Active Packaging Coatings

Bioactive Characterization of Packaging Foils Coated by Chitosan and Polyphenol Colloidal Formulations

Polypropylene (PP) and polyethylene (PE) foils, previously activated by ultraviolet (UV)/ozone, were functionalized using chitosan-extract nanoparticle dispersions. A solution of macromolecular chitosan was applied onto foils as a first layer, followed by the deposition of various extracts encapsulated into chitosan nanoparticles, which were attached as an upper layer. Functionalized foils were analyzed from a bioactive point of view, i.e., regarding antimicrobial and antioxidant activity. Desorption kinetics were also studied. Moreover, barrier properties were examined, as the most important parameter influencing antimicrobial and antioxidant activity. Finally, all these properties were correlated with different surface parameters, determined previously, in order to understand if there is any direct correlation between surface elemental composition, surface charge, contact angle, or morphology and a specific bioactive property. It was shown that great bioactive properties were introduced due to the additive effect of antimicrobial chitosan and antioxidative plant extracts. Moreover, oxygen permeability decreased significantly, and the migration of polyphenols and chitosan from the foil surface was below the OML (overall migration limit), which is very important for food industry applications. Furthermore, surface properties of foils influence to some extent the desired bioactivity.

Reactive Extrusion of Nonmigratory Antioxidant Poly(lactic acid) Packaging

Reactive extrusion of bio-derived active packaging offers a new approach to address converging concerns over environmental contamination and food waste. Herein, metal-chelating nitrilotriacetic acid (NTA) ligands were grafted onto poly(lactic acid) (PLA) by reactive extrusion to produce metal-chelating PLA (PLA-g-NTA). Radical grafting was confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy with the introduction of secondary alkyl stretches (2919 and 2860 cm^-1) and by X-ray photoelectron spectroscopy (XPS) with an increase in the atomic percentage of nitrogen. Compared to films prepared from native, granular PLA (gPLA), PLA-g-NTA films had lower contact angles and hysteresis values (86.35° ± 2.49 and 31.89° ± 2.27 to 79.91° ± 1.58 and 21.79° ± 1.72, respectively), supporting the surface orientation of the NTA ligands. The PLA-g-NTA films exhibited a significant antioxidant character with a radical scavenging capacity of 0.675 ± 0.026 nmol Trolox_(eq)/cm² and an iron chelation capacity of 54.09 ± 9.36 nmol/cm². PLA-g-NTA films delayed ascorbic acid degradation, retaining ∼45% ascorbic acid over the 9-day study compared to <20% for control PLA. This research makes significant advances in translating active packaging technologies to bio-derived materials using scalable, commercially translatable synthesis methods.

Efficiency of Novel Antimicrobial Coating Based on Iron Nanoparticles for Dairy Products’ Packaging

The main function of food packaging is to maintain food’s quality and safety. The use of active packaging, including antimicrobial materials, can significantly extend the shelf life of food. Many of these packaging solutions are based on the application of polymer films containing metal nanoparticles (e.g., Ag, Au, Cu) or metal oxides (e.g., TiO2, ZnO, MgO). However, the use of iron nanoparticles is rarely mentioned. In the study, polylactide (PLA) films containing zero-valent iron (ZVI) were made by casting method. Pure PLA films and PLA films with the addition of Fe2O3 were used as comparative materials. The composition and structure of ZVI/PLA films were evaluated with scanning electron microscopy. The XRD spectra performed on ZVI/PLA films confirmed the presence of iron in the packaging material and revealed their oxide form (Fe2O3). The addition of zero-valent iron in the concentration 1%, 3%, or 5% resulted in the formation of crystallographic planes measuring 40.8, 33.6, and 28.6 nm, respectively. The color and gloss of the films, and their antimicrobial activity against bacteria (Bacillus subtilis, Escherichia coli, Staphylococcus epidermidis) and fungi (Geotrichum candidum, Rhodotorula rubra) were also examined. The PLA films with addition of 3% of ZVI (w/w) inhibited the growth of all tested organisms in contrast to PLA and PLA/Fe2O3 films. The addition of ZVI to polymer matrix caused changes in its appearance and optical properties. The ZVI/PLA coating used on polyolefin film allowed to extend the shelf life of goat cheese packed in examined material to 6 weeks. Considering the antimicrobial properties of the ZVI/PLA films and PLA biodegradability the obtained material can be successfully applied in the food industry.

Response of Optically Transparent pH Sensing Films to Temperature and Temperature Variations

There are numerous applications for thin films based chemical pH sensors, in such areas as biomedical, military, environmental, food, and consumer products. pH sensitive films fabricated through the ionic self-assembled monolayers technique were made of polyelectrolyte polyallylamine hydrochloride and the water-soluble organic dye molecule Direct Yellow 4. The films were monitored in various environmental conditions and for selected periods, at temperatures varying between −13.7 and 46.2 °C. Absorbance measurements and atomic force microscopy performed before and after thermal treatment indicate that for optimized thickness and composition the films maintain their functionality and are not affected by long-term exposure at these temperatures.

PET and Active Coating Based on a LDH Nanofiller Hosting p-Hydroxybenzoate and Food-Grade Zeolites: Evaluation of Antimicrobial Activity of Packaging and Shelf Life of Red Meat

Layered double hydroxide (LDH) nanofillers were considered as hosts of p-hydroxybenzoate as an antimicrobial molecule for active coating. A food grade resin with LDH-p-hydroxybenzoate and two different types of food grade zeolites was used to prepare active coatings for Polyethylene terephthalate (PET) trays. The release kinetics of the active molecule were followed using UV spectrophotometry and the experimental results were analyzed with the Gallagher-Corrigan model. The thermal properties of the coating mixtures and the PET coating were analyzed and found to be dependent on the coating's composition. On the basis of CO2 transmission rate and off-odors tests, the best coating composition was selected. Global migration in ethanol (10% v/v), acetic acid (3% w/v), and vegetable oil, and specific migration of p-hydroxybenzoic acid revealed the suitability of the material for food contact. Antimicrobial tests on the packaging demonstrated a good inhibition against Salmonella spp. and Campylobacter jejuni. Red meat was packed into the selected active materials and results were compared to uncoated PET packaging. Color tests (browning of the meat) and analysis of Enterobacteriaceae spp. and total viable count evolution up to 10 days of storage demonstrated the capability of the considered active packaging in prolonging the shelf life of red meat.

Nanocomposite bilayers based on poly(vinyl alcohol) and chitosan functionalized with gallic acid

The development of active bilayer systems is a novel strategy for the application of active packaging to maintain or prolong the shelf-life of food products. A bilayer system was assembled in situ into a thermocompression unit through a two-step procedure. One of the layers was obtained by a casting process and consisted of a chitosan-based nanocomposite functionalized with gallic acid (GA); the other was shaped by the spreading of polyvinyl alcohol solution on the nanocomposite. Then, a stage of thermocompression formed the bilayer system. In this way, a feasible material with water vapor and oxygen barrier as well as UV barrier properties due to the presence of GA was designed by a thermocompression process which can be industrially scaled representing a technological progress. The formation of the bilayers was corroborated by SEM allowing discerning between both, the PVA layer and the nanocomposite layer. On the other hand, the corroboration of interactions between the layers of the system was carried out through ATR-FTIR and DSC analysis. The system was used as packaging of a food susceptible to undergo oxidation such as walnut flour, generating a delay in the formation of hydroperoxides and secondary oxidation compounds compared with a synthetic container. These results indicated that bilayer materials can be useful for the conservation of this type of foods.

Photocurable coatings prepared by emulsion polymerization present chelating properties

Herein, we present a method to synthesize a photocurable metal chelating copolymer coating via emulsion polymerization to enable a facile coat/cure preparation of metal chelating materials. The copolymer coating was a poly(n-butyl acrylate) based polymer (79 mol %) synthesized by emulsion polymerization, with iminodiacetic acid (2 mol %) and benzophenone moieties (19 mol %) to impart metal chelating and photocrosslinking properties, respectively. The copolymer was applied onto polypropylene films and was photocured (365 nm, 225 mW/cm², 180 s) to produce metal chelating film. The resulting metal chelating film had activity towards Fe³⁺ by chelating 10.9 ± 1.9 nmol/cm², 47.9 ± 5.3 nmol/cm², and 156.0 ± 13.8 nmol/cm² of Fe³⁺ at pH 3.0, pH 4.0, and pH 5.0, respectively. The metal chelating film controlled transition metal induced ascorbic acid degradation by extending half-life of ascorbic acid degradation from 6 days to 20 days at pH 3.0, and from 3 days to 6 days at pH 5.0, demonstrating its potential as an antioxidant active packaging material. Despite the introduction of polar iminodiacetic acid chelating moieties, the poly(n-butyl acrylate) based coatings retained low surface energies (24.0 mN/m) necessary to mitigate fouling and enable product release in packaging applications. This work overcomes a major knowledge gap in the area of functional coatings, by demonstrating a method by which critical properties such as control of surface energy, retention of mechanical properties, and scalability are integrated into the structure of a functional coating. The photocurable polymer coatings as reported here enable scalable production of active materials with metal chelating functionality, with applications in water treatment, trace metal detection, protein purification, and active packaging.

Facile Preparation of Epoxide-Functionalized Surfaces via Photocurable Copolymer Coatings and Subsequent Immobilization of Iminodiacetic Acids

Herein, we report a simple coat/cure preparation of epoxide-functionalized surfaces using a photocurable copolymer technology. The photocurable copolymer, poly(glycidyl methacrylate- co-butyl acrylate- co-4-benzoylphenyl methacrylate) (GBB), was synthesized by single electron transfer-living radical polymerization (SET-LRP). The epoxide content in the copolymer was tuned by controlling the content of glycidyl methacrylate. Three copolymers, GBB(1), GBB(2), and GBB(3), with epoxide contents of 22, 63, and 91 mol %, respectively, were cast onto polypropylene films and photocured by UV-light exposure. Subsequently, iminodiacetic acids (IDA) were immobilized onto the GBB-coated materials via a ring-opening reaction. The IDA-functionalized coatings GBB(1)-IDA, GBB(2)-IDA, and GBB(3)-IDA presented IDA contents of 1.47 ± 0.08, 18.67 ± 1.46, and 49.05 ± 2.88 nmol/cm², respectively, which increased as the epoxide content increased. The IDA-functionalized GBB coatings exhibited metal chelating capability toward transition metal ions (e.g., iron and copper). The reported photocurable copolymer technology offers a facile and tunable preparation of epoxide-functionalized surfaces, with potential extended applications in biopatterning, active packaging, and nanotechnology.

Polymeric Nanocomposites and Nanocoatings for Food Packaging: A Review

Special properties of the polymeric nanomaterials (nanoscale size, large surface area to mass ratio and high reactivity individualize them in food packaging materials. They can be processed in precisely engineered materials with multifunctional and bioactive activity. This review offers a general view on polymeric nanocomposites and nanocoatings including classification, preparation methods, properties and short methodology of characterization, applications, selected types of them used in food packaging field and their antimicrobial, antioxidant, biological, biocatalyst and so forth, functions.

Enzyme Crystals and Hydrogel Composite Membranes as New Active Food Packaging Material

The great antimicrobial and antioxidant potential of enzymes makes them prone to be used as active packaging materials to preserve food from contamination or degradation. Major drawbacks are connected to the use of enzymes freely dispersed in solution, due to reduced protein stability. The immobilization of enzymes on solid supports to create biocatalytic interfaces has instead been proven to increase their stability and efficiency. In this work, it is shown that enzymes crystallized on hydrogel composite membranes (HCMs) can exert an effective antimicrobial action, thus making the composite membrane and crystals biofilm a potential active substrate for food packaging applications. The antimicrobial hen egg white lysozyme is crystallized on the surface of the hydrogel layer of HCMs, and its activity is determined by measuring the decrease in absorbance of Micrococcus lysodeikticus culture incubated with the specimen. The overall catalytic efficiency of the antimicrobial HCMs increases by a factor of 2 compared to the pure enzyme dissolved in solution at the same quantity. Because the enzyme in crystalline form is present in higher concentration and purity than in the solution, both its overall catalytic efficiency and antimicrobial action increase. Moreover, the hydrogel environment allows a better protein stabilization and retention during crystals dissolution.

Atom Transfer Radical Polymerization Functionalization on Polypropylene Films for Immobilizing Active Compounds

This work proposes the surface chemical modification of polypropylene films (PP) by atom transfer radical polymerization (ATRP) using glycidyl methacrylate (GMA) as the graft monomer. At a later stage, the epoxy groups of PP-g-PGMA were used for covalent binding of glucose oxidase (GOD) to obtain an active material (PP-g-PGMA-GOD) with 9.38 ± 0.06 mg cm−2 of enzyme bonded on the surface of PP. Preliminary microbiological studies have shown that this methodology of covalent binding of the enzyme onto the PP surface allowed its activity to be maintained. Therefore, this advantage would give to PP-g-PGMA-GOD films a potential use as an active packaging material if further specific studies on their antimicrobial properties can be verified.

Alizarin Red S-Confined Layer-By-Layer Films as Redox-Active Coatings on Electrodes for the Voltammetric Determination of L-Dopa

The preparation of redox-active coatings is a key step in fabricating electrochemical biosensors. To this goal, a variety of coating materials have been used in combination with redox-active compounds. In this study, alizarin red S (ARS) was confined in layer-by-layer (LbL) films composed of poly(ethyleneimine) (PEI) and carboxymethylcellulose (CMC) to study the redox properties. A gold (Au) disc electrode coated with PEI/CMC LbL film was immersed in an ARS solution to uptake ARS into the film. ARS was successfully confined in the LbL film through electrostatic interactions. The cyclic voltammogram (CV) of ARS-confined PEI/CMC film-coated electrodes thus prepared exhibited redox waves in the potential range from -0.5 to -0.7 V originating from 9,10-anthraquinone moiety in ARS, demonstrating that ARS preserves its redox activity in the LbL film. An additional oxidation peak appeared around -0.4 V in the CV recorded in the solution containing phenylboronic acid (PBA), due to the formation of a boronate ester of ARS (ARS-PBA) in the film. The oxidation peak current at -0.4 V decreased upon addition of 3,4-dihydroxyphenylalanine (L-dopa) to the solution. Thus, the results suggest a potential use of the ARS-confined PEI/CMC films for constructing voltammetric sensors for L-dopa.

Retaining Oxidative Stability of Emulsified Foods by Novel Nonmigratory Polyphenol Coated Active Packaging

Oxidation causes lipid rancidity, discoloration, and nutrient degradation that decrease shelf life of packaged foods. Synthetic additives are effective oxidation inhibitors, but are undesirable to consumers who prefer "clean" label products. The aim of this study was to improve oxidative stability of emulsified foods by a novel nonmigratory polyphenol coated active packaging. Polyphenol coatings were applied to chitosan functionalized polypropylene (PP) by laccase assisted polymerization of catechol and catechin. Polyphenol coated PP exhibited both metal chelating (39.3 ± 2.5 nmol Fe(3+) cm(-2), pH 4.0) and radical scavenging (up to 52.9 ± 1.8 nmol Trolox eq cm(-2)) capacity, resulting in dual antioxidant functionality to inhibit lipid oxidation and lycopene degradation in emulsions. Nonmigratory polyphenol coated PP inhibited ferric iron promoted degradation better than soluble chelators, potentially by partitioning iron from the emulsion droplet interface. This work demonstrates that polyphenol coatings can be designed for advanced material chemistry solutions in active food packaging.

Correction: Bastarrachea, L.J., et al. Active Packaging Coatings. Coatings 2015, 5, 771–791

The authors wish to make the following correction to this paper [1]:[...]

Development of Antibacterial Composite Films Based on Isotactic Polypropylene and Coated ZnO Particles for Active Food Packaging

This study was aimed at developing new films based on isotactic polypropylene (iPP) for food packaging applications using zinc oxide (ZnO) with submicron dimension particles obtained by spray pyrolysis. To improve compatibility with iPP, the ZnO particles were coated with stearic acid (ZnOc). Composites based on iPP with 2 wt % and 5 wt % of ZnOc were prepared in a twin-screw extruder and then filmed by a calender. The effect of ZnOc on the properties of iPP were assessed and compared with those obtained in previous study on iPP/ZnO and iPP/iPPgMA/ZnO. For all composites, a homogeneous distribution and dispersion of ZnOc was obtained indicating that the coating with stearic acid of the ZnO particles reduces the surface polarity mismatch between iPP and ZnO. The iPP/ZnOc composite films have relevant antibacterial properties with respect to E. coli, higher thermal stability and improved mechanical and impact properties than the pure polymer and the composites iPP/ZnO and iPP/iPPgMA/ZnO. This study demonstrated that iPP/ZnOc films are suitable materials for potential application in the active packaging field.