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.     

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.     

活性包装薄膜中活性物质缓释技术研究进展

综述了活性包装薄膜中活性物质缓释技术的国内外研究进展,着重从活性物质释放速率的调控技术、影响因素以及释放动力学模型三方面进行了归纳,并对其未来发展趋势进行了展望。     

Characterization of bacteriocin-coated antimicrobial polyethylene films by atomic force microscopy

Antimicrobial agents can be used to give antimicrobial properties to polymeric materials used to envelope foods for packaging purposes. In this study, we exploited an atomic force microscopy (AFM) analysis for the characterization of plastic films activated with antimicrobial agents. The aim was to acquire information on the distribution of the antimicrobials on plastic materials with the ultimate scope of understanding the mechanisms of interaction between antimicrobials and materials to be used for food packaging. Four polyethylene films differing in linear, EVA, and erucamide content were activated by 3 different bacteriocins as antimicrobials, namely, nisin and bacteriocins Bac162W from Lactobacillus curvatus and BacAM09 from Lactobacillus plantarum. The spectrum of activity of the bacteriocins was assayed and shown to include several strains of Listeria monocytogenes. The plastic films were activated by a previously developed coating procedure and the surfaces of the active films were examined by AFM. In addition, roughness parameters related to the single surfaces were investigated by an appropriate software. Significant differences were found between the bacteriocin activated and control (nonactivated) films and the activated surfaces showed lower values of average roughness and surface area ratio. It was not always possible to obtain a homogeneous distribution of the bacteriocin preparation following the coating procedure. This result was dependent on the bacteriocin used and its distribution on the different plastic films. Overall, the bacteriocin Bac162W showed the most homogeneous distribution while surfaces treated with nisin, showing a sort of microtexturing, always gave the highest roughness values. Although the issue needs further investigation, the connection between AFM imaging, roughness, and antimicrobial distribution on active packaging showed the potential to improve the understanding of the interactions between plastic films and antimicrobial preparations that can be important for the innovation in food packaging and science.     

Partial Characterization of Nine Bacteriocins Produced by Lactic Acid Bacteria Isolated from Cold-Smoked Salmon with Activity against Listeria monocytogenes

Nine LAB bacteriocin-producers, isolated from vacuum-packaged cold-smoked salmon (CSS), were phenotypically and genotypically identified as Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus fermentum, Enterococcus faecium, and Pediococcus acidilactici. Their bacteriocins were partially characterized. The antimicrobial spectrum was determined against Listeria monocytogenes, E. faecalis, E. faecium, and Staphylococcus aureus. The molecular size of bacteriocins ranged from 2.8 to 4.5 kDa. They were inactivated by treatment with proteolytic enzymes but not by lipolytic or glycolytic enzymes. Maximal activity against L. monocytogenes ranged between 800 and 10000 AU/mL at pH 6.5. Most of the bacteriocins maintained full activity in a pH range of 2.0 to 8.0 but were partially or completely inactivated at pH 10.0. After heating at 60°C and 100°C, only two bacteriocins from Lb. curvatus strains partially lost activity. All bacteriocins showed a narrow spectrum of activity and a high anti-listerial activity, which is characteristic of the class IIa bacteriocins. Isolated bacteriocin-producing LAB could be used successfully in the bio-preservation of CSS and development of new potential bio-preservatives for CSS active against L. monocytogenes.     

绿茶多酚对马铃薯淀粉壳聚糖复合膜影响研究

为开发新型抗氧化活性包装材料,以马铃薯淀粉壳聚糖复合膜为基材,研究添加绿茶多酚对复合膜抗氧化能力、物理性能和化学结构影响。结果表明:添加绿茶多酚显著（p<0.05）提高了复合膜DPPH自由基清除能力,添加2%绿茶多酚的复合膜在3 min内自由基清除率达到94.48%,绿茶多酚添加也显著（p<0.05）地增强了复合膜的阻湿性。但添加绿茶多酚增加了复合膜红色和黄色、水溶性,降低了膜的柔韧性,红外光谱显示添加绿茶多酚影响了-O-H键的弯曲和伸缩振动,干扰了复合膜体间的氢键相互作用。研究结果表明添加0.5%绿茶多酚既能提高复合膜的抗氧化能力,又可使复合膜拥有较好的柔韧性。      

聚乳酸/曲酸抗氧化活性包装膜的制备及性能研究

以聚乳酸(polylactic acid, PLA)为基材,曲酸为抗氧化剂制备活性包装膜,研究了不同浓度曲酸对复合膜物理性能、力学性能及抗氧化活性等的影响,为开发新型食品活性包装材料提供依据。结果表明,加入曲酸后,薄膜的抗氧化性能显著提高。曲酸的加入也提高了复合膜的厚度,增加了膜的颜色,但不透明度降低。薄膜的断裂伸长率随曲酸浓度的增加而增加,红外光谱显示4%曲酸导致聚乳酸膜出现了新的■双键特征峰,显著加强聚乳酸膜分子链的相互作用,能够观察到苯环骨架的伸缩振动,新形成的■等化学键也导致薄膜有着较高的抗拉强度,表面产生了明显的波纹。综合来看,添加4%的曲酸能提高膜的抗氧化性能和力学性能,能获得理想的复合膜。     

Improvement of active chitosan film properties with rosemary essential oil for food packaging

Rosemary essential oil (REO) was used to develop an active film from chitosan. The effects of REO concentration (0.5, 1.0 and 1.5% v/v) on film properties were studied by measuring the physical, mechanical and optical properties of the REO‐loaded films. Scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy were used to study microstructure and the interaction of the chitosan‐based films. The solubility and water gain of the chitosan film decreased about 25% and 85%, respectively, by REO incorporation, up to 1.5% v/v, because of the interaction between hydrophilic groups of chitosan and REO as confirmed by FTIR. It was determined that REO improved the transparency of the films from 4.97 in neat chitosan up to 7.61; moreover, it reduced the films’ light transmission in UV light more than 25%. Films containing REO showed more antibacterial activity and total phenol content. The films containing REO showed potential to be used as active film in food preservation.     

贵州侗族酸肉中一株抗氧化弯曲乳杆菌LAB26的鉴定及特性

从贵州侗族酸肉中筛选出一株乳酸菌,其DPPH自由基清除率、羟自由基清除率、还原能力、抗脂质过氧化能力分别为(59.67±6.68)%、(153.17±5.50)%、(47.31±4.62)%、(55.00±5.19)%,并且菌株有良好耐受NaCl和NaNO2的性能。     

Migration of α-tocopherol from an active multilayer film into whole milk powder

Antioxidant active packaging is a promising technology for whole milk powder (WMP) protection. In this study, the migration of α-tocopherol from a multilayer active packaging (made of high density polyethylene, ethylene vinyl alcohol and a layer of low density polyethylene containing the antioxidant) to WMP was studied. A model based on the Fick’s diffusion equation was used to calculate the diffusion coefficients (D) of α-tocopherol as 2.34 × 10⁻¹¹, 3.06 × 10⁻¹¹, and 3.14 × 10⁻¹¹ cm² s⁻¹ at 20, 30 and 40 °C, respectively. The D at 20 °C was different from those at 30 and 40 °C (P < 0.05); but it was similar at 30 and 40 °C. This low influence of temperature on the migration of α-tocopherol from 20 to 40 °C assures the release at real storage and commercialization conditions in regions with warm/hot climate. The antioxidant delivering system delayed the lipid oxidation of WMP and it was more effective at 30 and 40 °C since the rate of oxidative reactions was higher at these temperatures than at 20 °C.     

Potential of a nisin-containing bacterial cellulose film to inhibit Listeria monocytogenes on processed meats

A bacterially produced cellulose film containing nisin was developed and used in a proof-of-concept study to control Listeria monocytogenes and total aerobic bacteria on the surface of vacuum-packaged frankfurters. Bacterial cellulose pellicles were produced by Gluconacetobacter xylinus K3 in Corn Steep Liquor-Mannitol Medium and were subsequently purified before nisin was incorporated into them. Investigations into the effect of nisin concentrations and contact times on incorporation of nisin into cellulose films showed that the lowest nisin concentration and shortest time needed for production of an effective antimicrobial cellulose film were 625IUml(-1) and 6h, respectively. The active cellulose films produced under these conditions did not, however, significantly reduce L. monocytogenes populations on frankfurters (P>0.05) during refrigerated storage for 14 days as compared to the controls. Films produced using a higher concentration of nisin (2500IUml(-1)) with the same exposure time (6h) resulted in a significant (P<0.05) decrease in L. monocytogenes counts on frankfurters of approximately 2logCFUg(-1) after 14 days of storage as compared to the control. Both the above-mentioned films showed a similar effectiveness in reducing total aerobic bacterial populations as measured by total aerobic plate counts on frankfurters. For both films, total aerobic bacterial levels were significantly (P>0.05) reduced by approximately 3.3logCFUg(-1) after 14 days of storage as compared to control samples. Bacterial cellulose films were demonstrated in this study to have potential applicability as antimicrobial packaging films or inserts for processed meat products.     

Synergistic antimicrobial effect of lactocin AL705 and nisin combined with organic acid salts against Listeria innocua 7 in broth and a hard cheese

The effectiveness of antimicrobial mixtures against Listeria innocua 7, used as a L. monocytogenes surrogate, was investigated in broth and a food system. Synergistic effects were found for nisin (Nis), potassium sorbate (PS), calcium propionate (CP) and sodium lactate (SL), Nis + PS being the most effective binary mixture that exhibited listericidal activity in broth. To assess the effect of adding lactocin AL705 (AL705) to Nis + organic acid salt combinations, tridimensional isobolograms were generated. Sub-MIC combinations of the antimicrobials exerted bactericidal activity against L. innocua 7 after AL705 addition to the binary mixtures. However, when applied on Sardo cheese contaminated with L. innocua 7 (initial inoculum 4.45 ± 0.06 CFU g⁻¹), only Nis + PS + AL705 produced count reductions respect to the control, reaching 3.04 ± 0.35 CFU g⁻¹ counts after 15 days at 15 °C. Ternary combinations containing AL705 showed potential to reduce antimicrobial usages for L. innocua 7 inhibition.     

海藻酸钠/玉米醇溶蛋白抗菌复合膜的制备及其性能

以海藻酸钠作为基质,加入玉米醇溶蛋白共混制备食品复合包装膜,通过对其物理性能和机械性能的测定分析,从而得到复合膜的最佳海藻酸钠-玉米醇溶蛋白配比,并进一步制作并加入百里香精油抗菌包合物,最终制备具有缓慢释放抗菌物质的活性抗菌复合膜并对其表征和抗菌性能进行分析。结果显示,海藻酸钠与玉米醇溶蛋白成膜液质量比为1∶1时,复合膜具有最佳物理性能和机械性能,此时的复合膜水蒸气阻隔性能和透光率较好,抗拉强度达到最大3.75 MPa,断裂伸长率达到最大42.13%。百里香精油包和物添加量为制膜液总质量的0.2%时,抗菌复合膜的表面平整度和抗菌性有较好的综合效果,并且抗菌效果与百里香精油包合物添加量呈正向关,可以根据此趋势调整添加量,生产所需物化及抗菌性能的抗菌复合膜。     

Characterisations of cassava starch and poly(butylene adipate-co-terephthalate) blown film with silicon dioxide nanocomposites

Films with high permeability are necessary for the packaging of agricultural products that respire to avoid anoxic conditions. This research developed and characterised bioplastic nanocomposite films with enhanced permeation and increased strength. Thermoplastic starch (TPS) was compounded with silicon dioxide (SiO₂) and blended with poly (butylene adipate-co-terephthalate) (PBAT) to produce bioplastic PBAT/TPS blend films via blown-film extrusion. Different SiO₂ contents (0.5%–1%) were dispersed in the matrices, causing interaction via hydrogen bonding with the TPS phase. SiO₂ at 1% significantly improved melting of the polymer blends, giving increasing amorphous ratios of the polymeric films. Microstructures and surface topography indicated voids between incompatible components and porous structures that improved permeation. Increasing SiO₂ content linearly enhanced oxygen and water vapour permeability by up to 39% and 16%, respectively. Tensile strength and elongation at break increased and decreased up to 40% and 32%, respectively, indicating increased rigidity due to adding solid nanoparticles to 1%. Migration phenomena of the film components, that is molecules with diol structures and silicon compounds depended on types of simulant and microstructures that induced swelling and release of the compounds. Film permeabilities increased, thereby facilitating air and humidity flow through the packaging.     

Characterization and antimicrobial activity studies of polypropylene films with carvacrol and thymol for active packaging

Antimicrobial active films based on polypropylene (PP) were prepared by incorporating thymol and carvacrol at three different concentrations: 4, 6 and 8 wt.% of both additives as well as an equimolar mixture of them. A complete thermal, structural, mechanical and functional characterization of all formulations was carried out. SEM micrographs showed certain porosity for films with high additives concentrations. A decrease in elastic modulus was obtained for the active formulations compared with neat PP. The presence of additives did not affect the thermal stability of PP samples, but decreased PP crystallinity and oxygen barrier properties. The presence of thymol and carvacrol also increased stabilization against thermo-oxidative degradation, with higher oxidation induction parameters. Finally, thymol showed higher inhibition against bacterial strain present in food compared with carvacrol, leading to higher antimicrobial activity. The obtained results proved the permanence of certain amounts of the studied additives in the polymer matrix after processing making them able to be used as active additives in PP formulations.