation characteristics of both bacteria. Copyright © 2012 Society of Chemical Industry     

In vitro evaluation of the probiotic potential of bacteriocin producer Lactobacillus sakei 1

Lactobacillus sakei 1 is a food isolate that produces a heat-stable antimicrobial peptide (sakacin 1, a class IIa bacteriocin) inhibitory to the opportunistic pathogen Listeria monocytogenes. Bacterial isolates with antimicrobial activity may be useful for food biopreservation and also for developing probiotics. To evaluate the probiotic potential of L. sakei 1, it was tested for (i) in vitro gastric resistance (with synthetic gastric juice adjusted to pH 2.0, 2.5, or 3.0); (ii) survival and bacteriocin production in the presence of bile salts and commercial prebiotics (inulin and oligofructose); (iii) adhesion to Caco-2 cells; and (iv) effect on the adhesion of L. monocytogenes to Caco-2 cells and invasion of these cells by the organism. The results showed that L. sakei 1 survival in gastric environment varied according to pH, with the maximum survival achieved at pH 3.0, despite a 4-log reduction of the population after 3 h. Regarding the bile salt tolerance and influence of prebiotics, it was observed that L. sakei 1 survival rates were similar (P > 0.05) for all de Man Rogosa Sharpe (MRS) broth formulations when tests were done after 4 h of incubation. However, after incubation for 24 h, the survival of L. sakei 1 in MRS broth was reduced by 1.8 log (P < 0.001), when glucose was replaced by either inulin or oligofructose (without Oxgall). L. sakei 1 was unable to deconjugate bile salts, and there was a significant decrease (1.4 log) of the L. sakei 1 population in regular MRS broth plus Oxgall (P < 0.05). In spite of this, tolerance levels of L. sakei 1 to bile salts were similar in regular MRS broth and in MRS broth with oligofructose. Lower bacteriocin production was observed in MRS broth when inulin (3,200 AU/ml) or oligofructose (2,400 AU/ml) was used instead of glucose (6,400 AU/ml). L. sakei 1 adhered to Caco-2 cells, and its cell-free pH-neutralized supernatant containing sakacin 1 led to a significant reduction of in vitro listerial invasion of human intestinal Caco-2 cells.     

Induction of bacteriocin production by coculture is widespread among plantaricin-producing Lactobacillus plantarum strains with different regulatory operons

We describe the bacteriocin-production phenotype in a group of eight singular bacteriocinogenic Lactobacillus plantarum strains with three distinct genotypes regarding the plantaricin locus. Genotyping of these strains revealed the existence of two different plantaricin-production regulatory operons, plNC8-plNC8HK-plnD or plnABCD, involving three-component systems controlled each of them by a specific autoinducer peptide (AIP), i.e. PLNC8IF or PlnA. While all of the strains produced antimicrobial activity when growing on solid medium, most of them halted this production when cultured in broth, thus reflecting the functionality of regulatory mechanisms. Antimicrobial activity in broth cultures was re-established or enhanced when the specific AIP was added to the culture or by coculturing with specific bacterial strains. The latter trait appeared to be widespread in bacteriocinogenic L. plantarum strains independently of the regulatory system used to regulate bacteriocin production or the specific bacteriocins produced. The induction spectrum through coculture, i.e. the pattern of bacterial strains able to induce bacteriocin production, was characteristic of each individual L. plantarum strain. Also, the ability of some bacteria to induce bacteriocin production in L. plantarum by coculture appeared to be strain specific. The fact that induction of bacteriocin production by coculturing appeared to be a common feature in L. plantarum can be exploited accordingly to enhance the viability of this species in food and feed fermentations, as well as to contribute to probiotic functionality when colonising the gastrointestinal tract.     

Modelling of the growth of populations of Listeria monocytogenes and a bacteriocin-producing strain ofLactobacillus in pure and mixed cultures

The cell growth biokinetics of Listeria monocytogenes and a bacteriocin-producing strain ofLactobacillus sake were studied. The organisms were grown both separately and together in a broth system. It was observed that Lact. sake was better suited to growth at low pH than L. monocytogenes. The presence of bacteriocin impacted on L. monocytogenes, by quickly reducing the number of these microbes in mixed populations. A model for the growth ofL. monocytogenes and Lact. sake populations grown separately and in mixed culture is proposed. The model includes a novel approach for better describing the effect of pH change, the ability of Lact. sake to produce bacteriocin and the effect of bacteriocin on L. monocytogenes in the broth culture. Additionally, terms are introduced that describe the competitive effect of one population on the other. The model is fitted to data collected for the growth of each population, either grown alone or together. There were no significant differences between the parameter estimates for each replicate, supporting the hypothesis that the proposed model is a useful representation of the growth and interaction of the two microbial populations.     

Improvement of Freeze-Dried Lactobacillus Plantarum Survival Using Water Extracts and Crude Fibers from Food Crops

A synbiotic product of combined Lactobacillus plantarum TISTR 875 with water extracts and crude fibers from corn, mungbean, and soybean was formulated to investigate the survival of L. plantarum during freeze-drying and storage. The impacts of those water extracts and crude fibers on probiotic survival were determined in both a cultural medium and a freeze-drying medium. L. plantarum cultivated in de Man, Rogosa, and Sharpe (MRS) broth containing 2 % of water extract from soybean with 2 % mungbean fiber showed only 0.11 log CFU/ml cell reduction. The survival of L. plantarum harvested at the late log phase, mid stationary, phase and late stationary phase did not show statistical significance (P?>?0.05), whereas an initial pH of 6.5 and growth temperature of 37 °C showed greater impact (P?<?0.05). The addition of corn extract to the freeze-drying medium as a cryoprotectant had a similar effect on L. plantarum survival as sucrose, but it was better (P?<?0.05) than fructo-oligosaccharide and exopolysaccharides from Weissella cibaria A2, soybean extract, mungbean extract, soybean, corn, and mungbean fibers. A protective coating of corn extract was revealed and observed using scanning electron microscopy. The freeze-dried L. plantarum, cultivated in MRS broth containing soybean extract and mungbean fiber with corn extract as a cryoprotectant, retained high viability of 7.21 and 6.88 log CFU/ml after 8-week storage in a vacuum-packed aluminum foil-laminated polyethylene sachet and a nitrogen-flushed glass vial, respectively.