Edible films and coatings are defined as thin layers made of natural polymers, used for wrapping or coating foods, representing an important role in their conservation, distribution, and marketing [34,35,36].

Edible films and coatings have different applications and a wide range of properties that could help the food industry to enhance quality and shelf-life. The addition of flavors, aromas, antimicrobial agents, antioxidants, pigments, and vitamins can improve food quality and reduce many problems with a direct impact on shelf-life [37]. The extensive use of petroleum-derived polymers and consequent packaging wastes cause adverse effects on environmental pollution [38]. These concerns allow the approach and the intensification of studies to other more sustainable, biodegradable, and non-polluting alternatives, such as edible films and coatings based on biopolymers. The films can be produced by wet or dry methods [39,40]. By wet processing, films (dried over a surface) and coatings (dried over foods) can be obtained [39]. Wet methods consist in spreading and solvent evaporation or “casting.” Edible coatings are formed by dipping, spraying, panning, fluidized bed, and enrobing, depending on the characteristics of the foods [39,41,42].

The production of edible films by dry methods can be achieved through extrusion or thermopressing/thermoforming [12,39]. The thermopressing/thermoforming technique is normally used for the production of plastic utensils and also involves high temperatures and pressure [12]. The technology has been recently applied to the production of bioactive films [43,44].

Edible films and coatings can be obtained from hydrocolloids, lipids, and their composites [12,16,18]. The use of this type of material can have several purposes, such as a barrier to moisture migration and gas flow, preservation of mechanical properties, and protection against microbial oxidation and deterioration, which can be increased by the addition of functional compounds [45,46]. Hydrocolloids usually provide better mechanical properties than lipids and hydrophobic substances [16]. Polysaccharide hydrocolloids are the most used components in the production of edible films and coatings [47]. However, these and other natural film-forming substances may need film additives such as plasticizers, crosslinking agents, emulsifiers, and reinforcements to improve or modify the basic functionality of the material film, such as mechanical resistance, water resistance, and elasticity [16,48]. Due to the limited function of a single-component edible film, composite films can be obtained by multiple biopolymers combined to create edible films with desirable properties [18,40].

Furthermore, active edible films can be created by the addition of functional compounds as anti-browning agents, colorants, flavors, nutrients, probiotics, nutraceuticals, antimicrobial and antioxidant compounds, etc. [60,61,62].

Films and coating obtained by biopolymers have several benefits due to their edible nature, availability, low cost, and biodegradability [67]. They are designed to deal with food’s susceptibility to physical/mechanical impacts, chemical reactions, and microbial development [68,69,70].

The main characteristics of edible films and coatings are related to (1) edibility and biodegradability; (2) physical and mechanical protection, pressure, vibrations, and other mechanical factors; (3) prevent and control of mass transfer or barrier functions (e.g., water vapor barrier, oxygen barrier, UV light barrier, organic vapor barrier, fat barrier); (4) active substance carriers and controlled release; (5) improvement of sensory properties; (6) shelf-life extension and safety enhancement; and (7) convenience and quality preservation [39,71,72].

Meat spoilage can be mainly caused by lipid oxidation, autolytic, enzymatic reactions, and microbial deterioration [4,5]. Several factors influence meat spoilage, such as storage temperature, presence of oxygen, moisture, light, endogenous enzymes, and microorganisms [2,3]. Alone or in combination, the action of these factors can cause changes in the color, odor, texture, and flavor of meat [2]. Compared to red meat, chicken meat has a shorter shelf-life mainly due to lipid oxidation and resulting off-flavors because of its higher content of unsaturated fatty acids [73]. Additionally, the original microbiota and meat processing conditions may contribute to the shorter shelf-life [73].

Edible films and coatings can present some benefits and economic impact on the meat industry. The prevention of moisture and weight loss, sensory changes in texture, flavor, odor, color, and dripping reduction can positively influence meat quality. Furthermore, the low oxygen permeability leads to the reduction of lipids oxidation, myoglobin oxidation, spoilage and pathogenic microorganisms, and partial inactivation of deteriorative proteolytic enzymes [74].

The addition of plant extracts and essential oils has gained prominence due to their antimicrobial and antioxidant potential. The use of antioxidant biocompounds in edible films and coatings formulations is mainly to prevent lipid oxidation, delay the development of off-flavors, and improve color stability [20]. Their activity has the ability to prevent chain reactions that initiate peroxidation, scavenging oxygen-reactive species, inhibit pro-oxidative enzymes, breaking auto-oxidative chain reactions, capturing O²⁻ radicals and preventing the development of peroxides, and chelate metal ions, preventing the generation of reactive species or lipid peroxides decomposition [20,75].

Antimicrobial compounds can be obtained from microorganisms, animals, and plants. The main bioactive compounds of vegetal origin with antimicrobial activity include phenolics, terpenes, aliphatic alcohols, aldehydes, acids, and isoflavonoids [21,76]. These compounds may have different mechanisms of action in microbial cells, such as changes in cell membrane permeability, cytoplasmic membrane disintegration, the release of cellular constituents, changes in phospholipid and fatty acid composition, changes in DNA and RNA synthesis, and destruction in protein translocation [74,77].

Typical levels encountered at the processing step for aerobic colony count are <10⁵ CFU/g, and for E. coli, <10² CFU/g [91]. Spoilage can be detected when the microbial population reaches about 10⁷–10⁸/cm² [92], which may result mainly in off-flavors, off-odors, and slime [2]. According to different authors, the combination of edible films/coatings with bioactive ingredients allowed to slow down the development of deteriorative and pathogenic microorganisms. It was possible to identify similarities in the behavior of spoilage indicator microorganisms. In general, the increase of counts over time is common among the developed works; however, it is also common the slowing down the development of counts compared to samples without the application of films, or with the application of films without the addition of antimicrobial compounds. Khan et al. [78] reported counts for aerobic mesophilic bacteria above 6 log CFU/g in broiler meat samples contained in plastic bags after 11 days, whereas samples packed in composite gelatin films with curcumin remained below 6 log CFU/g until 18 days.

Pseudomonas spp. are the most important group of microorganisms responsible for the spoilage of fresh meat when their counts reach 7–8 log [28]. Mehdizadeh and Langroodi [66] reported a 2.81 log to reduce Pseudomonas spp. compared to the control samples with the use of chitosan combined with propolis extract (1%) and Zataria multiflora Boiss EO (1%). In another study, Raeisi et al. [28] reported that samples coated with alginate + 5 mg/mL rosemary EO; alginate + 5 mg/mL cinnamon EO + 2000 IU/mL nisin; alginate + 5 mg/mL rosemary EO + 2000 IU/mL nisin; and alginate + 5 mg/mL cinnamon EO + 5 mg/mL rosemary EO never reached to 7 log CFU/g for Pseudomonas spp, throughout the storage period (15 days, 4 °C).

Coating and film laying has also been demonstrated to have a beneficial effect in the reduction of pathogenic microorganisms populations. Nouri Ala and Shahbazi [32] performed a study of chicken breast samples immersed in Listeria monocytogenes suspension and then coated in carboxymethyl cellulose (CMC) with the incorporation of Ziziphora clinopodioides EO (ZEO) and Mentha spicata EO (MEO). Significantly bacterial reductions were observed in groups with CMC + ZEO 0.5% + MEO 0.5% and CMC + ZEO 0.25% + MEO 0.5% on day 14 compared to day 0 at 4 °C by 2.44–2.62 and 2.91–3.03 log CFU/g, respectively. The same authors reported count reductions for Staphylococcus aureus, Escherichia coli O157:H7, Salmonella Typhimurium, and Campylobacter jejuni. In another study, Ca-alginate coatings combined with nisin, cinnamon EO, and rosemary EO delayed the development of L. monocytogenes in more than 2 log CFU/g in the last day of storage of chicken meat (15 days, 4 °C) [28].

The measurement of thiobarbituric acid reactive substance (TBARS), peroxide value (PV), and total volatile basic nitrogen (TVBN) has been widely used to estimate the extent of meat deterioration. Several authors have reported lower values in TBARS, PV, and TVBN values in samples treated with films/coatings compared with samples without any treatment [29,32,65,66,80,83,89,90]. The presence of antioxidants and very low permeability to oxygen and carbon dioxide are justified as the main reasons for these results, according to the authors.

There are no reference values for thresholds TBARS values because the numbers are influenced by some variables such as animal species, dietary status, age of the animals, type of meat (raw or cooked), and types of TBA methods used [93]. Although, some authors used values between 1 and 2 mg MDA/kg as the maximum acceptable values for chicken meat at which rancid off-flavors become noticeable [29,53,89]. Zhou et al. [90] refer that TBARS values of more than 0.5 mg/kg in chicken meat may be detectable by consumers as off-flavor. All studies for TBARS, showed lower values for samples with films incorporated with antioxidant compounds compared without any treatment, and almost all studies showed a similar increasing trend during the time for all treatments applied. Dalvandi et al. [89] reported values between 0.29 and 1.21 mg MDA/kg in chicken breast meat for 16 days at 4 °C. In another study, values for TBARS of chicken samples at 4 °C were between 0.207 mg/kg and 1.823 mg/kg. The highest value was obtained for control samples on day 10. For films with konjac glucomannan and Kappa-carrageenan incorporated with camellia oil, TBARS values were always lower than 1 mg/kg [90].

Different thresholds for TVBN are used in the scientific community in different studies. Yousefi et al. [83] used a threshold of 15 mg/100 g. Mehdizadeh and Langroodi [66] used a threshold of 28 mg/100 g. Nouri Ala and Shahbazi [32] and Dalvandi et al. [89] used 25 mg/100 g as a threshold that assures meat product freshness. Nouri Ala and Shahbazi [32] reported values always below the threshold established in samples coated with carboxymethylcellulose incorporated with Mentha spicata and Ziziphora clinopodioides during 14 days at 4 °C. Bacterial spoilage may increase TVBN values; thus, microbial control through the application of films or coatings with active compounds may contribute to a substantial reduction of TVBN [89,90].

Other indicators, such as a decrease in pH changes, a reduction in cooking losses, and a decrease in weight and moisture losses in samples treated with films or coatings incorporated with natural extracts or EO, are also reported by several authors [29,80,83,85]. The use of films or coatings can delay moisture and weight loss due to the barrier effect, such as low moisture absorption and water vapor permeability [19]. However, this is only possible until the film/coating is saturated [86].

It is known that the pH of meat affects its microbial stability and shelf-life. Some studies with the application of chitosan have demonstrated the ability of pH stability over the total storage time. The authors mention that this result may be due to the use of acetic acid in the preparation of the solution [87,88]. By regulating and stabilizing the pH, edible films and coatings can help maintain the desired color of meat. Color is one of the main attributes to determine food acceptance by consumers. The color properties of meat packed with films or coated depend on the film-forming materials, but mainly on the concentration of the natural compounds added. The addition of compounds that influences the color can have a negative effect on the samples. However, over storage time, this impact may be lower than the impact of color changes in the untreated samples, as their deterioration due to lipid oxidation, pigment degradation, and microbial growth provides very pronounced color changes, unlike samples where films or coating with natural compounds are applied as demonstrated by Mehdizadeh and Langroodi [66]. Additionally, the barrier properties of edible films and coatings mentioned before can prevent the escape of juices and minimize the contact of meat with oxygen. This can help preserve the natural color of fresh meat, limiting oxidation and maintaining its desirable appearance.

Whenever sensory analysis was carried out, the application of films or coatings showed an improvement in the product, namely in the color stability, taste, texture, odor, and total acceptance of the product [31,32,66,83,85,87,88]. However, some authors reported that the increase of EO or extract concentrations decreased sensory ratings. According to Mahdavi et al. [29], the use of chitosan and anise EO at 1% did not change the chicken burgers’ odor, but sensory ratings decreased with the increase of EO concentrations. Mehdizadeh and Langroodi [66] reported that concentrations higher than 1% of propolis extract and Zataria multiflora Boiss EO affects the taste and reduces sensory ratings of chicken breast fillets. Thus, the choice of film-forming materials and their concentrations, especially antimicrobial/antioxidant compounds, is very important to avoid negatively influencing the meat’s organoleptic characteristics.

As a consequence of the reported results of several studies, an increase in shelf-life is also expected. Several studies have demonstrated an increase in the shelf-life of chicken meat with different combinations of films or coatings with the addition of antioxidant and antimicrobial compounds. Garavito et al. [86] prepared edible coatings from guar gum, nisin, and oregano EO and conducted preservation tests of chicken breast fillets. According to them, the application of the coating increased the product shelf-life to 9 days compared to the control samples (6 days). Khan et al. [78], in a study with films made of bovine gelatin + carrageenan and curcumin, reported a shelf-life increase of up to 17 days in fresh broiler meat compared to control samples (10 days). Raeisi et al. [28] reported an extended shelf-life of about 6 days in chicken breast meat coated with alginate solution containing 5 mg/mL of cinnamon EO and 5 mg/mL rosemary EO. Mehdizadeh and Langroodi [66] reported an extension of the shelf-life of chicken breast meat to approximately 16 days with the use of chitosan, propolis extract (1%), and Zataria multiflora Boiss EO (1%). Considering the microbiological results, and comparing them with the limits considered acceptable (6–7 log CFU/g) mentioned in these studies, it was possible to increase meat’s shelf life between 4 and 12 days. In some of them, the shelf-life was longer than 15 days [28,66,78,80,83,89]. These results are promising, since the shelf-life of chicken meat is about 4–5 days. However, the other parameters should also be taken into consideration, especially the sensory evaluation. Although some authors report acceptable results for sensory evaluation throughout storage, others do not present data. Despite the observed results pointing to an increase in the shelf-life, there are differences among them. These differences are probably due to the antimicrobial and antioxidant capacity of the different active compounds used, as well as the ability of the film-forming materials to maintain their integrity throughout the storage time.