Preparation and Application of Edible Film Based on Sodium Carboxymethylcellulose-Sodium Alginate Composite Soybean Oil Body

Abstract

In the study, edible films were successfully prepared by incorporating soybean oil body (SOB) into sodium alginate-sodium carboxymethyl cellulose (SA-CMC) matrix. The effects of different concentrations (0–4% w/w) of SOB on the physicochemical and antioxidant activities of films were systematically evaluated based on mechanical strength, barrier properties, thermal stability, and preservation effect. Findings revealed that the oxidation resistance, water vapor barrier, and thermal stability enhanced after the addition of SOB, while the water content, water solubility, and swelling rate decreased. When 3% SOB was added, the edible film performed the best in terms of mechanical properties and thermal stability; water vapor permeability was reduced by 21.89% compared to the control group, and the fresh life of pigeon meat was extended by 5–7 days. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses showed that the addition of SOB results in a more stable molecular structure network, which improved its physical properties. Overall, the findings indicated that SOB improved the quality of edible films as an environmentally friendly food packaging material and increased the feasibility of edible film application in the food industry.

1. Introduction

Traditional petroleum-based plastics are widely used in food packaging because of their stable performance and low cost. However, environmental pollution and its potential toxicity pose a threat to human health, therefore edible packaging has been developed to replace traditional plastic packaging. Edible films not only provide an ideal material for food packaging but also improve the nutritional value of packaged products [1]. Edible films are composed of natural biopolymers (polysaccharides, proteins, and lipids) as the film-forming matrix, supplemented by cross-linking agents, plasticizers, and other film-forming additives, and are formed through the interaction of molecules [2]. These films are degradable, renewable, non-toxic, pollution-free with green labels, and used for fresh-keeping and daily food packaging. It has great potential for development in the food packaging industry [3,4].

Polysaccharides are one of the most used materials for edible films, with excellent film-forming properties and gas resistance [5]. Some studies found that Sodium Alginate (SA) and Carboxymethyl Cellulose (CMC) have cross-linking effects on composites [6], resulting in a more stable molecular structure in the interior of the film, which is an edible material with the potential to replace plastics [7]. However, as this polysaccharide is hydrophilic, there are some issues, such as moisture resistance and water resistance. Mixing polysaccharides with lipids and using their performance advantages can meet more packaging needs while also having significant development potential. Researchers have added hydrophobic compounds, such as vegetable oil and essential oil, to the polysaccharide membrane matrix to reduce its water vapor permeability [3,8]. However, the addition of lipids to hydrocolloid solutions necessitates emulsification and homogenization. To prevent this energy-intensive process, naturally emulsified oil droplets such as oil bodies can be added to the initial biopolymer solution instead of oil [9].

A plant suborganelle that stores triglycerides as an energy source for seed germination and seedling growth is known as the oil body [10]. Soybean seeds contain a high content of oil bodies (SOB) with particle sizes ranging from 0.4–2.0 μm [11], and the purified SOB is mainly composed of neutral lipid droplets surrounded by natural emulsifiers (87–91.89%), basic proteins and phospholipids [12]. The natural protein-phospholipid layer in SOB facilitates dispersion in the aqueous phase, resulting in a natural oil-in-water emulsion that does not require additional emulsifiers or homogenization. Therefore, directly adding SOB to the membrane matrix to generate an emulsion not only prevents the high-energy process required for lipid dispersion but also increases the hydrophobicity of the edible membrane [13]. SOB phospholipids also include micronutrients, such as tocopherols, phytosterols, and isoflavones, making them superior in terms of nutrient composition and antioxidant properties to other lipid substances [14]. Furthermore, SOB is often prepared using water extraction methods in the food industry, and there are no food safety issues such as solvent residue [15]. Researchers first explored the preparation of edible membranes using SOB. Wang [16] studied the film-forming characteristics of an emulsion formed when SOB was dispersed in a buffer and prepared an edible film combining SOB and CMC. The soybean oil body films exhibited good barrier properties. The film-forming properties of SOB were discussed. However, the film-forming mechanism and the interaction of various components in the film solution following SOB addition were not revealed.

Therefore, the goal of this study is to investigate the film-forming mechanism of SOB and its influence on the membrane matrix. The application of SOB for the preservation of pigeon meat was investigated using pigeons as food samples.

2. Materials & Methods

2.1. Materials

Soybeans were purchased from a local supermarket (Pingdingshan, China). Tianchengwangge (one month old) were obtained from Henan Tiancheng Pigeon Industry Limited Company. Sodium alginate and sodium carboxymethyl cellulose were provided by Henan Qihuali Biotechnology Co., Ltd. (Zhengzhou, China). 2,2-diphenyl-1-picrylhydrazyl(DPPH),2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and glycerin were supplied by Beijing Solaibao Technology Co., Ltd. (Beijing, China). All other reagents were of analytical grade.

2.2. Preparation of CA-SOB Films

Different concentrations of SOB solution were prepared by dispersing 0 g, 1 g, 2 g, 3 g, and 4 g soybean oil bodies in 200 mL of distilled water. Subsequently, 3 g of CMC, 3 g of SA, and 3 mL of glycerol were successively added to SOB solutions of different concentrations. After being thoroughly mixed using a high-speed homogenizer at final concentrations of 0% (CA-SOB0), 1% (CA-SOB1), 2% (CA-SOB2), 3% (CA-SOB3), and 4% (CA-SOB4 w/w), the mixture was continuously stirred at room temperature for 1 h, before being poured into a plate (90 mm, 40 mL mixture in each plate). After the bubbles were eliminated, all plates were dried at 50 °C for 24 h, and all CA-SOB films were peeled off.

2.3. Characterization of CA-SOB Films

2.3.1. Thickness

The thicknesses of the CA-SOB films were measured using a spiral micrometer with 10 random locations in different places per sample, with an accuracy of 0.001 mm [17].

2.3.2. Tensile Strength (TS) and Maximum Elongation at Break (EB)

The composite film samples were cut into rectangles of 10 mm × 60 mm, divided into five parallel groups, and measured using a TMS-PRO texture instrument (FTC, Virginia, USA) under the following conditions: weighing sensor 25 N; probe, A/MTG; initial clip distance: 20 mm; drawing rate: 0.5 mm/s. All samples were analyzed five times and the mean values were determined. TS and EB were calculated as follows:

$$\mathrm{T}\mathrm{S}=\frac{\mathrm{F}}{\mathrm{T}\mathrm{W}}$$

(1)

$$\mathrm{E}\mathrm{B}\left(\mathrm{\%}\right)=\frac{L-L_0}{L_0}\times 100\mathrm{\%}$$

(2)

where F represents the maximum tension of the sample at fracture (N), T represents the film thickness, and W represents the film width. L represents the elongation length of the film when it breaks, and L₀ represents the original length of the film.

2.3.3. Color Parameters

The film samples were assessed for color, including parameters L, a, b, and ΔE, using a WSC-S color difference meter (Shanghai Yidian Physical Optical Instrument Co., Ltd., Shanghai, China). The total color difference was calculated using the following equation [18]:

$$∆\mathrm{E}=\sqrt{{(∆\mathrm{a})}^2+{(∆\mathrm{b})}^2+{(∆\mathrm{L})}^2}$$

(3)

where ΔL, Δa, and Δb are the differences between the color and value parameters of the CA-SOB films.

2.3.4. Water Vapor Permeability (WVP)

The water vapor permeability was measured using the gravimetric method reported by Liu et al. [19]. A suitable glass bottle containing 10 mL of distilled water was sealed with the films and kept in a desiccator at room temperature for 48 h. WVP was calculated as follows:

$$\mathrm{W}\mathrm{V}\mathrm{P}=\frac{∆\mathrm{m}\times \mathrm{L}}{t\times \mathrm{A}\times ∆\mathrm{p}}$$

(4)

where t is the time (s), A is the measuring area (m²), Δp is the water vapor pressure difference between the two sides of the film, Δm is the weight change of the glass bottle (g), and L is the thickness of the film (m).

2.3.5. Water Content (WC), Swelling Rate, and Water Solubility (WS)

The film samples were cut into 20 × 20 mm pieces, weighed for m₀, and dried in an oven at 105 °C until a stable weight (m₁) was achieved. The dried film (m₁) was immersed in 100 mL water at 25 °C for 24 h. The films were dehydrated with filter paper and weighed to yield (m₂). The films were then dried at 105 °C for 24 h to obtain a constant weight (m₃) [19]. The WC, swelling ratio, and WS of the films were calculated using the following equations:

$$\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{n}\mathrm{t}\left(\mathrm{\%}\right)=\frac{m_0-m_1}{m_0}\times 100\mathrm{\%}$$

(5)

$$\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r} \mathrm{s}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{b}\mathrm{i}\mathrm{l}\mathrm{i}\mathrm{t}\mathrm{y}\left(\mathrm{\%}\right)=\frac{m_1-m_2}{m_1}\times 100\mathrm{\%}$$

(6)

$$\mathrm{S}\mathrm{w}\mathrm{e}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{g} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\left(\mathrm{\%}\right)=\frac{m_3-m_1}{m_1}\times 100\mathrm{\%}$$

(7)

where m₀ represents the wet weight of the film, m₁ represents the initial dry mass, m₂ represents the weight of the film after drenching it in water for 24 h, and m₃ represents the final dry mass.

2.3.6. Fourier Transform Infrared Spectroscopy (FTIR)

To obtain the infrared spectrum in the range of 650 cm⁻¹ to 4000 cm⁻¹ with a resolution of 4 cm⁻¹, a Fourier transform infrared spectrometer (PerkinElmer Spectrum, PerkinElmer Enterprise Management (Shanghai) Co., Ltd., Shanghai, China) was used to analyze the FTIR spectra of the films according to Wu’s method [20].

2.3.7. Scanning Electron Microscopy (SEM)

The microstructures and surface morphologies of the CA-SOB films were observed using SEM (Thermo Scientific Apreo 2C, Thermo Scientific Co., Ltd., Shanghai, China). The film samples were coated with a thin coating of gold before SEM analysis and then imaged at a voltage of 10 kV [21].

2.3.8. Thermal Gravimetric Analysis (TGA)

A thermogravimetric analyzer (Mettler Toledo, Zurich, Switzerland) was used to measure the thermal stability of the CA-SOB films. The samples (4 mg) were weighed, placed in a quartz crucible, and loaded into the instrument. The instrument was operated at a heating rate of 10 °C/min and a nitrogen flow rate of 20 mL/min from 30 °C to 600 °C [22].

2.3.9. X-ray Diffraction Analysis (XRD)

CA-SOB films were analyzed using an X-ray diffractometer (Ultima IV, Rigaku Corporation, Tokyo, Japan). Cu-Ka rays (λ = 1.542 Å) rays were employed at 40 kV and 100 mA, with a scanning rate of 4°/min, a step length of 0.01, and a diffraction angle (2θ) range of 5° to 60° [23].

2.3.10. Antioxidant Activity

ABTS Radical Scavenging Rate

The film sample (5 mg) was mixed with 20 mL of deionized water and stirred continuously for 2 h at room temperature until it dissolved. The ABTS + free radical- scavenging activity of the CA-SOB film solution was investigated using the method proposed by Gao et al. [24]. ABTS (7 mM) and potassium persulfate (2.45 mM) were mixed in a 1:1 ratio and reacted in the dark for 16 h at 25 °C. The prepared films were mixed with ABTS solution (3 mL) which was diluted with PBS buffer to obtain an absorbance of 0.70 ± 0.02 at 734 nm. The ABTS radical scavenging rate (%) is as follows:

$$\mathrm{A}\mathrm{B}\mathrm{T}\mathrm{S} \mathrm{r}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l} \mathrm{s}\mathrm{c}\mathrm{a}\mathrm{v}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{g} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}\left(\mathrm{\%}\right)=\frac{A_0-A_t}{A_0}\times 100\mathrm{\%}$$

(8)

where A₀ is the absorbance of the control, and A_t is the absorbance of the film sample.

DPPH Radical Scavenging Rate

According to the method described by Wu [20], the film sample (0.5 g) was mixed with deionized water (10 mL) and oscillated in the dark for 24 h to obtain a solution. After centrifugation (6000 r, 10 min), the supernatant was utilized for the free radical scavenging test. The supernatant (20 µL) was combined with DPPH solution (5 mL, 0.2 mmol/L DPPH solution, dissolved in 95% ethanol), and the reaction was run in the dark at 25 °C for 30 min. The absorbance was then measured at 517 nm. The DPPH free radical clearance was calculated as follows:

$$\mathrm{D}\mathrm{P}\mathrm{P}\mathrm{H} \mathrm{r}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{c}\mathrm{a}\mathrm{l} \mathrm{s}\mathrm{c}\mathrm{a}\mathrm{v}\mathrm{e}\mathrm{n}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{g} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}\left(\mathrm{\%}\right)=\frac{A_0-A_t}{A_0}\times 100\mathrm{\%}$$

(9)

where A₀ denotes the absorbance of the control, and A_t denotes the absorbance of the film sample.

2.3.11. Application of Preservation in Pigeon

The pigeon meat was stored at 4 °C for no more than 2 h from slaughter to the start of the experiment. To evaluate the CA-SOB films for applications in food packaging, pigeons were cut into pieces and sealed in CA-SOB0, CA-SOB1, CA-SOB2, CA-SOB3, and CA-SOB4; pigeon pieces without packaging were used as the control group. The total volatile basic nitrogen (TVB-N; mg/100 g sample) was used to determine the degree of spoilage [19,25].

2.3.12. Statistical Analysis

All experiments were repeated five times, and the experimental results were expressed as the mean value ± standard deviation. Mean values and standard deviations were calculated using GraphPad Prism 9.0 software. Analysis of variance (ANOVA) was used for statistics using SPSS 25.0 software. p < 0.05 was used to determine statistical significance.

3. Results and Discussion

3.1. Mechanical Properties

Table 1. The thickness, tensile strength (TS), elongation at break (EB), and water vapor permeability (WVP) of films.

Films	Thickness (mm)	TS (MPa)	EB (%)	WVP × 10−10 (g/(m·s·Pa))
CA-SOB0	0.209 ± 0.022 a	2.307 ± 0.017 e	41.6 ± 2.60 d	6.249 ± 0.121 a
CA-SOB1	0.230 ± 0.018 b	2.605 ± 0.026 d	58.6 ± 1.50 c	5.643 ± 0.079 b
CA-SOB2	0.263 ± 0.020 b	3.105 ± 0.032 b	73.0 ± 0.70 b	5.305 ± 0.146 c
CA-SOB3	0.269 ± 0.011 a	3.661 ± 0.067 a	78.6 ± 3.10 a	4.881 ± 0.130 d
CA-SOB4	0.270 ± 0.009 a	2.710 ± 0.033 c	70.5 ± 2.00 b	4.577 ± 0.173 e

Note: Significant differences are expressed by different letters (a–e) (p < 0.05).

shows the mechanical properties of the CA-SOB films, including thickness, tensile strength (TS), elongation at break (EB), and water vapor permeation (WVP) Thickness is an important parameter that influences the other significant properties of active films. Table 1 shows that the thicknesses of CA-SOB films ranged from 0.20 mm to 0.27 mm. The thickness of the addition of SOB increased the thickness and solid content of the CA-SOB film. However, SOB content was less than 5% and the thicknesses of SOB films had no obvious improvement.

The influence of different levels of SOB on the mechanical properties of the CA-SOB films was evaluated by TS and EB as shown in Table 1. Upon increasing the concentration of SOB, TS and EB showed a trend of increasing first and then decreasing, reaching the maximum value of CA-SOB3 (1.661 ± 0.067 MPa and 78.6 ± 3.10%, respectively), and then reducing significantly (CA-SOB4). Compared to CA-SOB0, the EB value of CA-SOB3 improved by 37%, and the TS increased significantly (p < 0.05) which could be attributable to the suitable concentrations of SOB [14,16], which enhanced the EB of CA-SOB films. This finding might be due to the addition of varied concentrations of SOB, which, as a natural pre-emulsified oil, can increase the flexibility and change the physical properties of the composite film [26].

WVP gradually decreased and reached a minimum value of 4.577 ± 0.173 for CA-SOB4 (p < 0.05). SOB plays a hydrophobic role in the membrane matrix reducing the WVP of CA-SOB films [27]. Furthermore, an excessive amount of SOB may hinder the formation of hydrogen bonds between the two polysaccharides, thus affecting their three-dimensional structure [28].

3.2. Chromaticity Analysis

The color of the film is a significant indicator for edible packaging since it affects the appearance of the product and the acceptability of consumers and is related to the additives in the film matrix [29].

Table 2. Effect of the SOB concentration on the color of films.

Fimls	L*	a*	b*	ΔE
CA-SOB0	70.18 ± 1.21 a	1.01 ± 3.57 e	1.79 ± 0.63 c	2.79 ± 2.54 c
CA-SOB1	69.36 ± 0.58 ab	1.05 ± 0.101 d	1.94 ± 2.43 c	4.61 ± 2.10 bc
CA-SOB2	69.20 ± 1.91 ab	1.63 ± 1.07 c	2.73 ± 1.11 bc	5.52 ± 1.80 abc
CA-SOB3	69.06 ± 1.53 b	2.59 ± 0.06 b	3.96 ± 1.86 b	8.00 ± 0.49 ab
CA-SOB4	68.78 ± 0.03 ab	2.68 ± 0.61 a	6.38 ± 0.02 a	8.60 ± 0.05 a

Note: Significant differences are expressed by different letters (a–e) (p < 0.05).

presents the colorimetric results for the prepared films. When compared to CA-SOB0, the L* of the edible film gradually reduced with the increase in SOB concentration, showing that the brightness of the composite film increased, however, the b* value increased from 1.79 of CA-SOB0 to 6.38 of CA-SOB4, indicating that the film gradually turned yellow. Furthermore, with an increase in SOB concentration, the color of the edible film darkened, and the brown color became more obvious [30]. This is in agreement with the results reported by Zhou et al. [31]. In this work, the addition of SOB to the film components increased a*, b*, and ΔE*, but decreased L*. The color variations may be ascribed to the unique compounds in the SOB affecting visible light absorption [10,11].

3.3. Water Content (WC), Swelling Rate, and Water Solubility (WS)

Figure 1 depicts water content, swelling rate, and water solubility. The CA-SOB3 film exhibited the lowest water content as the SOB concentration increased, highlighting that the hydrophilicity of the composite membrane decreased, which may have been caused by the hydrogen bond between SOB and the two polysaccharides [32]. The swelling rate of the SOB-added group was lower than that of the control group, which might be attributed to the structure, concentration, and glycerol content of the samples [33]. Generally, films with low solubility are often easier to utilize in food packaging applications [34]. Compared to CA-SOB0, the solubility of the composite film initially declined and then elevated, with CA-SOB3 showing the lowest solubility. These modifications may be due to the interaction of hydroxyl and amino groups between SOB, SA, and CMC, which reduced the number of hydrogen bonds in the composite film, and thus caused a decrease in solubility [35]. However, when the SOB content was greater than or equivalent to 4%, the SOB in the composite film aggregated to form larger oil droplets, and the sample demonstrated lower cohesion. The surface structure of the film was quite uneven, and cracks appeared in the internal structure, exposing more hydrophilic groups, and increasing the film’s solubility [36], which is consistent with the scanning electron microscopy observations.

3.4. FTIR Analysis

FTIR analysis was conducted to investigate the interactions between molecules in the film materials. Figure 2 depicts the FTIR spectra of CA-SOB composite films. The peaks at 3285 cm⁻¹ observed in the films were attributed to the stretching vibration of O–H [37]. The two peaks at 2882 cm⁻¹ and 2941 cm⁻¹ were related to the symmetric and asymmetric C-H vibrations, while the peaks at 1597 cm⁻¹ and 1411 cm⁻¹ were caused by antisymmetric and symmetric contraction of C-O (carbonyl), respectively [38]. The peak strength at 1030 cm⁻¹ was significantly reduced with the addition of SOB to the membrane matrix, possibly owing to the tensile vibration of C-O-C. These changes may be related to hydrogen-forming interactions between SOB and the hydroxyl and amino groups of the polysaccharides [39]. The absorption band intensities at 1597 cm⁻¹ and 1411 cm⁻¹ decreased as the SOB concentration increased. Similar changes have been reported in the spectra of black soybean seed extract and chitosan [40]. These results indicate that SOB can stabilize the structure and properties of the membrane more stable. FTIR analysis confirmed the interaction between SOB and the two polysaccharides, which had a significant impact on the physical and barrier properties of the resultant films [41].

3.5. SEM Analysis

The cross-section of the blank group revealed obvious voids and cracks (Figure 3). Following the addition of SOB, the cross-section of the film showed a uniform texture and the voids and cracks decreased significantly with the increase in concentration, and almost no cracks were observed especially in the longitudinal section. The structure of the composite film was compact, and the cracks in the transverse and longitudinal sections were significantly reduced when the SOB concentration was 3%. These findings were consistent with the WVP, TG, and FTIR results, which might be attributed to SOB forming hydrogen bonds with the two polysaccharides, resulting in a tighter three-dimensional network structure [32]. When the concentration of SOB was 4%, the surface cracks of the composite film increased compared to 3%, and the corresponding physical properties such as tensile strength and elongation at break decreased, which may be related to the excessive concentration of SOB. When the concentration of SOB was too high, the film aggregated and formed larger oil droplets. The composite film exhibited an irregular and uneven cross-sectional image [42].

3.6. TGA

Thermogravimetric analysis (TGA) is a tool used to measure the thermal properties of materials and the curve of weight change with temperature. In practical applications, heat seal ability is an important property of edible film packaging [43]. The effect of SOB on the thermal stability of the CA–SOB matrix was analyzed. Figure 4 displays the thermal gravity (TG) curves. The change in the quality of the composite throughout the heating process could be roughly divided into three stages. The first stage (70–100 °C) was mainly due to the weight change caused by the volatilization of bound and attached water in the sample. The addition of SOB delayed the volatilization of water in the sample, which was consistent with the earlier water vapor permeation results [44]. The second stage (190–400 °C) was induced by the glycerol breakdown in the composite film. The last stage (400–600 °C) was associated with the intermolecular force of the composite membrane or the destruction of hydrogen bonds between molecules [45]. Compared to the control group, the curve of the SOB group shifted to a higher temperature, especially when the SOB concentration reached 3%. The results demonstrated that the addition of SOB could hinder or delay the evaporation of volatiles from the membrane, resulting in a higher thermal stability of the membrane.

3.7. XRD Analysis

The crystalline patterns of CA-SOB films were studied using XRD analysis, which revealed intermolecular interactions among the components (Figure 5). Materials with high crystallinity show narrow peaks, whereas those with low crystallinity have wider and lower characteristic peaks [46]. SA exhibited a characteristic crystallization peak at 21.8°, matching the crystal plane (101). Compared to the control group, there was no obvious diffraction peak, but the peak intensity increased at 2θ = 21.8°, which may be due to the enhancement of intermolecular van der Waals forces caused by the addition of SOB [47]. The addition of SOB did not change the crystal structure of the edible film, but the peak movement degree became higher. This result demonstrated that SOB had good compatibility with the two polysaccharides, and the addition of SOB would not impact the original structure of the film [48].

3.8. Antioxidant Activity

Figure 6A and Figure 6B illustrate the free radical scavenging rates of ABTS and DPPH, respectively. The control film (CA-SOB0) had no scavenging activity for both DPPH and ABTS radicals, however, the radical scavenging rates surged as the SOB concentration increased. CA-SOB4 exhibited the highest ABTS and DPPH radical scavenging activities at 25.07% and 17.54%, respectively. SOB contains a variety of active substances and is available in the form of natural capsule oil, which may explain why the CA-SOB film possesses certain antioxidant properties [49,50]. During the detection of antioxidant activity, the solvent molecules from the external solution permeate the polymer network, causing the polymer network to swell and the active substance to enter the external solution [51]. Simultaneously, the swelling of the edible film in deionized water released internal active substances into the solution, elevating the scavenging rate of ABTS and DPPH free radicals [52].

3.9. Food Preservation Application Analysis

TVB-N is a non-flavored product that contains ammonia, dimethylamine, and other substances that may increase the pH of the packaging atmosphere [53]. The acceptability of the meat product was determined using untreated pigeon meat as a control, and a limited concentration of 25 mg N/100 g [54]. Figure 7 depicts the changes in the TVB-N values of all groups. The TVB-N values of all groups were significantly increased. In the control group, on day 12 of storage, the TVB-N content increased fast and reached 59.48 mg/100 g. The trend of TVB-N value in the CA-SOB0 group matched with the control group. On the 12th day, the TVB-N value of CA-SOB3 decreased by 32.75% compared to the control group. This result suggested that CA-SOB3 films could reduce pigeon spoilage to a certain extent.

4. Conclusions

In summary, CA-SOB films with SOB concentrations of 0%, 1%, 2%, 3%, and 4% were successfully prepared and displayed good physicochemical properties and antioxidant activities. The results revealed that the addition of SOB significantly improved the physical properties of the edible film, and the film showed an excellent water vapor barrier. The thermal stability of the CA-SOB film improved dramatically after adding SOB to the thermal stability test. FTIR, XRD, and SEM results showed that intermolecular hydrogen bonds were formed between the SOB and polysaccharide in the edible film, the internal structure of the film was compacted, and the surface texture was improved. CA-SOB3 demonstrated the best physical and chemical properties. When the concentration of SOB exceeded 4% (including 4%), SOB accumulated in the membrane matrix to form irregular large droplets, affecting the structure of the membrane. Overall, the findings showed that SOB offers great development potential in the field of edible food packaging materials.