Development and Application of Biodegradable Pectin/Carboxymethylcellulose Films with Cinnamon Essential Oil and Cold Plasma Modification for Chicken Meat Preservation

Abstract

The present study aimed to develop biodegradable films formulated with pectin/carboxymethyl cellulose (CMC) and cinnamon essential oil, investigating the effects of CP treatment time on the properties of the films. The developed films were used as packaging to evaluate the shelf life of chicken meat. Biodegradable films were produced from a film-forming solution containing pectin/CMC, glycerol (30%), and cinnamon essential oil (2%). All formulations included the essential oil, and the control group corresponded to the film that was not subjected to CP treatment. The CP treatments were applied at 22.5 L/min, 20 kV, and 80 kHz for 10, 20, and 30 min. The results showed that increasing CP treatment time led to a progressive reduction in apparent viscosity, indicating improved homogeneity of the polymer system. Hydrophobicity increased with treatment time, as shown by a higher contact angle (from 51.15° to 62.38°), resulting in lower water solubility. Mechanical properties were also enhanced, with tensile strength rising from 3.29 MPa to 6.74 MPa after 30 min of CP. Biodegradability improved with treatment time, reaching 99.51% mass loss after 15 days for the longest exposure. Films produced from the solution treated for 30 min (FCP30) were most effective in extending the shelf life of chicken breast fillets, reducing lipid oxidation (TBARS: 61.9%), peroxide content (58.7%), and microbial spoilage (TVB-N: 59.2%) compared to the untreated film. Overall, the results highlight the importance of CP treatment time as a key factor in enhancing film performance, supporting its application in sustainable active packaging.

1. Introduction

Petroleum-derived polymers, such as polystyrene, polypropylene, and polyethylene, have been widely used in food packaging due to their low cost, light weight, ease of processing, and durability. However, since they are neither biodegradable nor sustainably produced, these materials cause serious environmental impacts [1]. In this context, the development of edible films and coatings for food packaging has emerged as a promising strategy, as they are environmentally friendly and safe for human consumption [2].

Given this scenario, interest in more sustainable alternatives is growing, such as macromolecules extracted from natural sources, especially polysaccharides [3]. Natural biopolymers, such as pectin and carboxymethylcellulose (CMC), have attracted great interest in the production of edible films and coatings. These macromolecules, extracted from plant sources, are biodegradable, non-toxic, renewable, and exhibit good film-forming ability [3,4,5].

Pectin, for example, is a biopolymer naturally found in the cell walls of plant tissues, seeds, roots, leaves, flowers, and fruits. Due to its gelling ability, it is frequently used as a thickening and stabilizing agent in the food industry, in addition to acting as a plasticizer in biodegradable films and biomedical materials [6]. Carboxymethylcellulose (CMC), on the other hand, is an anionic and linear derivative of cellulose, soluble in water at room temperature, with a pH ranging between 5 and 9. In its chemical structure, the presence of hydroxyl groups allows it to interact with water, proteins, plasticizers, and salts, making it highly versatile in applications [7]. According to Rincón et al. [8], characteristics such as its low cost, biodegradability, and film-forming ability make it an ideal candidate for use in various packaging solutions, such as coatings and edible films.

The combination of pectin and CMC has proven to be especially promising in the formulation of biodegradable films and coatings, as the interaction between these two polymers can result in more cohesive structures with improved mechanical, barrier, and flexibility properties compared to their individual use [6]. Spinei et al. [9] produced films using the casting method with pectin, CMC, glycerol, and essential oils. It was reported that the addition of essential oil improved the mechanical properties and reduced the barrier characteristics. Wang et al. [10] reported that pectin/CMC composite films exhibited low mechanical strength and low water resistance. Despite the advantages, films formulated with these biopolymers often present limitations, such as low water resistance and inferior mechanical properties compared to conventional plastics [9,10].

To overcome these challenges, various strategies have been explored, including the incorporation of nanoparticles, essential oils, crosslinkers, plasticizers, and treatments such as gamma rays, laser, ultraviolet irradiation, ultrasonication, cold plasma (CP), microwaves, and high-pressure homogenization, which have been used to improve these properties and modify polymer surfaces [11,12,13,14].

Among the most studied essential oils for application in active packaging, cinnamon essential oil (Cinnamomum zeylanicum) stands out due to its well-known antimicrobial and antioxidant properties. Its composition is rich in bioactive compounds, such as cinnamaldehyde, which allows it to act as a natural functional agent without the need for synthetic additives, making it compatible with clean-label and sustainable food preservation strategies [15,16,17]. Although its flavor is distinct and may not traditionally be associated with poultry, the selection of cinnamon essential oil in this study was based primarily on its high effectiveness against foodborne pathogens and lipid oxidation, rather than on sensory compatibility. To minimize potential off-flavors and ensure safety and functionality, a concentration of 2% was selected based on previous studies reporting strong bioactivity at this level without compromising the structural integrity of the film or excessively altering sensory properties [15,17]. Higher concentrations were avoided due to the risk of overpowering aroma, while lower levels could compromise antimicrobial performance.

On the other hand, CP treatment has gained attention as an innovative non-thermal technique that can enhance film properties [18]. Modification by CP involves exposure to a variety of reactive chemical species (ROS), ultraviolet (UV) photons, atoms, electrons, and free radicals. This leads to changes in the chemical composition and microstructure of the material, which can affect surface energy, the concentration of polar molecules, and barrier and adhesive characteristics [14]. According to Goiana et al. [13], CP treatment modifies the surface of the films, reducing their solubility and increasing their hydrophobicity. This enhances their ability to prevent the penetration of moisture and oxygen, thereby increasing their effectiveness as food packaging materials. Tahsiri et al. [18] observed that CP treatment applied to films based on wild almond protein isolate and Persian gum improved the mechanical attributes of the films without compromising their antimicrobial and antioxidant properties.

Although CP treatment and essential oil incorporation have individually been shown to improve film performance, the optimization of CP treatment time in biopolymer matrices containing cinnamon essential oil remains underexplored. This study addresses this gap by evaluating the influence of different CP exposure times on the structural, mechanical, barrier, and functional properties of pectin/CMC-based films incorporated with cinnamon essential oil. In this context, the present study aimed to investigate the effects of CP treatment time on the properties of pectin–carboxymethylcellulose-based films with the addition of cinnamon essential oil, contributing to the development of more effective and sustainable biodegradable packaging for application in the food industry. Furthermore, in this study, the developed films were used as packaging to evaluate the shelf life of chicken breast fillets through microbial and chemical assessments under refrigerated conditions for 15 days.

2. Materials and Methods

2.1. Materials

Pectin from citrus fruit peel (galacturonic acid ≥ 74.0% on a dry basis, methyl ester of poly-D-galacturonic acid, CAS No.: 9000-69-5) and carboxymethyl cellulose (CAS No.: 9004-32-4) were obtained from Sigma Aldrich (St. Louis, MO, USA), while glycerol was obtained from ACS Científica (Sumaré, SP, Brazil). The essential oil of cinnamon (Cinnamomum cassia) was obtained from Ferquima Indústria e Comércio de Óleos Essenciais (Vargem Grande Paulista, SP, Brazil). All remaining reagents were of analytical grade and were purchased from Sigma Aldrich (St. Louis, MO, USA), and the reagents were freshly prepared on the day of analysis. Fresh chicken breast meat was purchased from a local market (João Pessoa, PB, Brazil). The samples were transported to the laboratory in polystyrene thermal boxes, kept refrigerated with ice packs, within a period of 45 min.

2.2. Preparation of the Film-Forming Solution

For the preparation of the film-forming solution, approximately 3 g of pectin was dissolved in 50 mL of distilled water and thoroughly mixed at 60 °C for 30 min using a constant temperature magnetic stirrer. Subsequently, 0.5 g of CMC was dissolved in 50 mL of distilled water and completely mixed at 50 °C for 30 min. The prepared solutions were mixed for 30 min at 50 °C, followed by the addition of glycerol (30%, w/w) and cinnamon essential oil (2%, w/w), and stirred for 30 min at 35 °C. These concentrations were established based on preliminary tests and previous studies by Zhang et al. [11] and Santos et al. [19].

2.3. Treatment of the Film-Forming Solution with Cold Plasma (CP)

The film-forming solution (300 mL) was subjected to CP treatment using a plasma jet generator (CTP-2000K, DBD-50 reactor, Nanjing Suman Co., Ltd., Nanjing, China). The process was conducted using atmospheric air. The flow rate, operating current, voltage, and frequency were 22.5 L/min, 0.024 mA, 20 kV, and 80 kHz, respectively. The plasma jet nozzle was consistently positioned at a fixed distance of 15 mm below the surface of the liquid, ensuring uniform exposure of the entire solution to the reactive plasma species. This configuration was maintained throughout all treatments to ensure reproducibility. The treatment times were maintained at 10, 20, and 30 min. These conditions were defined based on preliminary tests and previous studies by Zhang et al. [11] and Goiana et al. [13].

Shear Rate and Apparent Viscosity Measurements

The rheological properties of the film-forming solutions, both untreated and those subjected to CP treatment for 10, 20, and 30 min, were determined. Dynamic oscillatory measurements were performed using a Physica MCR 300 rheometer with cone-plate geometry, featuring a rotating cone of 50 mm in diameter and a gap of 0.05 mm. For apparent viscosity measurements, the shear rate ranged from 0.1 to 100 s⁻¹, and the test temperature was 25 °C. The variation of apparent viscosity with shear rate was recorded [20]. The experiments were carried out in triplicate.

2.4. Film Production

Film production was carried out based on the solution casting technique, as described by Santos et al. [19]. The film-forming solutions, both untreated and those subjected to CP treatment for 10, 20, and 30 min, were poured into glass plates previously coated with petroleum jelly to facilitate film removal after drying. The films were left to dry at room temperature for 24 h in a desiccator until characterization. All experiments were performed in triplicate to ensure consistency and reproducibility of the results. Films obtained from the untreated solution were designated as FNT, while those produced with solutions treated with CP for 10, 20, and 30 min were identified as FCP10, FCP20, and FCP30, respectively.

2.5. Film Characterization

2.5.1. Thickness

The thickness of the films was determined using a portable digital micrometer (model 110.284-NEW, Digimess, São Paulo, SP, Brazil). Ten measurements per sample were taken at randomly selected points. The average value was calculated and recorded to ensure accuracy.

2.5.2. Moisture Content

To determine the moisture content of the films, square film samples (4 cm × 2 cm) were dried in an oven at 105 °C until a constant weight was reached [21].

2.5.3. Water Vapor Permeability (WVP)

The WVP of the films was measured using the gravimetric analysis method specified in ASTM standard E96/E96M-16 [22]. Anhydrous CaCL₂ was placed in aluminum cups to achieve 0% relative humidity (0% RH1), and the cups were sealed with the films. These cups were then placed in a chamber containing a fully saturated NaCL solution to provide 75% relative humidity (RH2) and kept at 25 °C. The cups containing the films were shaken hourly for 8 h (accuracy of 0.0001 g). The samples were weighed every 24 h for 7 days. WVP was calculated according to Equation (1).

$$WVP={\displaystyle \frac{\left(\right(Ci/A)\times X) }{(P\times (RH1-RH2)}}$$

(1)

where Ci is the slope coefficient of the line generated by the weight gain of the silica over time; X is the thickness (mm) and A is the area of the film (m²); P is the water vapor saturation pressure at 25 °C (22.2 mmHg); RH1 is the relative humidity in the desiccator and RH2 is the relative humidity inside the capsule. The result was expressed in g·mm/kPa·h·m².

2.5.4. Solubility

The water solubility of the films was determined according to the experimental protocol described by Morais et al. [23]. For this purpose, the films were cut into 4 cm² pieces, and the samples were dried in a forced-air circulation oven (Tecnal, TE-394/3-MP, Piracicaba, SP, Brazil) at 105 °C for 24 h until a constant weight was reached. The samples were then immersed directly in 30 mL of distilled water at 25 °C for 24 h, after which they were removed, dried again at 105 °C for 24 h, and weighed until a constant weight was reached.

2.5.5. Contact Angle

The contact angle was determined according to the methodology previously proposed by Goiana et al. [13], using an optical contact angle meter, where a drop of water was placed on the surface of the films. Film samples (4 × 2 cm²) were fixed on a glass holder, and an image was captured when the drop touched the surface. The contact angle measurement was based on this image.

2.5.6. Tensile Strength and Elongation at Break

Tensile strength and elongation at break were determined according to method D828-97 [24], using a TA TX Plus texture analyzer (Stable Micro Systems, Surrey, UK). Samples (20 × 40 mm² dimensions) were cut from the center of the composites and subjected to tensile testing at a rate of 0.42 mm/s. The initial grip separation was 30 mm, and the test was carried out until the film broke. Tensile strength and elongation at break were obtained directly from the tangent in the linear region of the curve.

2.5.7. Color

The color of the films was determined using a portable digital colorimeter (FRU, WR-10QC, Shenzhen, China), in which the L* (lightness), a* (red/green intensity), and b* (yellow/blue intensity) parameters were obtained.

2.5.8. Surface Morphology

The surface microstructure of the films was analyzed using a scanning electron microscope (VEGA3 TESCAN, Medford, MA, USA) operating at 10 kV and a magnification of 1000×. All samples were properly dried, mounted on aluminum stubs with carbon adhesive tape, and gold-coated in an argon atmosphere.

2.5.9. Biodegradability

The films’ biodegradability was assessed according to the ISO 20200:2015 [25]. For this purpose, dry and fertile soil (NutriPlant, Barueri, São Paulo, Brazil) was distributed in polyethylene trays (25 cm × 40 cm × 13 cm) until reaching a height of 10 cm. Film samples (3 cm²) were fixed between two support screens, forming a system (screen + film + screen) that was completely buried horizontally inside the trays. The samples were kept under controlled conditions of temperature (28 ± 2 °C), relative humidity (67 ± 6%), and soil moisture (32 ± 2%). Mass loss was monitored over 15 days at regular intervals of 3 days. To maintain adequate soil moisture, water was sprayed regularly on the surface throughout the experimental period. The biodegradability of the films was expressed as the percentage of mass loss (%), calculated using the following Equation (2):

$$Mass loss \left(\%\right)=\left({\displaystyle \frac{W_0-W_t}{W_0}}\right)\times 100$$

(2)

where W₀: initial dry mass of the film (before burial); W_t: dry mass of the film at time t (after burial).

2.6. Application of the Films in the Storage of Chicken Meat Fillets

Fresh chicken breast meat was trimmed of visible fat and skin and aseptically cut into 30 g portions using sterilized stainless-steel knives and cutting boards previously disinfected with 70% ethanol under a laminar flow hood. The portions were handled with sterile gloves and immediately transferred to sterile surfaces to avoid microbial cross-contamination. For packaging, circular bags were manually fabricated using the developed films (FNT, FCP10, FCP20, FCP30). Circular sheets of film (approximately 12 cm in diameter) were heat-sealed along the edges using a manual impulse heat sealer (Registron^®, model RG-PFS300, São Paulo, SP, Brazil) at 130 °C for 3 s, forming sealed pouches with sufficient internal volume for the meat portion (Figure 1). After inserting the chicken fillets, the open edge was sealed under the same conditions. Packaging was conducted under ambient air conditions, with no use of modified atmosphere.

Unpackaged samples (i.e., exposed to air without film bags) were used as the control group. All packaged and control samples were then individually placed in clean, rigid plastic containers to prevent mechanical damage and cross-contamination during storage. The containers were stored at 4 °C for 15 days. Analyses were conducted on storage days 0, 3, 6, 9, 12, and 15, evaluating total volatile basic nitrogen (TVB-N), peroxide value, and thiobarbituric acid reactive substances (TBARSs).

2.6.1. Total Volatile Basic Nitrogen (TVB-N)

The TVB-N of chicken breast was determined using an automatic Kjeldahl nitrogen analyzer (LKN-9838, Laboao, São Paulo, SP, Brazil). Briefly, 10 g of meat was mixed with 75 mL of distilled water, and 1 g of magnesium oxide was homogenized for 30 min. The TVB-N value was expressed in mg/100 g [26]. Each test was performed in triplicate.

2.6.2. Peroxide Value

The peroxide value was determined according to the method proposed by Yu & Xu [27]. The meat samples (10 g) were thoroughly mixed with 30 mL of petroleum ether. The solution was extracted for 24 h before filtration and solvent removal by rotary evaporation. An aliquot of 3 g of the filtrate and 1 mL of potassium iodide solution with 60% (v/v) acetic acid/chloroform solution (30 mL) was mixed for 3 min in the dark. A total of 100 mL of deionized water was added, and the solution was titrated with 0.01 M Na₂S₂O₃ containing starch iodide indicator until the equivalence point. A reagent blank was prepared in the same way without chicken meat. The results were expressed in milliequivalents (meq) of active oxygen per kg of lipid (meq O₂/kg). Each test was performed in triplicate.

2.6.3. Thiobarbituric Acid Reactive Substances (TBARS)

For the TBARS analysis, 10 g of chicken meat was mixed with 25 mL of deionized water and homogenized for 2 min. Then, 25 mL of a 5% (w/v) trichloroacetic acid solution was added with stirring, and the mixture was left to rest for 30 min. After this period, 5 mL of the supernatant was collected and combined with 5 mL of a 0.02 mol/L thiobarbituric acid solution. The mixture was then heated in a water bath at 95 °C for 40 min. After cooling to room temperature, the sample was analyzed by spectrophotometry (model SP-2000 UV, Spectrum, Shanghai, China) at 532 nm. The results were expressed as malondialdehyde (MDA) content in mg per kg of sample (mg MDA/kg) [27].

2.7. Statistical Analysis

All experiments were performed in triplicate across at least three independent production batches. The results are presented as means ± standard deviations. One-way ANOVA followed by Tukey’s test (p < 0.05) was used to analyze significant differences, considering both within-batch and between-batch variability, thus confirming reproducibility among independent production batches. Statistical analyses were performed using the Assistant Beta 7.7 software (available as freeware from: http://www.assistat.com). URL (accessed on 10 January 2025).

3. Results and Discussion

3.1. Apparent Viscosity of the Film-Forming Solution

The determination of the apparent viscosity of the film-forming solutions is essential to predict their performance during processing and film formation. Viscosity directly influences spreadability, uniformity of the deposited layer, emulsion stability, and the ability to form cohesive and homogeneous films [28], thereby optimizing applications in packaging, coatings, and other areas. In this regard, Figure 2 shows the apparent viscosity profile of the film-forming solutions formulated with pectin, CMC, and cinnamon essential oil, before (FNT) and after CP treatment for 10, 20, and 30 min (FCP10, FCP20, and FCP30, respectively).

All solutions exhibited pseudoplastic behavior, with decreasing viscosity as the shear rate increased, a typical result of the orientation and alignment of polymer chains under flow, leading to a consequent reduction in flow resistance. Pseudoplastic behavior is highly desirable in film-forming solutions, as it combines good processability with stability at rest [29]. However, a systematic and significant reduction in apparent viscosity (p < 0.05) was observed with increasing CP exposure time, although not sufficient to alter its pseudoplastic behavior. This behavior was also previously observed by Zhang et al. [11] when evaluating the apparent viscosity of a gelatin-carboxymethylcellulose-based solution treated with CP for 10 min.

One justification for this reduction in viscosity is the occurrence of conformational rearrangements and/or partial rupture of secondary interactions (such as hydrogen bonds and electrostatic interactions) between the pectin and CMC molecules. Consequently, there is a partial disorganization of the three-dimensional network responsible for the solution’s viscosity [30]. The action of plasma may also oxidize functional groups on the polymer chains, such as hydroxyl, carboxyl, and methoxyl groups, altering the solubility and rigidity of the macromolecule. Such modifications reduce the hydrodynamic volume of the chains, which compromises their capacity for intermolecular interaction and, therefore, their contribution to the solution’s viscosity [14].

Furthermore, it can be concluded that CP treatment may have affected the distribution and stability of cinnamon essential oil in the polymer matrix. Plasma exposure can act as a form of assisted emulsification, increasing the dispersibility of lipophilic droplets, reducing the average size, or promoting changes in interfacial tension. This improved dispersion contributes to a more homogeneous system with lower resistance to shear, helping to reduce the apparent viscosity [31].

From a technological perspective, this modulation of viscosity is relevant, since less viscous solutions tend to exhibit better spreadability, facilitating the formation of more uniform films with lower thickness, which can directly impact the structure, barrier properties, and adhesion of the films to food surfaces [20]. Therefore, the results obtained suggest that CP, by acting directly on the colloidal matrix of the film-forming solution, functions as a modifying agent of the molecular structure of the polysaccharides, controllably reducing the system’s viscosity.

3.2. Physical, Barrier, and Mechanical Properties of the Films

Table 1. Physical, barrier, and mechanical properties of films produced with the film-forming solution of pectin/CMC and cinnamon essential oil, untreated (FNT) and treated with cold plasma for different durations: 10 min (FCP10), 20 min (FCP20), and 30 min (FCP30).

Parameters	FNT	FCP10	FCP20	FCP30
Thickness (mm)	0.14 ± 0.00 b	0.15 ± 0.001 a	0.14 ± 0.001 b	0.13 ± 0.00 c
Moisture content (%)	14.20 ± 0.23 a	13.41 ± 0.09 b	12.75 ± 0.13 c	10.03 ± 0.22 d
WVP (g·mm/kPa·h·m2)	1.33 ± 0.15 d	2.80 ± 0.11 c	3.25 ± 0.19 b	4.61 ± 0.34 a
Solubility (%)	80.66 ± 0.25 a	74.10 ± 0.16 b	69.53 ± 0.23 c	65.24 ± 0.18 d
Contact angle (°)	51.15 ± 0.40 d	53.29 ± 0.12 c	57.50 ± 0.20 b	62.38 ± 0.43 a
Tensile strenght (Mpa)	3.29 ± 0.21 d	4.32 ± 0.19 c	5.91 ± 0.15 b	6.74 ± 0.22 a
Elongation at break (%)	0.18 ± 0.05 d	0.26 ± 0.04 c	0.35 ± 0.11 b	0.47 ± 0.16 a

Caption: mean ± standard deviation. FNT: films produced with untreated solution (control); FCP10, FCP20, and FCP30: films produced with solutions treated with cold plasma for 10, 20, and 30 min, respectively; WVP: Water vapor permeability. ^a–d different letters in the same row indicate significant differences (p  ≤  0.05).

presents the physical, barrier, and mechanical properties of films formulated with pectin/CMC solutions and cinnamon essential oil, treated or not treated with CP. It is observed that the treatment induced significant changes (p < 0.05) in all analyzed parameters, with effects dependent on the exposure time of the film-forming solution to CP.

The films presented thicknesses ranging from 0.13 to 0.15 mm (p < 0.05), with a slight increase observed in FCP10. However, longer plasma exposure times (FCP20 and FCP30) resulted in significantly thinner films compared to the control. This reduction may be associated with partial breaking of polymer chains and/or molecular restructuring promoted by the plasma, which favors greater compaction of the matrix during drying. Additionally, the lower viscosity of the treated solutions (Figure 2) may have contributed to greater fluidity during the spreading of the solution on the plate, resulting in thinner films. These findings are consistent with trends observed in other biopolymer systems. For example, Spinei et al. [9] reported thicknesses between 54.1 and 63.1 µm for pectin/CMC films containing bee bread oil and suggested that the incorporation of lipophilic compounds may influence film structure and thickness depending on matrix interactions and processing conditions. Although their films were thinner than those obtained in the present study, both works highlight the sensitivity of film thickness to compositional and physicochemical modifications.

The results also indicated a progressive and significant reduction in moisture content with increasing plasma exposure time (p < 0.05), with moisture values ranging from 10.03% (FCP30) to 14.20% (FNT). This behavior can be attributed to modifications in the hydrophilic interactions of the polymer matrix, which may promote slight crosslinking and oxidation of hydroxyl groups, reducing the matrix’s affinity for water [11]. Moreover, the structural compaction resulting from prolonged exposure may hinder the diffusion of water molecules within the film. Goiana et al. [13] observed a moisture content of 18% for films produced with corn starch treated by CP for 20 min.

Interestingly, a significant increase in WVP was observed with increasing treatment time, with values ranging from 1.33 g·mm/kPa·h·m² (FNT) to 4.61 g·mm/kPa·h·m² (FCP30) (p < 0.05). Despite the reduction in moisture and thickness, the increase in WVP may be related to partial degradation of polymer chains or discontinuities in the matrix resulting from the physical action of plasma on the solutions [32]. Similarly, Tahsiri et al. [18] reported that CP treatment for 10 min affected the WVP of films based on wild almond protein isolate and Persian gum. This behavior demonstrates that although plasma promotes structural reorganizations, it can also compromise the continuous integrity of the polymeric vapor barrier, especially with prolonged exposure.

The solubility of the films (Table 1) progressively decreased from 80.66% (FNT) to 65.24% (FCP30) with increasing treatment time (p < 0.05), a positive result indicating greater resistance of the polymer matrix to dissolution. This behavior was also reported by Goiana et al. [13] for films produced with corn starch treated by CP for 20 min. This reduction may be attributed to possible plasma-induced crosslinking reactions, which generate stronger intermolecular bonds less susceptible to water action. Surface oxidation may also reduce the number of available hydrophilic groups, contributing to a more hydrophobic matrix and, consequently, lower solubility [33].

A significant increase in the hydrophobicity of the films was observed with plasma treatment, rising from 51.15° (FNT) to 62.38° (FCP30) (p < 0.05). This increase indicates that the treated films exhibited greater surface hydrophobicity, that is, lower affinity of the film surface for water. Additionally, plasma may promote structural rearrangements on the surface of the film-forming matrix, such as compaction or reorientation of molecular segments, hindering the initial penetration of water [34]. Santhosh et al. [35], when evaluating the effect of atmospheric CP treatment on the properties of edible films made from pea protein isolate, reported that the surface hydrophobicity of the films increased from 38.43° to 61.67° with increasing treatment time. In our study, the increase in contact angle aligns with the solubility results, which showed a significant reduction with longer plasma exposure time.

The integrity and stability of packaging materials strongly depend on their mechanical properties, which play a crucial role in ensuring their durability and resilience during harvesting, handling, and transportation [18,19]. In this context, the results for the mechanical parameters (tensile strength and elongation at break) of the produced films are shown in Table 1. Tensile strength increased significantly with treatment, especially in FCP30 (6.74 MPa, p < 0.05). This result can be explained by the reorganization and possible crosslinking of polymer chains promoted by the plasma, which makes the matrix more cohesive and resistant to rupture under tension [18]. Furthermore, the lower thickness and solubility, associated with greater compaction, favor the mechanical behavior obtained.

The progressive increase in deformation until rupture, especially in the FCP30 film (0.47%, p < 0.05), indicates an improvement in matrix flexibility, which may be related to the redistribution of intermolecular interactions and greater segmental mobility promoted by the treatment. Plasma can induce both the breaking of weak bonds and the reorientation of chains, favoring a less rigid and more elastic network [36]. This behavior is particularly desirable for films applied to food products, as it combines mechanical strength with the ability to adapt to the substrate. Santhosh et al. [35] reported that edible films made from pea protein isolate after 120 s of CP treatment showed an increase in tensile strength from 2.40 to 3.98 MPa, and elongation at break increased from 77.53 to 106.95%.

Overall, the results obtained demonstrate that CP was effective in modifying the physicochemical and functional properties of the films, making them stronger, less soluble, and more hydrophobic. However, it is important to highlight that all formulations analyzed contained cinnamon essential oil, and no cinnamon essential oil-free control group was included. While this choice allowed the focus to remain on CP exposure time, it limits the ability to isolate the specific contribution of CP from potential interactions with cinnamon essential oil. Future research should incorporate controls without cinnamon essential oil to better elucidate the individual and combined effects of CP on film structure and performance.

3.3. Color

Table 2. Color parameters (L*, a*, and b*) of films produced with the film-forming solution of pectin/CMC and cinnamon essential oil, untreated (FNT) and treated with cold plasma for different durations: 10 min (FCP10), 20 min (FCP20), and 30 min (FCP30).

Films		L*	a*	b*
FNT		40.77 ± 0.14 d	12.43 ± 0.30 a	48.79 ± 0.15 d
FCP10		46.72 ± 0.21 c	1.19 ± 0.19 c	52.11 ± 0.28 c
FCP20		61.05 ± 0.17 b	4.47 ± 0.42 b	64.87 ± 0.22 a
FCP30		63.71 ± 0.12 a	2.70 ± 0.10 bc	63.41 ± 0.19 b

Caption: mean ± standard deviation. FNT: films produced with untreated solution (control); FCP10, FCP20, and FCP30: films produced with solutions treated with cold plasma for 10, 20, and 30 min, respectively; ^a–d different letters in the same column indicate significant differences (p  ≤  0.05).

presents the color parameters of films obtained from film-forming solutions containing pectin/CMC and cinnamon essential oil, with and without CP treatment. The parameters L* (lightness), a* (red/green tendency), and b* (yellow/blue tendency) varied significantly among the treatments (p < 0.05), reflecting structural and chemical changes induced by the applied treatment. The control film (FNT), produced without exposure of the film-forming solution to plasma, showed the lowest lightness (L* = 40.77, p < 0.05), indicating a darker coloration, as well as higher values for the parameters a* (12.43) and b* (48.79) (p < 0.05), revealing a more reddish and yellowish hue, respectively. This coloration can be attributed to the presence of cinnamon essential oil in the formulation, whose phenolic compounds naturally impart yellowish to brownish tones to the material. With the application of CP to the film-forming solution, a significant increase in the lightness of the films was observed, particularly for treatments FCP20 and FCP30, whose L* values were 61.05 and 63.71 (p < 0.05), respectively. This increase may be associated with the structural modification of macromolecules, promoting better light dispersion on the film surface.

The a* parameter decreased in the plasma-treated samples, especially in FCP10 (1.19) and FCP30 (2.70) (p < 0.05), indicating a neutralization of the red hue. The decrease in a* may be related to the oxidation of natural pigments present in the essential oil or to a reduction in the concentration of chromophore groups due to the action of reactive species generated by the plasma. Meanwhile, the b* value, associated with the yellow hue, increased significantly with the treatment, peaking in the FCP20 sample (b* = 64.87), followed by FCP30 (63.41) and FCP10 (52.11). This increase may be linked to the formation of new oxygenated functional groups (such as carbonyls or carboxyls) generated by plasma-induced oxidation reactions, which can intensify the yellow hue of the films.

Overall, the results indicate that CP treatment of the film-forming solution significantly affects the color attributes of the films, making them visually lighter and less reddish. These changes can be advantageous or not, depending on the intended final application, since visual appearance directly influences the acceptability of biodegradable packaging and edible films. Furthermore, the observed effects reinforce the potential of CP as a tool for surface and functional modification of polysaccharide-based polymeric systems.

3.4. Morphology by SEM

Figure 3 presents representative micrographs obtained by scanning electron microscopy (SEM), highlighting specific surface features of the developed films with yellow annotations. These regions were selected to illustrate differences in morphology among samples (FNT, FCP10, FCP20, and FCP30). The films were prepared from solutions containing pectin/CMC and cinnamon essential oil. As reported by Santos et al. [19], the morphology of films is strongly associated with the chemical and structural nature of the biopolymers used, directly influencing properties such as permeability, solubility, and mechanical strength. In the control film (FNT), the circled region clearly shows surface roughness and visible cracks, which may compromise the physical integrity of the film and favor water vapor permeability. In contrast, the area highlighted in the FCP10 sample reveals a partially reorganized and smoother surface, suggesting that CP treatment altered the spatial arrangement of the polymer matrix.

It is important to highlight that, in this study, CP was applied directly to the film-forming solution, and not to the already formed film. Under this condition, the plasma acts by promoting physicochemical modifications in the solution constituents through the generation of reactive species (such as free radicals, ions, and electrons) that can break or reorganize chemical bonds, induce oxidation or crosslinking reactions, and alter the conformation of polymer chains [14,37]. These transformations directly impact molecular rearrangement during drying, which is reflected in the final morphology of the films.

In the highlighted region of FCP20, the surface appears more compact and homogeneous, possibly resulting from moderate chain rearrangement and improved molecular organization. Conversely, in the representative region of FCP30, fine surface cracks were identified, which may reflect a higher degree of chain modification due to longer CP exposure, potentially compromising matrix continuity and flexibility.

These results are consistent with previous studies, such as Gupta et al. [38], which demonstrated that CP treatment can promote improvements in the surface morphology of edible films by modulating molecular interactions between the present polymers. Therefore, the yellow-marked regions in Figure 3 illustrate how CP exposure time influences surface organization and supports the hypothesis that cold plasma is an effective tool for tailoring the microstructure of polysaccharide-based films.

3.5. Biodegradability

The evaluation of the biodegradability of polymeric films is fundamental in the characterization of materials intended for sustainable applications, especially those developed as alternatives to conventional fossil-based plastics. Understanding the behavior of these materials over time, under conditions simulating soil disposal, is essential to estimate their natural degradation capacity by the action of microorganisms present in the environment [23]. Figure 4 shows the mass loss evolution of the films during 15 days of soil exposure.

All samples showed a gradual mass reduction over time (p < 0.05), with approximately linear degradation behavior. The rate of loss was more pronounced during the first nine days, especially in the films treated with CP, indicating that the treatment contributed to accelerating the initial stages of biodegradation, such as hydrolysis of the polymer matrix and its subsequent fragmentation. Since plasma was applied directly to the film-forming solution, the high energy generated by the CP resulted in the breakage of molecular chains between pectin and CMC and a decrease in intermolecular interaction [11]. These modifications may have made the films more hydrophilic and susceptible to the action of enzymes and microorganisms present in the soil, favoring the bioavailability of the material for biological degradation.

From the 12th day onward, all films exhibited mass losses greater than 90% (p < 0.05), demonstrating that although CP accelerates the process, biodegradability is high in all cases. At the end of the 15 days, the plasma-treated films showed greater mass loss compared to the control (FNT), whose degradation reached 94.34% (p < 0.05). The treatments FCP10, FCP20, and FCP30 achieved mass losses of 98.30%, 99.12%, and 99.51%, respectively, indicating a positive correlation between plasma exposure time and the biodegradation rate. These results reinforce the hypothesis that CP treatment favorably modifies the chemical properties of the polymer matrix, increasing its susceptibility to microbial action in the soil. This characteristic is especially relevant for applications in biodegradable packaging intended for meat products, such as chicken meat, where a balance between technical performance and reduced environmental impact is desired.

3.6. Storage of Chicken Meat Fillets

The quality and stability of chicken meat fillets during refrigerated storage (4 °C) were monitored through parameters indicating microbial and oxidative deterioration: total volatile basic nitrogen (TVB-N) (Figure 5A), peroxide value (Figure 5B), and thiobarbituric acid reactive substances (TBARSs) (Figure 5C).

TVB-N is widely used as a chemical indicator of the deterioration of meat products, reflecting the release of volatile nitrogenous compounds such as ammonia (NH₃), trimethylamine (C₃H₉N), and dimethylamine (C₂H₇N) during microbial growth and protein degradation [23]. International legislation does not establish a single standardized limit for TVB-N levels in chicken meat.

The TVB-N values (Figure 5A) progressively increased in all samples, reflecting the action of spoilage microorganisms and the consequent degradation of proteins and volatile amines. However, the coated fillets showed significantly lower values (p < 0.05) than the control (without film), especially those packaged with films treated with CP. At the end of the storage period, the control sample reached 34.8 mg N/100 g, while the values for FNT, FCP10, FCP20, and FCP30 were 27.9, 23.3, 17.6, and 14.2 mg N/100 g, respectively. This corresponds to reductions of approximately 19.8% (FNT), 33.1% (FCP10), 49.4% (FCP20), and 59.2% (FCP30), demonstrating that the application of films, especially those modified by CP, was effective in containing microbial and enzymatic deterioration of the meat. The current findings agree with previous studies by Sheerzad et al. [39], which evaluated the shelf life of chicken meat coated with whey protein isolate, nanochitosan, bacterial nanocellulose, and cinnamon essential oil.

The enhanced performance of CP-treated films may be related to improved barrier and active properties. However, it is important to note that the water vapor permeability (WVP) of the films increased with CP treatment time, with FCP30 presenting the highest WVP. While higher WVP theoretically allows greater moisture exchange—especially in high-moisture products such as chicken—no perceptible or measurable moisture loss was observed in the coated fillets during the experimental period. This suggests that the increased WVP did not compromise the moisture content of the meat under the studied conditions. Moreover, even if moisture migration was facilitated to some degree, it is likely that the enhanced antioxidant and antimicrobial activity provided by the CP-treated films (particularly FCP30) played a more dominant role in delaying spoilage processes. Thus, the trade-off between increased WVP and improved bioactivity seems to be favorable in this context, as the films effectively extended shelf life despite the reduced moisture barrier.

In fact, the cinnamon essential oil played a central role in delaying the formation of nitrogenous volatiles. The CP treatment may have potentiated this effect by promoting greater retention or controlled release of bioactive compounds and/or by modifying surface properties that favor their activity.

Lipid oxidation is one of the main factors compromising the quality of meat products during storage, negatively affecting flavor, color, nutritional value, and food safety. Peroxide value is commonly used to monitor the early stages of this process, reflecting the formation of hydroperoxides as primary products of lipid oxidation [40]. Regarding the peroxide value (Figure 5B), a similar behavior was observed. The control fillet (without coating) also showed an increase over storage, reaching 1.72 meq/kg at 15 days, while the coated fillets presented reductions of up to 58.7% in the case of FCP30 (0.71 meq/kg). This indicates that plasma enhanced the antioxidant effect of the films, possibly by inducing modifications in the polymer matrix that resulted in a more efficient barrier to oxygen diffusion and/or greater retention of the active compounds from the essential oil, contributing to the inhibition of lipid peroxide formation. Oyom et al. [39], when developing an oleogel-based coating with thyme essential oil and applying it to the storage of fried chicken nuggets, observed that increasing the concentration of thyme essential oil led to a remarkable twofold reduction in peroxide values compared to the control.

Finally, advanced lipid oxidation was monitored through the TBARS assay (Figure 5C). A progressive increase in TBARS values was observed in all samples throughout storage, with the control fillet (without film) showing the highest values at all time points. On day 15, the control fillet reached 16.8 mg MDA/kg, while the fillets coated with untreated films (FNT) showed a value of 13.1 mg MDA/kg, corresponding to a 22.0% reduction. The samples coated with CP-treated films exhibited even more pronounced reductions: FCP10 (11.1 mg MDA/kg; 33.9% reduction), FCP20 (8.4 mg MDA/kg; 50.0%), and FCP30 (6.4 mg MDA/kg; 61.9% reduction). These results demonstrate that films containing cinnamon essential oil exert a significant protective effect against lipid peroxidation, likely due to the high concentration of phenolic compounds, such as cinnamaldehyde, present in the essential oil [15]. These compounds are capable of acting as free radical scavengers, interrupting the oxidative chain responsible for malondialdehyde (MDA) formation, the main marker measured by the TBARS assay. Xu et al. [40], when developing bioactive polyvinyl alcohol films with the addition of oregano essential oil microcapsules, reported that the packaging delayed lipid oxidation, protein degradation, and moisture loss in ready-to-eat chicken breasts.

In all cases, the results reinforce the finding that CP treatment appears to have enhanced the functionality of the films. This effect may be related to physicochemical modifications in the film structure, such as increased crosslinking, improved adhesion to the substrate, or greater retention and/or controlled release of the active compounds from the essential oil. The more pronounced reduction observed in the FCP20 and FCP30 films supports the hypothesis that the plasma exposure time positively influences the antioxidant efficacy of the material.

In summary, despite the trade-off between improved active properties and increased water permeability, pectin/CMC films with cinnamon essential oil—especially those treated with CP—effectively preserved chicken breast fillets, reducing oxidative deterioration and extending shelf life during refrigerated storage. This highlights the potential of CP as a tool for tailoring the functionality of biopolymer-based packaging.

4. Conclusions

CP treatment improved the mechanical strength, hydrophobicity, and biodegradability of pectin/CMC-based films. The FCP30 film notably extended the shelf life of chicken breast fillets by reducing TBARS (61.9%), peroxide value (58.7%), and TVB-N (59.2%). However, CP also increased the WVP, likely due to surface modifications or microstructural discontinuities, which may compromise the films’ barrier to moisture.

Despite this drawback, preservation outcomes suggest that the antioxidant and antimicrobial effects outweigh the increased WVP. Morphological analyses (e.g., AFM or profilometry) are needed to better correlate surface features with microbial growth. Rather than a limitation, the absence of sensory evaluation and pathogen-specific microbiological data should be seen as a critical direction for future research. Studies integrating consumer sensory panels and targeted microbial assays (e.g., Salmonella or Listeria inhibition) are essential to validate the practical applicability and safety of these films in real-world food systems. Furthermore, although a synergistic effect between CP and cinnamon essential oil was inferred, the lack of a cinnamon essential oil-free control limits definitive conclusions. Future studies should include appropriate controls and molecular analyses (e.g., FTIR, XPS) to clarify individual contributions, confirm interactions, and optimize CP exposure for practical applications.