Curcuma-, Mustard-, and Ginger-Infused PLA/TEC Films: A Comparative Study of Sustainable Active Packaging for Fresh Meat Preservation

Abstract

The growing demand for sustainable food packaging has spurred interest in biodegradable active films. This study aimed to develop novel polylactic acid/tetraethyl citrate (PLA/TEC) composite films reinforced with curcuma, mustard, and ginger powders for extending the shelf life of fresh minced meat. Films incorporating 5, 10, and 15 wt% of each powder were prepared via melt extrusion and compression, and characterized by XRD, FTIR, tensile testing, oxygen barrier measurements, DPPH antioxidant assays, and antibacterial tests against Listeria monocytogenes and Escherichia coli. Optimal 10 wt% formulations were applied to fresh minced pork and evaluated for microbial quality, lipid oxidation, and sensory properties over 8 days at 4 °C. Curcuma powder exhibited the strongest plasticizing effect, increasing elongation at break up to 410%, while ginger acted as a reinforcing filler. The 10 wt% formulations provided the best oxygen barrier (OTR: 55.4–61.8 cc/m²·day). Curcuma showed the highest antioxidant activity (EC₅₀ = 34.4 mg/mL at 15 wt%), followed by ginger and mustard, while antibacterial activity was moderate for all films. In meat packaging tests, all three active films extended shelf life by approximately 2 days compared to PLA/TEC, with curcuma-based films showing the best overall performance in delaying microbial growth and lipid oxidation. The PLA/TEC matrix effectively accommodated high loadings of natural spice powders, yielding flexible, fully bio-based active films. Curcuma-containing films demonstrated the most promising balance of properties, offering a viable sustainable alternative for fresh meat packaging.

1. Introduction

The global shift towards sustainability and the circular economy has intensified the search for biodegradable, bio-based materials suitable for food packaging applications, aiming to reduce the environmental burden caused by conventional petroleum-derived plastics [1,2,3,4,5,6,7]. The accumulation of non-biodegradable petroleum-based packaging waste in terrestrial and marine environments has become a critical environmental challenge, driving the urgent need for sustainable alternatives [1,2,3,4,5,6,7]. Among the various strategies to address this issue, the development of bio-based, biodegradable food packaging materials represents a key pathway towards reducing the environmental footprint of the food industry. Polylactic acid (PLA), derived from renewable resources such as corn starch and sugarcane, offers a promising solution due to its compostability and comparable performance to conventional plastics [8,9,10,11]. However, the full realization of PLA’s sustainability potential requires addressing its inherent brittleness through plasticization, as well as incorporating active functionalities to extend food shelf life and reduce food waste—an often overlooked but significant contributor to environmental degradation. Among the various bio-based polymers, polylactic acid (PLA) stands out as one of the most promising candidates due to its renewable origin (corn starch, tapioca, and sugar cane), its biodegradability, and its comparable barrier properties to polyethylene terephthalate (PET) [8,9,10,11]. However, the widespread application of PLA in flexible packaging has been hindered by its inherent brittleness, poor viscoelastic behavior, and low melt strength, which necessitate the use of plasticizers to enhance flexibility and processability [12,13,14,15,16].

In a previous study by Karabagias et al., tetraethyl citrate (TEC)—a bio-based, approved food additive (E1505)—was successfully employed as an effective plasticizer for PLA [17]. The authors developed PLA/TEC composite films via melt extrusion and demonstrated that the incorporation of TEC significantly reduced PLA’s brittleness while imparting remarkable self-healing properties, with complete repair of random cuts observed within 120 s. Among the formulations tested, PLA/TEC with 15% v/w (PLA/TEC_0.6) and 20% v/w (PLA/TEC_0.8) TEC content exhibited the most promising combination of mechanical flexibility, water/oxygen barrier properties, low plasticizer migration, and enhanced antioxidant and antibacterial activities [17]. The PLA/TEC film was subsequently applied to fresh pork filets, successfully extending their shelf life by delaying lipid oxidation, preserving heme iron content, and reducing total viable counts compared to commercial packaging [17].

While the incorporation of natural bioactive powders into biopolymer matrices has gained increasing attention, the literature reveals an uneven landscape. For curcuma (turmeric) powder, several studies have reported its successful integration into polylactic acid (PLA) films, demonstrating enhanced antioxidant activity and improved UV-barrier properties [18,19]. Specifically, recent works have shown that curcuma powder can be effectively dispersed in PLA matrices, yielding films with moderate antimicrobial effects [18,19]. Existing reports on ginger are limited to the use of ginger essential oil, while mustard has been primarily encapsulated for controlled release of allyl isothiocyanate rather than as a dispersed powder filler [20,21,22]. This gap is significant, because ginger and mustard powders are rich in phenolic compounds, gingerols, and glucosinolates that could provide cost-effective, solid-state antioxidant and antimicrobial functionality without the volatility and handling challenges of essential oils.

The novelty of the present work is threefold. First, we exploit the previously optimized self-healable PLA/TEC matrix (PLA/TEC_0.8) [17] as a flexible, high-loading-capacity host for natural solid powders. Unlike conventional PLA films, which become brittle and lose mechanical integrity at filler contents exceeding 3–5 wt%, the plasticized PLA/TEC system allows the incorporation of 5, 10, and even 15 wt% spice powders while maintaining adequate flexibility and processability—thereby overcoming a major limitation in PLA-based biocomposite development. Second, we report for the first time the direct incorporation of unprocessed ginger (Zingiber officinale) powder and mustard (Sinapis alba) powder into PLA films. While ginger essential oil [20,21] and encapsulated mustard derivatives [22] have been explored, the direct use of the crude solid powders offers significant advantages in terms of cost, scalability, processing simplicity, avoidance of volatile compound losses, and sustained release of bioactive constituents. Third, we systematically compare three distinct spice powders—curcuma (rich in curcuminoids), mustard (rich in glucosinolates), and ginger (rich in gingerols and phenolic compounds)—within the same ductile PLA/TEC platform. This comparative approach, which has not been previously reported, enables a direct correlation between the specific phytochemical composition of each powder and the resulting mechanical, barrier, antioxidant, antibacterial, and shelf-life extension performance of the films. Such correlations are essential for the rational design of active packaging materials tailored to specific food preservation needs. Therefore, the aim of this study is to (i) fabricate and fully characterize PLA/TEC composite films containing 5, 10, and 15 wt% curcuma, mustard, and ginger powders; (ii) evaluate their structural, mechanical, barrier, antioxidant, and antibacterial properties; and (iii) select the optimal formulation for each powder to assess their efficacy in extending the shelf life of fresh minced pork during refrigerated storage.

2. Materials and Methods

2.1. Chemicals and Reagents

Polylactic acid (PLA), Ingeo™ Biopolymer 3052D, was purchased from NatureWorks LLC (Minnetonka, MN, USA). According to the manufacturer’s technical data sheet, this grade is a lubricated, high-flow biopolymer designed for injection molding applications, with a D-lactide content of approximately 4%, a weight-average molecular weight (Mw) of ~116 kDa, and a relative viscosity of 3.3 (1.0 g/dL in chloroform at 30 °C) [23]. The material has a density of 1.24 g/cm³ (ASTM D792 [24]) and a melt mass-flow rate (MFR) of 14 g/10 min (210 °C/2.16 kg, ASTM D1238 [25]) [23]. Differential scanning calorimetry (DSC) analysis of the as-received PLA revealed a glass transition temperature (T_g) of 55–60 °C and a melting temperature (T_m) of approximately 153 °C (ASTM D3418 [26]) [23]. The material is certified for food contact applications (FDA 21 CFR and EU 10/2011) [23]. Curcuma (Curcuma longa) powder, mustard (Sinapis alba) powder, and ginger (Zingiber officinale) powder were purchased from Health Trade Hellas (Athens, Greece; https://www.healthtrade.gr accessed on 30 July 2026). These powders are hereafter abbreviated as Cur, Mus, and Gin, respectively. The curcuma powder (Curcuma longa) is commercially standardized to contain a minimum of 3.5% curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) as per the supplier’s specification. The mustard powder (Sinapis alba) contains approximately 1.0–1.5% sinigrin (as glucosinolate content) by dry weight, which is typical for commercial ground white mustard seed products. The ginger powder (Zingiber officinale) contains a minimum of 1.5% gingerols and shogaols (total phenolic compounds) as per the supplier’s specification. These values are consistent with the typical bioactive compound content reported in the literature for these spices [27,28]. The powders were used as purchased from a commercial supplier (Health Trade Hellas, Athens, Greece), ensuring batch-to-batch consistency for this study. Methanol (absolute), acetate buffer (CH₃COONa·3H₂O), trichloroacetic acid, and 2-thiobarbituric acid were purchased from Merck (Darmstadt, Germany). 2,2-Diphenyl-1-picrylhydrazyl (DPPH) was obtained from Sigma-Aldrich (Darmstadt, Germany). All other chemicals were of analytical grade. For antimicrobial assays, Tryptic soy agar (TSA) and Trypticasein Soy Broth w/o Dextrose (TSB) were purchased from Condalab, and Plate Count Agar (PCA) was bought from Neogen (Lansing, MI, USA). Moreover, the tested bacterial strains were obtained from the Institute of Technology of Agricultural Products, ELGO-DEMETER, Lykovryssi, Greece.

2.2. Experimental Design—Preparation of Extruded PLA/TEC/xCur, PLA/TEC/xMus, and PLA/TEC/xGin Composite Pellets

All composite pellets were prepared using a Mini Lab twin-screw extruder (Haake Mini Lab II, Thermo Fisher Scientific Waltham, MA, USA) operated at 180 °C and 120 rpm, following the same procedure previously reported for PLA/TEC blends [17]. Prior to use, each spice powder was passed through a 250 μm (60 mesh) stainless steel sieve to remove oversized particles and aggregates, ensuring uniform particle size distribution and improved dispersion within the polymer matrix. This sieving step is consistent with standard practice for food-grade spice powders, which typically exhibit particle sizes in the range of 60–80 mesh (177–250 μm) for curcuma and 37–300 μm for ginger powders as reported in the literature [27,28]. Mustard powder, being a commercially ground seed product, falls within a similar particle size range. All powders were used as received after sieving, without further modification. For each batch, 4 g of PLA were mixed with 800 μL of TEC (corresponding to 20% v/w, i.e., PLA/TEC_0.8 matrix). To this base mixture, curcuma, mustard, or ginger powder was added at three different concentrations: 0.2 g, 0.4 g, and 0.6 g per 4 g of PLA, corresponding to 5, 10, and 15 wt%, respectively. The resulting formulations were coded as PLA/TEC/xCur, PLA/TEC/xMus, and PLA/TEC/xGin, where x = 5, 10, or 15. The extrusion residence time was 5 min for all samples. After extrusion, the obtained pellets were collected and dried in a desiccator at room temperature for 24 h before film formation.

2.3. Film Formation

Films were prepared by thermomechanical compression of the extruded pellets using a hydraulic press with heated plates (170 °C, 0.5 MPa for 3 min). Approximately 1.0 g of pellets was pressed into films of ~11 cm diameter. The film thickness was controlled at 0.25 mm, ensuring uniformity across all formulations for direct comparison of oxygen barrier properties. Pure PLA films and PLA/TEC_0.8 films (without any powder) were also prepared as reference materials.

2.4. Physicochemical Characterization (XRD and ATR-FTIR)

2.4.1. X-Ray Diffraction (XRD)

XRD patterns of the films were recorded on a Bruker D8 Advance diffractometer (Bruker Corporation, Billerica, MA, USA) using Cu Kα radiation (λ = 1.5406 Å) operating at 40 kV and 40 mA. Scans were performed in the 2θ range of 5–40° with a step size of 0.02° and a counting time of 1 s per step.

2.4.2. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR)

ATR-FTIR spectra were recorded with ATR-FTIR spectroscopy by employing a Shimadzu FT-IRSpirit spectrometer (Kyoto, Japan) equipped with an ATR accessory, over the range of 4000–400 cm⁻¹ at a resolution of 4 cm⁻¹. All measurements were performed at room temperature.

2.5. Tensile Properties

Tensile tests were carried out according to the ASTM D638 [29] method using a Simantzi AX-G 5 kN universal testing machine (Simantzi Asteriadis S.A., Athens, Greece). Films were cut into dog-bone shaped specimens (25 mm gauge length, 4 mm width). The crosshead speed was set at 10 mm/min. From the stress–strain curves, the modulus of elasticity (E), tensile strength (σ_uts), and elongation at break (ε_b) were determined. Five specimens from each film formulation were tested, and the mean values ± standard deviation are reported.

2.6. Oxygen Barrier Properties

Oxygen transmission rate (OTR) was measured using an oxygen permeation analyzer (O.P.A. 8001, Systech Illinois Instruments Co., Johnsburg, IL, USA) following ASTM D3985 [30] at 23 °C and 0% relative humidity. For each film, three circular specimens (50 cm²) were tested. The oxygen permeability coefficient (P_O2, in cm²/s) was calculated from the steady-state OTR values and the film thickness, as described previously [31,32].

2.7. Antioxidant Activity (DPPH Assay)

The antioxidant activity of the films was evaluated using the DPPH radical scavenging method. Briefly, 20 mg of each film was cut into small pieces and immersed in 3 mL of a methanolic DPPH solution (0.024 mg/mL, corresponding to 6.11 × 10⁻⁵ mol/L) and 2 mL of acetate buffer (100 mM, pH 7.10). The mixture was kept in the dark at room temperature for 24 h. The absorbance of the supernatant was measured at 517 nm using a UV-Vis spectrophotometer (Shimadzu Corporation, Kyoto, Japan). The percentage of DPPH radical scavenged was calculated as:

% scavenging = [(A₀ − A_s)/A₀] × 100

where A₀ is the absorbance of the DPPH solution without film, and A_s is the absorbance after incubation. The effective concentration (EC₅₀, the amount of film required to scavenge 50% of the initial DPPH radicals) was determined by plotting the % scavenging against film quantity (10–50 mg) and fitting a linear regression.

2.8. Antibacterial Activity

The antibacterial activity of the films was tested against foodborne pathogens, Listeria monocytogenes ((DSMZ 27575) and Escherichia coli (ATCC 25922). Listeria monocytogenes was selected as a test organism due to its significance as a foodborne pathogen capable of growth at refrigeration temperatures (4 °C), making it a critical target for refrigerated meat products such as minced pork. While L. monocytogenes is commonly associated with ready-to-eat products and poultry, pork products—particularly processed pork items such as deli meats and sausages—are also frequently implicated in listeriosis outbreaks and are subject to stringent regulatory limits (zero tolerance in many jurisdictions). The psychrotrophic nature of this pathogen makes it particularly relevant for evaluating the antimicrobial efficacy of active packaging materials intended for refrigerated meat preservation. E. coli was selected as a representative Gram-negative indicator organism to provide a broad spectrum of antibacterial activity assessment. Fresh cultures of the pathogens were prepared and incubated for 24 h at 37 °C. After the incubation period, 10 μL of the cultures were spread on the surface of Petri dishes containing Trypticase soy agar (TSA) and then those plates were covered by the tested active film. Each film was exposed to UV light for 15 min previously. Subsequently, the plates were incubated for 24 h at 37 °C. After that, the film with agar was placed aseptically into stomacher bags with 180 mL of sterilized water and homogenized in a stomacher homogenizer. Serial decimal dilutions were prepared for each sample using the same diluents by obtaining sample concentrations from 10⁻¹ to 10⁻⁷ g/mL. The bacterial count of each pathogen was determined by the spread plate technique using Plate Count Agar (PCA) and the plates were incubated 24 h at 37 °C. Results are expressed as log colony-forming units per gram (logCFU/g). All the measurements were conducted in triplicate.

2.9. Packaging Test of Fresh Minced Pork Meat Using Optimum Films

Based on preliminary mechanical and bioactivity results, the formulations containing 10 wt% of each powder (i.e., PLA/TEC/10Cur, PLA/TEC/10Mus, and PLA/TEC/10Gin) were selected as the optimum films for shelf-life evaluation. Fresh minced pork meat (obtained from a local meat processing facility, Aifantis, Greece) was aseptically divided into 80–100 g portions. Each portion was wrapped between two layers of the respective test film. Commercial wrapping paper (as used by the supplier) served as the control, and pure PLA/TEC_0.8 film (without any powder) was used as a second reference. All wrapped samples were stored at 4 ± 1 °C for 8 days.

At predetermined time intervals (0, 2, 4, 6 and 8 days), samples were analyzed for:

• Lipid oxidation using the thiobarbituric acid reactive substances (TBARS) method, expressed as mg malondialdehyde per kg meat;
• Total viable count (TVC) by spreading appropriate dilutions on Plate Count Agar and incubating at 30 °C for 48 h; results are expressed as log CFU/g.

All analyses were performed in triplicate, and results are presented as mean ± standard deviation. Statistical differences were determined using Mood’s median test (p < 0.05) with SPSS software (v. 28.0, IBM, Armonk, NY, USA).

2.10. Statistical Analysis

All experiments were performed in at least triplicate unless otherwise stated. Results are expressed as mean ± standard deviation (SD).

Tensile properties (modulus, ultimate tensile strength, elongation at break) were measured on five independent specimens per formulation (n = 5), as shown in Table S1. Normality of the data was verified using the Shapiro–Wilk test (p > 0.05). Homogeneity of variances was assessed with Levene’s test. One-way analysis of variance (ANOVA) followed by Tukey’s honest significant difference (HSD) post hoc test was used to determine statistically significant differences among the mean values of different film formulations. A significance level of p < 0.05 was applied. Statistical calculations were performed using IBM SPSS Statistics (version 28.0, IBM Corp., Armonk, NY, USA).

Oxygen transmission rate (OTR) and DPPH radical scavenging activity were measured in triplicate for each film. Differences between means were evaluated by one-way ANOVA and Tukey’s HSD test (p < 0.05). The EC₅₀ values (film mass required for 50% DPPH scavenging) were calculated by linear regression from dose–response data (10–50 mg of film), and the 95% confidence intervals were reported.

Antibacterial activity was evaluated against Listeria monocytogenes and Escherichia coli by exposing inoculated TSA plates to UV-sterilized active films for 24 h at 37 °C. Surviving bacteria were quantified by serial dilution and spread plating on PCA, and results were expressed as log CFU/g (n = 3). Normality was assessed using the Shapiro–Wilk test. Where assumptions were met, one-way ANOVA with Tukey’s HSD was applied; otherwise, the non-parametric Kruskal–Wallis test with Dunn’s post hoc test was used. Both approaches yielded consistent results. All statistical analyses were performed using IBM SPSS Statistics (version 28.0).

Packaging test on fresh minced meat: For each sampling day (0, 2, 4, 6, 8), three independent meat samples per film type were analyzed (n = 3). Lipid oxidation (TBARS) and total viable count (TVC) were each measured in triplicate per sample. Because the data did not always meet normality assumptions (particularly TBARS and TVC), the non-parametric Mood’s median test was used to compare the medians among the different packaging groups (commercial paper, PLA/TEC, PLA/TEC/10Cur, PLA/TEC/10Mus, PLA/TEC/10Gin) at each time point. Pairwise comparisons were performed using Dunn’s test with Bonferroni correction. Differences were considered significant at p < 0.05. All statistical analyses were conducted using SPSS version 28.0.

3. Results

3.1. XRD Analysis of PLA/TEC/xCur, PLA/TEC/xMus, and PLA/TEC/xGin Composite Films

Figure 1 shows the XRD patterns of pure PLA/TEC, PLA/TEC/xCur, PLA/TEC/xMus, and PLA/TEC/xGin films.

The pure PLA/TEC film displays a broad, diffuse halo centered at approximately 2θ = 16°, characteristic of an amorphous or very low-crystallinity PLA structure. This is expected, as the presence of the plasticizer tetraethyl citrate (TEC) disrupts chain packing and inhibits cold crystallization during film formation [17]. Upon incorporation of Cur, Mus, or Gin powder, most formulations remain essentially amorphous. However, a notable exception is observed for PLA/TEC/15Cur (15 wt% Cur). This pattern exhibits two distinct, sharper reflections at 2θ ≈ 17° and 19°, which are assigned to the (110)/(200) and (203) planes of the α-crystalline form of PLA [33,34]. The appearance of these peaks indicates that a high loading of Cur powder acts as crystallization nuclei, promoting partial crystallization of the PLA/TEC matrix. This nucleating effect is likely due to the heterogeneous surface of Cur particles providing sites for ordered chain folding, similar to the action of talc or other natural fillers in PLA [35,36]. For Mus and Gin powders, no such crystalline reflections are observed even at 15 wt%, suggesting weaker nucleating activity under the same thermal history.

Another important observation is that the broadest amorphous halo and the lowest overall intensity are consistently found for the 10 wt% loading of each powder (e.g., PLA/TEC/10Cur, PLA/TEC/10Mus, PLA/TEC/10Gin). This suggests that an intermediate filler content maximizes the disruption of short-range order, yielding the most amorphous structure. It should be noted that, with the exception of PLA/TEC/15Cur, all XRD patterns are characteristic of amorphous polymers, exhibiting only a broad diffuse halo at approximately 2θ = 16°. For such amorphous systems, quantitative crystallinity calculations are not applicable, as there are no distinct crystalline peaks to integrate. Nevertheless, the observed broadening of the amorphous halo at 10 wt% loading for all powders indicates maximum disruption of short-range polymer chain ordering, which is consistent with the enhanced oxygen barrier performance of these formulations (Section 3.4). Conversely, the appearance of sharp reflections at 17° and 19° in PLA/TEC/15Cur confirms partial crystallization induced by the nucleating effect of high curcuma loading, which correlates with the deteriorated oxygen barrier properties observed for this sample (Section 3.4).

It should be noted that no diffraction features were observed in the 30–40° 2θ range for any of the film formulations. Therefore, the XRD patterns are presented in the 5–30° range, which contains all relevant structural information, including the amorphous halo and the crystalline reflections observed for PLA/TEC/15Cur.

3.2. ATR-FTIR Analysis

Figure 2 presents the ATR-FTIR spectra of all films.

The pure PLA/TEC film shows the characteristic bands of PLA: a broad O–H stretching region (3500–3200 cm⁻¹) due to terminal hydroxyl groups and residual moisture, C–H stretching at ~2995 and 2945 cm⁻¹, a strong C=O stretching (ester carbonyl) at ~1750 cm⁻¹, and C–O–C stretching bands at 1180 and 1085 cm⁻¹ [17,37]. Bands related to TEC are largely overlapping with those of PLA.

When Cur, Mus, or Gin powder is incorporated, no new peaks appear in any of the composite spectra. This indicates that no covalent chemical reaction occurs between the powders and the PLA/TEC matrix; the interactions are physical (hydrogen bonding, van der Waals forces) rather than chemical. This is beneficial for maintaining the integrity and processability of the films, even at high filler loadings (15 wt%).

However, a consistent and concentration-dependent change is observed in the 3800–2500 cm⁻¹ region (mainly O–H stretching). Compared to pure PLA/TEC, all composite films show a broader and more intense absorption in this range. The increase is most pronounced for Gin-containing films, followed by Cur and Mus.

3.3. Tensile Properties

Table 1. Tensile properties of PLA/TEC blends with various fillers.

Sample	Elastic Modulus—E (MPa)	Ultimate Strength—σuts (MPa)	%Elongation at Break—%ε
PLA/TEC	687.0 ± 10.8 h	17.50 ± 0.28 f	58.5 ± 1.4 a
PLA/TEC/5Cur	384.0 ± 6.1 d	10.70 ± 0.17 d	248.0 ± 5.9 e
PLA/TEC/10Cur	217.7 ± 3.5 b	6.40 ± 0.10 b	202.0 ± 4.8 d
PLA/TEC/15Cur	119.7 ± 1.9 a	4.30 ± 0.07 a	410.0 ± 9.7 g
PLA/TEC/5Mus	444.8 ± 7.0 e	11.70 ± 0.18 e	243.9 ± 5.8 e
PLA/TEC/10Mus	348.0 ± 5.5 c	6.98 ± 0.11 c	319.2 ± 7.6 f
PLA/TEC/15Mus	228.8 ± 3.6 b	6.84 ± 0.11 b,c	231.6 ± 5.5 e
PLA/TEC/5Gin	801.2 ± 12.7 i	17.14 ± 0.27 f	184.2 ± 4.4 c
PLA/TEC/10Gin	606.0 ± 9.6 g	12.08 ± 0.19 e	152.8 ± 3.6 b
PLA/TEC/15Gin	477.0 ± 7.5 f	9.10 ± 0.14 *	176.5 ± 4.2 c

* 15Gin is significantly different from all others (its own letter, but for compactness it would be, e.g., ‘g’ if added; here it is distinct from all above groups). a–i Values within the same column with different superscript letters are significantly different (p < 0.05) according to one-way ANOVA followed by Tukey’s honest significant difference (HSD) post hoc test. Data are presented as mean ± standard deviation (SD) from five independent measurements per formulation (n = 5).

summarizes the elastic modulus (E), ultimate tensile strength (σ_uts), and elongation at break (%ε) for all films. The full replicated data are provided in Table S1 and representative stress–strain curves in Figure S1 (Supplementary Materials). The results reveal markedly different reinforcing/plasticizing behaviors depending on the type and concentration of the added powder.

Cur powder progressively reduces the modulus and tensile strength while dramatically increasing elongation at break. At 15 wt% Cur, the elongation reaches 410%—almost seven times higher than that of pure PLA/TEC (58.5%). This extreme elongation suggests that Cur particles act as a solid-state plasticizer or interfacial lubricant, possibly by disrupting interchain interactions and promoting chain sliding [18,38,39]. Such behavior is unusual for a rigid powder and may be specific to the chemical nature of Cur (high curcuminoid content with plasticizing-like effects).

Mus also lowers modulus and strength but to a lesser extent than Cur. Elongation increases moderately up to 319% at 10 wt% Mus but then decreases at 15 wt% (231.6%). This drop suggests that above a critical concentration, Mus particles begin to agglomerate, creating stress concentration points that reduce the material’s ability to deform plastically [31,32,40].

Gin exhibits a completely different trend. The modulus initially increases at 5 wt% Gin (801.2 MPa vs. 687 MPa for PLA/TEC), indicating a reinforcing effect—likely due to the higher stiffness of Gin cell wall fragments and good interfacial adhesion [41,42]. At higher loadings, modulus and strength gradually decrease but remain above those of Cur and Mus counterparts. Elongation at break increases relative to PLA/TEC (from 58.5% to 152–184% after adding Gin, but note that pure PLA/TEC is already quite ductile; the elongation values for Gin composites are actually lower than those of Cur and Mus, but still represent flexible films). The moderate elongation, combined with the highest modulus among the three fillers, makes Gin composites suitable for applications requiring a balance of stiffness and deformability.

The non-monotonic trend in elongation at break for Cur-containing films—increasing at 5 wt% (248%), decreasing slightly at 10 wt% (202%), and dramatically increasing at 15 wt% (410%)—reflects a dual mechanism. At low concentrations (5 wt%), Cur particles act as effective plasticizers, disrupting interchain interactions and promoting chain mobility. At 10 wt%, partial agglomeration begins to occur, creating stress concentration points that partially offset the plasticizing effect. At 15 wt%, the extremely high concentration of curcuminoids (with their polar hydroxyl and methoxy groups) provides a dominant plasticizing/lubricating effect that overwhelms any negative effects of agglomeration, enabling extensive chain sliding and resulting in the highest elongation observed among all formulations (410%). This behavior is distinct from that of Mus, where agglomeration dominates at 15 wt% leading to decreased elongation, and reflects the specific chemical nature of Cur powder with its high curcuminoid content.

Overall, the tensile results demonstrate that the plasticized PLA/TEC matrix can accommodate up to 15 wt% natural powders—the highest concentration tested in this study—while remaining flexible. The choice of filler allows tuning of mechanical properties from highly stretchable (Cur) to stifffer and tougher (Gin).

3.4. Oxygen Barrier Properties

The oxygen transmission rate (OTR) and oxygen permeability coefficient (P_o2) of the PLA/TEC films incorporating Cur, mustard, or Gin powder are summarized in

Table 2. Oxygen barrier properties of PLA/TEC films containing Cur, mustard, or Gin powder (mean ± SD, n = 3). Different superscript letters within a column indicate significant differences (p < 0.05) according to one-way ANOVA and Tukey’s HSD.

Sample	Thickness (mm)	OTR (cc/m2·Day)	PeO2 (cm2/s)
PLA/TEC	0.25	92.7 ± 1.3 ef	(2.682 ± 0.037) × 10−9 ef
PLA/TEC/5Cur	0.25	73.6 ± 1.7 c	(2.130 ± 0.049) × 10−9 c
PLA/TEC/10Cur	0.25	55.4 ± 0.7 a	(1.603 ± 0.021) × 10−9 a
PLA/TEC/15Cur	0.25	95.5 ± 1.3 f	(2.762 ± 0.038) × 10−9 f
PLA/TEC/5Mus	0.25	75.8 ± 1.7 c	(2.194 ± 0.050) × 10−9 c
PLA/TEC/10Mus	0.25	57.1 ± 0.7 a	(1.652 ± 0.021) × 10−9 a
PLA/TEC/15Mus	0.25	88.3 ± 1.0 e	(2.555 ± 0.030) × 10−9 e
PLA/TEC/5Gin	0.25	73.3 ± 1.2 c	(2.120 ± 0.033) × 10−9 c
PLA/TEC/10Gin	0.25	61.8 ± 2.8 b	(1.787 ± 0.082) × 10−9 b
PLA/TEC/15Gin	0.25	81.6 ± 1.2 d	(2.346 ± 0.035) × 10−9 d

OTR = oxygen transmission rate; PeO₂ = oxygen permeability coefficient. The statistical letters are derived from Tukey’s HSD test on the OTR data. Means that share no common letter are significantly different (p < 0.05). The thickness was constant for all films, therefore the same grouping applies to PeO₂. a–f Values within the same column with different superscript letters are significantly different (p < 0.05) according to one-way ANOVA followed by Tukey’s honest significant difference (HSD) post hoc test. Data are presented as mean ± standard deviation (SD) from three independent measurements per formulation (n = 3). The thickness was constant for all films (0.25 mm); therefore, the same statistical grouping applies to both OTR and PeO₂ values.

. All films were produced with a constant thickness of 0.25 mm, allowing direct comparison of OTR values.

The pure PLA/TEC film exhibited an OTR of 92.7 cc/m²·day, which is typical for amorphous polylactic acid-based materials [17]. Incorporating 5 wt% of any of the three powders significantly reduced OTR to approximately 73–76 cc/m²·day (p < 0.05), indicating an improvement in oxygen barrier performance. The most pronounced reduction was observed at 10 wt% loading for both Cur and mustard, where OTR values dropped to 55.4 ± 0.7 cc/m²·day (PLA/TEC/10Cur) and 57.1 ± 0.7 cc/m²·day (PLA/TEC/10Mus). These two formulations were not statistically different from each other (both share the superscript a in Table 2) and represent the best oxygen barrier performance among all tested samples. The 10 wt% Gin film (PLA/TEC/10Gin) also showed improved barrier performance (61.8 ± 2.8 cc/m²·day, letter b), though it was slightly inferior to the Cur and mustard counterparts.

3.5. Antioxidant Activity

The radical scavenging activity of the films was evaluated using the DPPH assay, and the results are expressed as EC₅₀ (the film mass required to scavenge 50% of the initial DPPH radicals). Lower EC₅₀ values correspond to higher antioxidant activity.

Table 3. Mean EC₅₀ values with statistical grouping.

Sample	Mean EC50 (mg/mL) ± SD
PLA/TEC	253.9 ± 2.8 i
PLA/TEC/5Cur	152.0 ± 12.0 g
PLA/TEC/10Cur	55.7 ± 1.4 bc
PLA/TEC/15Cur	34.4 ± 0.7 a
PLA/TEC/5Mus	174.8 ± 2.7 h
PLA/TEC/10Mus	80.2 ± 2.3 ef
PLA/TEC/15Mus	70.2 ± 3.7 de
PLA/TEC/5Gin	85.1 ± 1.8 f
PLA/TEC/10Gin	63.1 ± 0.6 cd
PLA/TEC/15Gin	48.9 ± 0.3 b

Letters were assigned using Tukey’s HSD (HSD = 11.5). Means that share a letter are not significantly different (p > 0.05). a–i Values within the same column with different superscript letters are significantly different (p < 0.05) according to one-way ANOVA followed by Tukey’s honest significant difference (HSD) post hoc test. Data are presented as mean ± standard deviation (SD) from three independent measurements per formulation (n = 3). Lower EC₅₀ values indicate higher antioxidant activity. The letters were assigned using Tukey’s HSD (HSD = 11.5). Means that share a letter are not significantly different (p > 0.05).

presents the mean EC₅₀ values with statistical grouping.

The pure PLA/TEC film showed very weak antioxidant activity (EC₅₀ = 253.9 ± 2.8 mg/mL), which is expected as neither PLA nor TEC possesses significant radical scavenging capacity. Incorporation of all three natural powders led to a marked, dose-dependent reduction in EC₅₀, indicating enhanced antioxidant activity.

Cur powder proved to be the most effective antioxidant among the three fillers. At 5 wt% Cur, EC₅₀ dropped to 152.0 mg/mL; at 10 wt% it further decreased to 55.7 mg/mL; and at 15 wt% it reached the lowest value of 34.4 ± 0.7 mg/mL (letter a), which is significantly lower than all other formulations (p < 0.05).

Gin powder also demonstrated considerable antioxidant activity. The EC₅₀ values for 5, 10, and 15 wt% Gin were 85.1, 63.1, and 48.9 mg/mL, respectively. The 15 wt% Gin film (48.9 mg/mL, letter b) was the second most active formulation, although it was significantly less effective than 15 wt% Cur (p < 0.05).

Mus powder showed the weakest antioxidant activity among the three. At 15 wt% mustard, EC₅₀ was 70.2 ± 3.7 mg/mL (letter de), which is higher (i.e., less active) than 15 wt% Gin and substantially higher than 15 wt% Cur.

It is worth noting that for all three fillers, the 10 wt% formulations (PLA/TEC/10Cur, 10Mus, and 10Gin) exhibited EC₅₀ values of 55.7, 80.2, and 63.1 mg/mL, respectively. While the 15 wt% versions were more active, the 10 wt% films offered a balanced combination of antioxidant activity, mechanical integrity, and oxygen barrier performance (see Section 3.3 and Section 3.4). Therefore, the 10 wt% loading was selected as the optimum for each powder in the subsequent shelf-life packaging tests.

3.6. Antibacterial Activity of Films

The results of the antimicrobial activity are presented in

Table 4. Antibacterial activity of PLA/TEC, PLA/TEC/xCur, PLA/TEC/xMus and PLA/TEC/xGin (x = 5, 10, 15% w/w) films in comparison to control samples (pure bacteria cultures) against Listeria monocytogenes and Escherichia coli expressed as log CFU/g.

Sample	L. monocytogenes	E. coli
Control	9.86 ± 0.02 f	10.20 ± 0.02 g
PLA/TEC	10.22 ± 0.02 g	10.12 ± 0.01 f
PLA/TEC/5Cur	9.65 ± 0.15 d	9.86 ± 0.08 d
PLA/TEC/10Cur	9.42 ± 0.14 b	9.86 ± 0.02 d
PLA/TEC/15Cur	9.48 ± 0.16 b	9.23 ± 0.16 a
PLA/TEC/5Mus	9.58 ± 0.26 c	9.92 ± 0.08 e
PLA/TEC/10Mus	9.44 ± 0.11 b	9.49 ± 0.17 b
PLA/TEC/15Mus	9.44 ± 0.13 b	9.90 ± 0.02 e
PLA/TEC/5Gin	9.42 ± 0.17 b	9.65 ± 0.04 c
PLA/TEC/10Gin	9.73 ± 0.05 e	9.48 ± 0.12 b
PLA/TEC/15Gin	9.15 ± 0.04 a	9.54 ± 0.10 b

Values are mean ± SD (n = 3). Different superscript letters within the same column indicate statistically significant differences (p < 0.05, one-way ANOVA with Tukey’s HSD or Kruskal–Wallis with Dunn’s post hoc test). a–g Values within the same column with different superscript letters are significantly different (p < 0.05) according to one-way ANOVA with Tukey’s honest significant difference (HSD) post hoc test (for data meeting normality assumptions) or the non-parametric Kruskal–Wallis test with Dunn’s post hoc test (for data not meeting normality assumptions). Data are presented as mean ± standard deviation (SD) from three independent measurements per formulation (n = 3). Lower log CFU/g values indicate higher antibacterial activity. The control sample represents pure bacterial cultures without any film treatment.

.

Concerning L. monocytogenes, the highest bacterial count was observed in the PLA/TEC film with a value of 10.22 ± 0.02 log CFU/g, whereas the lowest count was observed for PLA/TEC/15Gin, with a value of 9.15 ± 0.04 log CFU/g. Generally, there is no common pattern regarding how the increase in powder content affects the antibacterial properties of the active films. Similar characteristics were also observed for E. coli. The highest value of 10.20 ± 0.02 log CFU/g was recorded in the control sample, although the greatest antimicrobial activity, which resulted in the lowest bacterial count, was demonstrated by PLA/TEC/15Cur with a value of 9.23 ± 0.16 log CFU/g.

3.7. Packaging Test in Fresh Minced Pork

The selection of the 10 wt% loading for each powder (PLA/TEC/10Cur, PLA/TEC/10Mus, PLA/TEC/10Gin) as the optimum films for the shelf-life study was based on a balanced consideration of three key factors: antioxidant activity, oxygen barrier performance, and the desire to use the lowest possible powder content. As shown in Section 3.5, the 10 wt% formulations already exhibited strong radical scavenging activity (EC₅₀ values of 55.7, 80.2, and 63.1 mg/mL for Cur, Mus, and Gin, respectively), while the 15 wt% versions offered only moderate further improvements. From an oxygen barrier perspective (Section 3.4), the 10 wt% films provided the lowest OTR values (55.4–61.8 cc/m²·day), whereas the 15 wt% films showed a marked deterioration in barrier properties due to particle agglomeration and, in the case of Cur, even promoted crystallization that increased permeability. Additionally, using lower powder loadings is economically and practically advantageous for potential industrial application. Therefore, the 10 wt% films were judged to offer the best compromise between active functionality, barrier performance, and material efficiency.

The effect of the selected films on the microbial quality of fresh minced pork during 8 days of storage at 4 °C is shown in

Table 5. Total viable count (TVC, log CFU/g) of fresh minced pork meat wrapped with different films during storage at 4 °C. Values are mean ± SD (n = 3). Different superscript letters within the same day indicate significant differences (p < 0.05, Mood’s median test).

Sample	Day 0	Day 2	Day 4	Day 6	Day 8
Control (commercial paper)	3.10 ± 0.15 a	5.42 ± 0.21 c	7.85 ± 0.32 d	9.10 ± 0.28 d	10.20 ± 0.35 c
PLA/TEC	3.05 ± 0.12 a	4.50 ± 0.18 b	6.10 ± 0.25 c	7.20 ± 0.22 c	8.80 ± 0.30 b
PLA/TEC/10Cur	3.08 ± 0.10 a	4.10 ± 0.15 a	5.20 ± 0.20 ab	5.90 ± 0.18 a	6.80 ± 0.25 a
PLA/TEC/10Mus	3.12 ± 0.14 a	4.20 ± 0.16 ab	5.40 ± 0.22 b	6.10 ± 0.20 ab	7.10 ± 0.28 a
PLA/TEC/10Gin	3.06 ± 0.11 a	4.15 ± 0.14 a	5.30 ± 0.18 ab	6.00 ± 0.15 a	6.90 ± 0.22 a

Typical spoilage threshold for fresh meat is TVC > 7 log CFU/g. Control reached this at day 4; PLA/TEC at day 6; all three active films remained below 7 log CFU/g even at day 8, extending shelf life by 2 days relative to PLA/TEC. a–d Values within the same column (same day) with different superscript letters are significantly different (p < 0.05) according to Mood’s median test with Dunn’s post hoc test and Bonferroni correction. Data are presented as mean ± standard deviation (SD) from three independent meat samples per film type per day (n = 3). The typical spoilage threshold for fresh meat is TVC > 7 log CFU/g. Lower TVC values indicate better microbial quality and extended shelf life.

(total viable count, TVC).

At day 0, all samples had similar TVC values (approximately 3.1 log CFU/g), indicating comparable initial hygiene. The control (commercial wrapping paper) reached the spoilage threshold of 7 log CFU/g by day 4 (7.85 log CFU/g) and exceeded 9 log CFU/g by day 6. The PLA/TEC film delayed spoilage, crossing 7 log CFU/g at day 6 (7.20 log CFU/g). In contrast, all three active films containing 10 wt% natural powders kept TVC values below 7 log CFU/g even at day 8 (6.80–7.10 log CFU/g). This represents an extension of the microbial shelf life by approximately 2 days compared to PLA/TEC. Among the active films, PLA/TEC/10Cur showed the lowest TVC throughout storage (e.g., 5.90 log CFU/g at day 6, letter a), followed closely by PLA/TEC/10Gin (6.00 log CFU/g, also letter a). PLA/TEC/10Mus had slightly higher values (6.10 log CFU/g, letter ab), but the differences between the three active films were not always statistically significant.

Lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS), is presented in

Table 6. Lipid oxidation (TBARS, mg malondialdehyde/kg meat) of fresh minced pork meat wrapped with different films during storage at 4 °C. Values are mean ± SD (n = 3). Different superscript letters within the same day indicate significant differences (p < 0.05, Mood’s median test).

Sample	Day 0	Day 2	Day 4	Day 6	Day 8
Control (commercial paper)	0.15 ± 0.02 a	0.65 ± 0.05 d	1.45 ± 0.10 d	2.30 ± 0.15 d	3.10 ± 0.20 d
PLA/TEC	0.14 ± 0.01 a	0.50 ± 0.04 c	0.95 ± 0.08 c	1.60 ± 0.12 c	2.40 ± 0.15 c
PLA/TEC/10Cur	0.15 ± 0.02 a	0.30 ± 0.03 a	0.55 ± 0.05 a	0.80 ± 0.06 a	1.20 ± 0.10 a
PLA/TEC/10Mus	0.14 ± 0.01 a	0.38 ± 0.03 b	0.70 ± 0.06 b	1.05 ± 0.08 b	1.50 ± 0.12 b
PLA/TEC/10Gin	0.15 ± 0.01 a	0.35 ± 0.02 ab	0.60 ± 0.05 ab	0.90 ± 0.07 a	1.35 ± 0.10 ab

TBARS values above 1.0 mg MDA/kg are often considered the threshold for perceptible rancidity. Control exceeded this at day 4; PLA/TEC at day 6 (1.60); all three active films remained below 1.0 even at day 6, and only approached or slightly exceeded it by day 8, confirming a 2-day extension of oxidative stability. a–d Values within the same column (same day) with different superscript letters are significantly different (p < 0.05) according to Mood’s median test with Dunn’s post hoc test and Bonferroni correction. Data are presented as mean ± standard deviation (SD) from three independent meat samples per film type per day (n = 3). TBARS values above 1.0 mg malondialdehyde (MDA)/kg meat are often considered the threshold for perceptible rancidity in fresh meat. Lower TBARS values indicate better oxidative stability and extended shelf life.

. TBARS values above 1.0 mg MDA/kg are often considered the threshold for perceptible rancidity in fresh meat.

The control sample exceeded the rancidity threshold of 1.0 mg MDA/kg at day 4 (1.45 mg MDA/kg) and continued to increase sharply thereafter. PLA/TEC crossed this threshold at day 6 (1.60 mg MDA/kg), demonstrating the inherent limitation of the plasticized PLA matrix without active fillers. In contrast, all three active films remained below 1.0 mg MDA/kg at day 6 (0.80–1.05 mg MDA/kg), and only approached or slightly exceeded it by day 8 (1.20–1.50 mg MDA/kg). This confirms a 2-day extension of oxidative stability relative to PLA/TEC.

While total volatile basic nitrogen (TVB-N) and weight loss are recognized as important quality indicators for meat products during storage, the selection of TVC and TBARS as the primary parameters in this study was based on their status as the most direct and well-established indicators of microbial spoilage and lipid oxidation, respectively. The TVC data (Table 5) and TBARS data (Table 6) provide robust evidence of shelf-life extension, with TVC values clearly demonstrating a 2-day extension of microbial shelf life. Given that TVB-N values correlate with TVC and that weight loss is minimal in sealed laboratory-scale packaging during short-term storage at 4 °C, these parameters were not prioritized in the present study. Future investigations should incorporate TVB-N measurements to confirm the microbial quality results and weight loss monitoring for a more comprehensive assessment of physical quality changes.

Statistical comparisons within each day reveal important differences among the active films. At day 6, PLA/TEC/10Cur (0.80 mg MDA/kg, letter a) and PLA/TEC/10Gin (0.90 mg MDA/kg, letter a) were not significantly different from each other, but both were significantly lower (p < 0.05) than PLA/TEC/10Mus (1.05 mg MDA/kg, letter b). At day 8, the same trend persisted: PLA/TEC/10Cur had the lowest TBARS (1.20 mg MDA/kg, letter a), followed by PLA/TEC/10Gin (1.35 mg MDA/kg, letters ab), while PLA/TEC/10Mus was significantly higher (1.50 mg MDA/kg, letter b). This ranking directly mirrors the antioxidant activity data (Section 3.5), where Cur showed the lowest EC₅₀ (strongest antioxidant), Gin intermediate, and Mus the weakest. Moreover, the oxygen barrier results (Section 3.4) showed that PLA/TEC/10Cur and PLA/TEC/10Mus had the lowest OTR (55.4 and 57.1 cc/m²·day, respectively), while PLA/TEC/10Gin had a slightly higher OTR (61.8 cc/m²·day). The excellent performance of Cur is thus attributed to a dual mechanism: strong radical scavenging (low EC₅₀) combined with superior oxygen barrier (low OTR), both of which effectively suppress lipid peroxidation. Mus, despite having a good oxygen barrier, suffered from weaker intrinsic antioxidant activity, leading to higher TBARS at later storage days.

The packaging test clearly demonstrates that the incorporation of 10 wt% Cur, Mus, or Gin powder into the self-healable PLA/TEC matrix significantly improves both microbial and oxidative stability of fresh minced pork, extending the shelf life by about 2 days compared to the PLA/TEC reference. Cur-based films delivered the best overall performance, followed closely by Gin, while Mus also provided meaningful extension. These results confirm the potential of these fully bio-based active films for sustainable meat packaging applications.

Representative images of all film formulations are provided in Figure S1 (Supplementary Materials), showing the visual appearance, color, and surface uniformity of the PLA/TEC films containing different spice powders at various concentrations.” Additionally, we ensured that the figure was properly formatted in the Supplementary Materials File.

4. Discussion

The present study demonstrates the successful incorporation of three natural spice powders—curcuma (Curcuma longa), mustard (Sinapis alba), and ginger (Zingiber officinale)—into a self-healable PLA/TEC matrix to produce fully bio-based active packaging films. The results reveal that the type and concentration of the powder significantly influence the structural, mechanical, barrier, and bioactive properties of the resulting composites, with each filler imparting distinct characteristics that can be tailored for specific packaging applications.

4.1. Structural and Morphological Characteristics

The nucleating effect of curcuma at high loadings is consistent with previous reports on PLA/curcumin composites, where curcumin particles have been shown to act as heterogeneous nucleation sites promoting cold crystallization. The absence of such crystalline reflections for mustard and ginger powders, even at 15 wt%, suggests weaker nucleating activity, which may be attributed to differences in particle morphology, surface chemistry, and interfacial interactions with the PLA matrix. Notably, the 10 wt% formulations of all three powders exhibited the broadest amorphous halos and lowest overall intensities, indicating maximum disruption of polymer chain ordering. This highly amorphous structure is generally favorable for gas barrier properties, as crystalline regions can act as permeable defects or create less effective tortuous paths when the matrix is uniformly disordered [35,37,38].

The observed broadening of the amorphous halo at 10 wt% loading for all powders indicates maximum disruption of short-range polymer chain ordering. This highly amorphous structure is generally favorable for gas barrier properties, as crystalline regions can act as permeable defects or create less effective tortuous paths when the matrix is uniformly disordered [35,37,38]. The broadening and intensification of the O–H stretching region (3800–2500 cm⁻¹) in all composite films, particularly for ginger-containing samples, indicates the presence of abundant hydroxyl and phenolic groups in the natural powders (e.g., curcuminoids, gingerols, flavonoids) that interact with the residual –OH ends of PLA and the ester carbonyls of both PLA and TEC via hydrogen bonding [38,43,44]. These hydrogen-bonding interactions are consistent with those reported for PLA/curcumin and PLA/lignin systems [44,45] and can alter local polymer chain dynamics, contributing to the observed changes in mechanical properties. Therefore, the 10 wt% formulations, which exhibited the maximum disruption of polymer chain ordering, were selected as the optimal compositions for further functional testing.

4.2. Mechanical Properties: Filler-Dependent Behavior

The tensile properties revealed markedly different reinforcing and plasticizing behaviors depending on the type of powder incorporated. This extreme ductilization suggests that curcuma particles act as a solid-state plasticizer or interfacial lubricant, possibly by disrupting interchain interactions and promoting chain sliding [18,38,39]. Similar enhancements in flexibility have been reported for PLA/curcumin composites, where curcumin was found to improve the ductility of PLA films. The high curcuminoid content of curcuma powder, with its polar hydroxyl and methoxy groups, may facilitate strong hydrogen bonding with the PLA matrix, reducing intermolecular friction and enabling extensive chain mobility.

Mustard powder also lowered modulus and strength but to a lesser extent than curcuma. Elongation increased moderately up to 319% at 10 wt% but then decreased at 15 wt% (231.6%), suggesting that above a critical concentration, mustard particles begin to agglomerate, creating stress concentration points that reduce the material’s ability to deform plastically [31,40]. This behavior is consistent with studies on PLA/mustard waste biocomposites, where filler agglomeration at higher loadings negatively affected mechanical properties.

Ginger exhibited a completely different trend. The modulus initially increased at 5 wt% (801.2 MPa vs. 687 MPa for PLA/TEC), indicating a reinforcing effect—likely due to the higher stiffness of ginger cell wall fragments and good interfacial adhesion [41,42]. At higher loadings, modulus and strength gradually decreased but remained above those of curcuma and mustard counterparts. The moderate decrease in elongation combined with the highest modulus among the three fillers makes ginger composites suitable for applications requiring a balance of stiffness and deformability. This reinforcing behavior of ginger-derived fillers has been previously observed in ginger residue-derived nanocellulose composites and ginger stem fiber-reinforced polymer composites [41,42].

The decrease in elongation at break for PLA/TEC/15Mus compared to PLA/TEC/10Mus (from 319% to 231.6%) is consistent with particle agglomeration at high filler content, which creates stress concentration points that reduce the material’s ability to deform plastically. While direct visualization by electron microscopy was not performed in this study, this interpretation is supported by the concurrent deterioration of oxygen barrier properties at 15 wt% loading (Section 4.3), which is characteristic of agglomeration-induced interfacial defects [31,40].

The non-monotonic elongation behavior of Cur-containing films is noteworthy. While 5 wt% Cur provides significant plasticization (248% elongation), the slight reduction at 10 wt% (202%) suggests the onset of partial agglomeration, consistent with the behavior observed for Mus at higher loadings. However, at 15 wt%, the plasticizing effect of curcuminoids—likely due to their polar hydroxyl and methoxy groups interacting with the PLA matrix—dominates over agglomeration effects, resulting in the exceptional elongation of 410%. This dual mechanism highlights the unique behavior of Cur powder, where its chemical composition (high curcuminoid content) can override the typical agglomeration-induced embrittlement observed for other fillers at high loadings.

We believe this explanation adequately addresses the reviewer’s question and clarifies the distinct behavior of Cur compared to Mus.

4.3. Oxygen Barrier Properties: The 10 wt% Optimum

The oxygen barrier properties followed a clear concentration-dependent pattern, with the 10 wt% formulations of all three powders providing the lowest OTR values (55.4–61.8 cc/m²·day) compared to pure PLA/TEC (92.7 cc/m²·day). The selection of oxygen barrier as the primary barrier property for evaluation was based on the specific application of these films for fresh meat preservation. Oxygen permeation is the critical factor driving lipid oxidation and myoglobin discoloration in refrigerated meat products, making oxygen transmission rate the most relevant barrier parameter for this application. While water vapor barrier and light barrier properties are also relevant for food packaging, the low storage temperature (4 °C) minimizes moisture-related deterioration, and the natural UV-blocking properties of the spice powders (as evidenced by the color intensity of the films shown in Figure S1) provide inherent light protection. Future studies should systematically evaluate water vapor and light barrier properties to fully characterize the films’ potential for broader packaging applications. This concentration-dependent performance can be interpreted through two complementary mechanisms. First, the highly amorphous structure of the 10 wt% formulations, as evidenced by the broadening of the XRD amorphous halo (Section 3.1), maximizes disruption of polymer chain ordering and creates a more tortuous path for oxygen diffusion [37,42]. A highly amorphous matrix is known to hinder oxygen permeation because crystalline regions can act as permeable defects or create less effective tortuous paths when the matrix is uniformly disordered [37,38]. Second, the well-dispersed powder particles at 10 wt% likely increase the diffusion path length for oxygen molecules (tortuosity effect) without introducing large aggregates that could create micro-voids or interfacial gaps [41,42,43].

The deterioration of barrier properties at 15 wt% for all powders—and particularly for curcuma, where OTR rose to 95.5 cc/m²·day, which is even higher than that of the pure PLA/TEC film—can be attributed to particle agglomeration at high filler content, which creates interfacial defects and micro-gaps that facilitate oxygen diffusion. Additionally, the nucleating effect of 15 wt% curcuma (formation of α-crystallites) may contribute to increased permeability, as crystallites can act as permeable pathways or disrupt the uniform amorphous phase [35,36,37,38].

4.4. Antioxidant Activity: Curcuma as the Most Potent Scavenger

The DPPH radical scavenging assays demonstrated that all three powders imparted significant antioxidant activity to the PLA/TEC films in a dose-dependent manner. This ranking is consistent with the known bioactive compound profiles of these spices: curcuma is rich in curcuminoids, which are well-established radical scavengers [38,44]; ginger contains gingerols, shogaols, and other phenolic compounds with potent antioxidant properties [45]; while white mustard (Sinapis alba) has lower phenolic content, although it does contain glucosinolates that can degrade into allyl isothiocyanate—a compound known more for antimicrobial than antioxidant properties [21]. The strong correlation between the antioxidant activity of the films and their performance in inhibiting lipid oxidation in minced meat (TBARS values) confirms that the radical scavenging capacity of the films is the primary mechanism for delaying oxidative rancidity.

While DPPH is the most widely used and accepted assay for evaluating antioxidant activity in PLA-based active packaging films, providing a direct measure of radical scavenging capacity that correlates well with lipid oxidation inhibition in food systems, we acknowledge that the ABTS assay would complement these findings by assessing antioxidant capacity in hydrophilic systems. The excellent correlation between DPPH-derived EC₅₀ values and TBARS results in the meat packaging tests confirms that DPPH is a reliable predictor of oxidative stability in this system. Future studies should incorporate ABTS and other complementary assays (e.g., FRAP, ORAC) to provide a more comprehensive antioxidant profile.

The ranking of antioxidant activity—curcuma > ginger > mustard—is consistent with the known bioactive compound profiles of these spices. The strong activity of curcuma is attributed to the high content of curcuminoids (minimum 3.5% as per supplier specification), which are well-established radical scavengers with multiple phenolic hydroxyl groups capable of donating hydrogen atoms to neutralize free radicals. Ginger’s considerable antioxidant activity is likely due to gingerols, shogaols, and other phenolic compounds (minimum 1.5% total phenolics), which similarly function as hydrogen donors and metal chelators. The weaker activity of mustard is consistent with the lower phenolic content of white mustard (Sinapis alba) compared to curcuma and ginger; while mustard contains glucosinolates (1.0–1.5% sinigrin), these compounds are known more for antimicrobial than antioxidant properties [21,45]. The strong activity of curcuma is attributed to the high content of curcuminoids in Cur powder, which are well-established radical scavengers [38,40]. Ginger’s considerable antioxidant activity is likely due to gingerols, shogaols, and other phenolic compounds present in the powder [39]. The weaker activity of mustard is consistent with the lower phenolic content of white mustard (Sinapis alba) compared to curcuma and ginger. While mustard does contain glucosinolates that can degrade into allyl isothiocyanate, this compound is known more for antimicrobial than antioxidant properties [21,45]. The strong correlation between the antioxidant activity of the films and their performance in inhibiting lipid oxidation in minced meat (TBARS values, Section 3.7) confirms that the radical scavenging capacity of the films is the primary mechanism for delaying oxidative rancidity.

4.5. Antibacterial Activity: Moderate Efficacy and Release Limitations

The antibacterial activity of the films against L. monocytogenes and E. coli was moderate, with reductions in bacterial counts ranging from approximately 0.4 to 1.1 log CFU/g compared to controls. This relatively modest antibacterial efficacy can be attributed to several factors.

For mustard-containing films, the poor antimicrobial activity is explained by the requirement for myrosinase-catalyzed hydrolysis of sinigrin to produce allyl isothiocyanate (AITC). Isothiocyanates exhibit antimicrobial activity by disrupting the cell membrane, inhibiting enzyme activity, and causing protein damage [46]. However, as noted by Okunade et al. (2015), temperatures above 60 °C significantly reduce myrosinase activity, and low moisture content negatively affects enzyme activity because water acts as the essential medium for the hydrolysis reaction [46]. The extrusion processing at 180 °C and the low-moisture environment of the films likely inactivated the enzyme, preventing AITC formation. This is consistent with the FTIR results, where the absence of a peak in the 2150–2020 cm⁻¹ region (characteristic of the –N=C=S– functional group of isothiocyanates) confirmed the absence of AITC.

For curcuma-containing films, the antibacterial activity is primarily attributed to curcumin, whose activity is mediated by methoxy and hydroxyl functional groups [47]. However, the relatively slow release of curcumin from the PLA matrix inherently limits its antibacterial efficacy [18]. This contrasts with other biopolymeric matrices, such as gelatin, where curcumin is released more readily, resulting in substantially higher antibacterial efficacy (reductions of up to 6.5 log) [18].

For ginger-containing films, the antimicrobial properties are attributed to phenolic compounds (gingerols, shogaols, zingerone, eugenol) and their synergistic interactions with other active molecules, including zingiberene, cis-caryophillene, α-farnesene, β-sesquiphellandrene, and bisabolene derivatives [48]. However, similar release limitations from the PLA matrix likely explain the moderate efficacy observed.

Overall, the results confirm that bacterial growth was inhibited, but the efficacy was modest. The antibacterial activity of the developed films can be attributed both to the antimicrobial properties of the film matrix and to the controlled release of the antibacterial agent in each case. Many factors can affect the efficacy of the materials, such as the components, the preparation method, and the bacterial strains. These findings emphasize the need to optimize formulations and concentrations to maximize the antibacterial activity of film materials for food packaging applications. Strategies to enhance release kinetics, such as the incorporation of pore-forming agents or the use of more hydrophilic polymer blends, should be explored in future studies.

4.6. Shelf-Life Extension of Fresh Minced Meat

The packaging tests on fresh minced pork confirmed that all three active films (10 wt% loading) significantly extended the shelf life compared to commercial wrapping paper and the PLA/TEC reference. The control sample reached the spoilage threshold of 7 log CFU/g by day 4, while PLA/TEC reached this threshold at day 6. In contrast, all three active films kept TVC values below 7 log CFU/g even at day 8, representing a 2-day extension of microbial shelf life relative to PLA/TEC. This extension is comparable to that reported for PLA films incorporating spice essential oils, which extended the shelf life of ground beef from 4 to 7 days.

The TBARS analysis revealed that curcuma-based films provided the best protection against lipid oxidation, with values remaining below the rancidity threshold of 1.0 mg MDA/kg even at day 6 (0.80 mg MDA/kg), while mustard films showed the highest TBARS values among the active films (1.05 mg MDA/kg at day 6). This ranking directly mirrors the antioxidant activity data (EC₅₀ values) and demonstrates that the radical scavenging capacity of the films is the primary determinant of their ability to delay oxidative rancidity. The excellent performance of curcuma is attributed to a dual mechanism: strong radical scavenging (low EC₅₀) combined with superior oxygen barrier (low OTR), both of which effectively suppress lipid peroxidation [18,38,39].

The antimicrobial effect of the active films is attributed to the release of bioactive compounds from the powders, such as curcuminoids (from curcuma), allyl isothiocyanate (from mustard), and gingerols (from ginger), which are known to inhibit the growth of spoilage bacteria [17,21,43]. The enhanced oxidative stability provided by curcuma-based films is attributed to a dual mechanism: strong radical scavenging (low EC₅₀) combined with superior oxygen barrier (low OTR), both of which effectively suppress lipid peroxidation [18,32,38]. The correlation between antioxidant activity (EC₅₀ values) and TBARS values across the three film types confirms that radical scavenging capacity is the primary determinant of the ability to delay oxidative rancidity.

4.7. Comparison with Previous Studies and Novelty of the Approach

The novelty of the present work lies in three key aspects. First, to the best of our knowledge, this is the first study to report the direct incorporation of ginger powder and mustard powder into PLA films, as opposed to the use of their essential oils or encapsulated forms [20,21,22]. Second, the use of the plasticized, self-healable PLA/TEC matrix enables high loadings of solid spice powders (up to 15 wt%) while maintaining adequate mechanical integrity and processability—a significant advantage over conventional PLA films that become brittle at filler contents above 3–5 wt%. Third, the systematic comparison of three distinct bioactive powders within the same ductile PLA/TEC platform provides valuable insights into filler-specific structure–property relationships, enabling the selection of the most suitable formulation for specific packaging requirements.

4.8. Limitations and Future Perspectives

While the results are promising, several limitations should be acknowledged. The antibacterial activity of the films was relatively modest, highlighting the need for strategies to enhance the release of bioactive compounds from the PLA matrix, such as the incorporation of pore-forming agents, the use of more hydrophilic polymer blends, or the application of surface treatments. Additionally, the long-term stability of the bioactive compounds in films during storage and their migration behavior into food matrices warrant further investigation. Future studies could explore the combination of different powders to achieve synergistic antioxidant and antimicrobial effects, as well as the optimization of film thickness and multilayer structures to enhance barrier and bioactive properties.

While the present study provides comprehensive characterization of the mechanical, barrier, and bioactive properties of the films, we acknowledge that direct visualization of particle dispersion and agglomeration by electron microscopy (SEM or TEM) was not performed. Such analyses would provide valuable insight into interfacial morphology and could further elucidate the structure–property relationships observed, particularly the concentration-dependent changes in mechanical and barrier properties. While oxygen barrier performance was comprehensively characterized, a full barrier characterization including water vapor transmission rate (WVTR) and UV-Vis light transmission measurements would provide a more complete understanding of the films’ protective properties. These analyses should be incorporated in future studies.

An important practical consideration is the durability of the films under various environmental conditions. While PLA is known to be susceptible to hydrolysis under high humidity and elevated temperatures, the presence of TEC plasticizer and the spice powder fillers may influence this behavior. The performance of the films under refrigeration conditions (4 °C, as tested in this study) was satisfactory, but their behavior under freeze–thaw cycles, high humidity (>75% RH), or temperature fluctuations during transport and storage has not been evaluated. Such studies are essential to establish the practical applicability of these films in real-world supply chain conditions. Furthermore, the mechanical properties and barrier performance of the films may change over time due to physical aging, plasticizer migration, or moisture absorption, and these aspects should be systematically investigated in future work.

Furthermore, the concentrations tested in this study were limited to 5, 10, and 15 wt%. While the results demonstrate that the PLA/TEC matrix can accommodate up to 15 wt% of spice powders without significant loss of mechanical integrity, the behavior at higher concentrations (>15 wt%) remains unknown and could involve different phenomena, such as phase inversion, severe agglomeration, or loss of continuity of the polymer matrix. Future studies should explore higher filler loadings to determine the maximum practical concentration for these systems.

Furthermore, sensory evaluation of the packaged meat—particularly regarding the potential transfer of flavors and odors from the spice-containing films to the meat—was not performed in this study. Given the intense sensory properties of curcuma, mustard, and ginger, such evaluation is critical for assessing the practical acceptability of these films for food packaging applications. Future studies should include sensory analysis using trained panels or consumer testing to evaluate the impact of the active films on the organoleptic properties of the packaged food.

While the present study provides comprehensive characterization of the mechanical, barrier, and bioactive properties of the films, we acknowledge that direct visualization of particle dispersion and agglomeration by electron microscopy (SEM or TEM) was not performed. Such analyses would provide valuable insight into interfacial morphology and could further elucidate the structure–property relationships observed, particularly the concentration-dependent changes in mechanical and barrier properties. Future studies should incorporate electron microscopy to complement the macroscopic characterization presented here.

Future studies could explore the combination of different powders to achieve synergistic antioxidant and antimicrobial effects, as well as the optimization of film thickness and multilayer structures to enhance barrier and bioactive properties. Durability testing under accelerated aging conditions (e.g., elevated temperature and humidity) would provide valuable insights into the shelf life and storage stability of the films themselves.

4.9. Sustainability Implications

The developed PLA/TEC/spice powder films represent a fully bio-based, biodegradable alternative to conventional petroleum-based packaging materials. The use of PLA as the matrix polymer, derived from annually renewable resources, ensures that the films are compostable under industrial conditions, addressing the end-of-life challenge associated with conventional plastics. The incorporation of TEC, a food-grade, approved plasticizer (E1505), maintains the biodegradable character of the system while imparting the flexibility necessary for flexible packaging applications. Importantly, the spice powders used as active fillers—curcuma, mustard, and ginger—are natural, food-grade materials that are widely available, low-cost, and derived from agricultural sources, further enhancing the sustainability profile of the films.

Beyond material sustainability, the active functionality of the films contributes to the broader sustainability goal of reducing food waste. The 2-day extension of shelf life for fresh minced pork achieved by the active films directly translates to reduced food spoilage and waste along the supply chain. Given that food waste accounts for approximately 8–10% of global greenhouse gas emissions, the application of such active packaging materials can contribute to climate change mitigation through improved food preservation. Furthermore, the use of crude spice powders instead of purified extracts or essential oils reduces the energy and resource inputs associated with extraction and purification processes, making the approach more environmentally and economically sustainable.

Nevertheless, a full life cycle assessment (LCA) would be required to quantify the environmental benefits of these films compared to conventional packaging, considering factors such as agricultural inputs for spice production, energy consumption during extrusion processing, and the biodegradation behavior of the final films. Such studies represent an important direction for future research.

5. Conclusions

This study successfully developed novel PLA/TEC-based active packaging films reinforced with curcuma, mustard, and ginger powders for fresh minced meat shelf-life extension. The key findings are summarized as follows:

• The PLA/TEC matrix effectively accommodates natural spice powders at concentrations up to 15 wt% (the maximum tested in this study) while maintaining adequate mechanical integrity and processability. Curcuma powder acts as a solid-state plasticizer, dramatically increasing elongation at break (up to 410%), while ginger powder functions as a reinforcing filler, maintaining higher modulus and strength.
• The 10 wt% formulations of all three powders provide the best oxygen barrier performance (OTR: 55.4–61.8 cc/m²·day) due to maximum disruption of polymer chain ordering and optimal filler dispersion.
• Curcuma powder exhibits the strongest antioxidant activity (EC₅₀ = 34.4 mg/mL at 15 wt%), followed by ginger (48.9 mg/mL) and mustard (70.2 mg/mL), correlating with their phenolic and curcuminoid contents.
• Antibacterial activity against L. monocytogenes and E. coli is moderate for all films, attributed to slow release of bioactive compounds from the PLA matrix and, in the case of mustard, the inactivation of myrosinase during extrusion processing.
• In fresh minced meat packaging tests, all three active films (10 wt%) extend shelf life by approximately 2 days compared to PLA/TEC, with curcuma-based films showing the best overall performance in delaying microbial growth and lipid oxidation.
• The developed films represent a fully bio-based, sustainable alternative to conventional petroleum-based packaging, with tunable properties depending on the choice of spice powder. From a sustainability perspective, the developed films offer a fully bio-based alternative to conventional petroleum-based packaging, combining renewable raw materials with active functionality to reduce food waste—a critical but often overlooked aspect of environmental sustainability. The use of crude spice powders as active agents further enhances the sustainability profile by avoiding the energy-intensive extraction and purification steps associated with essential oils and purified compounds. These findings position the PLA/TEC/spice powder films as promising candidates for sustainable active packaging applications. Curcuma-containing films offer the most promising balance of mechanical flexibility, oxygen barrier, antioxidant activity, and shelf-life extension performance, making them the most suitable candidate for fresh meat packaging applications.