**3. Types of Antimicrobial Packaging**

The antibacterial, antifungal, and antioxidant activities can be prompted by the main polymer used for packaging or by addition of numerous components from natural agents (bacteriocins, essential oils, natural extracts, etc.) to synthetic agents, both organic and inorganic (Ag, TiO<sup>2</sup> nanoparticles, ZnO, synthetic antibiotics, etc.) [46].

This review on antimicrobial packaging for various applications was supported with bibliometric analysis as a systematic approach. Data used in the present study were retrieved on 8 June 2021 from Scopus. Data from June 2021 onwards were not considered in this study for data consistency. Presently, to this writing, the keyword search analysis in Scopus on the query string (TITLE-ABS ("antimicrobial packaging")) AND TITLE-ABS (food\*) AND PUBYEAR < 2021 OR PUBDATETXT (("January 2021" OR "February 2021" OR "March 2021" OR "April 2021" OR "May 2021")) AND (EXCLUDE (PUBYEAR, 2022)) AND (LIMIT-TO (LANGUAGE, "English")) resulted in 306 documents (Figure 7) wherein 195 were research articles, 56 were book chapters, 33 were review works, 18 were conference papers, and 4 were books (8 June 2020).

**Figure 7.** Annual and cumulative publications on antimicrobial packaging for various applications.

There are several forms of antimicrobial packaging, which are (1) addition of sachets/pads containing volatile antimicrobial agents into packages, (2) incorporation of volatile and non-volatile antimicrobial agents directly into polymers, (3) coating or adsorbing antimicrobials onto polymer surfaces, (4) immobilization of antimicrobials to polymers by ion or covalent linkages, and (5) use of polymers that are inherently antimicrobial [25,109].

Overall, the antimicrobial packaging strategy is classified into two groups, either direct or indirect contact between antimicrobial surface and the preserved food [46]. Table 3 briefly explains the definition, types, and function of the antimicrobial packaging strategies.


**Table 3.** Description of antimicrobial packaging strategies.

Firstly, the most common strategy is by having the antimicrobial sachet or pad with antimicrobial substance inside a sachet and added to the food packaging [46,110]. The antimicrobial compounds are released from the sachets into the headspace of packaging or to the surface of food products and subsequently inhibit the growth of food-borne pathogens [111]. The most popular antimicrobial agents for active packaging include nisin, chitosan, potassium sorbate, silver substituted zeolite, and essential oils [112].

Secondly is the inclusion or embedding of antimicrobials directly into the interior of the polymer films. In this method, the antimicrobial compounds are inside polymer films and introduced during the manufacturing process of these films [111]. The materials used in edible films should be Generally Recognized as Safe (GRAS) and may be eaten with food [113]. Thirdly is by covering the polymer surfaces with a layer of antimicrobial. The antimicrobial agents are coated onto the surfaces of the polymer films [98]. Then, the antimicrobial substance would either evaporate into the headspace or migrate into the food through diffusion [110].

The following antimicrobial packaging strategy is immobilization of antimicrobials in the polymers using ion or covalent linkages. This method needs (1) antimicrobial agents with functional groups that can be linked to the polymers and (2) antimicrobial compounds containing functional groups such as enzymes, peptides, and polyamines [98]. Lastly is

the permanent existence of antimicrobial polymers. Some polymers used to construct films inherently have antimicrobial properties themselves [111]. For example, chitosan is categorized as an active food packaging material because of its inherent antimicrobial properties and capacity to carry various active components [114].

#### **4. Performance of Antimicrobial Packaging**

As mentioned before, antimicrobial packaging is frequently prescribed as a combination of antimicrobial material and agents based on a specific matrix, which, in turn, leads to different types of packaging functions and uses. The review of correlation analysis between antimicrobial properties in terms of its use and advantages toward its application in food safety is presented in Table 4. What stands out in this table is the general pattern of each antimicrobial agent such as volatile gas form [115], silver compound [96], sanitizer and fungicide [116], plant extract [115], plant essential oil [115,117–120], enzyme [121], chitosan [122,123], bacteriocin [124,125], and inorganic nanoparticle [126,127] in controlling the growth of microorganisms, which, in turn, leads to indicators of prolonged shelf life of food, which is the essence of food safety. An important finding that emerged from the data was that antimicrobial agents can inhibit the growth of pathogenic microorganisms in food such as *Bacillus cereus*, *Escherichia coli*, *Listeria monocytogenes*, *Salmonella* spp., *and Staphylococcus aureus* [128] (Table 4). In addition, a further striking factor to emerge from the table is how antimicrobial material also shows a similar ability to protect from microbial growth by adding value by controlling the moisture migration and nutrient oxidation [115]. Taken together, these trends suggest that there is an association between antimicrobial properties toward superior food safety and longest shelf life.

The next part of the review was concerned with the performance of antimicrobial packaging towards environmental impact, as shown in Figure 8. Looking at Figure 8, it is apparent that the antimicrobial packaging showed a positive impact on the environment as well as in the ecosystem cycle. One concept that emerged during the extensive review was antimicrobial agents and material that normally come under renewable raw material provide added value in ensuring ecosystem sustainability. This is because, if antimicrobial packaging is made from a combination of antimicrobial agents and materials that are based on renewable raw materials, it may accelerate the biodegradation process and further stabilize the ecosystem balance. These results suggest that antimicrobial packaging is not only able to show the ability of controlling the growth of microorganisms and prolonging the shelf life of food, which is very important in food safety, but also has a positive effect on the environment [129].

**Figure 8.** Interrelated antimicrobial packaging towards environmental impact.



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Many studies have been conducted on the mechanism of silver nanoparticles as an active packaging ingredient in packaging [53,55,58,133–139]. Figure 9 shows the possible mechanism of silver nanoparticles' action in the antimicrobial food packaging. The mechanism of the AgNPs were said to impede the cell wall synthesis in the cell [139]. Daneshniya et al. (2020) [140] reported that the AgNPs in the range of 1–10 nm in size attached to the cell membrane and disrupted the membrane functions such as permeability and respiration. The silver nanoparticles were believed to be penetrating the bacteria cell and causing further wreckage by associating with the thiol groups from the respiratory chain proteins and transport proteins such as DNA, glutathione (GSH), and thioredoxin, which led to hindering their functions [137]. The damage towards the thiol groups was also stated to be due to the release of silver ions (Ag+) from the silver nanoparticles that are very reactive when they are reacted with the cell membrane that was negatively charged [41]. The reaction resulted in further involvement in the bactericidal effect of silver nanoparticles and led to cell death [135,137]. However, the specific action of silver nanoparticles' mechanism was still unclear throughout these extensive studies.

**Figure 9.** Possible mechanism of silver nanoparticles towards microbes.

All organic and inorganic compounds that were widely studied in the past research such as chitosan, chitin, titanium oxide (TiO2), and copper (Cu) have shown great antimicrobial effects toward the bacteria, microorganisms, and enzymes, as mentioned in Table 5. Table 5 depicts the widely used material of antimicrobial agents in producing the antimicrobial food packaging.


**Table 5.** Advantages and disadvantages of widely used materials of antimicrobial agent for food packaging industries.

### **5. Issues Related to Antimicrobial Packaging**

Application of antimicrobial packaging systems based on biopolymers incorporated with different bioactive agents possesses immense potential for improving the food quality and safety along with a possible increment in shelf life. As mentioned earlier, a variety of bioactive substances, both synthetic and natural, such as essential oils, antimicrobial peptides, enzymes, etc., have been investigated and applied in antimicrobial packaging systems. Several investigations on the subject have indicated the potential of antimicrobial packaging systems in effectively inhibiting the targeted spoilage microorganisms, employing a suitable combination of biopolymer and a bioactive compound to produce an antimicrobial film [166].

Despite all the above advantages of antimicrobial packaging, there are some challenges and limitations, which should be discussed and overcome. One of the main challenges is health issues and risks regarding the safety and migration of nanoparticles of antimicrobial agents. The possibility of inhalation by the respiratory system, skin penetration through skin nodes, and unintentional migration and ingestion of nanoparticles by the digestive system might badly affect human health.

#### *5.1. Safety Issues*

Numerous studies have found that nanoparticles of antimicrobial agents are effectively proven in enhancing the barrier, mechanical, and antimicrobial properties of antimicrobial packaging when appropriate amounts of antimicrobial agents are incorporated into packaging materials. Figure 10 illustrates how nanoparticles of antimicrobial agents can improve the barrier properties as compared with pure polymer materials. Nanoparticle and pure polymer matrix properties are among the most important factors that determine the properties of the resulting composite. For food packaging applications, nanocomposites that have been studied the most are clay and polymer nanocomposites, while bio-based polymers that have been studied the most are PLA. These nanomaterials will intensify the water and serve as moisture-repellent properties of food packaging materials.

**Figure 10.** Water vapor and oxygen passing through (**a**) pure polymer materials and (**b**) nanoparticles.

However, there are a few limitations and issues that need to be reconsidered. In terms of migration, nanoparticles are susceptible to migrate from packaging into the food, which depend on nanomaterial characteristics such as size, concentration, shape, and dispersion. Other than those, there are environmental factors (temperature, mechanical stress), food condition (composition and pH), polymer properties (viscosity and structure), and contact duration. These will bring limitations and potentially result in adverse health effects. It has been reported that some nanoparticles can cause intracellular damage, pulmonary inflammation, and vascular diseases [167]. Thus, a detailed toxicological analysis is needed to explain the risks.

There are three types of migrations of substances into food: (1) overall migration limit (OML), which evaluates the total weight of extracted substances, which is non-specific and above the limit that is allowed to be penetrate into food; (2) specific migration limit, which measures the concentration of the material-specific restricted substances based on their toxicological risks using advanced detecting assays; and (3) maximum permitted quantity (QM), which measures the maximum level of the residual given substance that can migrate from a material into foodstuffs or simulants. To ensure the overall quality of the plastics, the overall migration to a food of all substances together may not exceed the OML, which, for polymers of about 60 mg/kg of food (or food simulant) or 10 mg/dm2 of the contact material, will usually be used for inertness of the substances. Regulation No. (EU) 10/2011 from Plastics Regulation and No. (EU) 2016/1416 from the European Commissionpublished Commission Regulation ensure the safety of plastic materials with the use of migration limits, which specify the maximum amount of substances allowed to migrate to food. They impose the permitted value of 5 to 25 mg zinc per kg food (25 to 5 mg/kg food) for food contact items based on the SML consideration. Furthermore, 40 mg/day of zinc daily consumption for the human body is the restricted amount level for food contact materials by the National Institutes of Health [168]. A nanocomposite containing 0.5 g/L 0.5 g/L ZnO NPs is the permitted level of value of migration [169]. There was a study conducted by Bumbudsanpharoke et al. who experimented and discovered the migration of Zn2+ from LDPE-ZnO nanocomposite films, in which the level of migrated Zn2+ (3.5 mg L−<sup>1</sup> ) was considered safe for human health due to a lower value than the specific migration limit provided by European Plastics Regulation (EU No. 10/2011) [170]. Examples for Specific Migration Limits are Polycyclic Aromatic Hydrocarbons (PAH) from carbon black and Bisphenol A (BPA) from polycarbonate plastic, most of the time known to be carcinogens. However, except in some cases, the level of migrated Zn2+ increased despite the migrated level being lower than the maximum migration limit based on the National Institutes of Health for food contact materials with the existence of essential oil in the nanocomposite [171].

#### *5.2. Production Cost*

Antimicrobials of nanoparticles are diversely used in packaging materials due to their advanced properties for industrial purposes. Most common uses of antimicrobial properties are Ag, TiO2, and ZnO of antimicrobial packaging systems. These types of nanoparticles are used in the lab and the production cost could be considered as way more affordable than the production cost for the real industry, in which the production costs required are 10 times more to be useful as the original one. The prices of antimicrobial agents are way more expensive in industrial scale, and scaling up the packaging for nanocomposites demands cutting-edge technologies, which may amplify the final cost, thereby reducing the market acceptability [172,173]. Apart from that, antimicrobial agents are frequently developed for a specific food and do not provide the same results with other types of food; thus, the price will be more expensive to buy several antimicrobial agents for several types of food.

#### *5.3. Strong Aroma, Flavor, and Color*

Essential oils of natural antimicrobial agents such as carvacrol, ginger/garlic oil, linalool, clove oil, thymol, basil, and cinnamaldehyde possess a high intensity of off-flavors. These types of essential oils have high antibacterial properties but have a strong smell and flavor, which inhibits the original flavor of the food, which represents the critical

challenges for the food industry. Moreover, they carry a striking color. It was mentioned by [174] Bhullar et al. in 2015 that around 85–99% of essential oils contain phenolic and hydrophilic volatile terpenoids, which cause a generation of intense reddish color to the films. Furthermore, they have a sharp flavor, which restricts their applications in the food packaging industry constituents [174].
