Development and characterization of sodium alginate reinforced Acridocarpus orientalis extract

Abstract

In this research, biodegradable sodium alginate films were synthesized by using stem extract of Acridocarpus orientalis to enhance antioxidant activity, antimicrobial activity, water vapor transmittance properties, release kinetics and physicochemical functionality. The films were produced by adding 0.2% and 0.4% (w/v) methanolic extract into a 2% (w/v) sodium alginate solution. The fabricated films were comprehensively analyzed for their mechanical, functional, release and physical properties. The films showed increase in tensile strength and elongation at break with the increased concentration of methanolic extract. Antioxidant activity, antimicrobial activity, and water vapor transmittance rate was also improved with increased concentration of extract. This improvement was due to the presence of phytochemicals like phenolic and flavonoid compounds in the extract. Altogether, these observations demonstrate the promise of A. orientalis extract as a natural functional additive to produce sodium alginate-based biopolymer films with enhanced functionality in active packaging.

Keywords:
sodium alginate; plant extract; biopolymer films; active packaging

1. Introduction

The increasing concern of environmental associated problems due to man-made plastics and the food preservation challenges have accelerated the search for environmentally friendly, bioactive packaging alternatives. While petroleum-derived plastics exhibit better barrier functionality and mechanical toughness, they are the major source of long-term environmental pollution and becomes a major threat to ecosystems as well as human health[¹]. As a result, there has been a growing effort to improve sustainable packaging systems from biodegradable polymers. Out of these, sodium alginate has been known for its good film-forming ability, hydrophilic nature, and ready availability in nature[²]. Alginate is known for its potential in food[³], biomedical[⁴], and pharmaceutical applications[⁵]. Alginate-based films demonstrated physical stability[⁶], poor barrier properties[⁷], and lack the functional features of active packaging, such as resistance to oxidative spoilage[⁸] and microbial contamination[⁹] etc.

Sodium alginate is a linear polysaccharide found in brown seaweed. It is composed of α-1,4 glycosidic linkage between β-D mannuronic acid (M) and α-L-guluronic acid (G)[¹⁰]. In addition, films prepared from pure sodium alginate tend to have low mechanical strength, poor antioxidant activity, and antimicrobial efficacy[¹¹]. To overcome these shortcomings, a range of natural and plant-based compounds has been added to the alginate matrix. Some of these include ficus extract[¹²], cinnamon essential oil[¹³], oregano oil[¹⁴], tea polyphenols[¹⁵], epigallocatechin gallate[¹⁶], palmarosa oil[¹⁷], carvacrol[¹⁸], and lemongrass oil[¹⁹]. The incorporation of these bioactive components not only increases the mechanical strength of the films but also confers functional properties. These bioactive compounds have inherent antimicrobial and antioxidant activities, thus enhancing the overall performance of the packaging material.

The film formed by pure alginate has poor mechanical properties due to its brittleness. To improve the flexibility, plasticizers are added to the polymer matrix. Several plasticizers, such as oils, fatty acids, and citric acid etc. have been explored where glycerol is most widely used due to its low cost and efficiency[²⁰]. Glycerol, a trihydrichol (C₃H₈O₃), is a colorless, viscous and hygroscopic liquid. It occurs naturally as glycerides, the basic structural unit of animal and vegetable fats and oils[²¹]. Glycerol is classified as "generally recognized as safe" (GRAS) and is commonly accepted for application as a multifunctional food additive and is also approved for certain food packaging applications[²²]. In addition to its use in food systems, glycerol finds widespread industrial usage as a major component in pharmaceuticals, cosmetics, oral care products, polyurethane foams, synthetic resins, and the production of ester gum[²³]. Its physicochemical characteristics, especially its plasticizer property, render it of major significance in designing biodegradable and bioactive polymer films for packaging[²⁴].

A. orientalis is a medicinal plant used mainly in Oman and UAE, used for headaches, muscle pain, paralysis, etc[²⁵]. It contains various phytochemicals such as flavonoids, tannins and phenolic derivatives. A study conducted by Ksiksi and Hamza[²⁶] found that A. orientalis has the potential for good antioxidant and anti-inflammatory activities. Another study in which Lotfy et al.[²⁷] reported that A. orientalis has a functional property that elevates the antioxidant protective enzyme. This bioactive compound present in this plant showed antifungal, phytotoxic, anticancer, and anti-lipid peroxidation properties, reported by Hussain et al.[²⁸].

In the present study, a new active packaging film is developed based on sodium alginate, glycerol, and A. orientalis steam extract for sustainable and functional food packaging applications. This research also investigates the effect of different ratios of A. orientalis steam extract on the film’s physical, transparency, visual, structural, antioxidant, antimicrobial, water barrier, release kinetics and thermal properties.

2. Material and Methodology

2.1 Materials

Sodium Alginate was purchased from Sisco Research Laboratories Pvt Ltd. Mumbai, India. Glycerol, used as a plasticizer, was obtained from BDH Laboratory (London, UK). All other chemicals used in the current study were of analytical grade.

2.2 Plant collection and identification

The plant taxonomist Dr. Syed Abdullah Gilani of the Department of Biological Science & Chemistry, University of Nizwa, Nizwa, Oman, identified the air-dried whole plant material of A. orientalis that was collected from various locations in the Al-Hamra, Ad-Dakhiliyah region in Oman (March-April 2022). The voucher specimen (ACO/04/22) has been deposited in the herbarium of the department.

2.3 Extraction, fractionation, and isolation

The plant materials were extracted and bioactive components were isolated as per our previous reported method[²⁵,²⁸,²⁹]. The air-dried ground plant material A. orientalis (6.5 kg) was extracted with methanol (8.5 L) at room temperature for 15 days (3 times). The extract was evaporated to yield a dark yellowish methanolic residue (540 g) that was partitioned in different solvents ^{based on increasing polarity to afford n-hexane (40.5 g),} CH₂Cl₂ ^{(80.0 g), EtOAc (45.5 g), n-}BeOH (66.0 g), and aqueous (280.0 g) fractions. According to the previous investigation, the ^CH₂^Cl₂ ^{soluble fraction (70-230 mesh, Merck) was loaded on silica gel column} chromatography to compounds 6 (8.4 mg), 7 (6.0 mg), 8 (28.5 mg), 9 (16.0 mg), 10 ^{(3.5 mg), 11 (6.0 mg), and 12 (8.0 mg) using increasing polarity systems of} CH₂Cl₂^{n-hexane, pure} CH₂Cl₂ ^{and up to 20% MeOH/} CH₂Cl₂^{. Similarly, the ethyl acetate fraction (30 g) was} subjected to CC over a silica gel column (70-230 mesh, Merck) using 10% EtOAc/n-hexane with a 5% increasing polarity system up to 100% EtOAc, then by the increasing percentage of MeOH from 1%, to 20%, and finally washed with 20% MeOH to get compounds 1 (40.7 mg), 2 (26.5 mg), 3 (1.8 g), 4 (22.0 mg), and 5 (10.5 mg)[²⁵,²⁸,²⁹]. The isolated compounds were identified as morin (1), morin-3-O-β-D-glucopyranoside (2), morin-3-O-α-L-rhamnopyranoside (3), quercetin (4), choerospondin (5), betulin (6), betulinic acid (7), β-sitosterol (8), β-sitosterol-3-O-β-D-glucopyranoside (9), 1-docosanol (10), 2,5-dimethoxy 1,4-benzoquinone (11), and 2,6-dimethoxy 1,4-benzoquinone (12), on the basis of their 1H NMR, 13C NMR, MS, and IR spectra analysis and by comparison with those reported data in the related literature (Figure 1).

Figure 1
Chemical structures of the isolated compounds 1-12.

2.4 Film development

The active film was prepared by dissolving 2% (w/v) sodium alginate in distilled water under continuous stirring at 45 °C for 2 hours, allowing a uniform and homogenous solution. To improve film flexibility, 1% (v/v) glycerol was added as a plasticizer during the mixing process. Then the solution is divided into three equal volumes and labelled (Table 1). Once the base solution was ready, it was enriched with 0% (w/v), 0.2% (w/v), and 0.4% (w/v) methanolic extract of A. orientalis stem. The mixture was then ultrasonicated for 10 minutes using a Bandelin Sonoplus LS 40 to promote even dispersion of the extract. Following this, 20 mL of the final film-forming solution was casted into petri dishes and allowed to dry at room temperature under controlled ambient conditions.

Table 1
The composition ratios of the components used for the fabrication of the films.

Code	Sodium Alginate (w/v)	Glycerol (v/v)	Acridocarpus orientalis (w/v)
SA1	2%	1%	-
SA2	2%	1%	0.2%
SA3	2%	1%	0.4%

2.5 Docking study

The molecular structure of sodium alginate was drawn on ChemDraw as given in literature[³⁰] and used as a receptor for molecular docking of compound 3. The polymer was consisting of the residues of β-1,4-linked-D-mannuronic acid (M-block) and α-1,4-linked-L-guluronic acid (G-block) (Figure 2). The structure of compound 3 was also generated on ChemDraw. Both the molecules were imported into Molecular Operating Environment (MOE 2024.06) for molecular docking[³¹]. Before docking, the structures were minimized with gradient of 0.1 Kcal/mol/Å2 with MMFF-94x force field. During minimization, protons were added, and partial charges were calculated on both molecules with MMFF-94x forcefield. To dock compound 3, initially we created the receptor by docking one unit of sodium alginate (consisting of one M and G block) on another unit of sodium alginate (consisting of two M and G blocks) through Proxy Triangle algorithm which tackles medium to large sized ligands which have a very large number of conformers. Affinity dG scoring function was used with 100 conformations of sodium alginate to score its docked conformers, and GBVI/WSA dG was used in refinement process with 50 conformers. After receptor preparation, Triangle Matcher placement method was used to dock compound 3 on the generated receptor, applying Affinity dG scoring function (with 100 conformations) and GBVI/WSA dG (with 50 conformations), as mentioned above. Inter-molecular interactions between molecules were examined at MOE interface and the figure is illustrated by MOE.

Figure 2
Structure of Sodium alginate.

2.6 Characterization

2.6.1 Film thickness

The film's thickness was measured by using a digital micrometer Dequmont digital Vernier caliper (ROHS NORM 2011/65/EU). Randomly, 3 positions of each film were measured, and for further analysis mean value was determined.

2.6.2 Transmittance

The transmittance of the film samples was measured using a YH1200 Haze meter (Guangdong Sanenshi Technology). For the analysis, the film samples were carefully placed in the instrument, ensuring proper alignment to avoid measurement errors.

2.6.3 Mechanical testing

Mechanical properties of the films, i.e., tensile strength (TS) and elongation at break (EAB), were assessed based on the ASTM D882-95 standard protocol[³²]. A Texture Analyzer (Model TA.XT Plus, Stable Micro Systems, Godalming, UK) fitted with a 10 kg load cell was used to carry out the analysis. Measurements of all samples were performed in triplicates to meet data reliability. Before testing, the film samples were pre-conditioned using Biobase Climate Chamber, China at room temperature and 50% relative humidity. Conditioned films were then cut into precise rectangular strips (60 mm × 7 mm) by using a scalpel. The strips were mounted between the grips of the texture analyzer with care. The initial grip separation was set to 40 mm, and the test was performed under a crosshead speed of 8.3 mm/sec. The resulting stress-strain values were recorded and analyzed using Exponent Connect software, from which both tensile strength and elongation at break values were calculated.

2.6.4 Antioxidant properties

The antioxidant activity of the film of sodium alginate (SA1) and different ratios of A. orientalis stem extract incorporated in sodium alginate films (SA2 – SA3) was determined quantitatively by the 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, according to the method of Brand-Williams et al.[³³] with slight adaptation. The technique takes advantage of the characteristic deep violet coloration of the DPPH• free radical in methanolic solution, which decreases upon receiving an electron or hydrogen donation from antioxidant constituents. 50 mg of film sample was homogenized with 1.95 mL of methanolic DPPH solution (Sigma-Aldrich, USA), mixed on a vortex for 30 s, and then incubated in the dark at ambient temperature for 30 min to avoid photodegradation. The absorbance was measured at 517 nm with a UV-Vis spectrophotometer. Radical scavenging activity was presented as percentage inhibition of DPPH, which was calculated from the average of three independent replicates (Equation 1).

$$\%inhibition=\left(Ac-At\right)/\left(Ac\right)\times 100$$ (1)

where: Ac is the absorbance of the reference solution; At is the absorbance of the experimental solution.

2.6.5 Antimicrobial analysis

The antimicrobial analysis of the fabricated film samples was tested using Escherichia coli (ATCC 25922, gram negative). The analysis was performed by using methodology described by Seol et al.[³⁴] and Matuschek et al.[³⁵]. Film samples cut into 1 cm diameter discs were placed onto nutrient agar plates inoculated with E. coli. After storing the assay in Climate Chamber (BJPX-A400, Biobase Bioland Co., Ltd., China) for 24 hours at 35 °C and 50% RH, the inhibition zone of the clear regions was noted which were formed around the film samples. These zones were calculated using millimeter scale and recorded. The average of the inhibition zone was used in further analysis.

2.6.6 Water vapor transmittance rate

The water vapor transmittance rate of the fabricated film samples was determined using gravimetric method using ASTM E96. Elcometer was used to measure the Water Vapor Transmittance Rate, where 5gm of silica gels was filled. The films samples were cut in a round shape then placed on elcometer and sealed. These sealed elcometers were placed on Climate Chamber (BJPX-A400, Biobase Bioland Co., Ltd., China) at 75% RH and 27 °C for 24 hours. Water vapor transmission rate (WVTR) is determined by measuring how fast water vapor passes through a film material under specified conditions. In desiccant-filled packages, water vapor moves through the film from the higher humidity outside to the lower humidity inside. As water vapor enters the package, its mass will increase and therefore so too will its weight. The WVTR was calculated using Equation 2.

$\text{WVTR}=\frac{\Delta \text{m}}{\text{A}\times \text{T}}$ (2)

where: m is the $\Delta$mass (gm) difference, A is the area (m²) of the film, and T (day) is the time.

2.6.7 Release kinetics

The release kinetics of the bioactive components was tested according to Regulation (EU) No 10/2011 of European Union. The analysis was performed using methodology described by Cabeza de Vaca et al.[³⁶] Nicosia and Licciardello[³⁷] which was performed on 3% acetic acid and 96% ethanol as a food stimulant cut into 3 $\times$ 3 cm and placed in 15 mL of both food stimulants for 24 hours at 27 °C in closed container. By using UV-Vis spectroscopy (Agilent Cary 60 UV-Vis from Agilent Technology Inc. USA) the absorbance was measured from 800-200 nm and recorded.

2.6.8 Scanning electron microscopy

The changes in the microstructure caused by different ratios of A. orientalis stem extract to the film of sodium alginate were studied with the help of a scanning electron microscope (SEM, Model JSM-6510LA, JEOL, Japan) at an accelerating voltage of 20 kV. Film samples were sliced with forceps to yield fragments of the appropriate size for SEM imaging. The fragments were mounted on aluminum stubs using double-sided carbon adhesive tape. For improving surface conductivity and image resolution, a thin layer of gold was applied to the film surfaces using a sputter coater before visualizing them under the SEM.

2.6.9 X-ray diffraction

The film samples were characterized by their crystalline structure and phase composition using a powder X-ray diffractometer (Bruker D8 Discover, Germany). The instrument was set to an accelerating voltage of 40 kV and used Cu Kα radiation of the characteristic wavelength 1.5418 Å as the X-ray source. Data collection was performed over a 2θ angular range of 5° to 55° with a step time of 0.500 s per point to provide high-resolution detection of diffraction peaks. Such an analysis revealed information about crystallinity, molecular dispersion, and potential structural changes caused by the introduction of functional components into the film matrix.

2.6.10 Thermal analysis

Thermal degradation behavior of the fabricated film samples was investigated by thermogravimetric analysis (TGA) using thermal analyzer (SDT Q600, TA Instruments, New Castle, DE, USA). About 10 mg of every film sample was analyzed by thermal scanning between 25 °C and 600 °C at a heating rate of 10 °C/min under a continuous nitrogen atmosphere to maintain an inert atmosphere to avoid oxidative degradation. The obtained TGA thermograms were employed to assess the thermal stability, decomposition processes, and the effect of methanolic extract incorporation on the films.

2.6.11 Statistical analysis

Three independent experiments were conducted on film samples to find the mean and standard error. By using one-way ANOVA followed by Fisher’s post-hoc test, the significant difference among these means was assessed. All the test was performed at 95% confidence level, statistical significance (p< 0.05).

3. Results and Discussions

3.1 Visual analysis

Figure 3 shows the visual morphology of the resultant film samples. The SA1 sample is a transparent sample with a homogeneous and smooth surface. The sample shows minimal haze that can be due to interaction between polysaccharide and plasticizer, thus leading to lower optical clarity. The SA2 and SA3 sample is relatively darker in color because of the addition of 0.2% and 0.4% A. orientalis extract. The decreased transparency of this film could be attributed to dispersion of the phytoconstituents of methanolic extract within the polymer matrix. In the SA3 specimen, the content of A. orientalis was raised to 0.4% in the sodium alginate solution. Due to increased loading of the bioactive compounds, this film exhibits more intense coloration and appreciable loss in transparency in comparison to the above two samples.

Figure 3
Visual appearance of the SA films loaded with A. orientalis.

3.2 Docking study

Compound 3 was suitably docked in between two molecules of sodium alginate with docking score of -5.36 kcal/mol. It showed interactions with both the monomers of sodium alginate. The hydroxyl moieties of compound 3 formed multiple hydrogen bonds with the polar oxygen of sodium alginate. The big polymer of sodium alginate (2 M and 2G blocks) interacted with sugar group and morin functional moiety of compound 3, while carbonyl group at morin group interacted with small sodium alginate moiety (1 M and 1G block). Due to these polar interactions, the compound is amalgamated between two sodium alginates which are also bonded to each other with hydrogen bonds. The binding mode of the compound 3 is shown in Figure 4.

Figure 4
The binding mode of compound 3 (magenta ball and sticks) are shown within the two molecules of sodium alginate. The big and small polymers of sodium alginate are depicted in green and orange color, respectively, while bonds are illustrated in black lines.

3.3 Film thickness analysis

The thickness of the film is controlled by parameters like the volume of solution cast, drying surface, fabrication method, and drying kinetics[³⁸]. Table 2 shows the thickness values of the fabricated film samples. Sample SA1 recorded a mean thickness of 0.08 mm. With the addition of bioactive components to the polymer solution, the thickness of the films was slightly changed. The films with 0.2% and 0.4% A. orientalis showed mean thickness values of 0.07 ± 0.011 mm and 0.08 ± 0.010 mm, respectively. The trend implies that addition of bioactive components does not significantly affecting the final film thickness.

Table 2
Thickness, optical and mechanical properties of the films.

Sample	Thickness (mm)	Transmittance (%)	TS (MPa)	EAB (%)
SA1	0.08±0.02a	86.95±0.072a	4.67±1.11 b	74.05±2.08c
SA2	0.07±0.01a	79.11±0.562b	6.14±0.85 ab	83.17±2.05 b
SA3	0.08±0.01a	79.26±0.416 b	7.89±1.37 a	93.74±2.13 a

• The values with different letters (a, b and c) inside a column indicate significant differences (p< 0.05).

3.4 Optical properties

Table 2 shows the transmittance measurements of the samples of films. The SA1 film recorded the highest value of transmittance at 86.95%, whereas SA2 and SA3 films recorded lower values of 79.11% and 79.26%, respectively. The decrease in optical transmittance of SA2 and SA3 is due to the inclusion of A. orientalis, which absorbs light and thus reduces transparency. The change in optical behavior of SA2 and SA3 could be due to the partial saturation of the matrix. Similar findings have been reported by Evcil et al.[³⁹] on chitosan with Crataegus orientalis extract.

3.5 Mechanical properties

The mechanical properties of biopolymer films, including tensile strength, elongation at break, deformability, and elastic modulus, are important, since packaging materials need to have enough structural integrity to resist mechanical stresses during handling, transportation, and storage[⁴⁰]. The mechanical properties of pure sodium alginate and sodium alginate combined with A. orientalis are detailed in Table 2. The pure sodium alginate and glycerol film (SA1) revealed tensile strength of 4.67 MPa and elongation at break 74.05%, the lowest tensile strength and elongation at break among the fabricated films. The SA2 film recorded a tensile strength of 6.14 MPa and elongation at break of 83.17%. The tensile strength increase compared to SA1 can be attributed to the interaction of the phenolic compounds present in A. orientalis extract with the polymer chains, which strengthens the matrix. The increase in elongation at break, however, indicates enhanced chain mobility. At higher extract concentration of 0.4% in SA3, tensile strength was 7.89 MPa and 93.74% elongation at break, showing highest mechanical strength and elongation among the fabricated film samples.

3.6 Antioxidant properties

The antioxidant property of sodium alginate and sodium alginate films with the incorporation of A. orientalis was analysed through the DPPH radical inhibition assay, as shown in Table 3. The SA1 film also displayed a low inhibition of 6.55%. The SA2 film showed a significantly better inhibition of 50.99%, which can be attributed to the presence of 0.2% A. orientalis extract. The improvement is primarily related to the presence of phenolic and flavonoids in the extract, which act as hydrogen donors to scavenge free radicals. The SA3 film exhibited the highest antioxidant activity of 58.3%. The increased concentration of extract enhanced the radical scavenging ability of the films and, consequently, their antioxidant activity. A study reported by Taoufik Ksiksi and Alaaeldin A. Hamza found that the A. orientalis showed the highest radical scavenging[²⁶].

Table 3
Antioxidant activity, antimicrobial activity and water vapor transmittance rate of the films.

Sample	DPPH Inhibition (%)	Antimicrobial Inhibition (mm)	Water Vapor Transmittance Rate (gm/m2-day)
SA1	6.55±0.52c	-	9.45±1.06a
SA2	50.99±2.30b	0.76±0.17a	7.22±1.06b
SA3	58.30±2.79a	1.02±0.11a	7.25±0.65b

• The values with different letters (a, b and c) inside a column indicate significant differences (p < 0.05).

3.7 Antimicrobial activity

The antimicrobial activity of sodium-alginate films was influenced by the incorporation of A. orientalis extract. The control film (SA1), containing 2% sodium alginate and 1% glycerol, showed no detectable inhibition, indicating that the polymer-plasticizer matrix did not possess inherent antimicrobial activity under the tested conditions. Similar findings have been reported for unmodified sodium-alginate films, which generally act as carriers rather than antimicrobial agents[⁴¹,⁴²]. Incorporating 0.2% A. orientalis extract produced an inhibition zone of 0.76 mm for SA2, whereas increasing the extract concentration to 0.4% resulted in a higher inhibition zone of 1.02 mm for SA3. Thus, doubling the extract concentration increased the mean inhibition value by approximately 34.2%. Previous investigations have confirmed that A. orientalis contains phenolic and flavonoid compounds and possesses concentration- and fraction-dependent biological activities. These compounds may alter microbial membrane permeability, interfere with cellular enzymes and proteins, cause leakage of intracellular components and disturb cellular metabolism[²⁶,⁴³].

3.8 Water vapor transmittance rate

The control sodium-alginate film (SA1) exhibited the highest WVTR of 9.45 g m⁻² day⁻¹, indicating comparatively greater water-vapor transmission through the polymer matrix. This behavior is expected because sodium alginate and glycerol are hydrophilic materials that readily interact with water molecules. Glycerol can also increase polymer-chain mobility and intermolecular spacing, thereby facilitating water vapor transport through alginate films[⁴⁴].

Incorporating A. orientalis extract significantly reduced the WVTR to 7.22 and 7.25 g m⁻² day⁻¹ for SA2 and SA3, respectively (p < 0.05). Compared with SA1, these values corresponded to WVTR reductions of approximately 23.67% for SA2 and 23.35% for SA3. The reduction in WVTR may be attributed to intermolecular interactions between the phytochemical constituents of A. orientalis and the sodium-alginate matrix. A. orientalis extracts containing considerable amounts of phenolic compounds, possessing hydroxyl groups capable of forming hydrogen bonds with the hydroxyl and carboxyl groups of sodium alginate[²⁶]. These interactions may produce a more compact polymer network, reduce the number of hydroxyl groups available for interaction with water and restrict the mobility of alginate chains. Similar reductions in water vapor permeability have been observed in sodium-alginate films containing olive and laurel leaf extracts, which were attributed to polymer-polyphenol interactions and the contribution of hydrophobic compounds[⁴²]. Although SA3 contained twice the concentration of A. orientalis extract compared with SA2, no significant difference was observed between their WVTR values. This indicates that increasing the extract concentration from 0.2% to 0.4% did not provide an additional water vapor barrier effect. The polymer-extract interactions responsible for reducing water vapor transmission may have reaches to saturation at 0.2% extract, or the additional extract may not have produced further changes in the diffusion pathway.

3.9 Release kinetics

The release of the extract component from the samples of 96% ethanol and 3% acetic acid as food simulants is illustrated in Figures 5a and 5b. In 96% ethanol, the control sample SA1 showed comparatively low absorbance throughout the wavelength range. The SA2 and SA3 exhibited markedly higher absorbance in the ultraviolet region, with a major absorption band at approximately 207 nm. A further spectral feature was observed around 453 nm. These signals indicate the presence of extract-derived compounds in the ethanol simulant. Both extract-containing samples showed considerably greater absorbance than the control.

Figure 5
(a) UV-Vis spectra of the food-simulant extracts in 96% ethanol; (b) UV-Vis spectra of the food-simulant extracts in 3% acetic acid.

In 3% acetic acid, SA2 and SA3 also demonstrated higher absorbance than the control. The absorption peaks observed at 234 and 275 nm, with the 0.4% extract-containing sample SA3 showed the most pronounced peak near 234 nm. The increased UV absorbance of the extract-containing samples compared with SA1 confirms migration or release of soluble extract constituents into the acidic food simulant. This higher release is attributed to higher scavenging of free radicals that promotes increase in antioxidant activity of the SA2 and SA3 film samples.

3.10 Scanning electron microscopy

The morphology, cross-sectional characteristics, and microstructural integrity of the cast films were analyzed through SEM. The addition of A. orientalis extract to the sodium alginate matrix has a profound effect on the surface of the films, as shown in Figure 6. Compared to the neat sodium alginate-glycerol film (SA1; Figures 6a and 6b), the bioactive-loaded films (SA2 and SA3; Figures 6c-f) showed no change on surface. Cross-sectional images also showed no apparent voids and cracks. This finding indicates uniform dispersion of the plant extract within the polymer matrix that results in enhanced structural and mechanical strength of the films.

Figure 6
SEM image of SA films loaded with A. orientalis.

3.11 X-ray diffraction

XRD diffractogram of the films prepared is shown in Figure 7, depicting the semicrystalline nature of pure sodium alginate (SA1) and A. orientalis impregnated sodium alginate films (SA2 and SA3). Usual diffraction peaks at 2θ = 13.6° and 21.4° were seen for amorphous regions of sodium alginate[⁴⁵]. The area under crystalline peak of the SA1 film became more SA3, signifying an enhancement of crystallinity upon addition of the natural extract[⁴⁶]. Such an increase in crystallinity could be due to the molecular interactions, which were mainly electrostatic forces and hydrogen bonding, between the bioactive compounds and the sodium alginate chains. Similar results were obtained when green propolis extract was added into sodium alginate films by Marangoni et al.[⁴⁷]. Similarly, Li et al.[⁴⁸] found improvement of crystallinity in sodium alginate-tannic acid composite films.

Figure 7
XRD graph of the SA films loaded with A. orientalis.

3.12 Thermal analysis

The thermal stability of the active films was assessed using TGA, as shown in Figure 8. At the temperature range of 25-600 °C, all film samples (SA1, SA2, and SA3) showed a common

Figure 8
TGA graph of the SA films loaded with A. orientalis.

three-step degradation pattern. The initial degradation step in the range of room temperature up to 163 °C was found to correspond with weight losses at 17.24% (SA1), 16.40% (SA2), and 15.44% (SA3), essentially related to bound and free moisture evaporation[⁴⁹]. The second substantial weight loss of about 50% at a temperature of about 223.5 °C is due cleavage of glycosidic bonds into polymer backbone [^[50]]. ^The third stage degradation starting from 225-600 °C, where the complete breakdown of the macromolecular ring structure, resulting in carbonization and leaving behind a solid residue or ash. The addition of A. orientalis into the sodium alginate matrix did not have a considerable impact on the thermal characteristics of the films, as indicated by the lack of prominent changes or shifts in the decomposition trends across the samples.

4. Conclusion

This research effectively created a new active packaging film using sodium alginate, glycerol, and A. orientalis stem extract for eco-friendly food packaging uses. The addition of the extract had an impact on films' physical, optical, structural, antioxidant, antimicrobial, water vapor transmittance and thermal properties. The release kinetics of extract from the fabricated film samples confirms the release in 96% ethanol and 3% acetic acid solution which enhances the antioxidant properties by 50.99% and 58.30% and antimicrobial properties to 0.76 mm and 1.02 mm. The water vapor transmittance rate was also decreased. The results confirm that A. orientalis extract can be used as a natural functional additive, enhancing the functionality of sodium alginate films and providing promise for use in active and green packaging systems.

6. Acknowledgements

The Authors are thankful to the Natural and Medical Sciences Research Center, University of Nizwa, Oman, for providing research facilities to conduct the current study.

Data Availability:

All data supporting the findings of this study are available from the corresponding author upon request.

How to cite:

Shah, Y. A., Gupta, A., Al-Harrasi, A., Rehman, N. U., Halim, S. A., Hayat, A., Afzaal, M., Ahmad, M. W., & Bhatia, S. (2026). Development and characterization of sodium alginate reinforced Acridocarpus orientalis extract. Polímeros: Ciência e Tecnologia, 36(4), e20260044. https://doi.org/10.1590/0104-1428.20260024

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[e-mail]

Editor-in-Chief:

Sebastião V. Canevarolo

Publication Dates

• Publication in this collection
  05 Oct 2026
• Date of issue
  2026

History

• Received
  15 Apr 2026
• Reviewed
  23 July 2026
• Accepted
  29 July 2026