Overview of Food Antimicrobial Packaging

Abstract

Acutely due to awareness that food products are highly vulnerable to microbial contamination, the food industry constantly tries to uncover new methods for the preservation of their products in order to guarantee their goods and processes continue to offer the highest quality and uphold safety standards throughout the production, storage, and distribution chain. Antimicrobial food packaging can play an important role in food shelf-life extension through the inhibition of microorganism growth present on the surface of food products. Antimicrobial packaging materials containing active substances incorporated into a polymer matrix or as surface coatings have begun to receive more attention for their use as antimicrobial control agents in food packaging systems. The most commonly used packaging materials are paper and plastics. However, from the ecological point of view, biopolymer-based materials have recently garnered more attention in the development of antimicrobial packaging as an alternative, due to their nontoxic biodegradability. In addition, the ongoing global spread of the pandemic caused by the SARS-CoV-2 has led to a preference for fresh food packaged in single-use food coverings. In order to address customer concerns and safeguard their health, the packaging industry could implement additional health safety measures, such as active packaging with antiviral properties.

1. Introduction

Packaging, as an essential component of both the food manufacturing process and the entire food supply chain, plays an essential role in the safeguarding of food products [1, 2]. A fundamental and vital role of food packaging is to preserve food quality and safety, reduce food waste and foodborne diseases, and limit the negative impact of uneaten food on the environment and the global economy [2]. It should be noted that the packaging itself is a coordinated system for product safety, as well as being an efficient and practical method for shipment, marketing, storage, retailing, and consumption to increase sales and profits for producers and retailers and maintain food quality for consumers. Packaging must be able to meet all quality requirements while being cost-effective and efficient. It is important to permit brands to form and standardize packaging and also to create effective advertising and make a large-scale distribution and global retailing possible [1]. However, it should not be forgotten that food packaging systems must primarily protect food from environmental contamination, shock, outside odor, dust, physical damage, and mechanical force, as well as temperature, moisture, gas release, light, microorganism contamination, water and water vapor, in addition to other external environmental factors during processing, transport/distribution, storage, and marketing. It should maintain the basic attributes of food, such as texture, color, taste, and quality of the food products, as well as microbial purity resulting from the increase in food shelf-life, and subsequently the reduction of food waste. The main causes of food deterioration, such as microbial spoilage or oxidation, may be avoided by the application of the appropriate packaging systems [3, 4, 5]. The oxidation of food products may result in decreased nutritional value, energy content, flavor, and color, thus decreasing the quality of food. On the other hand, microbial spoilage might not only result in a decrease in food quality [3, 4]. Foodborne diseases through the consumption of food products containing pathogenic bacteria or fungi can contribute to serious health issues or even the death of consumers [1, 3]. Fresh food and animal-originated food products are mostly contaminated by bacteria [3, 6]. Most frequently health issues are caused by pathogenic bacteria, such as Salmonella spp., Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, Clostridium spp., and Campylobacter jejuni [3, 7]. Filamentous fungi are also considered a severe pathogen in food products, due to their ability to penetrate and break down food using extracellular enzymes [1]. Vegetables, fruits, and grain crops are vulnerable to fungal strain contamination, mostly from Penicillium spp., Aspergillus spp., Botrytis spp., Sclerotinia spp., Alternaria spp., Fusarium spp., Rhizoctonia spp., Geotrichum spp., Phytophthora spp., and Pythium spp. [1, 8]. To avoid food oxidation or pathogen entry and any growth inside food products with extended shelf life during their storage, various active packaging systems can be used [1, 3, 4].

1.1 Packaging materials covered with active coatings

The modification of various polymers, including biopolymers, to obtain antimicrobial packaging that mainly includes polymer blending with bioactive components. Unfortunately, the negative effects of thermal processing on active agents during their incorporation into the polymer matrix can be seen. One solution to this problem is the coating of the polymer packaging surface. Fabrication of one-layer, bi-layer, tri-layer, and/or multilayer films through the use of a surface coating/covering technology is a promising strategy to improve the mechanical, barrier, or antimicrobial properties of traditional packaging materials for food packaging. Moreover, the surface coating method is more conducive to the migration of active substances and thus effectively protects the product [9, 10]. In the case of antimicrobial packaging, two important components, namely a polymer-based coating carrier, and an antimicrobial agent are very important. Antimicrobial coatings use many biobased carriers, such as carbohydrates, proteins, and lipids. Carboxymethyl cellulose (CMC) is a water-soluble derivative of cellulose that has the ability to form coatings and films in order to obtain an antimicrobial coating which may lead to increased food shelf-life. CMC is a linear polymer, it is long-chain and high molecular weight, make it a suitable polymer as a coating [11]. Starch as an inexpensive biodegradable polysaccharide is also used as a coating carrier, due to its renewable, nontoxic, multifunctional, biodegradable, and film-forming properties [12]. Among coating carriers, polysaccharides, such as pullulan, cellulose, or chitosan and its derivatives, are very attractive to provide barrier properties. Additionally, chitosan has been found to be stable and effective against a wide spectrum of microorganisms, where its antimicrobial activity depends on the concentration, molecular weight, and degree of deacetylation. Chitosan solutions in various organic acids may be prepared so that on drying, they form clear, flexible, and tough films/coatings [9, 13]. Mao et al. [9] noted that polymeric coatings based on caseinate, chitosan (CS), and polydopamine were used as carriers to obtain antibacterial packaging. As active agents, natural plant polyphenols and essential oil were used, and the effectiveness of these packaging materials was observed. Poly(vinyl alcohol) (PVA) and blends of PVA with starch have also been used as coating carriers due to their good film-forming and other functional properties, such as mechanical strength, water-solubility, oxygen barrier properties, transparency, and degradability [9]. In contrast to biopolymer and polymer films, paper-based packaging materials are mainly composed of fibrous cellulose pulp. This is a hydrophilic and porous material with a low barrier against water vapor and oxygen in comparison to plastic-based packaging materials. To improve these properties, covering a surface with coatings is necessary. Hydrophobic coating materials, such as paraffin wax and poly(butylene terephthalate) (PBAT), are considered promising candidates as biodegradable coating materials, due to their full biodegradability, thermoplasticity, low water vapor permeability, high flexibility, and good processability. The incorporation of active agents, such as antimicrobials and antioxidants, can make the coatings more valuable. Antimicrobial, active coating materials are usually prepared by blending or mixing antimicrobial substances with biopolymeric base carriers [14]. Recently, nanocellulose-based coatings are also used in food packaging due to their unique properties, such as biodegradability, mechanical properties, transparency, and antimicrobial activity against foodborne pathogens, including E. coli, S. aureus, S. Typhimurium, and L. monocytogenes [15, 16, 17]. The covering of polymer films or paper with functional bio-based, active coatings is a promising approach to improve packaging characteristics (e.g., antimicrobial, water vapor, and gas barrier properties) without compromising the biodegradable and/or recyclable features of packaging materials. The active coatings may demonstrate their effectiveness as antimicrobial packaging [11, 15, 16, 17]. In order to prepare antimicrobial coatings using the selected coating carriers, several categories of antimicrobial compounds, (described below in the next section) can be used [11].

1.2 Antimicrobial agents as additives to active packaging materials

Natural antimicrobial agents/compounds refer to a class of substances extracted from plants and animals or produced by microorganisms. These active agents may perform antagonistic actions against bacteria, viruses, yeast, or molds [18]. They also show anti-insect and antioxidant activity [19]. According to their biological origin, they can be divided into three categories: plant-derived antimicrobial agents, animal-derived antimicrobial agents, and microbial-derived natural antimicrobial agents. The food industry has used typically mainly chemical preservatives, such as hydrogen peroxide, sorbate, sorbic acid, benzoate, benzoic acid, and nitrite, to inhibit the growth of microorganisms responsible for food spoilage. Commercial preservatives may extend the shelf-life of food products; however, they may have unfavorable effects on the sensory properties of food [18, 20]. In order to extend the shelf-life of food and reduce health hazards, natural antimicrobial compounds, such as essential oils, propolis, lactoferrin, glucose oxidase enzyme bacteriocins, and probiotics extracted from animals, plants or produced by microorganisms could replace typical chemical preservatives. They could be used by the food packaging industry due to their nontoxic character [18]. Essential oils (EOs) play an important role in the design of antimicrobial packaging materials, as they exhibit a high and specific antimicrobial efficacy against a broad range of foodborne pathogens [3]. EOs are extracted from leaves, bark, flowers, and seeds of aromatic plants and are “generally recognized as safe,” (GRAS) [19]. Eos, such as thyme, clove, cinnamon and tea tree, peppermint, oregano, lemongrass, and citronella, are plant-derived compounds that exhibit promising inhibitory effects [3, 18, 21]. EOs from the Myrtaceae family such as cloves, eucalyptus, galbanum, thyme, and tea tree contain eugenol and terpinen-4-ol as major bioactive components. It has been reported that these active agents offer antifungal effects. The results indicate that they inhibit glycolysis, which in turn influences cell energy metabolism, therefore disturbing the normal physiological activity of fungal pathogens [21]. According to several studies, EOs from Lauraceae and Lamiaceae (e.g., thyme, rosemary, oregano, cinnamon, etc.), exhibit essential antibacterial activities against foodborne pathogens and are generally rich in phenolic compounds, such as carvacrol, thymol, cinnamaldehyde, or eugenol [20]. Typically, the antibacterial mechanism is based on chemical interaction with the bacterial membrane and mitochondria leading to altering of their permeability, destroying their structural order, resulting in a massive loss of cell contents, important ions and molecules, and eventually leading to the death of the cell [18, 20, 21]. Moreover, many studies have demonstrated that the minor components of EOs play an outstanding role in the antimicrobial activity of essential oil, probably by a synergistic effect with the other EO components. One known example is the synergistic interaction between p-cymene and carvacrol, while p-cymene barely inhibits bacterial cell growth. On the other hand, carvacrol itself has a proven antibacterial effect against a wide range of microorganisms. It has been shown that the growth of microorganisms was significantly inhibited by a mixture of p-cymene and carvacrol. Interestingly, this activity was significantly lower when each terpene acts separately on bacteria growth [20, 22]. To summarize, at present, according to their high antimicrobial activity, they are mainly essential plant oils that act as antimicrobial and antioxidant compounds and they are widely used in smart or bioactive packaging materials to prevent the surface growth of microorganisms in foods [18, 23]. Natural antimicrobial agents can be extracted from plants, such as black currant, apple, pomegranate, grape, and quince, as well as chokeberry, bilberry, raspberry, mulberry, blueberry, yerba mate, green tea, sour cherry, walnut, rosemary, thyme, cinnamon, oregano, cumin, and many others. Plant extracts contain a wide range of bioactive components that include, polyphenols, iridoids, amides, saponins, alkaloids, and glycosides, as well as tannins, terpenoids, and quinones, which all have been reported to have a broad spectrum of antimicrobial properties. [18, 24, 25, 26, 27]. The generic and quantitative contents of active compounds in plants vary widely. There are many factors that influence the composition and concentration of the active substances in plants and plant extracts, such as the organ, cultivar, and many various growth conditions, including weather. These factors all have a significant influence on the antimicrobial effect of the plant extracts [26, 27]. There are three main antimicrobial action mechanisms by plant extracts: (a) the inhibition of cytoplasmic membrane function (the destruction of the cell membrane and membrane proteins and causing damage to the cell wall of the microorganisms); (b) inhibition of nucleic acid synthesis (extracts may suppress DNA synthesis by inhibiting DNA gyrase activity); (c) inhibition of energy metabolism (extracts can inhibit ATP synthesis). Finally, plant extracts may influence biofilm formation by influencing the quorum sensing mechanism, pigment production, and bacteria swarming motility, as well as altering the structure of the biofilm itself. Although active compounds from extracts can have an inhibitory effect at higher concentrations, in the case of lower concentrations they may have a stimulatory effect, indicating a bacterial defense mechanism [18, 26, 27]. Due to strong antimicrobial and antioxidant properties, plant extracts rich in active compounds, such as polyphenols, can be used within the food industry as natural preservatives and limit the nowadays use of chemical preservatives. They can also be used within the food packaging industry to extend the shelf life of food products by inhibiting microorganism growth and spoilage processes [18, 26, 27]. Antimicrobial peptides (AMPs) can be synthesized artificially in the laboratory or produced by bacteria [28]. Antimicrobial peptides are mostly composed of 12 ~ 60 amino acids that offer antimicrobial activity and participate in the host defense system [18, 28]. AMPs may be synthesized via three main methods: enzymatic synthesis, chemical synthesis, and biosynthesis, using a DNA recombinant technique. Among these methods, chemical synthesis is very common and has attracted increasing attention in the food packaging industry. AMPs obtained from bacteria are known as bacteriocins [28]. These AMPs can offer broad activity to directly inhibit the growth of yeasts, molds, bacteria, viruses, or even cancer cells [18, 28]. Typically, so-called antibacterial peptides (ABPs) have been mainly found to be active against bacteria. They have a clear influence on the bacterial cell membrane and create pores on their surface, resulting in the leakage of the intracellular matrix. They may also penetrate the cell membrane and interact with intracellular structures and disturb many activities including DNA/RNA or protein synthesis, resulting in bacterial cell death. ABPs are mainly positively charged molecules and they exhibit a high ratio of hydrophobic amino acids, allowing them to selectively bind to negatively charged bacterial membranes. The action mechanism of ABPs leads to the perforation of the cell membranes and their death [18, 29]. This is quite different from the bactericidal mechanism of antibiotics and does not lead to the microorganism becoming resistant. Furthermore, AMPs do not easily bind to mammalian cell membranes, which finally could be very harmful. It should be emphasized that antimicrobial peptides generally do not have any toxic side effects, though some have antioxidant functions and have been seen to scavenge free radicals. Lysostaphin and nisin are good examples of bactericidal peptides that suppress the growth of gram-positive bacteria. Antifungal peptides (AFPs) also function as antimicrobial proteins. They interact with the cell membrane, resulting in the disruption and finally death of the cell. Good examples of AFPs are echinocandin, defensin, and heliomycin [28]. As emphasized in the work of Ramos [30], innovative solutions have been proposed to improve the structural and functional properties of biopolymer-based packaging materials, including the incorporation of low amounts of specific nanoparticles (NPs) devoid of any relevant alteration of their migration to ensure their suitability for their application in food packaging. The authors stressed that the use of metallic-based nanoparticles (NPs), rather than antimicrobial organic agents, offered some advantages, such as high antimicrobial activity, lack of negative influence on food sensory properties, and compatibility with harsh polymer processing conditions, making NPs highly suitable for food spoilage control. Many nanomaterials have been used for food packaging, such as silver NPs, copper NPs, zinc oxide NPs, and titanium dioxide NPs, as well as silicon dioxide NPs or mixtures of antimicrobial agents containing NPs. Several studies have confirmed that Ag-NPs, ZnO-NPs, and TiO2-NPs are often used in the packaging industry as antimicrobial agents [4, 30, 31, 32, 33, 34]. Ag-NPs were found to exhibit antioxidant activity and offer antibacterial effects against gram-positive bacteria, such as S. aureus, including methicillin-resistant S. aureus (MRSA), gram-negative E. coli, and Pseudomonas aeruginosa [35]. It has been shown that nano-biocomposite films based on PLA with modified cellulose nanocrystals (s-CNC) and Ag-NPs demonstrated high antimicrobial activity against E. coli and S. aureus. These materials showing homogeneous Ag dispersion in the polymer matrix, while also not affecting the PLA transparency, showed a significant improvement in barrier properties and antimicrobial activity [36, 37]. One should stress that consideration regarding human safety, as well as the environmental effects of packaging materials containing Ag-NPs in direct contact with food, have led several studies to report that these types of substances could be used for food preservation, due to their quality and safety [30, 36, 37]. The authors of several studies demonstrated that Ag nanoparticles migration levels were significantly below the legislative migration limits in Europe set by EU Regulation No. 10/2011 (for plastic materials intended to come into contact with food), such as in PLA nanocomposites and in poly(vinyl chloride) (PVC) [30, 38, 39, 40]. One of the most attractive nanoparticles that could be used in the packaging industry is nanosized ZnO. ZnO-NPs with unique morphologies, such as nanohelix and nanorings, may be easily synthesized and are cost-effective [32]. These nanoparticles have been explored as antimicrobial substances, used in antimicrobial food packaging as one of five various zinc compounds, which are regarded as being safe (GRAS) by the United States food and drug administration (USFDA, 21CFR182.8991) [41, 42, 43]. It was reported [32] that ZnO-NPs were highly reactive and induced reactive oxygen species (ROS), which causes single-stranded DNA breaks at a relatively low concentration of 10 mg/ml. Due to their high activity, ZnO nanoparticles offered a broad bactericidal effect on gram-positive and gram-negative bacteria and bacterial spores that typically are resistant to high pressure and high temperature [44, 45, 46] as well as yeasts and molds (Noshirvani et al. 2017). An additional advantage of ZnO-NPs is their UV-blocking properties [32]. The application of nanoparticles can improve the UV-shielding of all respective packaging film materials [47, 48, 49]. TiO2 nanoparticles have been reported by several authors [33, 50] to exhibit antimicrobial activity when exposed to UV light by generating reactive oxygen and hydroxyl radical (OH•) species (ROS) on its surface, resulting in the oxidation of the polyunsaturated phospholipids of microorganism cell membranes. As a consequence, the microorganism was inactivated. TiO2 nanoparticles have been used to inactivate a wide spectrum of microorganisms, such as E. coli, P. aeruginosa, Enterococcus faecalis, Cyanobacteria, Lactobacillus helveticus, Legionella pneumophila, Clostridium perfringens, Salmonella enterica Choleraesuis, Vibrio parahaemolyticus and L. monocytogenes [50]. The process of microorganism species inhibition by CuO-NPs was influenced by the concentration and size of nanoparticles. The CuO-NPs were confirmed to be active against gram-negative and gram-positive bacteria by transiting the microorganism cell membrane and then destroying their enzymes. The antifungal action of CoO-NPs was also observed. It should be mentioned that copper is very important in the case of active packaging because of its high activity against a wide spectrum of microorganisms. When copper ions are attached to a microbial cell they immediately donate and accept electrons, as a result, they show increased redox ability and the capability to inactivate the cell components and kill them [51].

1.3 Active packaging

Food packaging materials are very important in the food industry. The packaging material should isolate and preserve food from the external environment. It must be a nontoxic and impermeable physical barrier [4]. An important fact is that food packaging material should have very good mechanical, physical, chemical, water, and light barrier properties, and should be thermally stable and specifically processable during whole production and food packaging process. Additionally, it should be effective against microorganisms responsible for food spoilage [4, 51]. Various materials, such as glass, paper, paperboard, and metal have been used as packaging materials for many years because they are cheap, lightweight, and ecologically friendly [4]. Over the last decades synthetic, plastic materials have become an effective and dominant packaging material due to their light weight, high transparency, cost-effectiveness, and versatility. Moreover, these synthetic polymers have good mechanical, thermal, and barrier properties [4, 52, 53, 54]. Conventional food packaging is a passive, inert barrier that should protect food from the external environment. To extend the shelf-life of food products, food packaging has begun to evolve from simply passive to innovative interactive strategies, including intelligent, active, and smart packaging. This preservation is aided by active packaging that can even improve the quality of food through interactions between food products, surroundings, and the covering materials. Active packaging (AP) is defined as packaging that interacts with the packed food and environment dynamically to maintain both food product quality and extend shelf-life [1]. AP materials include additional ingredients in the packaging material or the package headspace to enhance system performance. Figure 1 shows the forms of active packaging which may be used for food product preservation [55].

Figure 1.

Typical forms of active food packaging systems according to Almasi et al. [55] (A) polymer covered with a coating containing active agents, (B) active agents incorporated into the polymer matrix, (C) active agents immobilized on the polymer surface, and (D) active sachets inside the food packaging.

Form A (Figure 1) shows active packaging materials covered with coatings containing active compounds that are heat-sensitive or incompatible with the polymer matrix. One of the most common types of food AP systems is form B. The uniform distribution of the active agents makes the incorporation of active compounds into the polymer matrix possible. It should be noted that active substances must have good compatibility and high resistance to polymer processing conditions and no adverse effects on polymer properties. It is also very important that the matrix should release these compounds gradually in control way to the food. The immobilization of active substances on the polymer surface by ion or covalent linkages requires the presence of functional groups on both the active compound and the polymer. This form (C) makes the strong bonding of active agents onto the polymers possible. It also allows the slow release of these substances into the food. The third form of active packaging is the introduction of pads or sachets containing active substances into the package [55]. Pads or sachets may be put in the packaging headspace in a free form, that alters the interior environment of the packaging by various mechanisms like an absorption and/or evaporation process, that in turn inhibit the growth of microorganisms or other food and hinder the deterioration processes. This form of active packaging, as well as the forms described above, are classed as “releasing systems” or “absorbing systems” based on their mode of action [1, 54]. “Absorbing system” means that the active components absorb unwanted substances from the food surface or the packaging during storage. Ethylene and oxygen scavengers were found to be very important examples of absorption systems. In the releasing system, antioxidants or antimicrobial agents migrate to the surface of food products, preventing food spoilage. They may be released by direct contact between the food and packaging material (leaching systems) or through gas-phase diffusion from the packaging layer to the food surface (volatile systems) [1, 55]. The type of food product, the gas composition, the particular packing machinery, type of package, headspace, additives (including antimicrobial additives), and storage temperature are significant factors that influence the shelf-life and the quality of packaged fresh or processed food. Considering both the type of packaging material and the type of food, the product can be stored under aerobic conditions in a modified atmosphere, or in a vacuum [1, 54, 55]. The selection of the proper storage conditions depends on the barrier against gasses and water vapor, hardness, stability, heat resistance capabilities, market requirements, and most important the cost of the packaging materials [1, 55]. The modified atmosphere packaging (MAP) preservation method has been used to protect food products against deterioration to extend their shelf-life [56]. MAP refers to the use of high-barrier packaging materials to package products in which gases, such as CO₂, N_2, and O₂, are mixed in selected ratios and introduced into the packaging material to inhibit the growth of microorganisms to reduce the enzymatic reaction and decrease the rate of lipid oxidation [56, 57, 58, 59]. Nitrogen, oxygen, and carbon dioxide are the most commonly used gases in MAP. The ideal CO₂ and N₂ concentration in MAP depends on the food products and the different gas atmospheres that have been used for specific food products. The shelf life of many food products is limited by microbiological growth in the presence of O₂ [56, 57]. Generally, the effect of MAP is conditioned by the concentrations of CO₂ available in the packaging. Carbon dioxide inhibits the growth of the microorganisms responsible for food spoilage growing in normal air conditions, such as P. sp. and Shewanella putrefaciens [56, 57, 58, 59]. The reduction in the amount of oxygen in the package may be a possible solution to preserve food and maintain its quality [57, 59]. Another option for extending the shelf life of food is to use vacuum packaging. As an example, a) the mixture of gases containing 40% CO₂, 30% N₂, and 30% O₂ was recommended for low-fat fish [57], b) the atmosphere of 40% CO₂, 10% N₂, and 50% O₂ was recommended for chilled beef steak [60], c) mixtures such as 80% O₂, 20% CO₂; 50%O₂, 20% CO₂, and 30% N₂, or 20% O₂, 20% CO₂, and 60% N₂ was recommended for dark-cutting beef stored under chilled and superchilled conditions [61], d) vacuum packaging and the mixture of gases for MAP containing 40% CO₂, 20% N₂, and 40% O₂ was recommended for pork steaks [62]. Packaging functionality depends on the maintenance of the modified atmosphere or vacuum inside the package for as long as possible, hindering gas diffusion through the material and damage from external forces. This happens through a layered composition of selected distinct polymer films [63]. A multilayered composition should provide improved food protection during storage. MAP packaging and vacuum typically comprises of low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), and ethylene vinyl alcohol (EVOH) as an oxygen barrier [63, 64]. PE films as flexible materials are often used to maintain a moisture barrier. PET is used as a semi-effective gas and moisture barrier that imparts rigidity and strength to the packaging [64]. There are two common methods for producing multilayer packaging materials: layer-by-layer deposition and coextrusion methods. In the layer-by-layer technique, the layers may be formed one by one. It is important that each layer is chemically or physically bonded to each other to form the multilayer film. In the coextrusion method, polymers or biopolymers with different properties may be combined. The good adhesion of layers and the appropriate controlling of the thickness are the advantages of coextrusion techniques. In this technology, the packaging materials are coextruded together through separate screws. Therefore, these polymers/biopolymers would not be mixed and the final coextrudes would have a layered structure [55]. It should be noted that multilayer packaging can consist of even up to 11 ultra-thin layers offering different barrier properties [53]. In addition, the combination of different, blended, or multilayered polymer films which are used as food packaging, pose a particular challenge for recycling because there are made up of a large group of polymers [65]. Multilayer packaging cannot be recycled using traditional recycling technologies, because these technologies exist to recycle single-component plastics. Multilayer plastics have become a waste stream, additionally contaminated with food and other impurities. Another disadvantage is that they are in most cases nonbiodegradable. The accumulation of a packaging waste stream may lead to an environmental health crisis characterized by the accumulation of plastic waste in oceans [64].

1.4 Biodegradable, active packaging materials

Biodegradable packaging materials have emerged as an alternative to replace multilayer plastics left as waste. Biodegradable films are usually obtained from biopolymers of high molecular weight and classified according to the nature of their components. These biopolymers may be applied in the form of films, thermoformed, or as a cover/coating (thin layer), through immersion or spraying of a film-forming solution [52]. Starch was found to be one of the most promising biopolymers to replace nondegradable traditional plastics. Poly(butylene adipate-co-terephthalate) (PBAT), as an aliphatic-aromatic co-polyester, is also a promising biopolymer due to its ease of processing and good mechanical properties [66]. Biopolymers, such as PLA (polylactide), PHA (polyhydroxyalkanoates), or PBS (polybutylene succinate), also belong to the bio-based and biodegradable plastic family [53]. To obtain biopolymer packaging materials with antimicrobial activity, the active substances should be introduced directly into the polymer matrix. A good example is cassava starch chitosan films containing oregano essential oil incorporated in a polymer matrix, produced though an extrusion process. These packaging materials were found to be active against gram-positive bacteria (B. cereus and S. aureus) and gram-negative bacteria (Salmonella enteritidis and E. coli) [66]. Another example is starch/PBAT films incorporated with ε-PL by Gao et al. [67]. ε-PL is a homo-polyamide produced by Streptomycetaceae and Ergot fungi. As an antimicrobial agent, ε-PL exhibits a broad-spectrum of antimicrobial activity gram-positive and against gram-negative bacteria, molds, and yeasts. The authors indicated that starch/PBAT films with ε-PL inhibited the growth of tested microorganisms, such as E. coli, S. aureus, and B. subtilis. Biodegradable polymers, polyvinyl alcohol, and starch were used to prepare blends with natural additives, such as propolis extract and anthocyanin incorporated into the blend matrix. Boric acid was used as a cross-linker. Five different concentrations of propolis extract ranging from 0.5, 2, 5, 10, to 20% were used to develop active composites. It was demonstrated that an active film based on PE containing 20% of propolis was active against E. coli and methicillin-resistant S. aureus, respectively [68]. These novel materials having at least one dimension of just a few nanometers belong to polymer bio-nanocomposites. Bio-nanocomposites are novel, high-performance, lightweight, and eco-friendly materials that can replace traditional nonbiodegradable packaging materials obtained from synthetic materials [51]. Bio-nanocomposites are mostly constructed on biopolymer matrixes reinforced by nanofillers. These materials were found to have improved mechanical, barrier, thermal, and even antimicrobial properties attributed to the presence of the nanomaterials in the polymer matrix. The bond between the nanoparticle and biopolymer results in improved mechanical and thermal properties of the packaging materials [1, 69]. Several of the aforementioned nanomaterials were used in food packaging materials. There were nanoparticles of silver, copper, zinc oxide, titanium dioxide [1, 30, 31, 32, 33], silicon dioxide [34], nanocellulose, nanoclays, and chitosan [30, 31, 32, 33, 70, 71]. Thymol and silver nanoparticles (Ag-NPs) were used by Ramos and coauthors [30] to develop poly(lactic acid) (PLA)-based films with antibacterial activity. Various amounts of thymol (6 and 8 wt%) and 1 wt% Ag-NPs were introduced into the PLA matrix to produce active nano-biocomposites. The authors indicated that PLA-based nano-biocomposites showed dose-dependent slight antibacterial activity against E. coli. In addition, these films inhibited the growth of S. aureus 8325-A. Tarabiah and coauthors [72] used polyethylene oxide (PEO) as semicrystalline polymer and carboxymethyl cellulose (CMC) to develop the biodegradable, nontoxic PEO/CMC blend matrix (70/30 wt.%) as a host blend. ZnO nanorods as a filler were introduced into the polymeric matrix with various concentrations (upto 0.6 wt.%). The authors demonstrated that these PEO/CMC/ZnO nano-biocomposites can be used as a UV-mask. They also showed that these films were active against S. aureus and E. coli. De Souza and coauthors [73] used ZnO and Ag-ZnO nanoparticles as fillers and introduced them into the PBAT, which is an aliphatic-aromatic completely biodegradable flexible polyester, synthesized from 1,4-butanediol, adipic acid, and terephthalic acid. The authors established that such nano-biocomposite was active against E. coli. They also confirmed the synergistic effect between ZnO and Ag nanoparticles. The active packaging from chitosan and chitosan containing titanium dioxide nanoparticles was developed by Kaewklin and his team [33] to extend the shelf-life of climacteric cherry tomatoes. They indicated that tomatoes packaged in a chitosan package with nanoparticles showed lower quality changes than those in a chitosan film and control. The results suggested that the chitosan films containing titanium dioxide nanoparticles as active compounds exhibited ethylene photodegradation activity when exposed to UV light and consequently delayed the ripening process and any changes in the quality of the tomatoes. Hu and coauthors [71] developed chitosan/ZnO bio-nanocomposite and then introduced several concentrations of this bio-nanocomposite (0–5wt %) into the matrix of starch to produce antimicrobial starch-based composite films. The authors confirmed that such bio-nanocomposite films offered antimicrobial activity. They were active against S. aureus and E. coli. In addition, the antimicrobial activity of the films positively correlated with the amount of ZnO-chitosan nanoparticles introduced into the matrix. However, high concentration of ZnO-chitosan nanoparticles as fillers affected the barrier and mechanical properties negatively. If we consider all of the properties, like mechanical properties, barrier performance, and the antimicrobial effect of the composite films, 3.0 wt% of ZnO-chitosan nanoparticles was proven to be the optimal concentration of the active compound in the biopolymer matrix. Ascorbic acid blended with various biopolymers, such as whey protein, gelatin, and alginate or CuO nanoparticles, were used to prepare nanocomposite films in food packaging applications. CuO-NPs were loaded with ascorbic acid (CuO@Ascor) and incorporated into two different biopolymers, such as chitosan and xanthan gum to form chitosan-CuO@Ascor (A CA) and xanthan gum CuO@Ascor (X CA) to establish and show the antimicrobial activity of wrapping packaging material [74]. The incorporation of the active compounds into the polymer matrix may be performed using the solution casting method or via the melt blending method (to avoid solvents). The first step of melt blending method is a regranulation, but before this process, active compounds have to be mixed with the selected additives, such as plasticizers or compatibilizers. If nanoparticles are used as active agents, selected additives should also be added to prevent agglomeration of the nanoparticles and to provide their uniform distribution into the polymer/biopolymer matrix. Then, polymer/biopolymer pellets must be mixed with the prepared mixture of active compounds with additives. As next step, material has to be extruded with a twin-screw extruder for incorporating an active agent into the polymer/biopolymer matrix. The thermal profile of the process depends on the polymer matrix and on active compounds. To obtain active packaging material, the final, modified, and active pellets must be extruded through a flat die using chill-roll cast film extrusion line or using a film-blowing machine [50, 67]. Table 1 shows additional examples of bio-nanocomposite films with an antimicrobial activity which may be used in food packaging.

NPs	Host matrix	Methods used for producing antimicrobial materials	Inhibition of microorganisms	Ref.
ZnO-NPs	Chitosan/ Cellulose/ Acetate /Phthalate	Active films with varying ratios of nano ZnO reinforcement were prepared by solvent casting method. They were stirred overnight on a magnetic stirrer prior to casting, then poured onto transparent sheets and dried for 9 days at room temperature.	E. coli / S. aureus	[75]
ZnO-NPs	Polyvinyl alcohol (PVA) / Starch	Powdered starch was dissolved in distilled water at a temperature of 95°C for 30 min. Then PVA was dissolved in distilled water at 95°C for 30 min under magnetic stirring. The solutions were mixed using magnetic stirring at 95°C for 30 min. Then ZnO-NP was added to obtain solution and stirred for another 20 min. The resulting solution was casted on a sterile glass petri plate and dried at 60°C for 24 h.	S. Typhimurium	[76]
ZnO-NPs	Chitosan/ Carboxymethyl-cellulose	Chitosan was mixed with acetic acid solution at 60 °C. Separately, CMC was dissolved in distilled water at 100°C. The biopolymer solutions were mixed. Then, the proper amount of ZnO-NPs was added to the CH/CMC solution and sonicated for 2 h at 25°C. The homogeneous suspensions were poured into a transparent glass petri dish and left at room temperature for 72 h.	P. aeruginosa, E. coli, Candidia albicans	[77]
ZnO-NPs	Chitosan/ Polyethylene (PE)	Chitosan powder was dissolved in acetic acid. Solution was kept for 24 h until powder was totally dissolved. 0.1% solution of commercial ZnO nanoparticles in ethanol was added to the prepared chitosan solution to obtain ZnO-chitosan nanocomposite. Then PE films were cleaned with 70% ethanol solution and dried at room temperature. The dried PE films were treated using a plasma instrument. After plasma treatment, chitosan-ZnO nanocomposite solution was sprayed on the PE surface and allowed to dry at room temperature.	E. coli, S. aureus, Salmonella enterica	[78]
ZnO-NPs	Polyhydroxy- alkanotes	The nanocomposites were prepared via the ultrasonication method followed by solution casting. The ZnO-NPs were dispersed in chloroform by ultrasonication at 100 W for 30 min. Subsequently, the PHBHHx was dissolved at 50°C in the dispersion of nano-ZnO. Then, the mixture was sonicated for 30 min. The obtained blend was poured into a glass petri dish and finally dried under vacuum for 48 h	S. aureus, E. coli	[79]
Ag-NPs	(PVA)- Montmorillo-nite; clay ginger extract	PVA was dissolved in mL distilled water under stirring at 80°C, then the ginger extract was added to the PVA solution and mixed for 2 h at room temperature. Then montmorillonite clay solution was added into it under stirring for 2 h at room temperature. After stirring, the AgNO3 solution was introduced into the solution. As the next step, it was kept under sunlight for 15 min, to accelerate the green synthesis of Ag-NPs by ginger extract. The solution was then mixed in a magnetic stirrer for 30 min and then casted onto petri plates and dried.	S. aureus, S. Typhimurium	[80]
Ag-NPs	Poly-3-hydroxybuty-rate-co-3-hydroxyvalerate (PHBV3)	Active PHBV nanocomposite films were prepared by melting compound of the masterbatch of the Ag-NPs and PHBV3. The PHBV18/Ag-NPs masterbatch was melt mixed with the required amount of virgin PHBV3 pellets to obtain blends with 8% of the; PHBV18/Ag-NPs. The PHBV blends were prepared in an internal mixer during 5 min at 60 rpm and 180°C. Then, the batches were subjected to a rapid cooling-down and they were subsequently compression molded into films using a hot-plate hydraulic press.	S. enterica, Listeria monocytogenes	[81]
Ag-NPs	Polyvinyl chloride	PVC was dissolved under agitation using a magnetic stirrer in 20 mL tetrahydrofuran containing industrial epoxidized soybean oil as a plasticizer and kept at 65°C for 120 s. The homogeneous solutions were mixed with various concentration of quercetin and silver nitrate (Ag-NPs). Next, the solutions were poured onto flat-surface glass plates and kept at 25°C until solvent evaporation.	Bacillus subtilis, Aspergillus niger, Fusarium solani	[82]
Ag-NPs	Carboxymethyl-cellulose sodium alginate	CMC and sodium alginate and AgNO3 were dissolved in water, followed by the addition of aniline to the above reaction mixture. The solution was heated at a constant rate of 5 °C per min to the boiling point of aniline (184°C). The reaction mixture was then cooled and dried.	Klebsiella pneumoniae, Streptococcus pyogenes	[83]
TiO2-NPs	Polyvinyl alcohol (PVA)-chitosan	PVA was dissolved in distilled water at 80°C. Chitosan solution was prepared by dissolving chitosan in acetic acid solution, and stirred overnight using a magnetic stirrer. The two solutions were mixed at a 1:1 ratio and at room temperature. TiO2 nanoparticles were incorporated into the PVA-CHI film-forming solutions using a homogenizer to avoid aggregation of the nanoparticles. The blend solution with TiO2-NPs was ultrasonically degassed, casted onto the glass plate, and dried at room temperature.	S. aureus, E. coli	[84]
Nano-cellulose	Chitosan /Polylactic acid / Rosin	Solutions of chitosan in acetic acid and Z PLA in ethanol were prepared by mixing for 15 min at 90°C. Then rosin was added into the solution and mixed for 10 min at room temperature. Glycerol was added and stirred for 10 min for complete homogenization. As the next step, mixtures were poured into petri dishes and dried at 40°C for 24 h	E. coli, B. subitilis	[69]

Table 1.

Examples of bio-nanocomposite films in food packaging applications.

1.5 Control release of active agent from antimicrobial package

Direct incorporation of active/antimicrobial compounds into the polymer matrix or into the biopolymer coating is the most common type of food active packaging system. In this system, the active substance and a biopolymer/polymer are combined to form a composite matrix. There are three types of release mechanisms of active additives from a matrix [55, 85] 1. A diffusion-induced release in which the active agents diffuse through the macro-porous or micro-porous structure of the matrix from the film/coating surface into the food. 2. A swelling-induced release in which the incorporated active compounds are unable to diffuse within the polymer matrix. Due to its diffusion coefficient being too low. In this case, if the polymer/biopolymer matrix/coating is placed in a compatible liquid medium, the polymer/biopolymer starts swelling because of the penetration of the fluids into the matrix/coating. The swelling causes an increase in the diffusion coefficient of the active substance, then diffusion of the active agents may begin. In addition, this type of release mostly occurs in moisture-sensitive packaging materials, such as polysaccharide-based or protein films/coatings. 3. A disintegration-induced release, which is caused by the cleavage, degradation, or deformation of a polymer/biopolymer. This type of release occurs in reactive nonbiodegradable polymers or biodegradable types, such as poly(lactide) (PLA), polyanhydrides, and poly(lactide-co-glycolide) [55]. Several approaches have been proposed to achieve a more controlled diffusion of active compounds from the polymer/biopolymer matrix. Each of them focuses on a factor that influences the release rate. There are techniques that may be used to improve active packaging material characteristics. Multi-discipline techniques, such as nano-reinforcements, micro- or nano-encapsulation, which alter the properties of the active agents and decrease their volatility, diffusivity, or a chemical modification of a polymer/biopolymer, such as irradiation, cross-linking with selected agents and the lamination of films can lead to a more controlled release of active/antimicrobial substances [55]. Physical techniques, such as corona discharge, ultraviolet (UV) radiation generating carboxylic acid groups, gamma-ray, electron beam, and plasma forms that break the covalent bonds at the surface, leading to hydrogen abstraction and the formation of surface radicals and laser treatments can change the chemical structure of polymers [86]. Wet chemical methods using strong acids, such as chromic, permanganate or nitric acid, and bases, such as potassium base, have also been found to be an effective surface modification that generated various groups, such as hydroxyl, carbonyl, and carboxylic acid groups [87]. A good example may be a modification performed by Mulla et al. [88] who modified a LLDPE film surface by chromic acid treatment and coating it with clove essential oil. The chromic acid made the surface of the film more porous, allowing it to be coated with clove essential oil as an antimicrobial agent. This packaging material was confirmed to be effective against S. Typhimurium and L. monocytogenes. Another example of active layer modification is described by Fajardo et al. [89] who fabricated gliadin films cross-linked with cinnamaldehyde, as a carrier of lysozyme. The gliadin film cross-linked with cinnamaldehyde preserved its integrity in water and led to a prolonged release of antimicrobial compounds. The authors confirmed that the cross-linking process led to a slower release of lysozyme exhibiting greater antimicrobial activity compared to an unmodified film.

1.6 UV-aging of antimicrobial packaging materials

In general, an active coated packaging material or packaging material containing antimicrobial agents incorporated into the polymer matrix should function during storage to inhibit microorganism growth to extend the shelf-life of the food product and maintain its quality. This means that the coatings and active films should offer sufficient resistance against ultraviolet (UV) radiation or be shielded against UV [90, 91, 92]. UV radiation is a part of the nonionizing region of the electromagnetic spectrum that comprises approximately 8–9% of total solar radiation. It can lead to a degradation/deterioration in the optical, physicomechanical, and antimicrobial properties of packaging materials. Introducing an active, antimicrobial agent sensitive to UV in a coating carrier or into a polymer matrix can lead to an inactivation of the coating or active film after UV-aging. Introducing an active compound that is resistant to UV in a coating carrier/polymer matrix, or adding a substance with shielding properties, can prevent the inactivation of the coating/active film after UV-aging [90, 92]. As a result of nanotechnology development, ZnO nanoparticles have been incorporated into the matrix of many polymers or many coating carriers to obtain active layers to enhance the properties of such films/coatings without significant influence on their transparency. Additionally, these nanoparticles have attracted great interest and the development of coating/film applications as agents to improve anticorrosion properties has increased, particularly as UV absorbers [90, 91, 92]. Many studies demonstrated that ZnO nanoparticles exhibited superior chemical stability under UV radiation compared to other UV absorbers [47, 48, 49, 93]. The aim of the work of Mizielińska et al. [92], was to examine the effect of accelerated UV-aging on the antimicrobial activity of PLA films containing ZnO nanoparticles incorporated into a polymer matrix against selected microorganisms. The active foil samples were irradiated with UV-A and Q-SUN. The authors were able to demonstrate that PLA films with incorporated zinc oxide nanoparticles did not inhibit the growth of S. aureus, B. cereus, E. coli, Bacillus atrophaeus, and Candida albicans cells, but decreased the cell number. Accelerated UV-A aging had no negative influence on the chemical composition and the antimicrobial activity of the active film against gram-positive bacteria but influenced the antimicrobial effectiveness of gram-negative and C. albicans cells. Q-SUN irradiation decreased the antimicrobial activity of films with incorporated nano-ZnO against B. cereus. The greater effectiveness of antimicrobial packaging materials containing ZnO nanoparticles was observed when the active agent was introduced into the methyl hydroxypropyl celluloses (MHPC) carrier which was used to coat PE films [90]. These active coatings completely inhibited the growth of S. aureus, B. cereus, E. coli, P. aeruginosa and reduced the number of C. albicans cells. The influence of accelerated UV-A and Q-SUN irradiation on the antimicrobial properties of these active layers was also analyzed. Accelerated Q-SUN and UV-A irradiation had no influence on the effectiveness of the covered foil samples against S. aureus, B. cereus, and E. coli. Q-SUN irradiation decreased the activity of the MHPC coating containing nanoparticles only against P. aeruginosa and C. albicans cells. The negative influence of UV-aging on the chemical composition of the coatings due to the presence of ZnO nanoparticles was not observed. Another example can be PLA films which were covered with an MHPC/cocoa butter carrier, containing Eucomis comosa extract as an active, antimicrobial agent [91]. The covered, active films were treated with accelerated UV-A and Q-SUN irradiation. Later, the authors analyzed the effect of UV-aging on the antimicrobial properties and chemical composition of the coatings. It was noted that MHPC/cocoa butter coating containing E. comosa extract reduced the number of S. aureus, B. cereus, and B. atrophaeus. The accelerated UV-A and Q-SUN irradiations altered the chemical composition of the coating, but they had no influence on the antimicrobial properties of E. comosa extract coatings against both S. aureus and B. cereus. It was confirmed that only Q-SUN irradiation decreased to a small degree the effectiveness of the coating against B. atrophaeus.

1.7 The antiviral properties of active food packaging

The ongoing global spread of a pandemic caused by the coronavirus, known as SARS-CoV-2, which caused severe acute respiratory syndrome (SARS), currently poses high risks to human health and the world economy. This virus belongs to a family of enveloped viruses with +ssRNA and crown-like spikes on their spherical surfaces. CoV virion is classified as a very pathogenic virus [94]. SARS-CoV-2 is the third virus in the coronavirus family that has globally caused serious ailments in humans [95]. The virus particles are transmitted through human-to-human contact or contact with infected individuals mediated through the eyes, mouth, nose, or through the inhalation of exhaled virus in respiratory droplets [94]. To prevent the transmission of the virus, the use of gloves and medical masks has become essential. For instance, the demand for disposable polymers/biopolymers is expected to increase by 40% in packaging. Safety concerns related to shopping in supermarkets and small markets during the COVID-19 pandemic have led to the use of fresh-food products offered in polymer containers by suppliers and consumers, as well as the use of single-use food packaging materials and polymer bags to carry groceries [94, 96, 97, 98]. Multilayered active packaging systems are being developed to improve packaging properties, such as barrier properties, mechanical properties, antimicrobial effectiveness against bacteria, and yeast and molds responsible for food spoilage. However, adding antiviral materials as a layer containing antiviral agents to a coating carrier or incorporating them into a matrix of active films is a strategic route to develop antiviral packaging systems. Multilayered packaging systems are being developed through coextrusion, lamination, or covering with coatings [95]. This safe packaging should have an internal coating or extruded film layer to protect food products and an external coating or extruded film layer with antiviral compounds to protect customers (Figure 2) [94, 95, 96, 97, 98]. Additionally, this packaging-coated material or material containing antiviral substance should be active during storage, meaning it should offer sufficient resistance against UV aging or be shielded against ultraviolet light through the shielding properties of additives [94, 96, 97, 98].

Figure 2.

Common forms of active food packaging systems with antiviral properties (A) polymer covered with the internal coating containing compounds active against microorganisms responsible for food spoilage and with the external antiviral coating and (B) two-layer film with an internal layer containing substances incorporated into the polymer matrix, active against microorganisms responsible for food spoilage and with an external layer containing substances incorporated into the polymer matrix, active against SARS CoV-2.

In order to prepare antiviral coatings or films, many compounds, which are effective against viruses, such as SARS-CoV-2, such as ZnO nanoparticles, Ag nanoparticles, essential oils, and plant extracts, may be used [94, 95, 96, 97, 98, 99, 100]. As an example, Mizielińska et al. [94] developed an active coating based on nanoparticles of ZnO, geraniol, and carvacrol. Then PE films were covered with the active coating (coating carrier containing antimicrobial compounds mixture) using unicoater at a temp. of 25°C with a 40 μm diameter roller. The coatings were dried for 10 min at a temp. of 50°C. The authors analyzed the antibacterial and antiviral activity of these coatings. Additionally, the synergistic effect of the layer obtained was analyzed. Testing antiviral activity with human pathogen viruses, such as SARS-CoV-2, requires immense safety measures. Due to these concerns, the authors used phi 6 phage from the Cystoviridae family as a surrogate for the study of SARS-CoV-2. This phage was found to be similar (morphology, envelope, capsid size, and genome material) to the known pathogenic virus responsible for the COVID-19 pandemic [101]. The results of the study demonstrated that coatings containing an increased amount of geraniol or carvacrol and a very small amount of nano-ZnO were confirmed to be effective against gram-positive and gram-negative bacteria. It should be mentioned that a synergistic effect between these active agents was noted. To summarize, PE films covered with coatings containing geraniol or carvacrol and a very small amount of ZnO-NPs (as internal layer) may be used as packaging materials to extend the quality and freshness of food products. The same coatings can also be used as the external layers offering antiviral properties, as they showed moderate activity against the phi 6 phage. It was assumed by the authors that these coatings would also be active against SARS-CoV-2 particles. Similar results were obtained by Ordon et al. [96] who indicated that active coatings containing a mixture of supercritical CO2 extracts of raspberry seeds, pomegranate seeds, and rosemary showed bacteriolytic activity against S. aureus and P. syringae cells and bacteriostatic activity against E. coli and B. subtilis strains. The authors have also confirmed a synergistic effect in the active additives/compounds in the coatings. These coatings may also be used as internal coatings for packaging-covered films to extend the shelf life of food and to maintain their quality. All active coatings developed by the authors may also be used as external layers with antiviral effectiveness, as these coatings demonstrated significant effects against the phi 6 phage. Summarizing, the coatings obtained by the authors [94, 96] had antibacterial and antiviral properties. Their additional advantage was that they were transparent (Figure 3).

Figure 3.

a) an active coating based on nanoparticles of ZnO, geraniol, and carvacrol; b) an active coating based on a mixture of supercritical CO2 extracts of raspberry seeds, pomegranate seeds, and rosemary.

The lower activity of the mixture of CO2 extracts of raspberry seeds, pomegranate seeds, and rosemary when incorporated into a PE matrix [98]. The results of these tests demonstrated that the LDPE film containing a mixture of these extracts in a matrix inhibited the growth of S. aureus and this was also confirmed to be active against B. subtilis. This active film did not inhibit the growth of E. coli and P. syringae strains, however, the number of their cells decreased significantly. The LDPE active film was also confirmed to be active against phi 6 phage particles, meaning that the active foil sample had antiviral properties. A PE foil covered with active layers containing mixtures of Styloscolex baicalensis and Glycyrrhiza L. extracts as antibacterial compounds were found to have bacteriostatic activity against S. aureus cells and bacteriolytic effect on B. subtilis [97]. The layers were confirmed to be inactive against E. coli and P. syringae cells. This means that the coatings could be used as internal layers covering packaging film to preserve food products against gram-positive bacteria. The authors have also indicated that the coatings were highly effective against phage phi 6 phage, used as a SARS-CoV-2 surrogate. This means that the coatings could also be used as external layers to limit the spread of SARS-CoV-2 via human physical contact.

1.8 An application of antimicrobial packaging

Foodborne diseases caused by the consumption of food products contaminated with pathogenic microorganisms contribute to serious health issues in approximately 30% of the world population [102]. Additionally, the food industry has been facing huge losses due to microbial contamination for many years [3, 103]. As per the available data from World Health Organization [3], it was estimated that 600 million people fall ill after consuming contaminated food and around 420,000 die every year across the world. To avoid microorganisms’ entry and growth inside food with extended shelf-life during their preservation, various packaging systems have been used. As a response to these needs, food packaging technology is constantly evolving from passive to innovative solutions, including active antimicrobial packaging [1]. The use of antimicrobial packaging is a practicable option to inhibit the growth of pathogenic microorganisms responsible for food spoilage and toxins in products throughout the postharvest period [1, 3]. The antimicrobial packaging described above may offer a potential solution for extending the shelf-life of packaged products without altering the food or the processes involved. The food could be healthier and free of preservatives, while still retaining all of the desirable qualities and food product safety requirements. The influence of antimicrobial packaging on the increased shelf-life of food products was proved by many researchers. Emamifar et al. [104] reported that LDPE nanocomposite packaging materials containing ZnO and Ag-NPs were conducive to prolong the shelf-life of fresh orange juice stored at 4°C. Several other researchers successfully developed an antimicrobial packaging material to preserve food products [105, 106, 107]. Li et al. [105] used coated materials, containing nano-ZnO particles to improve the shelf-life of freshly cut apples. Li et al. [107] used PLA-nanocomposite films to preserve cottage cheese. Zinoviadou et al. [108] used whey protein to isolate films containing antimicrobials to extend the shelf-life of fresh beef. Table 2 shows more examples of the applications of antimicrobial packaging in food preservation.

Coating carrier/; polymer matrix	Active compound	Methods used for producing antimicrobial materials	Food application	Main results	Ref.
TPS/PBAT nanocomposite	ZnO-NPs	The cassava starch powder was dried in a hot oven at 50°C overnight before compounding. Starch, glycerol, and; zinc oxide nanopowder were mixed for 10 min in a dough mixer at several ratios. The mixed materials were compounded in a twin-screw extruder by manual feeding. The heating profile and screw speed were set at 85°C to; 150°C and 180rpm. The TPS-ZnO compound was cut into 2.5 cm pellets using a pelletizer, then the pellets were manually blended with PBAT pellets using a twin-screw extruder in the temperature ranging from 80–145°C with a 180 rpm screw speed to form 2.5 cm pellets. The TPS/PBAT/ZnO-NPs pellets were then blown using a temperature; profile of 150–165°C with a screw speed and nip roll speed of 25–27 rpm and 2.7–3.2 rpm using a single-screw blown-film extruder	Pork	Microbial growth inhibition, shelf life extension	[109]
Chitosan nanocomposite	TiO2-NPs	Chitosan was dissolved in acetic acid solution with glycerol as plasticizer and the chitosan film-forming solution was shaken in a controlled-temperature water bath shaker at 90°C for 6 h. Then TiO2 nanopowders were added to the chitosan solution. As next step the solution was homogenized and subsequently degassed using a sonicator. The film-forming solution was casted and dried at 30°C.	Tomato-fruits	Extension of the shelf-life	[33]
Chitosan-potato protein-linseed oil	ZnO-NPs	Oil-in-water emulsion was prepared by adding linseed oil to potato protein solution. Then the mixture was stirred for 20 min at 10000 rpm to obtain emulsion. Then, chitosan solution (in acetic acid solution) was added to the emulsion. Subsequently, 1.5% glycerol was added as a plasticizer and homogenized by magnetic stirring. ZnO-NPs were added, and the final blend solution was sonicated for 20 min. Bubbles in the resultant solution was removed by vacuum processing. The solution was then poured into petri plates and dried at 40°C for 24 h.	Raw meat	Reduction of the number of bacteria	[110]
zein film	chitosan NPs encapsulated with pomegranate peel extract	Chitosan NPS were prepared by ionic gelation technique (chitosan was introduced into the acetic acid solution and mixed using magnetic stirrer followed by ultrasonication for 10 min. Then, sodium triphosphate pentabasic was added by drops into chitosan solution and mixed at 28°C for 2 h. Chitosan NPs were collected as a pellet after centrifugation. Pellets were washed with water and dehydrated using lyophilizer. For preparing PE doped chitosan NPs, pomegranate peel extract was added with the chitosan blend prior to the addition of sodium triphosphate pentabasic.). As next step, zein powder was dissolved in ethanol (96%) at 70°C. Then, glicerol plasticizer was added and mixed for 10 min. The temperature was reduced to 40°C and PE encapsulated chitosan NPs was included and mixed together for 30 min to obtain active nanocomposite film. Finally, the nanocomposite film solution was casted on sterile petri plates, and then dried at 50°C.	Fresh pork fish	Antimicrobial activity	[111]
starch-based nanocomposite	Thyme EO*, montmorillonite nanoclay	Starch was dissolved in water, moderately stirred at room temperature, and then heated to 80°C for 30 min. After gelatinization, glycerol was added as a plasticizer. Montmorillinite powder was separately dispersed into distilled water and stirred at 500 rpm for 48 h. Then, the dispersion was added to the starch-glycerol suspension solution and then the mixture was mixed at 5000 rpm for 10 min. As next step, the thyme essential oil, with the tween 80 as an additive, was incorporated into the film forming solution at several concentrations. Samples were then homogenized at 20,000 rpm for 5 min. The active films were obtained via casting process in which the dispersion solutions were spread over a Teflon plate and then dried for 24 h at room temperature	Baby spinach leaves	Antibacterial activity	[112]
MC**/PC***/alginate film	A) organic acids /rosemary extract/asian spice EO*; B) organic acids /rosemary extract/asian spice EO*	Two types of films matrices based on 1) MC and 2) a blend of PC/alginate were used to obtain active films. Two antimicrobial formulations A: organic acids mixture + rosemary extract + Asian spice essential oil and B organic acids mixture + rosemary extract + Italian spice were introduced separately in each type of films during casting process.	Fresh broccoli	Antibacterial activity	[113]

Table 2.

Some applications of antimicrobial packaging.

^*

Eos: essential oils.

^**

MC: methylcellulose.

^***

PC: polycaprolactone.

1.9 Conclusions

Around 100 million tons of food products are wasted annually in the EU, which influences negatively on the environment. It was estimated that food waste would rise up to 200 million tons by 2050. Even if the relationship between shelf-life and food waste is not obvious, a huge part of food waste is related to the short shelf-life of fresh food products [2]. Antimicrobial packaging may be a solution to this problem. The fundamental role of antimicrobial packaging is to extend the shelf-life of food products by inhibiting the growth of microorganisms causing food spoilage. Longer shelf-life of food may lead to limit food waste and foodborne diseases and decreasing the negative impact of uneaten food on the environment and economy [3]. However, the long use of petroleum-based, antimicrobial packaging materials has also a negative influence on the environment because, after a single use of food packaging, 40% of these materials end up in landfill that corresponds to 9 million tons of plastic packaging waste accumulated in soils [3, 53]. Therefore, in 2015, the European Commission adopted a “circular economy action plan” with the goal to set the European Union on the course of the transition toward a more sustainable model for economic development [53]. Matthews et al. [53] mentioned that the main purpose of the EU’s action plan is to maximize the usefulness of materials and resources and keep them in the economy for as long as possible to limit waste. The authors underlined that a circular economy could grow Europe’s resource productivity by up to 3% annually by 2030. Two of the five important sectors identified in this action plan are food waste and plastics. The use of renewable/biobased sources for packaging materials has become a huge challenge. As a result of awareness in recent years, according to the latest data, the market for bio-based packaging material is predicted to increase from USD 81.70 billion in the year 2020 to USD 118.85 billion by 2026 [3]. In fact, biodegradable and biobased/renewable polymers production capacity is estimated to grow from around 2.11 million tons in 2018 to 2.62 million tons in 2023 [114]. Furthermore, special research attention has to be paid to biodegradable and bio-based packaging materials with antimicrobial activity, where active compounds are incorporated into polymers/biopolymers to increase the quality and shelf-life of the packaged foods. To avoid food contamination and spoilage, active agents should exhibit a potent antimicrobial activity to meet the expectations of ideal antimicrobial packaging [3, 114, 115]. Extensive research on the development of innovative, antimicrobial, and eco-friendly packaging has been undertaken to control the growth of bacteria, yeast, and fungi in food products. Additionally, antimicrobial packaging materials should preserve not only food but also protect consumers’ health. During a COVID-19 pandemic, not only SARS-CoV-2 virus particles may be present on the surface of the package. Frequent hand disinfection leads to the appearance of bacterial cells that are resistant to disinfectants and these bacteria may also be present on the package and consistently transmitted by hands. This review highlights that an external coating or external, extruded film layer of the packaging with antiviral and antibacterial properties may be a novel solution to protect customers against bacterial cells and viruses transmitted through packaging-to-human [94, 96, 97, 98].

Summarizing, it should be underlined that the global food packaging market reached a value of US$ 345.3 billion in 2021 [116], including only $9.6 billion (2.78%), which was reached by antimicrobial food packaging. However, it is projected that the antimicrobial food packaging market will hit around USD 19.7 billion by 2030 [117]. Many end-user sectors, including the beverage and food industry, are already interested in the various kinds of antimicrobial packaging, such as cartons and pouches, bags, trays, cans, cups, blister packs, and many more. There are companies that possess antimicrobial packaging materials in their offer as the answer to these demands. Dunmore a global manufacturer of laminated and coated films/foils developed and launched a new coated, polyester film (PET and BOPP) which is scratch-resistant and antimicrobial. This packaging material contains silver ions as active agents and it is effective against a wide spectrum of microorganisms [118, 119]. Klöckner Pentaplast Group is a leader in high-barrier protective packaging which extends the shelf-life of many food products. This company expanded its offer with new low-cost and effective antimicrobial performance films [118, 120]. Avient Corporation developed GLS TPEs (thermoplastic elastomer TPE) with antimicrobial additives, available as Versaflex™ and OnFlex™ grades. GLS TPEs with antimicrobial agents are commercially available in the United States and Asia. The company is focused on the development and additional antimicrobial formulations, which may be used as active additives to packaging materials [121, 122]. Cartro, a packaging business with headquarters in Mexico, and Mondi Ltd., one of the most important packaging manufacturers, partnered successfully in 2020. These companies decided to develop antimicrobial packaging for fresh and regional goods. Moreover, in the same year, Parkside Flexibles introduced new packaging materials covered with an antibacterial coating in partnership with Touch guard company [117]. Many companies are now focused on developing and launching antimicrobial packaging or active additives for packaging materials. Many global manufacturers offer high-barrier packaging that allows extending the shelf-life of food products by packing them in a MAP system or in a vacuum. The most important companies that have such packaging materials or active agents/additives in their portfolio are: PREXELENT^®, Aptar CSP Technologies, BASF Group, Dow, BioCote, and MICROBAN [117, 118, 123, 124, 125, 126, 127, 128, 129].