**1. Introduction**

Packaging is a billion global industry and plays a significant role for essential items for consumer goods ranging from basic chemicals to household and personal care products, drinks, foods, medical devices, and much more. The value of the packaging industry is highly expanding due to competitiveness in making commodities and luxury packaging. To date, the applications of plastics in the packaging sectors have been increasing at a fast speed due to their benefits of being commercially low cost and possessing intrinsic characteristics of plastic films in packaging industries. The most frequent plastic films used

**Citation:** Kamarudin, S.H.; Rayung, M.; Abu, F.; Ahmad, S.; Fadil, F.; Karim, A.A.; Norizan, M.N.; Sarifuddin, N.; Mat Desa, M.S.Z.; Mohd Basri, M.S.; et al. A Review on Antimicrobial Packaging from Biodegradable Polymer Composites. *Polymers* **2022**, *14*, 174. https:// doi.org/10.3390/polym14010174

Academic Editor: Evgenia G. Korzhikova-Vlakh

Received: 8 November 2021 Accepted: 24 November 2021 Published: 2 January 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

in the development of the packaging industry include polypropylene (PP), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET). The unique properties of plastics such as low cost and superior processability and having good barriers, mechanical properties, good sealing characteristics, and high transparency make them a favorable material [1]. In addition, they can be totally recycled and are lightweight alternatives to traditional, non-recyclable materials due to their super functionality [2–4]. Despite all the listed usefulness and benefits, the use of plastics as base materials in the packaging system suffered from the limitations of the materials themselves, such as the harmful chemicals and waste that packaging leaves behind. The wide usage of plastic packaging has caused serious plastic waste disposal problems, which, in turn, create massive environmental pollution [5]. In 2018, the World Wildlife Fund also reported that China, Indonesia, Malaysia, the Philippines, Thailand, and Vietnam contributed around 60% of the estimated 8 million tonnes of plastic that enter the world's oceans every year [6]. This threat to the environment is basically due to the significant level of highly toxic emissions, composting management issues, and alteration in carbon dioxide cycle [7]. Furthermore, disposed packaging plastics in many countries are rarely recycled due to technical issues and socio-economic constraints. For example, in China, there is only about 20% of recycled plastic waste as compared with 1 million tons of plastic generated [8]. Moreover, a huge proportion of the used plastic materials is either deposited in landfills or contributes to litter everywhere, surrounding the environment, which ends up putting stress and strain on the environmental balance. The alternative way to minimize the waste contributed by plastic is to use compounds from nature. Therefore, this phenomenon has stimulated the attention of many researchers to develop sustainable, active packaging material [9]. Therefore, the design of the packaging should consider not only shelf-life, cost, and protection, but also user-friendliness and environmental sustainability [10].

The consumption of food packaging was said to have increased during this pandemic (Figure 1) [11]. A comparison of different regions shows that the consumption of food packaging before and after the Covid-19 pandemic vary strongly. Apparently, Indonesia has contributed to a large amount of food packaging consumption before the pandemic caused by Covid-19. During the pandemic, Hong Kong passed as the highest region consuming food packaging. Because of the pandemic, there is a high concern regarding the hygiene and safety aspects by customers. Most people have resorted to their last option of buying bulk stocks of groceries or having their meals taken away. According to the Agriculture and Horticulture Development Board (AHDB) in its 2020 article on *'Takeaway food performance during Covid-19'*, the pandemic effect has urged people to switch from dine-in to takeaway-delivery due to social distancing recommendations.

One of the important safety aspects related to food packaging is its influence towards the microbial shelf life of food. In the environment where we live, there are millions of microbes, most of which are not visible to the human eye. The microbes, such as viruses and bacteria, have a very simple composition and replicate very quickly. For instance, a single bacteria can generate up to 500 new bacteria within 3 h through binary fission. Some of these bacteria and viruses may cause infections, ranging from mild to deadly diseases. Throughout human existence, dangerous microbes have been a source of horrifying epidemics such as plague, cholera, tuberculosis, etc. Although they are invisible, microbes continue to cause health problems, especially to the respiratory, digestive, and nervous systems. The types of diseases found today have been extremely difficult to prevent and cure due to high levels of antimicrobial resistance. Microbes can be transmitted in the following ways: (1) Coughing and sneezing, (2) Breathing contaminated air, (3) Contact with infected people by shaking hands, and (4) Contact with the infected objects or contaminated surfaces, water, or food. The threat posed by bacteria has inspired numerous researchers to research and develop unique antimicrobial plastic packaging for farm, food, and cosmetics.

**Figure 1.** COVID-19's impact on consumers ordering food, APAC 2020, by country or region. Modified from [11].

The reactions of bacteria, enzymes, molds, and some microorganisms towards the surrounding humidity and temperature on different types of foods also contribute to food spoilage in the food packaging [12–15], as displayed in Figure 2 [16]. Figure 2 shows that *Shewanella putrefaciens'* growth rate on fresh fish was the highest compared to Pseudomonas spp. and *Brochothrix thermosphacta*, which was around 0.5 per hour at 20 ◦C. On the other hand, bacteria and yeast on cooked and cured pork products showed the lowest growth rate, which was less than 0.1 per hour at around 12 ◦C. However, *Monascus ruber* (fungus) showed a unique growth rate, which started when the temperature was at 20 ◦C with less than 0.2 per hour and rose gradually to more than 0.6 per hour. Some researchers did their research on how to lower this carbon footprint [17,18].

There are a number of limitations in current packaging, which are non-sustainable production, legislation, cost pressures, and consumer education. Helping consumers to understand the importance of packaging, whether it is in food, drink, or medicine or giving economical access to products they need every day to make their life easier, safer, and more confident not only about the products they buy but the role of the packaging it is served in helps ensure those products maintain freshness, quality, and efficacy. Thus, poor barrier properties to water, vapor, and gases are the important critical issues in packaging. Fresh products like vegetables and fruits need to be packaged in an oxygen-permeable membrane environment, whereas processed products do not require much transfer. Another challenge faced by many producers is speed to market. A shorter research and development (R&D) process is needed for the development of packaging, which is around 9 months instead of the 12 to 18 months for the current packaging development cycle. Food waste reduction as well as new consumer experiences in new consumption occasions for the benefits of consumers and protecting the food quality are among the biggest challenges for current packaging right now. Additionally, bringing new, innovative products and at the same time maintaining sustainability goals and profitability goals both for consumers and the packaging company are the reforms that need to be made. The excessive growth of microorganisms because of contamination and temperature abuse, the high degrees of

nutritional qualities to the oxidation, and laws of nutritional qualities to the interaction with extreme factors are among examples of food quality and safety issues.

**Figure 2.** Growth rate of various types of microbes depending on the time. Modified from [16].

Antimicrobial packaging was introduced to combat this problem so that the shelf-life storing of the food can be extended, reducing food waste [19,20]. Apparently, antimicrobial agents had been applied to be incorporated with the food packaging [21–25] The antimicrobial properties in antimicrobial agents have made them become suitable to be incorporated with food packaging [26–28]. According to Rhim et al., antimicrobial-function nanocomposites were found effective for minimizing the growth of contaminant pathogens that exist after the post-processing, extending food shelf-life and enhancing food protection [29].

The usage of green polymers together with nanoparticles such as silver nanoparticles (AgNPs) as an antimicrobial agent is common in food packaging industries [30,31] since the characteristics of silver nanoparticles are good enough to make them a widely used nanofiller for making packaging because of their antimicrobial properties. Fillers are substances that are applied to regular packaging products, typically in low percentages, to improve the performance of the original content. In a composite, it is basically the mixture of the regular packaging material and a filler [32]. From the collective reviews that were done, it can be summed up that those researchers mostly used silver nanoparticles (AgNPs) as their antimicrobial agent because of their effective antimicrobial performance, low toxicity, and high thermal stability, and they have continued to gain attention since. In addition, it is possible to significantly increase the stability and mechanical strength of poly-saccharide films by adding AgNPs [33]. Evidently, a few articles that have been published in the field of bio-composites and bio-nano composites agreed on the potent properties of silver nanoparticles in making antimicrobial food packaging with a longer shelf-life [31,34,35].

Even though biopolymers are environmentally friendly and considered as most fascinating packaging materials, the industrial applications are restricted due to several factors such as their oxygen/water vapor barriers, thermal resistance, and other mechanical properties associated with costs [36]. In order to encounter these challenges and urge the industrial applications of biopolymers for packaging materials, there is the requirement for advanced research to effectively improve their stability, quality, nutritional values, and microbial resistance. Moreover, the barrier properties need to be intensified. Biodegradable polymers containing starch/cellulose fibres are most likely to make a solid growth in applications. Numerous approaches for elevating the properties and performance of antimicrobial packaging materials, such as chemical and physical modifications, polymeric blending, and nanocomposites, have indicated a bright potential for many types of applications.

Hence, more advanced research tools and huge investment are required to obtain fully sustainable materials with antimicrobial activity and effective alternatives for the existing ones. The enhancement of a moisture barrier and mechanical and other properties of biodegradable polymer will benefit the significant innovation in these packaging materials. Moreover, an increment in the use of biodegradable packaging must be intensified by more composting infrastructure. The development of specialised recycling procedures for these types of packaging should be considered. Despite all the advantages related to the use of silver nanoparticles with biodegradable polymers for sustainable packaging and a safer environment, several important constraints are minimizing the toxicity and environmental risks impacted from the packaging waste containing these nanoparticles.

Both functional and technical gaps have been the limitation barriers toward the development and applications of antimicrobial packaging materials in industries. Several limitations include vapor and air barriers, the stability of antimicrobial agents under processing conditions, and the low processability of bioplastics' toxicity as well as the changes in mechanical properties of the packaging materials. Accordingly, further research work should be focused on filling the void linking the antimicrobial actions to microbial growth kinetics in the packaged foods in both lab and industrial approaches. Close collaboration between both academic and industrial players could be an effective alternative to filling the gap between commercial aspects and research. Synergism and blending of nanocomposites would be the core tools as the useful strategies for improving antimicrobial performances for improving antimicrobial packaging and preventing some of the limits encountered during activity. This would contribute to the initial essays on the research and development of antimicrobials' packaging.

In addition, a forecast of market demand shows that the estimated global market growth for antimicrobial packaging was exponentially increased, as indicated from a growing Compound Annual Growth Rate (CAGR) value from 2020 until 2024. The contribution in the increasing economic value of these antimicrobial packaging products from biodegradable polymer composites is driven by the growing awareness of the consumers towards the consumption of sustainable and green packaging. Consumers are now consciously aware of the possible threat coming from synthetic food preservatives to human health, as some are potentially transformed into carcinogenic agents, thus indirectly helping in reducing the dependency on the consumption of synthetic preservatives. The use of these antimicrobial packagings from biodegradable polymer composites will be greatly beneficial in accelerating the transition towards preservative-free food products. The vast potential of antimicrobial packaging in sustaining the freshness of some selected highly perishable food including meat and poultry, seafood, fruits and vegetables, baked goods, and cheese and dairy-based products has contributed to the rise in the market demand, thus creating growth profitability for the players operating in the global market.

This review focused on the summary of current trends and applications of antimicrobial biodegradable films in the packaging industry as well as the innovation of nanotechnology to provide high efficiency of novel, bio-based packaging systems. For that reason, the influence of attractive product packaging plays an important role in the consumer purchasing decision. Most consumers are looking into new, added value possessed in the advanced packaging technology over the traditional packaging. The ideal antimicrobial packaging materials should be equipped with intelligent indicators' technology to measure certain crucial conditions, such as temperature, pH value, and humidity, to show the degree of bacterial contamination developed in packaged food throughout its shelf life. Universal protocol standards are needed not only to evaluate their antimicrobial activity against common food-borne bacteria and maintaining food quality, but also to meet consumer

sensory preferences. The alternative packaging asserts to perform similarly as conventional packaging in terms of achieving expected shelf life of food, durability, sealing strength, printability, and flexibility. The integration of these responsive technologies into food packaging will provide a massive impact in the food processing industries, to fulfil the growing demand for packaged, ready-to-eat foods that are distinguished as a primary driver of future packaging trends.

### **2. Antimicrobial Packaging Agents**

Antimicrobial packaging can be produced by the addition of antimicrobial agents such as chitosan and essential oil into the systems [37,38]. The incorporation of antimicrobial agents can be done by several techniques such as direct addition, encapsulation, coating, or grafting into or onto the matrix [39]. Meanwhile, polymeric materials are often used in conventional packaging systems. These polymers can be obtained from various sources and they can be classified based on their biodegradability. A current trend has been focusing on replacing non-biodegradable polymers to biodegradable polymers due to environmental concern, legislative rules, and consumer demands for green products. In view of this, the antimicrobial packaging has also been shifted to produce products from natural resources for both the host polymer and the antimicrobial agents. The types, advantages, and their limitations will be discussed in the following subtopic.

Various types of antimicrobial agents have been investigated for their potential applications in the antimicrobial packaging, and some of the examples are presented in Figure 3. Each of the antimicrobial agents has a unique mechanism and reacts differently to different types of microorganisms. In this case, the types of antimicrobials sometimes set restrictions for their applications. In general, these compounds can be classified into synthetic and natural classes based on their sources and physiologies. The synthetic antimicrobial agents can be further categorized as organic and inorganic. The literature reports various types of synthetic antimicrobial agents such as metallic nanoparticles (Ag, Cu, S) [40], oxide nanoparticles (ZnO, TiO2, CuO) [41], clay nanoparticles (bentonite, cloisite, montmorilonitrile) [42], chelating agents [43], volatile compounds (SO2, ClO2, ethanol) [44], organics acids and their salts [45], etc. [25,46]. The type of antimicrobial agents selected may differ depending on for which application the packaging material is being used. Basically, synthetic organic compounds containing ethylene diamine tetraacetic acid (EDTA), parabens, fungicides, and other chemicals are the major antimicrobial compounds used in the food packaging industry [47]. In particular, metal and metal oxides are potential antibacterial agents, but issues concerning their long-term impact on the environment and human health remain unresolved. On the other hand, the use of silver-based antimicrobial packaging for food purposes is expected to grow and has been used in countries such as Japan and the United States [48].

**Figure 3.** Classification of antimicrobial agents. Modified from [49].

There were two ways of synthesizing the AgNPs in biological methods, which are intracellular or extracellular [50–52]. For the extracellular process, it involves trapping the metal ions on the outer surface of the cells. Then, it aims to reduce the silver in the presence of biomolecules. On the other hand, for the intracellular, the process takes place inside the microbial cells [53]. Extracellular synthesis was shown to be preferable in most studies compared to intracellular due to its simplicity, lower cost, and preferred largescale production [51,53,54]. Additionally, some of the advantages of using this biological method are that it is environmentally friendly, does not produce any toxic residue, and is cost-effective [53–59]. Figure 4 shows the illustration of biological synthesis of silver nanoparticles using plant extraction.

Next, chemical synthesis of silver nanoparticles was also reviewed [53,55,59]. In this method, chemical reduction was discussed [53,55]. Reducing, stabilizing, or capping agents were used in this method. The size distribution of the produced silver nanoparticles was stated to be influenced by these agents [57]. The simple equipment used and the convenience of the chemical reduction are the benefits of using this method [60]. Nonetheless, this method is not widely preferred due to the requirement of using harmful chemicals such as sodium citrate, borohydride, potassium bitartrate, and sodium dodecyl, which are very toxic [53,61]. Additionally, this method was mentioned to yield toxic by-products during the process [59]. Figure 5 shows chemical synthetization of silver nanoparticles.

**Figure 4.** Biological synthesis of silver nanoparticles using plant extraction.

**Figure 5.** Chemical synthetization of silver nanoparticles through chemical reduction.

The positive attributes, such as being biocompatible, safe, and non-toxic to the environment, can be especially effective in food packaging, while posing no hazard to humans [62]. Natural antimicrobial agents come from various sources and they can be obtained from animals, plants, or microbial sources [63]. Some commonly used antimicrobial agents are from animal sources such as proteins (lactoferrin, ovotransferrin), enzymes (lysozyme, lactoperoxidase), and polysaccharides (chitosan). Additionally, microbial products such as nisin, pediocins, and bacteriocins are often used as antimicrobial agents in packaging. In a similar way, plant-derived antimicrobial agents are usually obtained in a form of essential oil or extract. Some of the most effective natural extracts are ginger, garlic, oregano, thyme, cinnamon, clove, coriander, and more. The presence of active compounds in these materials such as flavanols, terpenes, anthocyanins, phenolic acids, tannins, and stilbenes is responsible for the antimicrobial effects for specific microorganisms. Moreover, they could provide additional health benefits such as being nutritional supplements [48]. From this point of view, the use of antimicrobial agents from plant-derived sources could be an excellent choice especially for food packaging purposes. At present, the challenge related to the plant-derived antimicrobial compounds is due to their loss during hightemperature processing and reduced antimicrobial efficiency [64]. Other factors that restrict their application are the production cost and sometimes the strong aroma produced [63].

#### *2.1. Polymeric Matrix Used in Antimicrobial Packaging*

The selection of a polymeric material is dependent on the intended use on application and highly depends upon the properties of the polymer matrix [65]. Polymers such as poly(ethylene terephthalate) (PET), polyethylene (PE), poly(vinyl chloride) (PVC), polypropylene (PP), polystyrene (PS), and others have been investigated in this field. PVC is one of the examples used for polymers for packaging in the world. It has several advantages including flexibility, toughness, light weight, and ease of processing. Studies on PVC loaded with silver nanoparticles [66], zinc [67], and orange essential oil [68] have been reported. PET is another type of polymer that is useful and has the potential to be as good as PVC. This polymer has a good mechanical strength and toughness [69]. Further, PE is another widely used polymer. Low-density polyethylene (LDPE) is the cheapest among other polymers. Meanwhile, PP with high grade has a high melting point; thus, it is suitable for high-temperature packaging [47]. These materials are often used because of their good properties and relatively low cost [70]. Table 1 shows some examples of petroleum-based polymers that have been studied as a host with a variety of antimicrobial agents for packaging materials.


**Table 1.** Petroleum-based polymers for antimicrobial packaging.

Nanoparticle (NP); Pentaerythritol p-hydroxybenzoate ester-based zinc metal alkoxides (PHE-Zn); Layered double hydroxide para-hydroxybenzoate (LDH-p-hydroxybenzoate); Essential Oil (EO); graphene oxide/poly(4-vinylbenzyl chloride), GP(VBC).

### *2.2. Antimicrobial Packaging from Bio-Based Polymers*

Despite the excellent performance of the petroleum-based polymers, they possess several limitations. One of the main constraints is their non-biodegradable properties that can cause short- and long-term pollution [69]. To address this issue, much attention has been given by the researchers and industries in developing antimicrobial packaging from bio-based polymers [82]. The use of bio-based polymers in place of traditional petroleum-based polymers could avoid the disposal problem and produce products that are environmentally friendly, safer, and non-toxic. Additionally, these materials give advantages in the sense that they are renewable and available abundantly in nature. The general classification of bio-based polymers is depicted in Figure 6. They can be broadly classified into three categories, which are (1) polymers directly extracted from biomass sources, (2) polymers chemically synthesized from bio-derived monomers, and (3) polymers produced directly by microorganisms [83]. Polymers such as poly(lactic acid) (PLA), starch, cellulose, and chitosan are gaining more favor in the antimicrobial packaging.

**Figure 6.** Classification of bio-based polymers based on their origin.

PLA is a type of biodegradable and renewable polymer that has been studied extensively for antimicrobial packaging. PLA is obtained from two major pathways: ring opening of lactide or direct polycondensation of lactic acid, a monomeric precursor derived from renewable resources. The monomer was produced from the fermentation process of sugar feedstock such as dextrose or chemical synthesis. Sugar feedstock can be obtained in two ways: firstly, directly from sources (sugar cane, sugar beets) or secondly, through conversion of starch from corn, potato, wheat, rice, or agricultural waste [70]. PLA

has mechanical properties that are almost similar to commercial thermoplastics like PET, making it possible to be applied in a wide range of products [84]. Starch is a promising biodegradable and biocompatible polymer in the packaging industry. It is non-toxic and readily available. However, starch has a strong hydrophilic behavior, thus making it sensitive to moisture [85]. Meanwhile, cellulose is the most abundant renewable material, and it can exist in various forms upon modification. In packaging, cellulose can act as a filler or host polymer [86]. Chitosan is another attractive polymer that has been frequently investigated for antimicrobial packaging. Chitosan is generated from the deacetylation reaction of chitin. Chitosan possesses antimicrobial properties and, thus, can be used as a host and antimicrobial agent at the same time [47]. Table 2 shows some examples of bio-based polymers reported for antimicrobial packaging in recent years. They are being used with a variety of antimicrobial agents, both natural and synthetic, with various types of preparation methods involving solvent casting and encapsulation and being targeted for different types of microorganisms. In a way, bio-based polymers show a great potential in antimicrobial packaging; however, their relatively high cost compared to the traditional polymers somehow limits their applications on a larger scale.


**Table 2.** Antimicrobial packaging systems utilizing bio-based polymers.

*Thymus vulgaris* essential oil (TV-EOs); ethanolic extract of Mediterranean propolis (EEP); Silver modified montmorillonite (Ag-MMT).
