Development of active plastic crate and evaluation of phytopathogenic and pathogenic food spoilage micro‐organism inhibition

BACKGROUND: The plastic crates used in fruit and vegetable shipping can be vehicles of disease dissemination among production fields, since there is a chance of phytopathogenic micro‐organism adhesion on the crate surfaces when in contact with soil, contaminated produce or handling. The aim of this study was to develop an active plastic crate incorporated with a triclosan‐based antimicrobial agent and to evaluate its efficiency of micro‐organism inhibition. RESULTS: Staphylococcus aureus (a human pathogen), Clavibacter michiganensis ssp. michiganensis and Erwinia carotovora ssp. carotovora (phytopathogens) were the most sensitive micro‐organisms when in contact with samples of plastic crate incorporated with 30 g kg^?1 of antimicrobial agent. They presented diameters of approximately 5.0, 3.5 and 3.5 cm respectively in the halo test. Mean specific growth rates decreased in samples with 30 g kg^?1 of antimicrobial agent, compared with control samples, from 1.13 to 0 h^?1 for S. aureus, from 1.26 to 0.47 h^?1 for Escherichia coli and from 1.75 to 0.18 h^?1 for Listeria monocytogenes. The antimicrobial agent did not influence the mechanical properties of the crates. CONCLUSION: The active plastic crate has great potential to contribute to the safety of horticultural produce by restraining the proliferation of micro‐organisms among production fields. Copyright © 2008 Society of Chemical Industry     

Melt Production and Antimicrobial Efficiency of Low-Density Polyethylene (LDPE)-Silver Nanocomposite Film

Colloidal silver nanoparticles with a size of 5.5 ± 1.1 nm were prepared by chemical reduction using polyethylene glycol (PEG). Silver nanoparticles were incorporated into low-density polyethylene (LDPE) by melt blending and subsequent hot pressing at 140 °C to produce nanocomposite film with an average thickness of 0.7 mm. PEG was added at 5% weight of polymer as a compatibilizer agent in order to prevent agglomeration and provide uniform distribution of nanoparticles in polymer matrix. Antimicrobial activity of silver nanocomposites against Escherichia coli ATCC 13706, Staphylococcus aureus ATCC12600, and Candida albicans ATCC10231 was evaluated by semi-qualitative agar diffusion test and quantitative dynamic shake flask test. Mechanical properties of nanocomposites were not significantly different from silver-free LDPE-containing PEG films (p > 0.05), and silver nanoparticles did not form chemical bonding with the polymer. LDPE-silver nanocomposite samples by more than 6.69 ppm silver nanoparticles showed considerable antimicrobial clear zone. LDPE-silver nanocomposite affected growth kinetic parameters of the examined bacteria and is more efficient on S. aureus than E. coli. Polyethylene-silver nanocomposites containing 22.64 ppm silver nanoparticles could reduce 57.8% growth rate and 23.3% maximum bacterial concentration and increase 35.8% lag time of S. aureus. This study shows the potential use of LDPE-silver nanocomposite as antimicrobial active film. Antimicrobial efficiency of silver nanocomposite depends on silver nanoparticles concentration; however, high level of silver nanoparticles may lead to weakening of mechanical properties.     

Antimicrobial activity and mechanism of PLA/TP composite nanofibrous films

Electrospinning is conducted with polylactic acid (PLA) and tea polypheno (TP) to obtain PLA/TP composite nanofibrous films with high antimicrobial activity. An investigation of the composition, antimicrobial activity, and mechanism of these composite nanofibrous films was conducted by using infrared spectroscopy (FT-IR), inhibition zone method, fluorescence activated cell sorter (FACS), and transmission electron microscope (TEM). IR spectra results showed that TP and PLA composited well through valence bonds in PLA/TP composite nanofibrous films. Ranges of the inhibition zone for the growth of Escherichia coli (E. coli) and Staphylococcus (Staphylococcus aureus) were 3.67 and 3.71?cm in pure PLA nanofibrous films, but 5.17 and 5.67?cm in PLA/TP composite nanofibrous films, respectively. Results indicated that the antimicrobial activity of PLA/TP composite nanofibrous films were much higher than that of pure PLA nanofibrous films. Meanwhile, the antimicrobial activity against S. aureus was also slightly higher than E. coli. FACS results showed that the positive rate of PLA/TP composite nanofiber films was greater than that of pure PLA nanofibrous films, increasing from 1.45 and 0.78% to 9.26 and 6.47% against S. aureus and E. coli, respectively. The result of TEM indicated that PLA/TP composite nanofibrous films led to the death of bacteria by destroying the integrity of cell membrane.     

Physical,antimicrobial and antioxidant properties of starch‐based film containing ethanolic propolis extract

Propolis is a natural product that meets the requirements as functional additive for food packaging due to its antioxidant and antimicrobial activities. In this work, ethanolic propolis extract (EPE) was incorporated in cassava starch films, and characterisations with respect to their microstructure, mechanical properties, water vapour permeability (WVP), moisture sorption kinetics as well as antimicrobial and antioxidant capacities were performed. The results showed that tensile strength was not affected (P > 0.05) by the presence of EPE but Young's modulus decreased about 50% when compared to control films possibly because of EPE plasticiser effect. When 1% EPE was used, changes in moisture sorption properties were detected by a slightly hydrophobic character at films WVP. When extracted from the films, propolis retained its antioxidant activity. The films exhibited antimicrobial activity against Staphylococcus aureus and Escherichia coli even at low EPE concentrations (0.5%) mainly due to its phenolic compounds.     

Mechanical,Physical, Antioxidant,and Antimicrobial Properties of Gelatin Films Incorporated with Thymol for Potential Use as Nano Wound Dressing

The aim of this study was to determine the properties of gelatin films incorporated with thymol. Gelatin films were prepared from gelatin solutions (10% w/v) containing thymol (1, 2, 4, and 8% w/w), glycerol (25% w/w) as plasticizer, and glutaraldehyde (2% w/w) as cross‐linker. Cross‐likened films showed higher tensile strength, higher elongation at break, lower Young's modulus, lower water solubility, lower swelling, lower water uptake, and lower water vapor permeability. Incorporation of thymol caused a significant decrease in tensile strength, increase in elongation at break, decrease in Young's modulus, increase in water solubility, decrease in swelling and water uptake, and increase in water vapor permeability slightly. The films incorporated with thymol exhibited excellent antioxidant and antibacterial properties. The antibacterial activity of the films containing thymol was greatest against Staphylucoccus aureus followed by Bacillus subtilis followed by Escherichia coli and then by Pseudomonas aeruginosa. Thus, gelatin films‐containing thymol can be used as safe and effective source of natural antioxidant and antimicrobial agents with the purpose of evaluating their potential use as modern nano wound dressing. Practical Application : This study clearly demonstrates the potential of gelatin films incorporated with thymol as natural antioxidant and antimicrobial nano film. Such antimicrobial films exhibited excellent mechanical, physical, and water activities and could be used as antibacterial nano wound dressing against wounds burn pathogens.     

Antimicrobial effectiveness of oregano and sage essential oils incorporated into whey protein films or cellulose‐based filter paper

BACKGROUND: In this study the antimicrobial effectiveness of oregano and sage essential oils (EOs) incorporated into two different matrices, whey protein isolate (WPI) and cellulose‐based filter paper, was analysed. RESULTS: Antimicrobial properties of WPI‐based films containing oregano and sage EOs were tested against Listeria innocua, Staphylococcus aureus and Salmonella enteritidis. Oregano EO showed antimicrobial activity against all three micro‐organisms. The highest inhibition zones were against L. innocua. However, sage EO did not show antimicrobial activity against any of the micro‐organisms. Antimicrobial activity was confirmed for both EOs using cellulose‐based filter paper as supporting matrix, although it was significantly more intense for oregano EO. Inhibition surfaces were significantly greater when compared with those of the WPI films. This finding is likely due to the higher porosity and diffusivity of the active compounds in the filter paper. CONCLUSION: The interactions between the EOs and the films have a critical effect on the diffusivity of the active compounds and therefore on the final antimicrobial activity. As a result, to obtain active edible films, it is necessary to find the equilibrium point between the nature and concentration of the active compounds in the EO and the formulation of the film. Copyright © 2010 Society of Chemical Industry     

Antimicrobial activity of soy edible films incorporated with thyme and oregano essential oils on fresh ground beef patties

Antibacterial activity of soy protein edible films (SPEF) incorporated with 1, 2, 3, 4 and 5% oregano (OR) or thyme (TH) essential oils was evaluated against Escherichia coli, E. coli O157:H7, Staphylococcus aureus, Pseudomonas aeruginosa and Lactobacillus plantarum by the inhibition zone test. Effects of SPEF containing 5% OR and TH or a mixture of OR + TH (ORT) were also tested on fresh ground beef during refrigerated storage (at 4 °C). OR and TH incorporated SPEF exhibited similar antibacterial activity against all bacteria in inhibition zone test. While E. coli, E. coli O157:H7 and S. aureus were significantly inhibited by antimicrobial films, L. plantarum and P. aeruginosa appeared to be the more resistant bacteria. SPEF with OR, ORT, and TH did not have significant effects on total viable counts, lactic acid bacteria and Staphylococcus spp. when applied on ground beef patties whereas reductions (p < 0.05) in coliform and Pseudomonas spp. counts were observed.     

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.     

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.     

Antimicrobial activity of Zataria multiflora Boiss. essential oil incorporated with whey protein based films on pathogenic and probiotic bacteria

The antimicrobial potential of whey protein isolate (WPI) edible films containing 1–4% (v/v) Zataria multiflora Boiss. essential oil (EO) on food‐borne pathogenic bacteria (Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Bacillus cereus) and probiotic bacteria (Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus casei subsp. casei) was evaluated. WPI films incorporated with 2% (v/v) of this EO inhibited the growth of all tested pathogenic bacteria and gram‐negative bacteria were more sensitive than gram‐positive bacteria. Incorporation of the EO at higher than 2% (v/v) showed significant antimicrobial effects (P < 0.05) for S. enteritidis and L. acidophilus. The growth of all probiotic lactic acid‐producing bacteria also inhibited when 2% of the EO was added. Comparison of an image processing‐based method with conventional method for measuring of inhibitory effects of edible films exhibited high correlations (R² ≥ 0.876) between the two methods. These results revealed that Z. multiflora Boiss. EO is a good antimicrobial additive for some food applications when included into WPI edible films.     

Application of chitosan-incorporated LDPE film to sliced fresh red meats for shelf life extension

Chitosan lactate was impregnated as an antimicrobial additive into low density polyethylene (LDPE) with different concentrations. The antimicrobial effectiveness was tested with three pathogenic bacteria, specifically Listeria monocytogenes, Escherichia coli and Salmonella enteritidis. Also, these chitosan incorporated films were applied on red meat surfaces to determine the effectiveness of chitosan on color shelf life extension and microbial growth inhibition. Chitosan was exposed to 0.1% peptone water containing the three pathogens in separate tests and inhibited microbial growth a higher levels with increasing concentration of chitosan in the film matrix. Oxygen permeability was not affected by the incorporation of chitosan, while the water vapor permeability increased with the addition of chitosan. Film elongation decreased with the addition of chitosan. When chitosan incorporated films were applied on fresh red meat, microorganisms on the meat surface were not inhibited but significant extension of red color shelf life were observed in refrigerated, sliced red meats.     

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.     

Antimicrobial efficacies of essential oils/nanoparticles incorporated polylactide films against L. monocytogenes and S. typhimurium on contaminated cheese

Polylactide based films were formulated by incorporating polyethylene glycol, selected nanopowders (zinc oxide, silver-copper), and essential oils (cinnamon, garlic, and clove) by solvent casting method. Films were tested against three foodborne pathogens (one gram-positive and two gram-negative) for their antibacterial activity. The effectiveness of selected cinnamon oil-based film was ascertained by performing a challenge test with cheese as a food model. In vitro antibacterial efficacies of nanopowders and essential oils were also determined by the decimal reduction concentrations and the minimum bactericidal concentrations for those foodborne pathogens. It was observed that nanopowders exhibited considerably poorer decimal reduction concentrations and minimum bactericidal concentration values in comparison to the essential oils. Silver-copper alloy nanopowders exhibited lower decimal reduction concentrations and minimum bactericidal concentrations values than ZnO against tested pathogens whereas essential oils showed distinct antimicrobial effectiveness against all those pathogens with in vitro decimal reduction concentration values of 87–157 and 77–220 µg/mL for cinnamon and clove oils, respectively. Among the various formulations, it was observed that only essential oils (especially cinnamon and clove) incorporated films exhibited a significant antimicrobial activity against the selected microorganisms. These results indicate that the poor antibacterial activity of the nanopowders and the hydrophobicity of polylactide could be responsible for the ineffectiveness of nanopowders in polylactide based films. Furthermore, the challenge test indicated the polylactide/polyethylene glycol/cinnamon oil film was appropriate to inhibit the growth of L. monocytogenes and S. typhimurium on cheese up to 11 days at refrigerated storage.     

The antimicrobial,mechanical, physical and structural properties of chitosan–gallic acid films

Chitosan films incorporated with various concentrations of gallic acid were prepared and investigated for antimicrobial, mechanical, physical and structural properties. Four bacterial strains that commonly contaminate food products were chosen as target bacteria to evaluate the antimicrobial activity of the prepared gallic acid–chitosan films. The incorporation of gallic acid significantly increased the antimicrobial activities of the films against Escherichia coli, Salmonella typhimurium, Listeria innocua and Bacillus subtilis. Chitosan films incorporated with 1.5 g/100 g gallic acid showed the strongest antimicrobial activity. It was also found that tensile strength (TS) of chitosan film was significantly increased when incorporating 0.5 g/100 g gallic acid. Inclusion of 0.5 g/100 g gallic acid also significantly decreased water vapor permeability (WVP) and oxygen permeability (OP). Microstructure of the films was investigated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and it was found that gallic acid was dispersed homogenously into the chitosan matrix.     

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 Activity and Hydrophobicity of Edible Whey Protein Isolate Films Formulated with Nisin and/or Glucose Oxidase

The use of edible antimicrobial films has been reported as a means to improve food shelf life through gradual releasing of antimicrobial compounds on the food surface. This work reports the study on the incorporation of 2 antimicrobial agents, nisin (N), and/or glucose oxidase (GO), into the matrix of Whey protein isolate (WPI) films at pH 5.5 and 8.5. The antimicrobial activity of the edible films was evaluated against Listeria innocua (ATCC 33090), Brochothrix thermosphacta (NCIB10018), Escherichia coli (JMP101), and Enterococcus faecalis (MXVK22). In addition, the antimicrobial activity was related to the hydrophobicity and water solubility of the WPI films. The greatest antibacterial activity was observed in WPI films containing only GO. The combined addition of N and GO resulted in films with lower antimicrobial activity than films with N or GO alone. In most cases, a pH effect was observed as greater antimicrobial response at pH 5.5 as well as higher film matrix hydrophobicity. WPI films supplemented with GO can be used in coating systems suitable for food preservation.     

Incorporation of Essential Oils and Nanoparticles in Pullulan Films to Control Foodborne Pathogens on Meat and Poultry Products

The incorporation of essential oils and nanotechnology into edible films has the potential to improve the microbiological safety of foods. The aim of this study was to evaluate the effectiveness of pullulan films containing essential oils and nanoparticles against 4 foodborne pathogens. Initial experiments using plate overlay assays demonstrated that 2% oregano essential oil was active against Staphylococcus aureus and Salmonella Typhimurium, whereas Listeria monocytogenes and Escherichia coli O157:H7 were not inhibited. Two percent rosemary essential oil was active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 1%. Zinc oxide nanoparticles at 110 nm were active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 100 or 130 nm. Conversely, 100 nm silver (Ag) nanoparticles were more active against S. aureus than L. monocytogenes. Using the results from these experiments, the compounds exhibiting the greatest activity were incorporated into pullulan films and found to inhibit all or some of the 4 pathogens in plate overlay assays. In challenge studies, pullulan films containing the compounds effectively inhibited the pathogens associated with vacuum packaged meat and poultry products stored at 4 °C for up to 3 wk, as compared to control films. Additionally, the structure and cross‐section of the films were evaluated using electron microscopy. The results from this study demonstrate that edible films made from pullulan and incorporated with essential oils or nanoparticles may improve the safety of refrigerated, fresh or further processed meat and poultry products.     

Development of Antibacterial Carboxymethyl Cellulose‐Based Nanobiocomposite Films Containing Various Metallic Nanoparticles for Food Packaging Applications

In this study, silver (Ag), zinc oxide (ZnO), and copper oxide (CuO) metallic nanoparticles were used in preparation of carboxymethyl cellulose (CMC) nanobiocomposite films. Scanning electron microscopy (SEM), X‐ray diffraction (EDXA), water vapor permeability (WVP), ultraviolet and visible light (UV–Vis) spectroscopy, and mechanical and microbial tests were used to determine the characteristics of the obtained active films. SEM results showed that the CMC nanobiocomposite films had roughness deflection levels and the EDXA test confirmed the presence of Ag, ZnO, and Cuo nanoparticles in the biopolymer tissue. UV–Vis spectroscopy confirmed that with addition of metallic nanoparticles to the pure CMC film, absorption rate increased and WVP decreased. In the mechanical tests, addition of nanoparticles also increased the tensile strength of the films, and the nanobiocomposite films exhibited higher resistance compared to the pure CMC film. Films incorporating metallic nanoparticles showed antibacterial properties against Escherichia coli and Staphylococcus aureus growth. Thus, nanobiocomposite films can be used as active packaging films and could increase the shelf‐life of the food.     

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.     

Stability and Antimicrobial Activity of Allyl Isothiocyanate during Long-Term Storage in an Oil-in-Water Emulsion

Abstract: This study investigated the stability and antimicrobial activity of allyl isothiocyanate (AITC) in medium chain triglyceride (MCT) or soybean oil (SBO) dispersed in an oil-in-water (o/w) system during long-term storage. Oil type, content, and oxidative stability affect the stability and antimicrobial activity of AITC during storage. High oil content is favorable for AITC stability in the emulsion. Notably, AITC with MCT is more stable than AITC with SBO with the same oil content. Consequently, AITC with MCT is more effective than AITC with SBO in inhibiting G(−) bacteria (E. coli O157:H7, Salmonella enterica, and Vibrio parahaemolyticus) and G(+) bacteria (Staphylococcus aureus and Listeria monocytogenes).