Migration of Antimicrobial Silver from Composites of Polylactide with Silver Zeolites

ABSTRACT: Silver ion migration and antimicrobial activity of PLA (polylactic acid-polylactide)/silver zeolite composites were investigated. Films prepared by solution-casting/solvent evaporation, or by melt-mixing/compression molding were compared. Silver migration to food simulants and TSB (tryptone soy broth) was quantified at different temperatures. Antimicrobial activity against Staphylococcus aureus and Escherichia coli was measured following the Japanese Industrial Standard JIS Z 2801. All types of PLA/silver zeolite composites released Ag⁺ ions. A more intense ionic exchange with the zeolites and a significant, but low, antimicrobial activity in solution were found in cast films. To attain antimicrobial effects, however, migrated ions ought to be in the range of the legal limit of 0.05 mg Ag⁺/kg food stated by the European Food Safety Agency (EFSA). Silver migration and antimicrobial activity were sensitive to the methodology chosen to process the PLA films, the ionic strength of the medium, and the ion motility in the polymer matrix. Practical Application: Silver exchanged zeolites incorporated in food contact polymers are gaining importance as antimicrobial agents. Migration of silver ions from polymer matrices, however, is legally restricted. Therefore a compromise between silver migration and antimicrobial activity needs to be critically analyzed to validate novel materials in food packaging applications.     

Effect of active packaging incorporated with triclosan on bacteria adhesion

ABSTRACT: Antimicrobial polyethylene and cellulose based films incorporated with triclosan were studied. The antimicrobial efficacy, the hydrophobicity, microscopic and the mechanical characteristics of the films, as well free energy of adhesion between bacteria and antimicrobial films were evaluated. It was observed that both polyethylene and cellulose based films incorporated with the antimicrobial were homogeneous. Furthermore, the addition of triclosan did not affect mechanical characteristics of the films (P > 0.05). However, triclosan incorporated into polyethylene films reduced its hydrophobicity while antimicrobial cellulose based films became more hydrophobic. The adhesion was thermodynamically favorable between tested bacteria and polyethylene films. On the other hand, the adhesion to triclosan cellulose based film was thermodynamically unfavorable to Staphylococcus aureus and Escherichia coli and favorable to Listeria innocua and Pseudomonas aeruginosa. Polyethylene and cellulose based films showed inhibitory effect against S. aureus and E. coli, being the inhibition halo higher for polyethylene films. This study improves the knowledge about antimicrobial films.     

Physiochemical and antimicrobial properties of edible aloe/gelatin composite films

Edible antimicrobial aloe/gelatin composite films with different ratio of freeze–dried aloe leaf gel powder and gelatin (aloe/gelatin = 5/0, 4/1, 3/2, 2/3, 1/4 and 0/5) were fabricated. The thickness of the resulting films was between 0.055 (aloe/gelatin = 0/5) and 0.157 mm (aloe/gelatin = 4/1). The mechanical properties including maximum elongation, tensile strength, elongation at break and break strength were determined. The mechanical properties were increased with the increasing amount of gelatin used in the composite formulation. The tensile strength for composite films with the ratio of 4/1, 3/2, 2/3, 1/4 and 0/5 was 4.12, 5.29, 6.96, 11.47 and 37.76 MPa, respectively. Citrobacter freundii, Escherichia coli, Enterobacter aerogens, Serratia marcescens, Staphylococcus aureus and Bacillus cereus were used in antimicrobial activity test. The results showed that antimicrobial activities of the composite films increased as the amount of aloe gel powder used in the composite films increased. The average area of inhibitory zones for films with composition of aloe/gelatin = 1/4 and aloe/gelatin = 4/1 was 1.63–2.38 and 3.82–4.80 cm², respectively.     

The release rate and antimicrobial activity of calcium-alginate films containing self-microemulsifying Thymus vulgaris essential oil against Escherichia coli and Staphylococcus aureus

The aim of this study was to fabricate antimicrobial calcium-alginate-based films containing the self-microemulsifying thyme essential oil (TEO) formulations using Tween 80 as the surfactant, and acetic (AA) or propionic (PA) acids as the cosurfactants. A Ca-alginate film containing nano-emulsified TEO as well as a neat Ca-alginate film were considered as the controls. The scanning electron microscopy micrographs showed a highly porous texture for SME films, which resulted in an increase in water vapor permeability and water absorption capacity of these films. The SME films released the TEO completely within 155 min and inhibited the growth of S. aureus and E. coli in in vitro antimicrobial tests. The population of S. aureus and E. coli reduced significantly in ground beef covered with SME films. The results of this study showed that self-microemulsifying TEO films could effectively increase the shelf life of ground beef by controlling its microbial population.     

Preparation of active antimicrobial methyl cellulose/carvacrol/montmorillonite nanocomposite films and investigation of carvacrol release

Methyl cellulose (MC)/carvacrol (CRV)/montmorillonite (MMT) nanocomposite films were prepared to obtain active antimicrobial packaging materials. The characterization of film samples by X-ray diffraction and transmission electron microscopy showed that composite films were of nano structures. CRV addition to the MC film and MC/MMT nanocomposite films led to a decrease in the thickness and opacity values of them, whereas MMT addition to the film matrix caused an increase in these values. Thermal stability of films slightly increased with increasing MMT concentration in film matrix. CRV release from films was investigated at different temperatures for 30 days. An increase in the MMT concentration matrix caused a decrease in CRV release at 25.0 ± 0.5 °C and in 60 ± 4% relative humidity (RH). CRV release increased with temperature at a constant RH. The antimicrobial activities of films were tested against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by the microatmosphere method and these organisms were completely inhibited on the nutrient broth/bacteriological agar medium when film samples containing 11.1 ± 0.2 mg CRV were present. MC/CRV film and MC/CRV/MMT-60% nanocomposite films on sausage reduced E. coli and S. aureus counts by 0.9 and 0.7 log cfu/mL, respectively, compared to the control film. The amount of CRV release from developed antimicrobial films can be controlled by MMT concentration within the film matrix and by the storage temperature of film.     

Antimicrobial,Rheological, and Thermal Properties of Plasticized Polylactide Films Incorporated with Essential Oils to Inhibit Staphylococcus aureus and Campylobacter jejuni

Polylactide (PLA) is the most mature biobased and biodegradable polymer. Due to its inherent brittleness, the polymer cannot be used as a packaging material without plasticizer. An attempt was made to develop antimicrobial plasticized PLA film by incorporating polyethylene glycol (PEG) and 3 essential oils (EO), namely cinnamon, garlic, and clove by solvent casting method. Physical, thermal, and rheological properties of those films were evaluated for practical applications whereas the antimicrobial properties were tested against Staphylococcus aureus and Campylobacter jejuni—pathogens related to poultry industry. Both PEG and EOs led to the formation of flexible PLA/PEG/EO films with significant drop in the glass transition temperature (T_g), and mechanical property. Time–temperature superposition (TTS) principle was employed to melt rheology of EO‐based films at selected temperature, and rheological moduli superimposed well in an extended frequency range. Among EOs, cinnamon and clove oil–based films (PLA/PEG/CIN and PLA/PEG/CLO) exhibited a complete zone of inhibition against C. jejuni at the maximum concentration (1.6 mL per 2 g PLA/PEG blend) whereas the garlic oil–based film (PLA/PEG/GAR) had the lowest activity.     

Characteristics of microcapsule of red ginger (Zingiber officinale var. Rubrum) essential oil produced from different Arabic gum ratios on antimicrobial activity toward Escherichia coli and Staphylococcus aureus

Essential oil has antimicrobial activity. Encapsulation of essential oil might affect its antimicrobial activity. The present study was aimed to study the characteristic of red ginger essential oil microcapsule obtained from varying Arabic gum ratios on the growth inhibition of E. coli dan S. aureus. Red ginger essential oil from steam distillation was coated using Arabic gum with ratio 1:3, 1:4, 1:5 (w/b). The 1:3 (v/w) ratio of red ginger essential oil and Arabic gum showed the best microcapsule characteristics with average inhibition diameter zones 5.67 mm for E. coli and 6.67 mm for S. aureus, and reduction of bacterial count for E. coli 1.8 log CFU/g and S. aureus 2.3 log CFU/g, yield of microcapsule 51.54%, water activity 0.207, water content 3.57%, solubility 97.46%, surface oil 0.08%, and particle size 258.2 µm. The major component of red ginger essential oil was ar-curcumene, zingiberen, β-bisabolene, β-sesquiphellandrene, and camphene.     

Extraction and application of natural silk protein sericin from Bombyx mori as antimicrobial finish for cotton fabrics

In this study, we developed an effective technology for the extraction of sericin from the cocoons of Bombyx mori silk worms. Sericin was extracted with ice cold ethanol to obtain crude extract. Sericin extract was coated onto cotton fabric by a pad–dry–cure method. FTIR characterization of the sericin-coated cotton fabric showed distinct amide peaks. The test organisms that were used in the study to assess the antimicrobial activity of sericin were Escherichia coli and Staphylococcus aureus according to AATCC standard. The antimicrobial activity of the sericin thus extracted was assessed by both qualitative (agar diffusion and parallel streak method) and quantitative (percentage reduction test) methods. An inhibition zone of 28 mm and 30 mm for E. coli and S. aureus by agar diffusion method and a zone of 40 mm and 42 mm for E. coli and S. aureus by parallel streak method were obtained. Quantitative assessment by percentage reduction test showed a reduction percentage of 89.4% and 81% for S. aureus and E. coli, respectively. Results suggested that sericin might be a valuable ingredient for the development of antimicrobial textiles.     

Antimicrobial activity of greater galangal [Alpinia galanga (Linn.) Swartz.] flowers

Using the agar disc diffusion method, the potential antimicrobial activity of edible galangal [Alpinia galanga (Linn.) Swartz.] flower against Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, and Shigella, and the effects of different drying methods and solvent types on the flowers’ antimicrobial activity were investigated. Oven-dried ethanol (OD Ethanol) extract from galangal flower was the most effective against S. aureus with inhibition zone of about 26–31 mm and the minimum inhibitory concentration (MIC) ranging from 0.352–0.547 mg/mL. No antimicrobial activity was observed on E. coli O157:H7 and Salmonella. Overall antimicrobial activity of oven-dried samples extracted with ethanol (OD Ethanol) was the highest with inhibition zone of 8.94 mm and MIC of 1.457 mg/mL. In contrast, freeze-dried samples extracted with ethanol (FD Ethanol) exhibited the lowest overall antimicrobial activity (7.05 mm and 2.470 mg/mL). This is the first report describing antimicrobial activity of galangal flowers against Grampositive S. aureus.     

Antimicrobial activity of Yerba Mate (Ilex paraguariensis) aqueous extracts against Escherichia coli O157:H7 and Staphylococcus aureus

Abstract: Bioactive compounds from natural plant sources are becoming increasingly important to the food industry. Ilex paraguariensis is used in the preparation of a widely popular tea beverage (Yerba Mate) in the countries of Uruguay, Paraguay, Argentina, and Brazil. In this study, extracts of 4 brands of commercial tea, derived from the holly plant species, Ilex paraguariensis, were evaluated for their ability to inhibit or inactivate bacterial foodborne pathogens. The ultimate goal was to evaluate potential use of the extracts in commercial applications. Dialyzed aqueous extracts were screened for antimicrobial activity against Escherichia coli O157:H7 and Staphylococcus aureus. S. aureus was found to be the more sensitive to extracts than E. coli O157:H7. Minimum bactericidal concentrations (MBCs) were determined to be approximately 150 to 800 μg/mL and 25 to 50 μg/mL against E. coli O157:H7 and S. aureus, respectively. A Uruguayan brand had reduced activity against E. coli O157:H7 compared to the Argentinean brands tested. It was concluded that Yerba Mate could be used as a potential antimicrobial in foods and beverages against these pathogenic bacteria. Practical Application: Soluble extracts from Yerba Mate are natural antimicrobials that can be incorporated into food products to achieve longer shelf life.     

Characterization of solution blown thermoplastic polyurethane nanofibers modified with Szygium aromaticum extract

Abstract

Antibacterial wound dressing mats were produced via coating solution blown TPU nanofiber mats with Szygium aromaticum extract (clove oil). Soxhlet extraction was used to obtain clove oil (CO) and according to gas chromatography–mass spectrometry analysis, it was shown that extract was mostly composed of eugenol and β-caryophylene, which exhibit superior antimicrobial activity. TPU nanofiber mats were coated with obtained clove oil in order to obtain antibacterial nanofibers. Even 2?mg/cm² clove oil coated TPU nanofibers (E2/TPU) exhibited a zone of inhibition around 24 and 22?mm against S. aureus and E. coli, respectively. On the other hand, air permeability of nanofibrous mats decreased with the increasing amount of clove oil over 5?mg/cm², because clove oil caused changes in nanofiber morphology. However, the presence of clove oil did not affect the morphology of E2/TPU, where air permeability values of those dressings were close to that of neat TPU nanofiber mats.     

Properties and antimicrobial activity of edible films incorporated with kiam wood (Cotyleobium lanceotatum) extract

The antimicrobial properties of wood extracts are well known; however their application to edible films is limited. In this study, the minimum bactericidal concentration (MBC) of kiam wood extract was established as 300 mg/L at which bacterial growth was completely inhibited. The antimicrobial properties of hydroxypropyl methylcellulose (HPMC) films containing 1-5 fold of MBC of kiam wood extract were tested against Escherichia coli O175:H7, Staphylococcus aureus and Listeria monocytogenes. The edible films containing kiam wood extract exhibited more effective impact on the growth reduction of L. monocytogenes than S. aureus and E. coli (p < 0.05). The use of kiam wood extract at 1 and 2 fold of MBC incorporated into edible HPMC films did not exhibit any antimicrobial activity. However, the inhibitory effect of edible HPMC films containing kiam wood extract was observed at 3, 4 and 5 fold of MBC. The greatest zone of inhibition was observed at 5 fold of MBC incorporated in edible HPMC films. Tensile strength and elongation at break significantly decreased with the incorporation of kiam wood extract, whereas water vapor permeability and film solubility increased. The color of edible films became darker and more reddish-yellowish as well as having a lower transparency as the level of kiam wood extract was increased. Kiam wood extract incorporated in edible film provided the films with a rougher surface than pure edible film. Our results pointed out that the incorporation of kiam wood extract as a natural antibacterial agent has potential for use in extending the shelf life of food products.     

Microtiter plate-based assay for screening antimicrobial activity of melanoidins against E. coli and S. aureus

A rapid plate reader based method examining the antimicrobial activity of both model and food melanoidins (coffee, beer, sweet wine) is described. Antimicrobial activity against Escherichia coli and Staphylococcus aureus is evaluated as area under the growth curve compared to a control. Method was settled for an aqueous melanoidin concentration of 2 mg/ml inoculated to 10⁶ cfu/ml culture. All tested model and food melanoidins exerted antimicrobial activity in some extent, but inhibition was significantly higher over S. aureus (Gram-positive) than E. coli (Gram-negative). Antimicrobial activity can be further quantified by expressing it as OTEV (oxytetracyclin equivalent value, μg/l) which could serve to compare the results obtained within different laboratories, methodologies and/or compounds. Results indicate that both strains have different sensitivity against the presence of melanoidins and probably different mechanism of inhibition. Procedure can be used for a rapid screening of the potential antimicrobial properties of melanoidins, and subsequently to Maillard reaction products as well, against pathogenic strains in order to isolated substances with biological activity.     

Nanoencapsulation and immobilization of cinnamaldehyde for developing antimicrobial food packaging material

Use of antimicrobial coatings on food packaging is one of the important technologies of active packaging for improving food safety. There is growing demand for natural antimicrobials because of fear of adverse health effects of synthetic preservatives. The objectives of this study were to compare antibacterial properties of free and nanoencapsulated cinnamaldehyde in solution; polylactic acid (PLA) surfaces cast with cinnamaldehyde; and glass and PLA surfaces coated with cinnamaldehyde nano-liposomes. Cinnamaldehyde was nano-encapsulated by lipid bilayers of polydiacetylene – N-hydroxysuccinimide (PDA–NHS) nano liposomes and immobilized on glass slides and PLA films. Glass surfaces immobilized with nano-encapsulated cinnamaldehyde showed significant antibacterial activity against Escherichia coli W1485 and Bacillus cereus ATCC 14579, with reductions of 2.56 log₁₀ CFU/ml and 1.59 log₁₀ CFU/ml respectively in 48 h. PLA films cast with cinnamaldehyde also showed significant antibacterial activities against E. coli W1485 (2.01 log₁₀ CFU/ml reduction) and B. cereus (4.81 log₁₀ CFU/ml reduction). However, when the liposomal encapsulated cinnamaldehyde was immobilized on PLA films, it did not show any antibacterial activity. Glass surfaces coated with nano-encapsulated cinnamaldehyde may be used as an active packaging material in preserving liquid foods; however, further study is required to improve antimicrobial activities of PLA surfaces.     

Effects of chitosan on the physicochemical and antimicrobial properties of PLA films

Films based on polylactic acid (PLA) and different amounts of chitosan powder (CH), were prepared by extrusion. The effects of CH particle size (715 and 180 μm) and the amount of chitosan incorporated in the PLA matrix (5% or 10% on PLA basis) were investigated in terms of physicochemical characteristics and antimicrobial activity of the films. The incorporation of CH particles led to less rigid and less stretchable films. Thermal properties of PLA were not affected by chitosan addition. Water vapor permeability of the composite films was higher than pure PLA films. PLA:CH composite showed significant antimicrobial activity against total aerobial and coliform microorganisms, especially when the particle size of CH was reduced.     

Hurdle Effect of Antimicrobial Activity Achieved by Time Differential Releasing of Nisin and Chitosan Hydrolysates from Bacterial Cellulose

We investigated the combined antimicrobial effect of nisin and chitosan hydrolysates (CHs) by regulating the antimicrobial reaction order of substances due to differential releasing rate from hydroxypropylmethylcellulose‐modified bacterial cellulose (HBC). The minimum inhibitory concentration of nisin against Staphylococcus aureus and that of CHs against Escherichia coli were 6 IU and 200 μg/mL, respectively. Hurdle and additive effects in antimicrobial tests were observed when nisin was used 6 h before CH treatment against S. aureus; similar effects were observed when CH was used before nisin treatment against E. coli. Simultaneously combined treatment of nisin and CHs exhibited the low antimicrobial effect. HBC was then selected as the carrier for the controlled release of nisin and CHs. A 90% inhibition in the growth of S. aureus and E. coli was achieved when 30 IU‐nisin‐containing HBC and 62.5 μg/mL‐CH‐containing HBC were used simultaneously. The controlled release of nisin and CHs by using HBC minimized the interaction between nisin and CHs as well as increased the number of microbial targets.     

还原氧化石墨烯增强聚乳酸纳米纤维膜的制备及其性能

针对静电纺聚乳酸(PLA)纳米纤维膜力学强度不高的问题,将一定质量的还原氧化石墨烯(rGO)分散于PLA和二甲基甲酰胺(DMF)纺丝溶液中,通过静电纺丝法制备PLA/rGO复合纳米纤维膜。对纺丝液的流变性能以及复合纳米纤维膜的形貌结构、微观结构和力学性能进行分析,采用四唑盐比色法对复合纳米纤维膜的细胞相容性进行表征。结果表明:rGO成功地复合至PLA纳米纤维中,且以不规则球状形式分布于PLA纳米纤维膜中;rGO的复合显著提升了PLA纳米纤维膜的力学强度,当rGO质量分数为0.6%时,复合纳米纤维膜的断裂强度达2.02 MPa,是纯PLA纳米纤维膜2.3倍;培养1、3和7 d后,小鼠胚胎成骨细胞可在复合纳米纤维膜上生长和增殖,表明PLA/rGO复合纳米纤维膜具有较好的细胞相容性。     

Atomic force microscopy study of the antimicrobial activity of aqueous garlic versus ampicillin against Escherichia coli and Staphylococcus aureus

BACKGROUND: In this study the effects of ampicillin and aqueous garlic extract on Escherichia coli (ATCC 9637) and Staphylococcus aureus (ATCC 25923) were compared. Atomic force microscopy (AFM) was used to study the possible mechanisms of membrane disruption. RESULTS: Ampicillin disrupted the cell membrane of E. coli, inducing pores and cell leakage. Aqueous garlic extract also induced leakage from the cell membrane in E. coli, but no pores were observed. The trend in Young's modulus for E. coli was E_native ≈ E_age > E_amp. In contrast, S. aureus incubated with low ampicillin (≤50µg mL^?1) and garlic (≤50 mg mL^?1) concentrations showed no significant changes in surface morphology compared with the untreated bacterium. The trend in Young's modulus for S. aureus was E_native ≈ E_age ≈ E_amp. CONCLUSION: The trend E_native ≈ E_age for E. coli and S. aureus supports the hypothesis that the compounds in garlic show intracellular activity. This proof‐of‐concept study of the aqueous crude isolate of garlic points to the feasibility of further AFM investigations to compare the antimicrobial properties of various pure thiosulfinate isolates found in garlic. Copyright © 2009 Society of Chemical Industry     

Constituents,Oxidant-Antioxidant Profile,and Antimicrobial Capacity of the Essential Oil Obtained from Ferulago Sandrasica Peşmen and Quézel

Chemical constituents, total phenolic content, total oxidant status, total antioxidant status, lipid hydroperoxides, total free –SH levels, and antimicrobial activity of essential oil obtained from the Ferulago sandrasica (Umbelliferae) were investigated. The essential oil was obtained by hydrodistillation using a Clevenger-type apparatus. The chemical constituents were analyzed by gas chromatography‐mass spectrometry. The main components of the essential oil were ocimene (30.5%), carene-δ-3 (27.4%), and α-pinene (17.8). The antimicrobial activity was tested by a disc diffusion method against E. coli MC 400, E. coli ATCC 25922, E. coli 0157 H7, E. colaecea ATCC 23355, E. feacalis ATCC 19433, P. aeruginosa NRRL B-2679, S. aureus ATCC 25923, B. nischenoformis NRRL B-1001, S. aureus ATCC 33862, B. cereus NRRL B-3711, B. subtilis NRRL B-209, M. luteus NRRL B-1013, L. monocytogenes ATCC 7644, B. subtulis ATCC 6633.     

GEO添加量对PLA/GEO复合膜性能及双孢蘑菇保鲜效果的影响

本文研究了不同浓度（0%、5%、7.5%、10%和12.5%）的葡萄柚精油（GEO）对聚乳酸(PLA)/葡萄柚精油复合膜的热性能,结构性能,机械性能,气体阻隔性能和抗菌性能等方面的影响。GEO通过减少聚合物链段的分子间作用力,从而改善复合膜的柔韧性,对复合膜起到一定的增塑作用。GEO的添加降低了PLA相的结晶性。随着GEO浓度的增加,复合膜的水蒸汽阻隔性能显著降低。但是,复合膜的抗菌活性因GEO的加入得以提高。将聚乳酸/葡萄柚精油复合膜应用于双孢蘑菇保鲜。结果表明,聚乳酸/葡萄柚精油复合膜与纯聚乳酸膜、低密度聚乙烯膜相比较,更能有效地保持蘑菇的硬度,阻止微生物生长,维持较好的总体接受度。因此,聚乳酸/葡萄柚精油复合膜可作为一种有效的包装材料,用于延长双孢蘑菇的货架期。