Comparative Study on the Inactivation and Photoreactivation Response of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> Seafood Isolates and a <Emphasis Type="Italic">Listeria innocua</Emphasis> Surrogate after Pulsed Light Treatment

The inactivation and photoreactivation response of six seafood-isolated Listeria monocytogenes and one Listeria innocua strain after pulsed light (PL) treatment was evaluated. The lower inactivation levels found after exposure of treated samples to daylight during the first 90 min of storage confirmed that both L. innocua and L. monocytogenes have the capability to photorepair PL-induced DNA damage upon appropriate conditions. Photoreactivation levels from 0.2 to 2.1 log CFU cm^?2 were observed depending on treatment intensity (fluence) and Listeria strain. Complete photorepair of PL-caused damage was not found even after treatments inducing low inactivation levels. Photoreactivation increased up to 2.1 log with the applied fluence up to a threshold able to cause between 2.4 and 5.4 log reductions under dark storage. Photorepair was not avoided but lower photoreactivation was observed after higher fluence inducing more than 6 log reductions under dark storage. Both L. innocua and L. monocytogenes serotype 1/2b exhibited the highest photoreactivation levels whereas serotypes 1/2a showed the lowest ones. The overall inactivation and photoreactivation responses of tested Listeria strains were comparable indicating that L. innocua may be a good surrogate for the safe evaluation, optimization and validation of PL technology to control L. monocytogenes in food products and food processing facilities.     

Study of the Effect of High Hydrostatic Pressure (HHP) on the Osmotic Dehydration Mechanism and Kinetics of <Emphasis Type="Italic">Wumei</Emphasis> Fruit (<Emphasis Type="Italic">Prunus mume</Emphasis>)

Osmotic dehydration (OD) is the most important procedure for obtaining candied wumei (Prunus mume), which is a very popular snack in Eastern Asian countries. This study aims to evaluate the effects of high hydrostatic pressure (HHP) pre-treatment (50–400 MPa) on the mass transfer kinetics and on the water diffusivity of wumei fruit during OD and to investigate the effect on water distribution and cell viability aspects. The results showed that HHP increased initial rate and effective diffusivity of mass transfer values compared to non-treated samples. Time domain nuclear magnetic resonance revealed that, upon HHP treatment, the water redistributed in vacuole, cytoplasm/extracellular spaces, and cell wall/membrane. The application of 400 MPa probably caused some irreversible damages to the cell membranes. The cell viability study determined by fluorescein diacetate staining showed a loss of cell viability at pressures higher than 200 MPa. HHP exhibited an effective pre-treatment to increase mass transfer of wumei fruit during OD process.     

Modeling the Inactivation of <Emphasis Type="Italic">Listeria innocua</Emphasis> and <Emphasis Type="Italic">Escherichia coli</Emphasis> in Fresh-Cut Tomato Treated with Pulsed Light

The effectiveness of pulsed light (PL) treatments to inhibit microorganisms on fresh-cut tomatoes (Lycopersicon esculentum Mill., cv. Daniela) was investigated. Tomato slices inoculated with Escherichia coli or Listeria innocua were exposed to PL treatments (4, 6, or 8 J cm^?2 fluence) and kept cold at 4 °C for 20 days. L. innocua and E. coli counts, gases in the headspace of the containers (O₂ and CO₂), pH, titratable acidity, and soluble solid content were monitored throughout the cold storage. The PL treatments reduced significantly (p < 0.05) initial loads of both microbes. The effect of the PL fluence on the survival number of microoganisms was described by a log-linear model (R ² = 0.849–0.999). At any fixed time within the cold storing, the microbial counts for untreated samples were always higher than those cut tomatoes that had been previously PL-treated. The behavior of L. innocua and E. coli during the storage were well adjusted (R ² > 0.930) by Gompertzian models; the studied microorganisms exhibited different patterns during the storage period. On the other hand, O₂ and CO₂ partial pressures in containers with fresh-cut tomatoes were also significantly affected by PL treatments (p < 0.05). The highest PL fluence caused the greatest changes of O₂ and CO₂ contents. In addition, the application of PL triggered an acceleration of the O₂ consumption during the cold stage. PL treatments might be used to effectively extend the safety of fresh-cut tomatoes over 12 days of storage against E. coli and L. innocua growth.     

Synergistic Processing of Skim Milk with High Pressure Nitrous Oxide,Heat, Nisin,and Lysozyme to Inactivate Vegetative and Spore-Forming Bacteria

Individual and combined effects of high pressure nitrous oxide (HPN₂O), heat, and antimicrobials on the inactivation of Escherichia coli, Listeria innocua, and Bacillus atrophaeus endospores in milk were all evaluated after 20-min treatments. Stand-alone milk treatments with HPN₂O (15.2 MPa), heat (45 and 65 °C), or nisin (50 and 150 IU mL^?1) resulted in log₁₀ reductions ranging only from 0.1 to 2.1 for E. coli and L. innocua. Combining HPN₂O (15.2 MPa) with heat (65 °C) inactivated 6.0 and 5.1 log₁₀ in the vegetative bacteria, respectively. Similarly, reductions of 5.9 and ≥ 6.0 log₁₀ of respective E. coli and L. innocua cells in milk were achieved through a combination of HPN₂O (15.2 MPa), heat (65 °C), and nisin (150 IU mL^?1). A 2.5 log₁₀ cycle inactivation of spores was obtained by HPN₂O, nisin (at both 50 and 150 IU mL^?1), and lysozyme (50 μg mL^?1) at 85 °C. Combining these processing techniques resulted in significantly greater microbial inactivation (p < 0.05) than the sum of individual reductions from each treatment alone, indicating synergistic effects. HPN₂O irrespective of processing temperatures did not cause any occurrence of sub-lethally injured cells or disruption in colloidal stability of milk at 65 and 85 °C (p ≥ 0.05). Color and pH changes in milk following the most demanding treatment conditions were minimal.     

Grape Processing by High Hydrostatic Pressure: Effect on Use of Non-<Emphasis Type="Italic">Saccharomyces</Emphasis> in Must Fermentation

Vitis vinifera (variety Tempranillo) grapes were pressurized at 400 MPa by high hydrostatic pressure for 10 min and the effect on wild microbial populations, phenol extraction and wine composition was monitored. After treatment, the grapes were inoculated and fermented with Saccharomyces cerevisiae and several non-Saccharomyces yeasts: Schizosaccharomyces pombe, Torulaspora delbrueckii, Metschnikowia pulcherrima and Lachancea thermotolerans. S. pombe was used as sole fermentative yeast, but T. delbrueckii, M. pulcherrima and L. thermotolerans were used in sequential cultures with S. cerevisiae to completely ferment the sugars. The HHP treatment reduces strongly or eliminates wild microorganisms, especially yeasts, facilitating the growth and development of non-Saccharomyces yeasts. Thus, it helps to get either a better expression of enzymatic activities or metabolites production of non-Saccharomyces affecting wine quality.     

Effect of Low-pressure Cold Plasma (LPCP) on the Wettability and the Inactivation of <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Listeria innocua</Emphasis> on Fresh-Cut Apple (<Emphasis Type="Italic">Granny Smith</Emphasis>) Skin

The aim of this study was to investigate the effect of low-pressure cold plasma (LPCP) on the inactivation of Escherichia coli and Listeria innocua on fresh-cut apple skin and its influence on wettability. Cold plasma treatments have shown to be effective to decontaminate foods, but their effect on the wettability has not been well studied. Surface-inoculated apple samples were treated with argon (Ar), nitrogen (N2), oxygen (O₂), and argon-oxygen (Ar-O₂) cold plasma using a commercial LPCP unit. Three different models were used to fit bacterial survival curves after the LPCP treatments. Changes in surface wettability were also determined by measuring the contact angle. The LPCP treatments using Ar, O₂, or Ar-O₂ mixture for 20 min were the most effective to inactivate E. coli with O₂, while the LPCP treatment with N2 for 20 min reduced L. innocua the most for (p?<?0.05). The highest increase in surface wettability was observed in samples treated for 20 min with O₂ and Ar-O₂. Different LPCP treatments have not great effectivity on the inactivation of E. coli and L. innocua on fresh-cut apple surface, but the all treatments changed the surface wettability of apples, making it more hydrophilic. This can be considered as a negative effect of the LPCP treatment because it can facilitate the adhesion and proliferation of re-contaminating microorganisms. More research should be undertaken to explore the use of other gases and complex surfaces.     

High Hydrostatic Pressure and Mild Heat Treatments for the Modification of Orange Peel Dietary Fiber: Effects on Hygroscopic Properties and Functionality

Fruit by-products, such as orange peels, are non-conventional sources of dietary fiber (DF) suitable for developing food ingredients with novel applications. Orange peels were processed at 600 MPa (come up time–CUT, 2, 5, 10, or 20 min) and two temperatures (55 or 70 °C) with the aim to study changes in total (TDF), soluble (SDF), and insoluble (IDF) dietary fiber contents, water-/oil-holding capacity (WHC/OHC), solubility, swelling capacity (SC), pH, tap density, and hygroscopic properties. Increments of 1.9 times on the SDF content were observed after HHP treatment at 55 and 70 °C, compared to the untreated sample content (7.17% dw). Constant values of TDF (51.2–54.6% dw) suggested the significant conversion of assayable IDF to SDF. An increase on SC (6.5%) and OHC (20.1%) values were observed in samples treated with CUT at 70 and 55 °C, respectively. Compared to control samples, HHP (55 °C/5 min) exerted changes on moisture isotherms expressed as relative water sorption content. HHP improved the adsorption and desorption water retention of samples in the 0.1–0.93 a _w range studied. Results indicate that HHP combined with heat treatment has potential to modify the functionality of orange peels with short processing times.     

Application of the SureTect Detection Methods for <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> and <Emphasis Type="Italic">Listeria</Emphasis> spp. in Meat,Dairy, Fish,and Vegetable Products

The aim of this study was to evaluate the application of the Listeria monocytogenes and Listeria spp. SureTect detection methods for a rapid and sensitive detection in an ample range of food products: raw pork and poultry meat, Spanish chorizo, pate, smoked salmon, raw sheep milk cured cheese, and ready-to-eat lettuce salad. The combination of a 24-h enrichment in the 24 Listeria Enrichment Broth (LEB) coupled to a rapid bacterial DNA extraction and real-time polymerase chain reaction (RTi-PCR) using the specific SureTect methods detected down to 2–6 L. monocytogenes CFU per sample in less than 27 h on the food categories tested. Furthermore, the applicability of L. monocytogenes and Listeria spp. SureTect detection methods in real samples was assessed using 303 food samples, obtaining at least the same analytical performance as the international reference method ISO 11290-1.     

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     

Effect of High Hydrostatic Pressure and Temperature on Enzymatic Activity and Quality Attributes in Mango Puree Varieties (cv. Tommy Atkins and Manila)

Pectinmethylesterase (PME), peroxidase (POD), and polyphenoloxidase (PPO) residual activities (RAs) and physicochemical parameters (pH, total soluble solids (TSS), water activity (a_w), viscosity and color) of Tommy Atkins and Manila mango purees (MPs) were evaluated after high hydrostatic pressure (HHP) treatments at 400–550 MPa/0–16 min/34 and 59 °C. HHP treatment applied at 59 °C induced higher enzyme inactivation levels than the treatment applied at 34 °C in both MPs. The lowest RA of PME (26.9–38.6%) and POD (44.7–53%) was achieved in Manila MP treated at 450 MPa/8–16 min/59 °C and 550 MPa/4–16 min/59 °C, respectively. Otherwise, Tommy Atkins puree pressurized at 550 MPa/8–16 min/59 °C had the lowest PPO RA (28.4–34%). A slight decrease in pH and TSS values of both HHP-processed MPs at 34 and 59 °C was observed, whereas the a_w remained constant after processing. The viscosity of MPs tended to augment up to 2.1 times due to the application of HHP. No significant changes were observed in color parameters of Tommy Atkins MP, except at 550 MPa and 59 °C where higher yellow index (YI) (122.4?±?3.3) and lower L* (37.3?±?5.3) were obtained compared to the untreated MP. HHP caused an increase in L* values in Manila MP, whereas no clear trend was observed in YI. HHP processing at 550 MPa combined with mild temperature (59 °C) during 8 min could be a feasible treatment to reduce enzymatic activity and preserve fresh-like quality attributes in MP.     

Non-Thermal Pasteurization of Orange (<Emphasis Type="Italic">Citrus sinensis</Emphasis> (L.) Osbeck) Juices Using Continuous Pressure Change Technology (PCT): a Proof-of-Concept

Non-thermal pasteurization of orange juices using a continuous pressure change technology (PCT) device was investigated on pilot plant scale for the first time. PCT treatment was conducted by pressurizing orange juice and nitrogen at moderately high pressures (P?=?25 or 50 MPa) in a tubular continuous reactor. Abrupt decompression was achieved by a relief valve at the end of the tubular system. As compared to freshly squeezed juice, PCT treatment slightly reduced levels of carotenoids, vitamin C and hesperidin by 19, 5, and 14 %, respectively. Peroxidase was completely inactivated, whereas residual pectin methylesterase activities amounted to 26–27 %. Simultaneously, total aerobic plate counts were substantially reduced by at least 3.4 log₁₀ cfu/mL. The mean volume-weighed particle diameter d ₄₃ was drastically reduced from 652 μm in freshly squeezed juice to 6 and 31 μm at 25 and 50 MPa, respectively. Concomitantly, CIE-L*a*b* color values indicated a brighter and more intense yellow color of PCT-treated juices. While cloud separation in freshly squeezed juice was completed within 3 days, cloud stability in PCT-treated juices was retained for 5 days.     

Pressure-Thermal Kinetics of Furan Formation in Selected Fruit and Vegetable Juices

Furan, a potential carcinogenic compound, can be formed in array of processed foods. The objective of this study was to conduct kinetic studies in pineapple juice and assess the interactive effects of pressure (0.1 to 600 MPa) and temperature (30 to 120 °C) on furan formation. Additional experiments were carried out in tomato, watermelon, cantaloupe, kale, and carrot juice to understand the influence of matrix and juice pH. Furan was monitored in raw (control) and processed samples by automated headspace gas chromatography mass spectrometry, and quantified by calibration curve method with d₄-furan as internal standard. The data were modeled using zero-, first-, and second-order equations. The zero-order rate constants (k _T,P ), activation energy (E _a ), and Gibbs free energy of activation (ΔG ^?) of furan formation in thermally processed (TP; 90–120 °C) pineapple juice were found to be 0.036–0.55 μg/kg/min, 98–114 kJ/mol, and 173.9–180.5 kJ/mol, respectively. Furan concentration was negligible and close to the detection limit (0.37 μg/kg) after pressure treatment (600 MPa at 30 °C) of juice samples. For similar process temperatures, the rate constants of pressure-assisted thermally processed (PATP; 600 MPa at 105 °C) pineapple juice were lower than that of TP samples. Furan formation was influenced by juice matrix and pH. On the other hand, PATP markedly suppressed furan (0.7 to 1.6 μg/kg) in these selected juices. In conclusion, furan formation increased with process temperature and treatment time, while pressure treatment at ambient temperature did not promote its production. Furan formation in TP fruit juices was also influenced by juice matrix and pH, but these were not the significant factors for PATP-treated juices.     

Quality Changes in Mango Juice Treated by High-Intensity Pulsed Electric Fields Throughout the Storage

The effect of high-intensity pulsed electric fields (HIPEF) processes on Listeria innocua inhibition, physicochemical parameters and activity of oxidative enzymes of mango juice was evaluated to set the optimal HIPEF treatment time. Quality parameters, microbial population and bioactive compounds of HIPEF-treated (35 kV/cm, 1800 μs) and thermally treated (TT) (90 °C, 60 s) mango juices were studied and compared with those non-treated during 75 days of storage at 4 °C. HIPEF treatment for 800 μs ensured 5 log reductions of L. innocua. Polyphenoloxidase (PPO), lipoxygenase (LOX) and peroxidase (POD) residual activities were significantly reduced to 70, 53 and 44%, respectively, at treatment times of 1800 μs. Similar sensory properties compared with fresh mango juice were attained from product treated at 1800 μs. Moreover, fresh mango juice colour (L* = 38.79, h° = 106.57) was preserved after HIPEF treatment throughout storage. Moulds and yeasts and psychrophilic bacteria counts in HIPEF-treated (1800 μs) mango juice remained below 6 log cycles CFU/mL up to 2 months of refrigerated storage. The content of total phenolic compounds in those HIPEF-treated increased from 333 to 683 μg of GAE/mL from day 0 to the end of storage. Hence, the application of HIPEF may be a feasible treatment in order to ensure microbiological stability, high bioactive compound content and fresh-like characteristics of mango juice.     

Effects of High-Pressure Processing with or without Blanching on the Antioxidant and Physicochemical Properties of Mango Pulp

The effects of high-pressure processing (HPP 300 MPa/15 min, 400 MPa/5 min, 500 MPa/2.5 min, and 600 MPa/1 min) and high-temperature/short-time processing (HTST 110 °C/8.6 s), with or without blanching, on mango pulp were comparatively evaluated in terms of the antioxidant compounds, antioxidant capacity, sugars, and color. Blanching treatment significantly increased the total phenol content and the antioxidant capacity of mango pulp, but did not change the levels of L-ascorbic acid, carotenoids, sugars, and visual color (total color difference, △E?<?2.00). Both HPP and HTST treatments significantly increased the total phenol content and antioxidant capacity of un-blanched mango pulp, but no significant changes occurred in the blanched mango pulp. HPP did not affect the levels of L-ascorbic acid, carotenoids, and sugars in mango pulp regardless of blanching. However, HTST significantly decreased the fructose and glucose levels, as well as induced the isomerization of β-carotene, with the increase in 13-cis-β-carotene accompanied by the decrease in all-trans-β-carotene. Moreover, HPP-treated mango pulp consistently showed lower △E values than those HTST-treated samples, regardless of blanching.     

Evaluation of Consumer Acceptance and Quality of Thermally and High Hydrostatic Pressure Processed Blueberries and Cherries Subjected to Cellulose Nanofiber (CNF) Incorporated Water-Resistant Coating Treatment

This study evaluated the influence of cellulose nanofiber (CNF) incorporated layer-by-layer water-resistant coating on consumer acceptance of blueberries and cherries processed in light syrup thermally (TP, 97 °C for 7 min) or non-thermally (high hydrostatic pressure (HHP), 414 MPa for 10 min). The coating technique was validated on canned blueberries in a commercial canning operation. Consumers (n?=?75 and 77 for blueberry and cherry study, respectively) scored overall, color, aroma, and texture likeness of coated and uncoated processed fruits using a 9-point hedonic scale and firmness intensity using a 5-point just about right (JAR) scale. Coating treatment significantly (P?<?0.05) increased aroma and texture liking scores of TP and HHP blueberries compared with uncoated ones, but did not impact overall and color liking scores. Coated TP (2.67) and HHP (2.96) blueberries received closer to JAR score in firmness that uncoated ones (1.88 and 2.57, respectively). Informing consumers about the benefit of developed coatings altered consumers’ attitude from negative (~?80 and ~?57% gave “neutral” and “disliking” scores on TP and HHP samples, respectively) into positive status (“I would like the overall appearance”). Coating treatment resulted in higher aroma liking scores in HHP cherries, but decreased (P?<?0.05) overall and color liking scores on both TP and HHP cherries due to the presence of visible coating substances onto fruit surface. In commercial canning process, coated blueberries showed great retention of bioactive compounds and firmness. This study demonstrated that CNF incorporated layer-by-layer coating is promising to produce high quality of processed fruits in light syrup.     

Development and characterization of reconstituted hydrogel from <Emphasis Type="Italic">Aloe vera</Emphasis> (<Emphasis Type="Italic">Aloe barbadensis</Emphasis> Miller) powder

Structural and rheological characterization of reconstituted hydrogels developed from A. vera non-fibrous alcohol insoluble residue (NFAIR) powder using different methods [viz., shaking (S), heating-shaking (HS), and heating (H)] and concentrations (viz., 0.2–1.6 %, w/v) was carried out. Functional group distribution by FTIR spectroscopy and Congo red (CR) method revealed the presence of acetylated acemannan in A. vera powder. Dynamic oscillation studies of A. vera (NFAIR) fluids at all concentrations of 0.2–1.6 %, w/v, showed gel strength in the order of H > HS > S method. However, in H method, increase in concentration from 0.2 to 1.6 %, w/v showed the conformational transition from semi-diluted solution to weak gel nature. Rheological models described the effect of heating temperatures (HT); 30–90 °C, and times (Ht); 15–60 min on viscoelastic behavior in reconstituted A. vera fluids. The reconstituted A. vera hydrogel prepared with a concentration of 1.6 %, w/v using 50 °C (HT) and 30 min (Ht) condition showed a good agreement with the Power law (storage modulus, G′) and Weak gel model (complex modulus, G*) fitted data (R² > 0.94) resulting higher viscoelastic moduli intercepts; G′₀ (71.5 Pa s ^n′), G″₀ (33.5 Pa s ^n″), lower slopes; n′ (0.22), n″ (0.06), higher network strength (A _F , 121.3 Pa s^1/z ) and number of network (z, 5.3) values. The obtained results suggested that heating at 50 °C/30 min can develop aqueous weak gel networks of A. vera with enhanced gel strength which may be utilized as a novel gelling agent for wide variety of targeted applications in food and pharmaceutical sectors.     

Properties of a fibrinolytic enzyme secreted by <Emphasis Type="Italic">Bacillus subtilis</Emphasis> JS2 isolated from saeu (small shrimp) <Emphasis Type="Italic">jeotgal</Emphasis>

Bacillus species were screened to be used as starters for jeotgals, salted and fermented Korean sea foods. A strain, JS2, showing strong fibrinolytic activity was isolated from saeu (small shrimp) jeotgal, and identified as Bacillus subtilis. Bacillus subtilis JS2 grew well at 20% (w/v) NaCl concentration. SDS-PAGE of culture supernatant from JS2 showed 3 major bands of 27, 29, and 60 kDa in size. Fibrin zymography showed that the 27 kDa band was the major fibrinolytic protein. The gene, aprEJS2, was cloned and introduced into B. subtilis WB600 using pHY300PLK. A B. subtilis transformant harboring pHYJS2 showed higher fibrinolytic activity than B. subtilis JS2. aprEJS2 was overexpressed in Escherichia coli BL21 (DE3). The optimum pH and temperature for AprEJS2 were pH 8.0 and 40 °C, respectively. Km and V_max values were determined. AprEJS2 has strong α-fibrinogenase activity and moderate β-fibrinogenase activity.     

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.     

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.     

Application of High Pressure for Selective Activity Regulation of Starter Cultures Aminopeptidases Involved in Ripening of Brined Cheeses

The combined effect of high pressure processing and temperature on aminopeptidases activity of lactic acid bacteria used as starter cultures in brined cheese manufacturing, in order to find the optimum process conditions for acceleration of the significant long-duration cheese ripening step, was investigated.The effect of high hydrostatic pressure (HP) (100–450 MPa) combined with temperature (20–40 °C) on the activity of five aminopeptidases (PepN, PepX, PepY, PepC, and PepA) of Streptococcus thermophilus ACA-DC 0022 and Lactococcus lactis ACA-DC 0049, used as the starter culture for white Greek brine cheese (feta) production, was studied. S. thermophilus aminopeptidases PepN, PepX, PepA, and PepC were activated at pressures up to 200 MPa, and all studied temperatures (20–40 °C), while for L. lactis, PepN, X, and Y were activated at pressures up to 300 MPa and temperatures up to 30 °C and PepA at the same temperature range but milder pressures (up to 200 MPa). For L. lactis, PepC an increase in activity was observed at all studied pressures but only at 20 °C. A multi-parameter equation was used for predicting the activation of all aminopeptidases in the pressure and temperature domain. Overall, processing at 200 MPa and 20 °C may be selected as the optimum conditions for maximum activation of all aminopeptidases of both S. thermophilus ACA-DC 0022 and L. lactis ACA-DC 0049. A 20-min treatment at these conditions leads to an average threefold increase in activity which could lead to better and faster maturation of white cheese.