Novel silver-based nanoclay as an antimicrobial in polylactic acid food packaging coatings

This paper presents a comprehensive performance study of polylactic acid (PLA) biocomposites, obtained by solvent casting, containing a novel silver-based antimicrobial layered silicate additive for use in active food packaging applications. The silver-based nanoclay showed strong antimicrobial activity against Gram-negative Salmonella spp. Despite the fact that no exfoliation of the silver-based nanoclay in PLA was observed, as suggested by transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS) experiments, the additive dispersed nicely throughout the PLA matrix to a nanoscale, yielding nanobiocomposites. The films were highly transparent with enhanced water barrier and strong biocidal properties. Silver migration from the films to a slightly acidified water medium, considered an aggressive food simulant, was measured by stripping voltammetry. Silver migration accelerated after 6 days of exposure. Nevertheless, the study suggests that migration levels of silver, within the specific migration levels referenced by the European Food Safety Agency (EFSA), exhibit antimicrobial activity, supporting the potential application of this biocidal additive in active food-packaging applications to improve food quality and safety.     

Silver nanoparticles: A novel antibacterial agent for control of Cronobacter sakazakii

Silver nanoparticles (AgNP) have been widely applied because of their broad spectrum of antimicrobial activities against bacteria, fungi, and viruses. However, little research has been done to evaluate their effects on Cronobacter sakazakii, an opportunistic pathogen usually infecting infants and having a high fatality rate. The aims of this work were to investigate the antibacterial property of novel, synthesized, positively charged silver nanoparticles against C. sakazakii and to discuss the potential antibacterial mechanisms involved. In this study, the spherical and face-centered cubic silver nanoparticles had a mean particle size of 31.2 nm and were synthesized by reducing Ag⁺ using citrate and dispersed by glycerol and polyvinylpyrrolidone (PVP) under alkaline conditions. Minimum inhibitory concentrations (MIC) and inhibition zone tests showed that the AgNP exhibited strong antibacterial activity against 4 tested C. sakazakii strains with mean MIC of 62.5 to 125 mg/L and average inhibition zone diameters of 13.8 to 16.3 mm. Silver nanoparticles caused cell membrane injury accompanied by adsorption of AgNP onto the cell surface, as shown by changes in cell morphology, cell membrane hyperpolarization, and accelerated leakage of intracellular reducing sugars and proteins outward from the cytoplasm. In addition, dysfunction of the respiratory chain was induced after treatment with AgNP, which was supported by a decrease in intracellular ATP and inhibition of related dehydrogenases. This research indicates that AgNP could be a novel and efficient antibacterial agent to control C. sakazakii contamination in environments producing powdered infant formulas from milk.     

Study of silver ion migration from melt-blended and layered-deposited silver polyethylene nanocomposite into food simulants and apple juice

Colloidal silver nanoparticles were prepared via chemical reduction using polyethylene glycol (PEG) as a reducing agent, stabiliser and solvent. Silver polyethylene nanocomposites were produced via two methods, namely: melt blending and layer-by-layer (LBL) deposition of silver nanoparticles onto a polyethylene film. The silver ion release from either melt-blended or LBL-deposited nanocomposites into a food simulant and apple juice during 30 days at 4°C and 40°C was determined by atomic absorption spectroscopy. The effects of incorporating or coating of silver nanoparticles, silver concentration, contact media, temperature and time on silver ion migration were evaluated using factorial design. The diffusion coefficients of silver ions into the food simulants and apple juice were calculated using the Miltz model. The results indicated that the production method of nanocomposite, silver concentration, temperature, time and contact media showed a significant effect (p < 0.05) on silver ion migration. The quantity of silver ion migration from the nanocomposites into the food simulants and apple juice was less than the cytotoxicity-level concentration (10 mg kg^?1) in all cases over 30 days. The coating of silver nanoparticles, higher silver concentration in the nanocomposite, higher temperature and acidic property of contact liquid all promoted the silver ion release from the nanocomposite films. The migration of silver ions from nanocomposites obeyed first-order diffusion kinetics.     

Silver migration from nanosilver and a commercially available zeolite filler polyethylene composites to food simulants

Polyethylene composites containing Agion^TM commercial silver ion filler at three different percentage fill rates (0.5, 1.0 and 2% w/w) and polyethylene composites containing laboratory produced silver nanoparticles (Agnps) at two different percentage fill rates (0.1 and 0.5% w/w) underwent migration tests according to Commission Regulation (EU) No. 10/2011. Migrated silver in the two simulants (acidified water with 3% acetic acid and distilled water) was quantified using two techniques: inductively coupled atomic emission spectroscopy (ICPAES) and Hach Lange spectroscopy. The former had higher sensitivity with mean silver migration from Agion composites (n = 12) ranging from < 0.001 to 1.50 × 10^?2 mg l^–1. Mean silver migration from Agnps composites ranged from 4.65 × 10^?2 to 0.38 mg l^–1 and 8.92 × 10^?2 and 5.15 × 10^?2 mg l^–1 for Hach Lange spectrophotometry and ICPAES, respectively. Both percentage fill rate in the composite and the simulant type, as factors, were found to be significant in both silver migration from Agion (p < 0.0001 and < 0.01, respectively) and Agnps (p < 0.05 and < 0.01, respectively). Transmission electron microscopy (TEM) imagery showed differences in size distributions and morphology of particles (shape and degree of agglomeration) before and after migration. PE composites containing 0.5% Agion, simulating contact with non-acidic foods, was the only scenario that did not exceed the permitted migration level of non-authorised substances given in EU 10/2011. This study illustrates the need for careful engineering of the composite filler system to conform to limits with cognisance of food pH and percentage fill rate.     

Characterisation and potential migration of silver nanoparticles from commercially available polymeric food contact materials

The potential for consumer exposure to nano-components in food contact materials (FCMs) is dependent on the migration of nanomaterials into food. Therefore, characterising the physico-chemical properties and potential for migration of constituents is an important step in assessing the safety of FCMs. A number of commercially available food storage products, purchased domestically within the United States and internationally, that claim to contain nanosilver were evaluated. The products were made of polyethylene, polypropylene and polyphenylene ether sulfone and all contained silver (0.001–36 mg kg^–1 of polymer). Silver migration was measured under various conditions, including using 3% acetic acid and water as food simulants. Low concentrations (sub-ppb levels) of silver were detected in the migration studies generally following a trend characterised by a surface desorption phenomenon, where the majority of the silver migration occurred in the first of three consecutive exposures. Silver nanoparticles were not detected in food simulants, suggesting that the silver migration may be due solely to ionic silver released into solution from oxidation of the silver nanoparticle surface. The absence of detectable silver nanoparticles was consistent with expectations from a physico-chemical view point. For the products tested, current USFDA guidance for evaluating migration from FCMs was applicable.     

Contents of Ag and other metals in food-contact plastics with nanosilver or Ag ion and their migration into food simulants

Six nanosilver-labelled products and five silver ion (Ag⁺)-labelled products were investigated to measure the migration of Ag from food-contact plastics, including nanosilver into various food simulants. The products were obtained in Japanese markets in 2012. Zinc (Zn), another major antimicrobial agent, and three harmful metals, cadmium (Cd), lead (Pb) and arsenic (As), were also examined. Ag and Zn were detected in all six nanosilver products at concentrations of 21–200 and 8.4–140 mg kg^?1, respectively. These metals were also detected in all five Ag⁺ products at the same level as nanosilver products. Cd, Pb and As were not detected in any sample. Migrations of Ag and Zn were highest in 4% acetic acid, but also observed in water and 20% ethanol. Big differences were not observed in the migration ratio between nanosilver products and Ag⁺ products. The ultrafiltration experiments suggested that the Ag that migrated from nanosilver products into 4% acetic acid was in its ionic form, while that into water and 20% ethanol was in its nanoparticle form.     

Postharvest Quality of Fresh-Cut Carrots Packaged in Plastic Films Containing Silver Nanoparticles

Active food packaging containing antimicrobial additive goes beyond traditional functions of packaging, once it can extend food shelf life maintaining its quality, safety and reducing postharvest losses by controlling food spoilage. Among several antimicrobial additives employed in polymeric films for packaging, metallic nanoparticles outstand due to its facility for synthesis, low-cost of production, and intense antimicrobial properties. In this work, extruded plain films of low-density polyethylene (LDPE) containing silver nanoparticles (AgNPs) embedded in SiO₂ and TiO₂ carriers (namely MS and MT, respectively) were produced and used as active packaging for maintaining the physicochemical and microbiological quality of carrots (Daucus Carota L. cv. Brasília). The neat (LDPE) and composite films containing MS and MT were characterized by scanning electron microscopy and permeability to oxygen and used for packaging fresh-cut sliced carrots stored at 10 °C for 10 days. After the storage time, the physicochemical properties of carrots were characterized, while the antimicrobial properties of films and AgNP migration were investigated. Our results revealed that both MT and MS packages showed antimicrobial activity even for films containing low concentration of AgNP. In addition, AgNP antimicrobial activity demonstrated to be carrier-dependent, once MT-LDPE showed improved performance compared to MS-LDPE. Regarding the physicochemical properties of packaged carrot, lower soluble solids and weight loss and higher levels of ascorbic acid were observed for carrots packaged with MT-LDPE films (compared to MS-LDPE), leading to a better postharvest quality conservation. Such differences observed in physicochemical properties of carrots are related to the distinct antimicrobial and film permeability properties for each composite film. In addition, under the conditions employed in this study, AgNP migration from the packages to fresh-cut carrot was not observed, which is highly desirable for food packaging safety, indicating the potential of such active packages for food preservation application.     

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.     

Antimicrobial activity of nanosilver-coated socks fabrics against foot pathogens

Nanotechnology can be used in engineering-desired textile attributes, such as fabric softness and durability in fibres, yarns and fabrics. Nanocoating the surface of socks is one approach to the production of highly active surfaces with UV blocking, antimicrobial and self-cleaning properties. Synthesis of silver nanoparticles in this project was carried out chemically by wet reduction method (Ag-chem) and biologically by using neem (Azadirachta indica) leaves (Ag-neem). The formation of silver nanoparticles was monitored by UV–visible spectroscopy, which revealed the surface plasmon resonance peak at 420?nm for Ag-chem and 430?nm for Ag-neem, and transmission electron microscopy, which showed nanoparticles of various shapes and sizes (～5–50?nm). Quantification of the prepared silver nanoparticles was done by atomic absorption spectroscopy, which revealed 0.044?M Ag⁺ and 0.042?M Ag⁺ ions in Ag-chem and Ag-neem, respectively. Coating of the socks fabrics (nylon and cotton) was carried out by exposing these fabrics to the prepared nanoparticle solutions on a gyratory shaker overnight. Antimicrobial activity of the Ag-chem and Ag-neem was carried out by performing minimum inhibitory concentration (MIC) and disc diffusion test against Sarcina lutea, an odour-producing organism, Klebsiella pnuemoniae, Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus and Candida albicans, organisms causing foot infections. P. aeruginosa and S. lutea were found to be most sensitive to either of the above preparations. Ag-chem was found to be more effective than Ag-neem. Nylon and cotton socks fabrics were coated with each of the above preparations. The antibacterial efficacy of the nanosilver-finished fabrics was checked by zone inhibition test, antibacterial test and wash fastness test. In both cases, coated nylon fabrics showed better antimicrobial activity than coated cotton fabrics. S. lutea and K. pneumoniae showed greater zones of inhibition than the other test organisms. Nylon fabric coated with Ag-chem and Ag-neem gave maximum reduction in viable count of all test organisms as compared to cotton fabrics. Higher reduction in the viable count of all test organisms was observed with Ag-chem-coated nylon fabrics. Thus, coating of the nylon socks fabric with silver nanoparticles can be used as an effective way to combat foot-borne pathogens and thereby reducing discomforts like foot odour, perspiration, complications due to diabetes, athlete’s foot, etc.     

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.     

Effects of food components on the antimicrobial activity of polypropylene surfaces containing silver ions (Ag+)

The aim of this study was to investigate the influence of food components on the antimicrobial properties of surfaces containing silver. The antimicrobial activity of a polypropylene compound with a zirconium phosphate–based ceramic ion exchange resin containing silver was investigated by comparing the surface count of bacteria on sample and reference surfaces. Different food components were added to the inocula to investigate their influence on the extent of antimicrobial activity in comparison with pure inoculum (Pseudomonas fluorescens in saline solution). In the experiments with pure inoculum, a marked reduction in bacterial counts on samples containing silver was observed (7.4 log₁₀ units). However, protein‐rich food strongly reduced or completely inhibited the antimicrobial activity of silver. Almost all other tested components from the carbohydrate or lipid group did not affect the antimicrobial activity. Overall, the effect and the risks of materials containing silver needs to be analysed individually for the respective application.     

Migration of silver from commercial plastic food containers and implications for consumer exposure assessment

Food storage containers with embedded silver as an antibacterial agent promise longer durability of food. For risk assessment the release of this silver into the stored food and resulting human exposure need to be known. For the purpose of exposure assessment, silver migration from commercial plastic containers with declared content of ‘nano-’ or ‘micro-silver’ into different food simulants (water, 10% ethanol, 3% acetic acid, olive oil) was quantitatively determined by ICP-MS and the form of the released silver was investigated. The highest migration of silver was observed for the acidic food simulant with 30 ng silver cm^?2 contact surface within 10 days at 20°C. In a second and third use cycle, migration dropped by a factor of up to 10, so that the maximum cumulated release over three use cycles was 34 ng cm^?2. The silver release over time was described using a power function and a numerical model that simulates Fickian diffusion through the plastic material. The released silver was found to be in ionic form, but also in the form of silver nanoparticles (around 12%). Consumer exposure to the total amount of silver released from the food containers is low in comparison with the background silver exposure of the general population, but since natural background concentrations are only known for ionic silver, the exposure to silver nanoparticles is not directly comparable with a safe background level.     

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.     

Preservation of aseptic conditions in absorbent pads by using silver nanotechnology

Silver nanoparticles have been formed in fluff pulp and nanostructured Lyocell fibres by immersion in silver nitrate, and a subsequent transformation of the adsorbed silver ions into elementary silver nanoparticles by physical (thermal/UV) or chemical (sodium borohydride) methods. Microscopy revealed that nanoparticles generated by physical methods were regular in shape and efficiently dispersed, while the chemical reduction produced highly aggregated nanoparticles. Nanoparticle size has been found relevant to guarantee high antimicrobial activity, being the samples with big aggregated silver nanoparticles almost inefficient. Indeed a satisfactory correlation between silver ion release and the antimicrobial efficiency against Escherichia coli and Staphylococcus aureus could be confirmed, and furthermore, the highest concentrations tested were efficient to reduce the microbial load in poultry exudates. This work demonstrates that especially designed absorbent materials could be optimised to preserve aseptic conditions during manipulation, leading to feasible applications of a silver based nanotechnology in food technology.     

Antioxidant migration resistance of SiOx layer in SiOx/PLA coated film

As novel materials for food contact packaging, inorganic silicon oxide (SiO_x) films are high barrier property materials that have been developed rapidly and have attracted the attention of many manufacturers. For the safe use of SiO_x films for food packaging it is vital to study the interaction between SiO_x layers and food contaminants, as well as the function of a SiO_x barrier layer in antioxidant migration resistance. In this study, we deposited a SiO_x layer on polylactic acid (PLA)-based films to prepare SiO_x/PLA coated films by plasma-enhanced chemical vapour deposition. Additionally, we compared PLA-based films and SiO_x/PLA coated films in terms of the migration of different antioxidants (e.g. t-butylhydroquinone [TBHQ], butylated hydroxyanisole [BHA], and butylated hydroxytoluene [BHT]) via specific migration experiments and then investigated the effects of a SiO_x layer on antioxidant migration under different conditions. The results indicate that antioxidant migration from SiO_x/PLA coated films is similar to that for PLA-based films: with increase of temperature, decrease of food simulant polarity, and increase of single-sided contact time, the antioxidant migration rate and amount in SiO_x/PLA coated films increase. The SiO_x barrier layer significantly reduced the amount of migration of antioxidants with small and similar molecular weights and similar physical and chemical properties, while the degree of migration blocking was not significantly different among the studied antioxidants. However, the migration was affected by temperature and food simulant. Depending on the food simulants considered, the migration amount in SiO_x/PLA coated films was reduced compared with that in PLA-based films by 42–46%, 44–47%, and 44–46% for TBHQ, BHA, and BHT, respectively.     

Nanosilver in dairy applications – Antimicrobial effects on Streptococcus thermophilus and chemical interactions

Milk spoilage continues to be a major problem. Incorporation of silver into milk packaging might solve this problem. We evaluated the antimicrobial and chemical effects of silver in milk. Antimicrobial experiments were performed by measuring milk acidification by Streptococcus thermophilus at temperatures of 43, 33 and 23 °C and concentrations of silver nanoparticles at 10, 50, 100 and 200 mg/L. Chemical interactions were investigated using potentiometric measurements. Ag⁺ interacted with milk constituents. Nanosilver was antimicrobially effective at all temperatures and at 100 mg/L. At least 5 mg/L are required by using AgNO₃. Practical use of silver for dairy applications is not expected, due to the required high silver concentrations.     

Hollow PET fibers containing silver particles as antibacterial materials

Silver ions can effectively kill bacteria due to their adsorption onto the negatively charged bacterial cell wall, thus deactivating cellular enzymes, disrupting membrane permeability, and ultimately leading to cell lysis and death. In this study, silver particles incorporated into hollow polyethylene terephthalate (PET) fibers are utilized as an antibacterial composition against the bacterium, Staphylococcus aureus. Also, a silver ion–bacterium model similar to the predator–prey model is established to analyze the inhibitory effect of silver ions on S. aureus. In contact with an aqueous solution, silver ions are released from hollow PET fibers into the solution. When a silver ion in an active medium is absorbed by a bacterium, the bacterium dies and the concentration of silver ions lowers in the medium. To keep the concentration of silver ions in the medium constant, another silver ion is released from the hollow fiber, making the silver ion–bacterium model much simpler to be solved analytically. This study shows that there is an optimal concentration of silver ions at which minimal cytotoxicity and maximal antibacterial efficacy can be achieved. To support this, experimental verification is also carried out in this study.     

A Review of Poly(Lactic Acid)‐Based Materials for Antimicrobial Packaging

Poly(lactic acid) (PLA) can be synthesized from renewable bio‐derived monomers and, as such, it is an alternative to conventional petroleum‐based polymers. Since PLA is a relatively new polymer, much effort has been directed toward its development in order to make it an acceptable and effective option to the more traditional petroleum‐based polymers. Commercially, PLA has received considerable attention in food packaging applications with a focus on films and coatings that are suitable for short shelf life and ready‐to‐eat food products. The potential for PLA to be used in active packaging has also been recognized by a number of researchers. This review focuses on the use of PLA in antimicrobial systems for food packaging applications and explores the engineering characteristics and antimicrobial activity of PLA films incorporated and/or coated with antimicrobial agents.     

Biodegradable polylactic acid polymer with nisin for use in antimicrobial food packaging

ABSTRACT:  Biodegradable polylactic acid (PLA) polymer was evaluated for its application as a material for antimicrobial food packaging. PLA films were incorporated with nisin to for control of foodborne pathogens. Antimicrobial activity of PLA/nisin films against Listeria monocytogenes , Escherichia coli O157:H7, and Salmonella Enteritidis were evaluated in culture media and liquid foods (orange juice and liquid egg white). Scanned electron micrograph and confocal laser microscopy revealed that nisin particles were evenly distributed in PLA polymer matrix on the surface and inside of the PLA/nisin films. PLA/nisin significantly inhibited growth of L . monocytogenes in culture medium and liquid egg white. The greatest inhibition occurred at 24 h when the cell counts of L. monocytogenes in the PLA/nisin samples were 4.5 log CFU/mL less than the controls. PLA/nisin reduced the cell population of E. coli O157:H7 in orange juice from 7.5 to 3.5 log at 72 h whereas the control remained at about 6 log CFU/mL. PLA/nisin treatment resulted in a 2 log reduction of S. Enteritidis in liquid egg white at 24 °C. After 21 d at 4 °C the S. Enteritidis population from PLA/nisin treated liquid egg white (3.5 log CFU/mL) was significantly less than the control (6.8 log CFU/mL). E. coli O157:H7 in orange juice was more sensitive to PLA/nisin treatments than in culture medium. The results of this research demonstrated the retention of nisin activity when incorporated into the PLA polymer and its antimicrobial effectiveness against foodborne pathogens. The combination of a biopolymer and natural bacteriocin has potential for use in antimicrobial food packaging.     

Assessment of the migration potential of nanosilver from nanoparticle-coated low-density polyethylene food packaging into food simulants

An experimental nanosilver-coated low-density polyethylene (LDPE) food packaging was incubated with food simulants using a conventional oven and tested for migration according to European Commission Regulation No. 10/2011. The commercial LDPE films were coated using a layer-by-layer (LbL) technique and three levels of silver (Ag) precursor concentration (0.5%, 2% and 5% silver nitrate (AgNO₃), respectively) were used to attach antimicrobial Ag. The experimental migration study conditions (time, temperature and food simulant) under conventional oven heating (10 days at 60°C, 2 h at 70°C, 2 h at 60°C or 10 days at 70°C) were chosen to simulate the worst-case storage period of over 6 months. In addition, migration was quantified under microwave heating. The total Ag migrant levels in the food simulants were quantified by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Mean migration levels obtained by ICP-AES for oven heating were in the range 0.01–1.75 mg l^?1. Migration observed for microwave heating was found to be significantly higher when compared with oven heating for similar temperatures (100°C) and identical exposure times (2 min). In each of the packaging materials and food simulants tested, the presence of nanoparticles (NPs) was confirmed by scanning electron microscopy (SEM). On inspection of the migration observed under conventional oven heating, an important finding was the significant reduction in migration resulting from the increased Ag precursor concentration used to attach Ag on the LDPE LbL-coated films. This observation merits further investigation into the LbL coating process used, as it suggests potential for process modifications to reduce migration. In turn, any reduction in NP migration below regulatory limits could greatly support the antimicrobial silver nanoparticle (AgNP)-LDPE LbL-coated films being used as a food packaging material.