The control of Listeria innocua and Lactobacillus sakei in broth and meat slurry with the bacteriocinogenic strain Lactobacillus casei CRL705

The effect of the bacteriocin-producing strain, Lactobacillus casei CRL705, in the control of Listeria innocua 7 and Lactobacillus sakei CRL1424 in MRS medium and meat slurry during the storage under vacuum at chill temperatures was evaluated. L. sakei CRL 1424 isolated from vacuum-packaged contaminated raw meat was identified as the predominant indigenous lactic acid bacterial flora. Co-inoculation of MRS broth at 8°C with L. casei CRL705 caused growth inhibition of L. sakei CRL1424 and L. innocua 7 after 10 and 4 days of storage, respectively. At 4°C the complete inhibition of both strains occurred within 14 and 8 days for L. sakei CRL1424 and L. innocua 7, respectively. Bacteriocin activity in broth was observed to be maximal at 8°C reaching 2130 AU ml⁻¹ after10 days and 400 AU m1⁻¹ after 8 days of storage, while at 4°C maximal activities, 690 and 30 AU ml⁻¹ were obtained at 14 and 10 days, respectively. Addition of bacteriocinogenic strain to the meat slurry did not allow the growth of L. sakei and L. innocua, showing a bacteriostatic effect during 21 days of storage at 4°C. In addition, L. casei CRL705, as a protective culture did not change significantly the pH of the meat slurry in the assayed storage conditions. The results presented here confirm that the bacteriocinogenic strain L. casei CRL705 can be used as a useful tool to improve the microbial stability and safety in the commercial meat preservation.     

<Emphasis Type="Italic">Listeria</Emphasis> Inactivation by the Combination of High Hydrostatic Pressure and Lactocin AL705 on Cured-Cooked Pork Loin Slices

The effect of the bacteriocin lactocin AL705 in combination with high hydrostatic pressure (HHP) on the inactivation of Listeria innocua 7, a nonpathogenic indicator for Listeria monocytogenes, deliberately inoculated (ca. 6.4 log CFU/g) onto the surface of ready-to-eat (RTE) sliced cured-cooked pork loin, was evaluated. Nontreated pork slices (control) and treatments subjected to lactocin AL705 (105 AU/ml) and/or HHP (400 or 600 MPa) were prepared. L. innocua 7 was monitored at days 1, 20, and 40 of storage at 4 °C. The results showed a complete inhibition of L. innocua 7 after the combined treatment with lactocin AL705 and 600 MPa and no regrowing of cells up to 40-day storage. The treatment at 600 MPa alone was not enough to avoid regrowth of L. innocua. Ultrastructural cell damage was observed at the cytoplasm and cell membrane/wall levels with all treatments; however, complete cell lysis was observed only with the combined treatment. HHP in combination with lactocin AL705 provided a wider margin of safety as post-processing listericidal treatment of RTE cured-cooked meat products.     

Characterization of a multilayer film activated with Lactobacillus curvatus CRL705 bacteriocins

BACKGROUND: Bacteriocins produced by lactic acid bacteria offer enormous promise for food safety preservation. In this study an active multilayer film obtained by the incorporation of lactocin 705 and lactocin AL705, two bacteriocins produced by Lactobacillus curvatus CRL705 with antimicrobial activity against Lactobacillus plantarum CRL691 and Listeria innocua 7, respectively, was characterized for its potential application in active packaging technology. Film activity performance at different storage conditions, bacteriocins transfer into water and sunflower oil, and film surface properties were evaluated. RESULTS: Film activity against L. innocua 7 was maintained during 2, 4 and 6 weeks at 30, 10 and 5 °C respectively. At 30 and 10 °C, activity loss against L. plantarum CRL691 was observed on the second week of storage and after the fourth week at 5 °C. Results showed no significant difference for active multilayer film contact angle and seal properties compared to the control (without bacteriocins). A decrease in lactocin 705 inhibitory activity after sunflower oil contact was observed, while lactocin AL705 remained unaffected. After water contact, film activity was retained for both bacteriocins. CONCLUSIONS: As demonstrated by antimicrobial activity and physico‐mechanical properties retention, lactocin 705 and AL705 active multilayer film present potential for application in active packaging technology. Copyright © 2011 Society of Chemical Industry     

Development of an active wheat gluten film with Lactobacillus curvatus CRL705 bacteriocins and a study of its antimicrobial performance during ageing

Antimicrobial wheat gluten film was obtained at pilot scale by Lactobacillus curvatus CRL705 bacteriocins inclusion in the film-forming solution. Bacteriocins’ minimum inhibitory concentration for the film activation was 2133 AU cm^?3 (lactocin AL705) and 267 AU cm^?3 (lactocin 705). Mechanical and barrier properties as well as film ageing kinetics were not significantly affected by the addition of bacteriocins. The antimicrobial film performance during ageing was assessed. Film activity against Listeria innocua 7 and Lactobacillus plantarum CRL691 was observed over 50 days of ageing. Even when the release of bacteriocins from the film upon water contact was observed for both bacteriocins at the beginning of the ageing period, and anti-Listeria activity was delivered to the simulant up to the 15th day of ageing, film residual activity for both bacteriocins was observed over 50 days. The results confirm the potential of a gluten film doped with L. curvatus CRL705 bacteriocins as a carrier of bacteriocins to avoid Listeria and lactic acid bacterial growth, thus enhancing quality and safety in foods.     

Reduction of Listeria monocytogenes in cold‐smoked salmon by bacteriophage P100, nisin and lauric arginate,singly or in combinations

Three GRAS antimicrobials including, lauric arginate (LAE), bacteriophage P100 (phage P100) and bacteriocin nisin, were evaluated either singly or in combinations for the reduction of initial load of Listeria monocytogenes in cold‐smoked salmon (CSS). The stability of phage P100 in the presence of LAE (200 ppm) and nisin (500 ppm) or at 10× and 100× of these concentrations was determined at 4 °C or 30 °C for 24 h in a broth model. Phage P100 was found to be highly stable in the presence of these antimicrobial agents as plaque‐forming units (PFU) did not vary between control and antimicrobial‐treated phage. The survival of L. monocytogenes in the presence of phage P100, nisin and LAE showed remarkable reduction within 24 h both at 4 °C or 30 °C in broth. Treatment of CSS containing 3.5 log CFU cm^?2 L. monocytogenes with phage P100 (10⁸ PFU mL^?1), nisin (500 ppm) and LAE (200 ppm) showed strong listericidal action and reduced the L. monocytogenes by 2–3 log CFU cm^?2 after 24 h. Among the combined treatments, phage P100 + LAE or nisin + LAE exhibited the most listericidal action in which L. monocytogenes cells were reduced to undetectable level within 24 h in CSS.     

Control of food spoiling bacteria in cooked meat products with nisin,lacticin 3147, and a lacticin 3147-producing starter culture

Nisin, in the form of the commercial product Nisaplin, and lacticin 3147 in whey powdered form were added to minced pork-meat in amounts of 0.15% (w/w) and 1.5% (w/w), respectively. The meat was cooked and inoculated with a Staphylococcus aureus strain of meat origin and a Listeria innocua strain at a level of 10⁷ or 10⁵ CFU g^–1. The batches were stored vacuum-packaged for 21 days at 8 °C. Nisin and lacticin 3147 immediately reduced the L. innocua population at the time of inoculation. Nisin showed higher inhibitory activity than lacticin 3147. During the storage period, a slight L. innocua growth was observed in the batches inoculated with the larger inoculum, and a bacteriostatic effect was observed against Listeria in the batches inoculated with 10⁵ CFU g^–1. Nisin maintained a constant S. aureus population in the cooked batch inoculated with 10⁷ CFU g^–1, although the bacteriocin was capable of reducing the amount of S. aureus by 90% in the batch inoculated with 10⁵ CFU g^–1. On the other hand, lacticin 3147 did not show an inhibitory effect against S. aureus in the cooked meat. The starter culture Lactococcus lactis DPC 303-T4 (containing the conjugative plasmid encoding production of lacticin 3147) was inoculated in a portion of a Longissimus dorsi pork muscle with brine. L. lactis DPC 303-T4 performed a good fermentation, but lacticin 3147 production was not found after 7 days at 12 °C of storage.     

Development and characterization of an active polyethylene film containing Lactobacillus curvatus CRL705 bacteriocins

The development and characterization of a bacteriocin-containing polyethylene-based film is described, incorporating lactocin 705 and lactocin AL705, produced by Lactobacillus curvatus CRL705, and nisin. Three different procedures to obtain lactocin 705 and AL705 solution were evaluated, with the partially purified aqueous bacteriocin solution showing the highest inhibitory activity against indicator strains (Lactobacillus plantarum CRL691 and Listeria innocua 7). Pouch contact, soaking and a contact method were compared for incorporating bacteriocins onto PE-based films. Contact between the PE film and bacteriocin solution was the most effective, resulting in a more uniform distribution of bacteriocins on the film surface and using less active solution. The minimal inhibitory concentration of bacteriocin solution was 267 AU cm^?3 (lactocin 705) and 2133 AU cm^?3 (lactocin AL705), while the minimal contact time was 1 h. When relative inhibition area for antilisterial activity of the active films was compared, those treated with L. curvatus CRL705 bacteriocins displayed higher inhibitory activity than nisin-treated films. Functional properties of active PE-films containing lactocin 705 and AL705 showed no differences compared with non-active control films. Bacteriocin-active PE-based films are shown to be highly effective in inhibiting growth of Listeria. The potential use of commercially available packaging films as bacteriocins carriers may benefit active-packaging systems.     

Functionalisation of rice bran assisted by ultrasonication and fermentation for the production of rice bran–lingonberry pulp-based probiotic nutraceutical

A probiotic nutraceutical based on functionalised rice bran (RB) supplemented with lingonberry (Vaccinium vitis-idaea L.) pulp (LP) at various levels (10–50 g/100 g d.w.) was developed. Prior to immobilisation of lactic acid bacteria (LAB) cells, RB-LP matrix was structured by ultrasound (US) (850 kHz; power 160 W) for 20 min at 40 °C. Xanthan gum and sodium alginate were used for the stabilisation of RB-LP matrix. Survival and fermentative activity of the immobilised LAB cells was studied by monitoring pH, cell number, antimicrobial activity, lactic acid and acetic acid production. US treatment increased by 17.5% soluble dietary fibre (SDS) contents in RB but reduced on average by 49.9% hyperoside, quercetin, quercitrin and coumaric acid contents in LP material. RB substrate supplemented with LP (20–50 g/100 g d.w.) resulted in higher antimicrobial activity against Escherichia coli, Salmonella typhimurium and Staphylococcus aureus for Lactobacillus brevis, and against Bacillus cereus and Staphylococcus aureus for Pediococcus acidilactici. RB-LP matrix stabilised with alginate–xanthan and alginate maintained 8.09–8.67 log CFU g⁻¹ live cells of immobilised L. brevis after 7 weeks of storage at 4 °C. In the case of protection under simulated in vitro digestion conditions, RB-LP gels with sodium alginate demonstrated the highest cell survival with 4.25 CFU g⁻¹ viable cells remaining in the product and 5.23 log CFU g⁻¹ live cells in the digestion medium.     

Combination of high-frequency ultrasound with propyl gallate for enhancing inactivation of bacteria in water and apple juice

This study evaluated a combination of high-frequency ultrasound (HFU, 1 MHz, 1.6 W/cm²).and a food-grade antioxidant, propyl gallate (PG, 10 mM), to enhance inactivation rates of Listeria innocua and Escherichia coli O157:H7 in water and clarified apple juice. Treatment times ranged from 5 to 20 min. The study also assessed the potential mechanisms of synergistic interactions based on an evaluation of changes in bacterial permeability, morphology, and intracellular oxidative stress. Within 15 min of treatment time, HFU + PG significantly (reduced by 5.5 log CFU/mL, P < 0.05) decreased the bacterial load of both L. innocua and E. coli O157:H7 from an initial inoculum of 6.5 log CFU/mL in both water and clarified apple juice. Overall, L. innocua demonstrated significantly higher resistance to inactivation than E. coli O157:H7 using a combination of HFU + PG. The synergistic antimicrobial activity of HFU+ PG resulted in enhanced membrane damage and oxidative stress induction in bacteria compared to the individual treatments of HFU or PG alone.Industrial relevanceThis study evaluates the synergistic combination of high frequency ultrasound and the food grade antioxidant propyl gallate for non-thermal processing of liquids. The results illustrate significant (>5 log CFU) and rapid inactivation (∼15 min) of inoculated model Gram positive and Gram negative bacteria in apple juice using a synergistic combination of propyl gallate and high frequency ultrasound. The synergistic interactions result in enhanced membrane damage and oxidative stress induction in bacteria. These results illustrate potential of the synergistic non-thermal thermal processing method for processing liquid beverages. Further studies are required for evaluating the scale up and optimization of the novel processing technology and enhancement in quality attributes of beverages.     

Potential of nisin-incorporated sodium caseinate films to control Listeria in artificially contaminated cheese

A sodium caseinate film containing nisin (1000 IU/cm²) was produced and used to control Listeria innocua in an artificially contaminated cheese. Mini red Babybel^® cheese was chosen as a model semi-soft cheese. L. innocua was both surface- and in-depth inoculated to investigate the effectiveness of the antimicrobial film as a function of the distance from the surface in contact with the film. The presence of the active film resulted in a 1.1 log CFU/g reduction in L. innocua counts in surface-inoculated cheese samples after one week of storage at 4 °C as compared to control samples. With regard to in-depth inoculated cheese samples, antimicrobial efficiency was found to be dependent on the distance from the surface in contact with the active films to the cheese matrix. The inactivation rates obtained were 1.1, 0.9 and 0.25 log CFU/g for distances from the contact surface of 1 mm, 2 mm and 3 mm, respectively. Our study demonstrates the potential application of sodium caseinate films containing nisin as a promising method to overcome problems associated with post-process contamination, thereby extending the shelf life and possibly enhancing the microbial safety of cheeses.     

Bacterial inactivation and quality changes in fresh-cut avocado treated with intense light pulses

This study investigated the impact of intense light pulses (ILP) on inactivation of Listeria innocua and Escherichia coli as well as quality changes in fresh-cut avocado. Cylinders of avocado inoculated with L. innocua or E. coli were placed in plastic trays, which were sealed with a 64-μm-thick polypropylene film (oxygen permeability of 110 cm³ O₂ m⁻² bar⁻¹ day⁻¹ at 23 °C and 0% RH) and subjected to 15 or 30 pulses at fluencies of 0.4 J/cm² per pulse and then stored for 15 days at 5 °C. In addition to L. innocua and E. coli counts, the headspace atmosphere, pH, colour and firmness were measured. The growth of E. coli and L. innocua was more effectively inhibited when increasing treatment intensity. Hence, significant inactivation was obtained in samples treated with 15 and 30 pulses for L. innocua (2.61 and 2.97 log CFU/g, respectively) and E. coli (2.90 and 3.33 log CFU/g, respectively) just after processing. Oxygen concentrations were significantly reduced, whereas CO₂ and ethanol concentrations increased due to product respiration; however, ethylene production was decreased by the effect of ILP treatments. The use of 30 pulses affected the colour and firmness of fresh-cut avocado, causing browning and softening.     

Shelf life and quality of probiotic yogurt produced with Lactobacillus acidophilus and Gobdin

This study evaluated the effect of dry white mulberry and walnut paste (Gobdin, a traditional Turkish food) in probiotic yogurt on the survival of Lactobacillus acidophilus and yogurt properties. Six different yogurts were produced with 0%, 5% and 10% Gobdin using Lactobacillus bulgaricus + Streptococcus thermophilus and with 0%, 5% and 10% Gobdin using L. bulgaricus + S. thermophilus + L. acidophilus. The physical, chemical, microbiological and sensorial properties of the yogurts were evaluated based on storage at 4 ± 1 °C. Probiotic shelf life and the most suitable combinations were determined. The highest L. acidophilus count (8.65 log cfu g^?1) was found in the 5% Gobdin‐supplemented yogurt on the 7th day of storage, while the lowest count (8.11 log cfu g^?1) was found in the probiotic control yogurt on the 21st day. Although the L. acidophilus counts in the probiotic yogurts declined during storage, all values found throughout the 21‐day storage period were >8 log cfu g^?1. This is above the level necessary to provide the desired therapeutic effect in probiotic products (10⁶–10⁷ cfu g^?1). The highest overall acceptability score was obtained on the first day from the yogurt with 5% Gobdin. However, all yogurt samples had general acceptability scores between 7 and 8 points from a 9‐point maximum. Thus, this study determined that a new functional yogurt can be produced using L. acidophilus with 5% Gobdin.     

Listeria innocua Multi-target Inactivation by Thermo-sonication and Vanillin

Hurdle technology combining an emerging preservation technique such as low-frequency ultrasound is an alternative for processing juices that are susceptible to suffer a loss of quality due to traditional heat treatments. Predictive microbiology allows evaluation of the effectiveness of preservation techniques and its combinations in order to enhance both food quality and safety. Listeria innocua inactivation by thermo-sonication along with vanillin was investigated. Fermi model (R ² _adj= 0.970 ± 0.02) and surface response methodology (p < 0.05) were utilized in order to evaluate the survival of L. innocua to a multi-target treatment and to predict the interactions of studied techniques, high-intensity/low-frequency ultrasound (20 kHz/400 W) at selected wave amplitudes (60, 75, or 90 μm), temperature (40, 50, or 60 °C), and vanillin (200, 350, or 500 mg/kg). A combination of ultrasound, vanillin, and temperature enhanced L. innocua inactivation as described by Fermi parameters a and t _c, which decreased as the studied effects increased. A multi-target inactivation effect was observed for a temperature range of 45–55 °C.     

Effects of Antimicrobial Coatings and Cryogenic Freezing on Survival and Growth of Listeria innocua on Frozen Ready‐to‐Eat Shrimp during Thawing

Foodborne pathogens such as Listeria monocytogenes could pose a health risk on frozen ready‐to‐eat (RTE) shrimp as the pathogen could grow following thawing. In this study, antimicrobial‐coating treatments alone, or in combination with cryogenic freezing, were evaluated for their ability to inhibit the growth of Listeria innocua, a surrogate for L. monocytogenes, on RTE shrimp. Cooked RTE shrimp were inoculated with L. innocua at 3 population levels and treated with coating solutions consisting of chitosan, allyl isothiocyanate (AIT), or lauric arginate ester (LAE). The treated shrimp were then stored at –18 °C for 6 d before being thawed at 4, 10, or 22 °C for either 24 or 48 h. Results revealed that antimicrobial coatings achieved approximately 5.5 to 1 log CFU/g reduction of L. innocua on RTE shrimp after the treatments, depending on the inoculated population levels. The coating‐treated shrimp samples had significantly (P < 0.05) less L. innocua than controls at each thawing temperature and time. Cryogenic freezing in combination with coating treatments did not achieve synergistic effects against L. innocua. Antimicrobial coatings can help to improve product safety by reducing Listeria on RTE shrimp.     

Developing an antimicrobial packaging of ready-to-eat pomegranate arils based on vapors of brandy or distillery ethanol

Despite the increasing pomegranate consumption, the ready-to-eat (RTE) arils are highly perishable and this negatively impacts their commercialization. Nowadays, mild pre-packaging decontamination interventions (washing with sanitizing agents or exposure to ultraviolet light) in sequence or not with modified atmospheres packaging technologies are applied. Even though, the latter combination of methods provides them a shelf-life of 10–14 days at cold storage, several negative effects have been also reported (i.e., degradation of anthocyanins). Thus, the aim of the study was to evaluate the effect of alternative, mild antimicrobials such as the vapors of distillery ethanol and brandy on microbial, physical, textural, sensorial, and multispectral imaging attributes of RTE arils during storage at different temperatures in perforated bags. Lactic acid bacteria (LAB) and yeasts/moulds were the dominant spoilage microbiota of RTE arils, regardless of storage temperature and antimicrobial. Vapors produced by both volatile antimicrobials significantly inhibited (p < 0.05) the growth of LAB and yeasts/moulds, at all storage temperatures. For instance, at 4 °C, when population of TVC on controls was 6.9 log CFU g^− 1 (day 23), the respective counts on arils treated with distillery ethanol or brandy followed the order: 4.9 log CFU g^− 1 (1 mL of ethanol) > 3.9 log CFU g^− 1 (1 mL of brandy) > 2.2 log CFU g^− 1 (2 mL of ethanol) > 1.2 log CFU g^− 1 (2 mL of brandy). Moreover, arils exposed to distillery ethanol and brandy vapors showed lower weight loss (%) compared to controls, while the firmness was reduced, regardless of treatment and storage temperature. Color measurements and evaluation of multiple sensory attributes revealed that arils exposed to brandy vapors showed more intense red color and look fresher compared to controls for longer storage time. The latter observation was also validated by multispectral image analysis, since the results suggested that arils packaged with distillery ethanol or brandy maintained their anthocyanin and carotenoids content at higher levels than controls, at 4 °C. Thus, such preservation methods may open new perspectives on mild antimicrobial packaging in order to extend shelf-life of perishable minimally processed fruits, like pomegranate RTE arils.     

Palatability and hygiene characteristics of dry-aged pork and optimisation of dry ageing period

To improve upon understanding of the quality characteristics of dry-aged pork, pork belly and arm shoulder were dry-aged for 0, 7, 14, 21 and 28 days. Their physicochemical, free amino acid (FAA) content and microbiological analysis were performed to evaluate palatability and hygiene. After 28 days of ageing, total FAA content increased by 56.1% and 71.4% for pork belly and arm shoulder, respectively. The amount of individual FAAs increased, except for glutamine. At 28 days, total bacteria and coliform continuously increased to 4.40 and 4.43 log (CFU g⁻¹) for pork belly sample, respectively, and 5.92 and 4.26 log (CFU g⁻¹) for arm shoulder sample, respectively; moreover, E. coli was first detected and Salmonella spp. and Listeria spp., which are considered indicators of meat food poisoning, were not detected. Altogether, extended dry ageing period can impose a potential hygiene concern, though palatability is increased, requiring optimisation in the dry ageing process.     

Antimicrobial Polylactic Acid Packaging Films against Listeria and Salmonella in Culture Medium and on Ready-to-Eat Meat

The contamination of Listeria monocytogenes and Salmonella spp. in ready-to-eat (RTE) meat products has been a concern for the meat industry. In this study, edible chitosan-acid solutions incorporating lauric arginate ester (LAE), sodium lactate (NaL), and sorbic acid (SA) alone or in combinations were developed and coated on polylactic acid (PLA) packaging films. Antimicrobial effects of coated PLA films on the growth of Listeria innocua, L. monocytogenes, and Salmonella Typhimurium in a culture medium (tryptic soy broth, TSB) and on the surface of meat samples were investigated. Antimicrobial PLA films containing 1.94 mg/cm² of chitosan and 1.94 μg/cm² of LAE were the most effective against both Listeria and Salmonella in TSB and reduced them to undetectable level (<0.69 log CFU/ml). The same PLA films with LAE significantly (p?L. innocua, L. monocytogenes, and S. Typhimurium on RTE meat during 3 and 5 weeks’ storage at 10 °C, achieving 2–3 log reduction of Listeria and 1–1.5 log reduction of Salmonella as compared with controls. PLA films coated with 1.94 mg/cm² of chitosan, 0.78 mg/cm² of NaL, and 0.12 mg/cm² of SA significantly reduced the growth of L. innocua but were less effective against Salmonella. The combination of NaL (0.78 mg/cm²) and SA (0.12 mg/cm²) with LAE (1.94 μg/cm²) did not generate additional or synergetic antimicrobial effect against Listeria or Salmonella on the meat surface. L. innocua had a similar sensitivity to the film treatments as L. monocytogenes, suggesting that L. innocua may be used as a surrogate of L. monocytogenes for further scaleup and validation studies. The film treatments were more effective against the microorganisms in TSB culture medium than in RTE meat, which suggests that in vivo studies are a necessary step to develop antimicrobial packaging for applications in foods.     

Inactivation mechanisms of electron beam irradiation on Listeria innocua through the integrity of cell membrane,genomic DNA and protein structures

As a non-thermal sterilisation technology, electron beam irradiation (EBI) has attracted great interest for microbial inactivation in food preservation. This study aims to investigate the effects of EBI on membrane permeability, physiological status, morphological structure, genome integrity and protein structures of Listeria innocua irradiated at doses of 0.75, 1.50, 2.25, 3.00, 3.75 and 5.00 kGy. The results showed that EBI noticeably reduced the total microbial counts of L. innocua by more than 7 log CFU mL⁻¹ with 5.00 kGy treatment. The cell membrane permeability increased, resulting in the leakage of intracellular substances and changes in cell physiological status, which was proven by the cell staining and electron microscopy (EM) observations. Moreover, the integrity of genomic DNA and protein secondary structure, but not the protein primary structure were also disrupted. These findings provide the intrinsic mechanisms for the inactivation of L. innocua affected by EBI, which could serve as a theoretical basis for a better application of EBI in food sterilisation.     

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.     

Effects of curing additives on the control ofListeria monocytogenesby lactocin 705 in meat slurry

Meat slurry inoculated withListeria monocytogenes(4.00 cfu g⁻¹) was mixed with different levels of curing additives and their influence on the inhibitory effect of lactocin 705 (17,000 AU ml⁻¹) was evaluated at 20°C. Inhibition ofL. monocytogeneswas 1.90 and 1.00 log less in meat slurry with 5 and 7% NaCl than in meat slurry without added sodium chloride. When nitrite and bacteriocin were added together, less nitrite (200 μg g⁻¹) was required to obtain the sameListeriapopulation (3.00 log cfu g⁻¹) as when 800 μg g⁻¹NaNO₂was used. However, when compared with lactocin 705 alone, lessListeriainhibition was observed showing also a protective effect of NaNO₂. When ascorbic acid and alginate meat binder were assayed in the presence of the bacteriocin, the inhibition ofL. monocytogeneswas less effective, but when sodium lactate (2%) was added to the meat slurry, almost no protective effect was observed. These results indicated that the use of lactocin 705 to controlL. monocytogeneswas less effective in the presence of curing ingredients.