Fabrication of levan derived from Priestia koreensis HL12 into polyvinyl alcohol and gelatin based composite film for food packaging

TL;DR

Researchers made edible food packaging films using levan from a bacteria, combining it with gelatin and polyvinyl alcohol to improve performance.

Contribution

First integration of levan from Priestia koreensis HL12 into PVA/gelatin-based composite films for food packaging.

Findings

PVA/GE/20%LV film showed highest elongation at break (166%) and lowest swelling index.

SEM and FTIR confirmed successful crosslinking and film morphology.

20% levan content provided optimal mechanical and thermal properties for packaging.

Abstract

This study presents the first report on the integration of levan produced by Priestia koreensis HL12 into PVA/gelatin-based composite films and provides a comprehensive characterization of the resulting edible films. The properties of PVA/gelatin composite films were enhanced by incorporating levan at different ratios (10, 20, 30, 40, and 50 wt% relative to PVA). A small amount of glycerol was added as a plasticizer, and the three components were crosslinked using genipin. The PVA/gelatin/levan composite films were fabricated via the solvent casting method. The fabricated films exhibited smooth surface morphologies and a gradual color transition from blue to violet with increasing levan content. Scanning electron microscopy (SEM) was used to examine film morphology, while Fourier transform infrared spectroscopy (FTIR) confirmed crosslinking interactions between genipin and gelatin in the PVA/gelatin/levan component. Thermogravimetric analysis (TGA) was employed to evaluate thermal stability, and tensile testing was conducted to determine mechanical strength as a function of levan content. Among the formulations, PVA/GE/20%LV film exhibited enhanced thermal stability (from 321 to 314 °C) compared to PVA/GE/0%LV, the highest elongation at break (166%), and the lowest swelling index. These findings highlight the potential of levan from P. koreensis HL12 as a functional biopolymer, with the PVA/GE/20%LV film identified as the most suitable formulation for edible food packaging applications.

Image 1

•Hydrogel based composite was successfully prepared from levan, gelatin and polyvinyl alcohol.•Genipin was chemically employed as a crosslinker agent for composite films formation.•Levan was successfully prepared from Priestia koreensis HL12.•The 20% levan composite film exhibited optimal mechanical and physicochemical properties for packaging applications.

Hydrogel based composite was successfully prepared from levan, gelatin and polyvinyl alcohol.

Genipin was chemically employed as a crosslinker agent for composite films formation.

Levan was successfully prepared from Priestia koreensis HL12.

The 20% levan composite film exhibited optimal mechanical and physicochemical properties for packaging applications.

Figures

FTIR spectra of as-synthesized levan produced by *P. koreensis* HL12 and commercial levan isolated from Timothy grass.Fig. 1

Photo-image of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 2Table 1Mechanical properties of PVA/GE/LV composite films with varying levan contents.Table 1SamplesTS (MPa)EL (%)Thickness (mm)PVA/GE/0%LV8.653 $[eqn]$ 0.22898.500 $[eqn]$ 2.5980.153 $[eqn]$ 0.007PVA/GE/10%LV8.643 $[eqn]$ 0.228100.677 $[eqn]$ 1.1550.154 $[eqn]$ 0.004PVA/GE/20%LV8.033 $[eqn]$ 0.533166.000 $[eqn]$ 1.7320.162 $[eqn]$ 0.005PVA/GE/30%LV8.103 $[eqn]$ 0.851144.333 $[eqn]$ 4.0410.155 $[eqn]$ 0.012PVA/GE/40%LV8.12

Morphological properties of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 4

Tensile strength and elongation at break of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 5

Full text

Introduction

1

With the increasing global demand for safe and sustainable food packaging, advanced packaging technologies have attracted considerable attention due to their roles in preserving food quality, extending shelf life, and facilitating storage and distribution [1,2]. In recent years, edible packaging has emerged as an attractive alternative to conventional materials because of its biodegradability, safety, and potential nutritional benefits [3,4]. Edible films are commonly fabricated from biopolymers such as polysaccharides, proteins, and lipids, which offer advantages including low density, good barrier properties, and mechanical flexibility. These materials have been widely explored for applications in fruits, vegetables, bakery products, and pharmaceutical-related packaging.

Polyvinyl alcohol (PVA) is a hydrophilic polymer containing abundant hydroxyl groups, which confer excellent film-forming ability, good gas and oxygen barrier properties, mechanical strength, and biodegradability. Consequently, PVA has been widely used in food packaging applications. However, its high-water sensitivity and low water resistance limit the performance of neat PVA films [5,6]. To address these limitations, PVA is often blended with other biopolymers.

Gelatin, derived from the partial hydrolysis of collagen, has been widely applied in food, cosmetic, and pharmaceutical industries. Despite its biocompatibility and film-forming ability, gelatin exhibits drawbacks such as low mechanical strength and heat sensitivity, necessitating blending with other polymers to improve its functional properties [5]. Recent studies have shown that PVA–gelatin-based edible films exhibit enhanced mechanical performance and biodegradability, making them promising candidates for eco-friendly packaging materials [[7], [8], [9]]. Nevertheless, their broader application remains constrained by limited antimicrobial activity, brittleness, and processing challenges.

To overcome these limitations, the development of sustainable hydrogel-based composites has been proposed as an alternative strategy, particularly due to their tunable properties and improved degradability after end use. In this context, levan-based hydrogel has attracted increasing interest. Levan is a naturally occurring polysaccharide-based polymer (fructan) produced by plants and microorganisms [10]. It consists primarily of fructose units linked by β-(2→6) glycosidic bonds, with variable β-(2→1) branching depending on the producing organism, resulting in diverse physicochemical properties. Levan exhibits excellent solubility, favorable mechanical properties, strong adhesion, and high thermal resistance. Moreover, its unique molecular architecture, high biocompatibility, and intrinsic bioactivity make it an attractive additive for biopolymer-based materials.

Priestia koreensis HL12 is a novel and promising levan-producing microorganism, capable of converting high concentrations of sucrose into levan with high yield. Genomic analysis identified key enzymes involved in levan biosynthesis, and the strain achieved approximately 55% conversion from 200 to 300 g/L sucrose [11]. Previous studies have demonstrated the effectiveness of levan in edible film applications. Mantovan et al. incorporated levan into cassava starch films, resulting in improved water solubility, mechanical properties, and reduced water vapor transmission [12]. Gan et al. reported that levan-containing biopolymer composites enhanced mechanical properties and extended the shelf life of strawberries in active packaging systems [13]. Similarly, Wang et al. showed that levan/chitosan films exhibited improved mechanical strength, reduced swelling, and lower water vapor permeability for pork packaging applications [14].

The objective of this study is to develop a levan-based hydrogel composite for sustainable edible packaging applications. This work reports, for the first time, the fabrication of PVA/gelatin composite films incorporating levan derived from P. koreensis HL12 produced via sucrose bioconversion. Levan was biosynthesized using sucrose as the primary carbon source and subsequently integrated into PVA–gelatin matrices. The physicochemical properties of the resulting hydrogel composites were systematically evaluated, demonstrating the potential of HL12-derived levan as a novel biopolymer additive for sustainable edible films and food packaging applications.

Materials and methods

2

Materials and chemical reagents

2.1

Sucrose, starting chemical reagent for levan synthesis, was purchased from Carlo Erba Reagents, Co., Ltd. The levan producing bacterial strain P. koreensis HL12 was isolated from soil attached to sago palm root, Trang, Thailand. Ammonium sulphate, magnesium sulphate and dipotassium phosphate were purchased from Sigma Aldrich, Co., Ltd. Polyvinyl alcohol with the molecular weight of 100,000 g/mol was purchased from Chem-Supply, Co., Ltd. Glycerol, genipin and ethanol were purchased from Merck, Co., Ltd. Gelatin was also purchased from QRec, Co., Ltd. Levan isolated from Timothy grass was purchased from Megazyme. Co., Ltd. All of chemical reagents were analytical grade and used as received without further purification.

Preparation of levan based polysaccharide from Priestia koreensis HL12

2.2

P. koreensis HL12 was cultured in 5 mL of LB broth with shaking speed 200 rpm at 30 °C for 18 h. The 1% (v/v) inoculum was added in 50 mL of SUC medium containing 200 g/L sucrose and then incubated with shaking speed 200 rpm at 30 °C for 24 h. The bacterial cells were removed by centrifugation at 8000×g for 5 min at room temperature. The levan polymer precipitation was performed by adding cold absolute ethanol with a ratio of 1:3 of supernatant to ethanol [11]. The levan was collected by centrifugation at 12,000×g for 5 min at room temperature and subsequently dried in a fume hood at room temperature. The antimicrobial activity of levan produced by P. koreensis HL12 was tested. Escherichia coli DH5α was uniformly spread onto LB agar plates. Wells were then created using a sterile cork borer, and each well was loaded with 100 μL of levan solution (500 g/L). The plates were incubated at 37 °C for 24 h. Distilled water was used as a negative control.

Development of levan, polyvinyl alcohol and gelatin-based hydrogel composite

2.3

A 10 wt% polyvinyl alcohol solution was prepared by dissolving in deionized water at 90 °C for 90 min. In parallel, a 5 wt% gelatin solution was prepared in deionized water at 35 °C for 30 min. The two solutions were consequently mixed, and then 200 μL of glycerol was added. Subsequently, 10–50 wt% of as-synthesized levan was incorporated. The mixture was continuously stirred at 50 °C for 1 h. Then, 60 μL of 5 wt% genipin solution was added, and the mixture was stirred at 50 °C for an additional hour. The mixture was cast onto a plastic plate (2.7 × 4.5 × 1.5 cm) and dried at 25 °C at 60% relative humidity for 48 h.

Instrumental analysis

2.4

Fourier transform infrared (FTIR)

2.4.1

FTIR was used to determine the functional group of hydrogels. The measurement was conducted by the guidance of FTIR instrument using Transmittance Mode. The FTIR spectra was obtained in the range of wavenumber from 4000 to 500 cm^−^^1^ with a resolution of 2 cm^−^^1^ (Invenio® FTIR spectrometer, Bruker). Prior to analysis, samples were stored in oven to prevent the moisture adsorption onto surface.

Thermogravimetric analysis (TGA)

2.4.2

The thermal decomposition of hydrogels was evaluated using a thermogravimetric analyzer (TGA2, Mettler Toledo). TGA studies were carried out in nitrogen atmosphere at a flow rate of 60 mL/min. The temperature was set up from 30 °C to 700 °C with a heating rate of 10 °C/min. The weight of sample was only 10 mg. The experiment was conducted for 3 times for each measurement to prevent the error.

Scanning electron microscope (SEM)

2.4.3

Morphological properties of hydrogel were investigated by scanning electron microscope (JEOL JSM7800F). Before analysis, the sample was sputter-coated with gold in order to enhance the electrical conductivity. The experiment was set up with the accelerating voltage of 15 kV and magnification of 60×.

Mechanical properties

2.4.4

The mechanical properties of specimens were characterized according to a modified ASTM D1708 standard. The samples were prepared in a rectangular shape with dimensions of 10 mm in width and 45 mm in length. Tensile strength was measured using a universal testing machine (H50KT Tinius Olsen, UTM) at a crosshead speed of 5 mm/min, using a 50 N load cell with an initial gauge length of 20 mm. Six measurements were tested for each sample group. The data was reported as a statistical average and standard deviation.

Contact angle measurement

2.4.5

The contact angle of sample (Biolin Theta Lite Optical Tensiometers) was measured to study the wettability by dropping DI water onto the sample surface. A droplet volume of DI water (50 μL) was carefully dropped using a micro-syringe with a 0.8 mm needle.

Determination of physico-chemical properties of levan derived from P. koreensis HL12 into polyvinyl alcohol and gelatin-based composite

2.5

Swelling behavior

2.5.1

To estimate the swelling ratio of composite films, the samples were cut to 10 × 10 mm, then dried at 60 °C for 24 h. The dried samples were immersed in DI water (40 mL) for 24 h. The swollen samples were withdrawn and weighed after removing the superficial water using a filter paper. The swelling ratio was calculated from equation (1):

$$[eqn]$$

where, W_1_ and W_t_ represent the weight of the dried sample and the weight of the swollen sample at different time intervals, respectively.

Moisture content

2.5.2

To estimate the moisture content, the samples (10 × 10 mm) were weighed and then dried at 60 °C for 24 h. The equilibrium moisture content was calculated using Equation (2).

$$[eqn]$$

where, W_1_ and W_2_ represent the initial weight of each sample and the constant dry weight, respectively.

Water solubility

2.5.3

To evaluate water solubility, the samples were cut to 10 × 10 mm and dried at 60 °C for 24 h. The dried samples were immersed in DI water (40 mL) for 24 h. The sample residue was dried at 60 °C for 24 h and weighed. The water solubility was calculated from equation (3):

$$[eqn]$$

where W_2_ and W_3_ represent the initial dry weight of each sample and the residual dry weight after the test, respectively.

Results and discussion

3

Development of levan, polyvinyl alcohol and gelatin-based hydrogel composite

3.1

In this work, levan polysaccharide was synthesized as an extracellular form by P. koreensis HL12 via enzymatically route. The FTIR spectra of levan synthesized by P. koreensis HL12, compared with commercial levan isolated from Timothy grass, showed highly similar characteristic absorption bands, confirming the presence of comparable functional groups (Fig. 1). A characteristic peak at 3263 cm^−1^ was observed and attributed to O–H stretching vibrations, indicating the presence of hydroxyl groups in the levan structure. Furthermore, the peaks at the wavenumbers of 2935 cm^−1^ and 1430 cm^−1^ were observed and attributed to C–H stretching vibrations, which typically correspond to the main chain of the levan polysaccharide. In addition, the peaks at the wavenumbers of 1641 cm^−1^ and 1126 cm^−1^ were observed and assigned to C–O stretching vibrations, referring to an organic structure composed of fructose units linked predominantly by β-(2→6) glycosidic bonds. Two characteristic peaks at 938 cm^−1^ and 853 cm^−1^ were observed, which are typically associated with pyran ring vibrations [15,16]. The antimicrobial property of the levan synthesized from P. koreensis HL12 was subsequently evaluated by the agar disc diffusion test against Escherichia coli DH5α. The results demonstrated that levan produced by P. koreensis HL12 exhibited inhibitory activity against E. coli DH5α, a representative Gram-negative bacterium, indicating its potential antimicrobial functionality (Fig. S1). In contrast, distilled water that used as the negative control showed no antimicrobial activity. This result is consistent with previous findings that levan samples produced by Bacillus haynesii that posed broad-spectrum antimicrobial activity against pathogenic microbial species including E. coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans [17]. Furthermore, levan synthesized from coconut inflorescence sap using Bacillus subtilis also exhibited inhibitory effect against E. coli [15]. These results demonstrate the bioactivity of levan, highlighting its potential as a promising bio-based polymer for the development of functional materials.Fig. 1FTIR spectra of as-synthesized levan produced by P. koreensis HL12 and commercial levan isolated from Timothy grass.Fig. 1

Subsequently, the as-synthesized levan produced by P. koreensis HL12 was used for the preparation of hydrogel composites based on polyvinyl alcohol and gelatin. Based on Fig. 2 illustrating the photo-image of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan, the thickness of samples was approximately 0.147–0.162 mm as shown in Table 1. All hydrogel composite samples are typically presented as high transparency. The “SCI-TU” can be seen when hydrogel composites were presented at the front. However, it was observed that the color of hydrogel was changed from blue shade to violet shade. This was probably due to the presence of genipin. It was used to be a crosslinking agent in order to form a reaction between amine group of gelatin and polyvinyl alcohol [18]. Therefore, with high content of levan, the color of hydrogel composite was slightly changed to violet shade. Genipin was commonly used as a crosslinker for biomaterials containing primary amine groups. The mechanism was initiated by the nucleophilic attack of primary amine groups on the C-3 atom of genipin, leading to the opening of the dihydropyran ring. Subsequent nucleophilic substitution and molecular rearrangement can result in the formation of secondary amine and heterocyclic structures. The generation of blue–violet pigments and the crosslinking have been reported, depending on pH, temperature, concentration, amino source, and the surrounding environment [19]. Although maintaining constant genipin concentration, pH, temperature, and cross-linking time in this study, a distinct color variation was observed following the incorporation of levan. This observation indicated that the color change was influenced not only by genipin concentration or reaction time, but also by environmental modifications to the genipin-derived chromophore structures [20].Fig. 2. Photo-image of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 2. Table 1Mechanical properties of PVA/GE/LV composite films with varying levan contents.Table 1. SamplesTS (MPa)EL (%)Thickness (mm)PVA/GE/0%LV8.653 $[eqn]$ 0.22898.500 $[eqn]$ 2.5980.153 $[eqn]$ 0.007PVA/GE/10%LV8.643 $[eqn]$ 0.228100.677 $[eqn]$ 1.1550.154 $[eqn]$ 0.004PVA/GE/20%LV8.033 $[eqn]$ 0.533166.000 $[eqn]$ 1.7320.162 $[eqn]$ 0.005PVA/GE/30%LV8.103 $[eqn]$ 0.851144.333 $[eqn]$ 4.0410.155 $[eqn]$ 0.012PVA/GE/40%LV8.120 $[eqn]$ 0.599110.667 $[eqn]$ 1.1550.151 $[eqn]$ 0.005PVA/GE/50%LV8.173 $[eqn]$ 0.258101.667 $[eqn]$ 2.8870.147 $[eqn]$ 0.003Table notes: TS = tensile strength; EL = elongation at break. Values are expressed as mean ± SD (n = 3).

Physico-chemical properties of levan derived from P. koreensis HL12 into polyvinyl alcohol and gelatin-based composite

3.2

The physicochemical properties of polyvinyl alcohol–gelatin hydrogel composites incorporating levan from P. koreensis HL12 were subsequently evaluated. FTIR analysis was carried out to define the functional group of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan. Fig. 3a displays the FTIR spectra of the polyvinyl alcohol–gelatin hydrogel composite with added levan. The spectra reveal similar characteristic peaks, attributable to the presence of shared functional groups in both levan and the hydrogel matrix. The broad band observed at around 3280 cm^−1^ corresponds to O–H stretching vibrations of hydroxyl groups and overlaps with the N–H stretching vibration (amide A) of gelatin [21]. The peak at 2939 cm^−1^ was associated with C–H asymmetric stretching of the CH_2_ group. Similarly, the peak at 1654 cm^−1^ was attributed to the C

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O stretching vibration (amide I). The peaks at 1545 cm^−1^ and 1235 cm^−1^ were assigned to the N–H stretching of amide II and amide III, respectively [22]. Furthermore, the peak at 1095 cm^−1^ was attributed to the C–N stretching vibration, while the peak at 1729.83 cm^−1^ was due to C–H stretching [23]. Finally, the peak at 874 cm^−1^ was considered to correspond to the pyran ring vibrations of levan and the C–C vibrations of PVA [16].Fig. 3(a) FTIR spectra and (b) Thermal decomposition behavior of polyvinyl alcohol and gelatin-based hydrogel composites containing levan at different concentrations.Fig. 3

The thermal decomposition behavior of the film composites is shown in Fig. 3b. It indicated that the addition of levan resulted in a similar pattern. The decomposition process occurred in three distinct regions. From ambient temperature to 200 °C, it exhibited an initial weight loss of approximately 20 wt%, attributed mainly to the evaporation of water and volatile components. Then, when the temperature range of 200 and 500 °C was tested, it was characterized by a major weight loss of 62 wt%. The temperature range of 200–300 °C was associated with the thermal decomposition of gelatin and glycerol, as well as the cleavage of β-(2→1) glycosidic bonds in levan [24,25]. The 260–380 °C range was attributed to PVA decomposition. In addition, the temperature range of 300–500 °C was associated with the degradation of β-(2→6) glycosidic bonds in levan, which may partially overlap with PVA decomposition [25,26]. After that, when the temperature was increased above 500 °C, the weight loss remained relatively constant, leaving a residual mass of approximately 10–17 wt%. This residue was attributed to the overlapping pyrolysis of PVA and gelatin [27]. As shown in Fig. 3b, the incorporation of levan resulted in a shift of the main decomposition temperature compared to the PVA/gelatin film, suggesting that the presence of levan influenced the thermal degradation behavior of the composite films (from 321 to 314 °C). This observation was consistent with previously reported results, in which composite films with increased levan content exhibited lower degradation temperatures [13].

Then, the morphological properties of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan were evaluated using SEM technique. All of microstructures were typically presented in a similar manner (Fig. 4). The surface was smooth. No crack in between levan and polyvinyl alcohol matrix was presented, suggesting that levan was successfully integrated into hydrogel matrix. These results indicate that levan was chemically crosslinked within the polyvinyl alcohol/gelatin hydrogel network, conferring excellent compatibility among the constituent components. Previously, water-soluble levan-based composites synthesized from B. haynesii have been demonstrated to exhibit substantial potential for biomedical applications [17]. The yellow circle was employed to report the existence of genipin after reaction. This observation was consistent with the photographic images shown in Fig. 2, the hydrogel exhibited a blue coloration, indicative of successful covalent crosslinking between levan and the polyvinyl alcohol matrix.Fig. 4. Morphological properties of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 4

The mechanical properties of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan have been analyzed (Fig. 5). Tensile strength and elongation at break were selected as key mechanical parameters for evaluation. Fig. 5 and Table 1 display the mechanical properties. As summarized in Table 1, the tensile strength remained consistent at approximately 8 MPa, while elongation at break ranged from 98% to 166%. Statistical analysis indicated that increasing levan concentration did not significantly affect the tensile strength. The highest elongation at break was observed at 20 wt% levan, which represented the optimal plasticizing concentration. At this ratio, levan enhanced the mobility of PVA/GE biopolymer chains. However, beyond this concentration, excess levan may disrupt the composite film's polymer network. Consequently, the addition of levan improves the extensibility and flexibility of the composite films. It was consistent with previous studies [13].Fig. 5. Tensile strength and elongation at break of polyvinyl alcohol and gelatin-based hydrogel composite with addition of levan (a) 0 wt%, (b), 10 wt%, (c) 20 wt%, (d) 30 wt%, (e) 40 wt%, and (f) 50 wt%.Fig. 5

Table 2 presents contact angle measurements for PVA/gelatin-based composite films. All samples exhibited contact angles between 53° and 64°, indicating a predominantly hydrophilic surface. This behavior facilitated interactions with water molecules. This result was consistent with the FTIR results (Fig. 3). It confirmed the presence of abundant hydroxyl functional groups within the polymer matrix. PVA contained hydroxyl groups in its molecular structure, leading to high hydrophilicity and water solubility. Gelatin was noted as a hydrophilic polymer that possessed carboxyl and amino functional groups. In addition, levan was structurally defined as a polysaccharide with excellent water solubility. Based on the intrinsic characteristics of these three biopolymers, the incorporation of levan did not induce the hydrophobicity. The films remained hydrophilic, indicating that levan addition did not enhance the composite films' hydrophobicity.Table 2. Physicochemical properties of PVA/GE/LV composite films with varying levan contents.Table 2. SamplesCA (°)SI (%)MC (%)WS (%)PVA/GE/0%LV53.65 ± 1.98122.43 ± 3.277.25 $[eqn]$ 2.3873.41 $[eqn]$ 4.10PVA/GE/10%LV58.18 ± 0.51108.44 ± 2.8013.51 $[eqn]$ 2.3476.40 $[eqn]$ 4.70PVA/GE/20%LV58.49 ± 2.2667.76 ± 0.9514.00 $[eqn]$ 4.3483.41 $[eqn]$ 1.38PVA/GE/30%LV57.41 ± 0.4679.72 ± 4.1617.68 $[eqn]$ 0.8783.72 $[eqn]$ 1.98PVA/GE/40%LV64.54 ± 1.0983.79 ± 3.3519.63 $[eqn]$ 2.8083.94 $[eqn]$ 2.53PVA/GE/50%LV63.81 ± 0.44110.97 ± 0.6818.47 $[eqn]$ 0.5082.44 $[eqn]$ 2.52Table notes: CA = contact angle; SI = swelling ratio; MC = moisture content; WS = water solubility. Values are expressed as mean ± SD (n = 3).

Moisture content represented the ability of a film to retain or resist moisture under specific environmental conditions and was related to its moisture barrier performance. This property was crucial for maintaining product integrity during storage and handling. Table 2 shows that the moisture content increased with increasing levan content. This trend may be associated with the aggregation of levan chains, which enhances intermolecular hydrogen bonding and promotes moisture absorption from the surrounding environment, consistent with previous study by Gan et al. [13]. The swelling behavior was evaluated to assess the water absorption capacity of the composite films, as shown in Table 2. The swelling index values indicate that the addition of 20 wt% levan decreased the swelling ratio of the composite films from 122.43% to 79.72% compared with the PVA/GE composite film without levan. These results suggest that the incorporation of levan, particularly at 20 wt%, reduced the water absorption capacity of the composite films. Water solubility was considered as an important parameter for evaluating the biodegradability and structural integrity of composite films [28]. As shown in Table 2, the increase of levan content can be induced to increase the water solubility of the composite film. It was changed from 73.41% to 82.44%. This behavior can be attributed to the hydrophilic characteristic. Consequently, the incorporation of levan did not improve water resistance but rather increased the films' water solubility. A similar trend was observed for moisture content, which increased with increasing levan content. This result is consistent with the FTIR analysis, which confirmed the presence of hydroxyl groups in the composite films. Interestingly, the swelling behavior and elongation at break showed a different trend. The swelling ratio decreased while the elongation at break increased as the levan content increased to 20 wt%. However, further increasing the levan content beyond 20 wt% resulted in a higher swelling ratio and a lower elongation at break. This trend suggests improved structural integrity at this composition. Based on the mechanical and physico-chemical properties, a levan content of 20 wt% was identified as the optimal composition for edible films intended for food packaging applications.

Conclusion

4

Levan was successfully biosynthesized from sucrose by Priestia koreensis HL12. In application, the PVA/GE/LV composite films were successfully fabricated using genipin crosslinking. The synthetic film had a blue shade owing to the reaction between genipin and the primary amines present in gelatin. Whereas, when the amount of levan rose, the color of the synthetic film changed from blue to violet. As the amount of levan increased to 20 wt%, the PVA/GE/LV composite films exhibited higher physico-chemical properties, mechanical strength, and improved thermal stability than the PVA/gelatin film. However, levan incorporation had no significant effect on the surface wettability, and all composite films exhibited a hydrophilic surface. For these reasons, the PVA/GE/LV composite films for food packaging were supposed to increase the food shelf life. Overall, the PVA/GE/20%LV composite film demonstrated optimal physico-chemical, mechanical, and thermal properties, making it a suitable candidate for edible food packaging applications.

CRediT authorship contribution statement

Natnicha So-udorn: Conceptualization. Hataikarn Lekakarn: Data curation. Daran Prongjit: Formal analysis. Benjarat Bunterngsook: Formal analysis. Sarute Ummartyotin: Writing – review & editing, Writing – original draft.

Research data policy and data availability statements

Data supporting the study are available from the authors upon reasonable request.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.