Edible Biopolymers-Based Materials for Food Applications—The Eco Alternative to Conventional Synthetic Packaging

The problem of waste generated by packaging obtained from conventional synthetic materials, often multilayer, has become more and more pressing with increasing consumption. In this context, nature and humanity have suffered the most. In order to address this phenomenon, global and European organizations have launched and promoted programs and strategies. Replacing petroleum-based packaging with biopolymer packaging has proven to be a real alternative. Thus, the substitution of plastics with biodegradable, non-toxic, edible materials, which can be obtained from marine or agro-industrial waste, is of interest. In the present study, we aimed to develop natural edible materials, obtained entirely from biopolymers such as agar and sodium alginate and plasticized with glycerol and water. Designed to be used for food and food supplements packaging, they can be completely solubilized before consumption. The films were developed through a casting method and were tested in order to identify the physical, optical, and solubility properties. According to the results, the most suitable composition for use as a hydrosoluble packaging material contains agar:alginate:glycerol in a 2:1:1 ratio. The microstructure indicates a homogeneous film, with low roughness values (Rz = 12.65 ± 1.12 µm), high luminosity (92.63), above-average transmittance (T = 51.70%), and low opacity (6.30 A* mm−1). The obtained results are of interest and highlight the possibility of substituting intensely polluting materials with those based on biopolymers.


Introduction
The packaging for the food and medical industry involves a number of multidisciplinary areas, such as engineering, chemistry, biotechnology, and microbiology. The efficiency of a good packaging material is influenced by its ability to preserve the nutritional and sensory qualities of the product contained, to preserve the consumption and microbiologically safety, and, last but not least, to facilitate the promotion and sale of the product. The main feature of a good packaging material is to maintain the quality and shelf life of the product from manufacturing to the consumer. The shelf life represents the time from product development to consumption, the period in which the product retains its quality under certain storage conditions (according to the manufacturers' specifications). Therefore, the shelf life of food is highly associated with the inherent characteristics of the food and the environmental conditions exposed during transport and storage and, most importantly, with the quality of the packaging system used [1]. large and very large factories [22]. Such a strategy should point out that the degree of global urbanization will increase from 54% (2020) to 75% (2050) [23]. The circular economy uses existing materials, to which it assigns new values, and avoids overexploitation [24]. The current trend is to use biodegradable, compostable, or renewable materials, or those which ultimately lead to zero waste.
This paper aims to develop and test completely natural and edible foils that can be used as packaging material for powdered food supplements. Based on the use of biopolymers such as agar and sodium alginate, but also glycerol for plasticization, the materials obtained were tested to identify specific characteristics. Thus, the physical and optical properties, such as microstructure, microtopography, and the uniformity and regularity of surfaces, but also the thickness, the retraction ratio, the color parameters, the transmittance, and the opacity were evaluated. The determinations were supplemented with the evaluation of solubility (water solubility, swelling ratio, moisture content, water activity index), and microbiological characteristics.
The food supplement industry is constantly growing, especially due to changing habits and refining consumer tastes. Usually, this type of packaging is multilayer, difficult to sort and impossible to recycle. The materials developed represent a viable option for conventional packaging.

Materials and Methods
All the substances used for the development of the films were purchased from the company Sigma Aldrich (Romanian branch from Bucharest).
To obtain the film-forming solutions, a volume of 150 mL of water and different amounts of biopolymers and plasticizer were used, with a total mass of 4 g. The different masses of plasticizer were 0.5, 0.75, and 1 g, and the mass of biopolymers varied in the range of 0-3 g, as shown in Table 1. followed by 250 rpm until at the end of the allotted time ( Figure 1). Subsequently, they were poured onto the silicone foil and maintained until completely dry. •

Evaluation of physical and optical properties
To evaluate the microstructure and microtopography of the samples obtained, the films were tested using the Mahr confocal microscope (Marf Surf). These properties, in conjunction with the other tests, are important for any newly developed material, particularly for materials that will subsequently be used in packaging and must meet a number of conditions, including maintaining the quality of the product, from manufacturer to the final consumer, especially because the visual aspect is important and is used as a marketing strategy. In this sense, we made a series of determinations.

•
The evaluation of thickness and retraction ratio Thickness is an important feature for a film that will be used as packaging material for various products. The Mitutoyo micrometer was used to measure the thickness in at least 5 different areas of the film; the noted result represents their arithmetic mean.
The retraction ratio was calculated according to the following formula: Retraction ratio, (%) = (initial film thickness − final film thickness) initial film thickness * 100 • The determination of color, transmittance, and opacity The color of the samples was evaluated using the Konika Minolta CR 400 colorimeter (Konika Minolta, Tokyo, Japan), and was observed on different areas of the film surface. The method evaluates the color of the products using the CIELAB system, and the determinations aimed at identifying the luminosity (L*) and the coordinates a* (green-red) and b* (blue-yellow). In the CIELAB system, the luminosity has values between 0 (black range) up to 100 (absolute white). In order to establish the results, five readings were performed, and the final value represents their arithmetic mean. Both the transmittance and the opacity of the films were evaluated using the Ocean Optics HR 4000 CG-UV-NIR spectrophotometer (Ocean Optics, Douglas, AZ, USA). Thus, 1 cm × 3 cm specimens were introduced into the spectrophotometric tank and the values indicated at the wavelength of 660 nm (for transmittance) and 600 nm (for opacity) were read.
Opacity (O) is calculated according to the formula: where A is absorbance and T is thickness (mm). The evaluation of these characteristics is important for maintaining the quality of packaged products (depending on the content, there are products that degrade under the

•
Evaluation of physical and optical properties To evaluate the microstructure and microtopography of the samples obtained, the films were tested using the Mahr confocal microscope (Marf Surf). These properties, in conjunction with the other tests, are important for any newly developed material, particularly for materials that will subsequently be used in packaging and must meet a number of conditions, including maintaining the quality of the product, from manufacturer to the final consumer, especially because the visual aspect is important and is used as a marketing strategy. In this sense, we made a series of determinations.

•
The evaluation of thickness and retraction ratio Thickness is an important feature for a film that will be used as packaging material for various products. The Mitutoyo micrometer was used to measure the thickness in at least 5 different areas of the film; the noted result represents their arithmetic mean.
The retraction ratio was calculated according to the following formula: Retraction ratio, (%) = (initial film thickness − final film thickness) initial film thickness * 100 • The determination of color, transmittance, and opacity The color of the samples was evaluated using the Konika Minolta CR 400 colorimeter (Konika Minolta, Tokyo, Japan), and was observed on different areas of the film surface. The method evaluates the color of the products using the CIELAB system, and the determinations aimed at identifying the luminosity (L*) and the coordinates a* (green-red) and b* (blue-yellow). In the CIELAB system, the luminosity has values between 0 (black range) up to 100 (absolute white). In order to establish the results, five readings were performed, and the final value represents their arithmetic mean. Both the transmittance and the opacity of the films were evaluated using the Ocean Optics HR 4000 CG-UV-NIR spectrophotometer (Ocean Optics, Douglas, AZ, USA). Thus, 1 cm × 3 cm specimens were introduced into the spectrophotometric tank and the values indicated at the wavelength of 660 nm (for transmittance) and 600 nm (for opacity) were read.
Opacity (O) is calculated according to the formula: where A is absorbance and T is thickness (mm). The evaluation of these characteristics is important for maintaining the quality of packaged products (depending on the content, there are products that degrade under the action of light rays) and in the marketing strategy of the product, as colored packaging is often more interesting than colorless [25].

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The solubility of films is an important feature, especially when they are intended for use as packaging materials, as their physical properties can be affected by environmental humidity [26]. As the films developed are intended to be used for the packaging of food, which requires solubilization, and consumed with them, the assessment of solubility is of the utmost interest. Moreover, knowing these characteristics, it can be indicated the type of products which can be packaged in various materials. Depending on the moisture content and the final values of the hydration capacity and swelling ratio index, the path of the foils can be traced as packaging materials for various products.
The standardized method according to STAS 90-88 was used to determine the humidity. Thus, the film samples (3 cm × 3 cm) were weighed and maintained for 24 h at 110 • C, then reweighed. The values obtained were used in the following formula: where W 0 represents the mass of the sample before drying (g) and W1 is its mass after drying (g).
To determine films' water solubility, specimens similar to those used to determine moisture content (3 cm × 3 cm) were weighed and kept for 8 h in containers with 50 mL of water. After 8 h, the samples were dried using a hot air oven (Memmert Schwabach, Germany) for 24 h at 110 • C. The result was calculated according to the following formula: where W 0 is the mass of the sample before immersion in water (g) and W 1 is the mass of the sample (g) after 24 h. The hydration capacity of the foils was determined by maintaining a sample (3 × 3 cm) for 30 s to 20 min in water with a temperature of 22 ± 2 • C. After the predetermined time, the sample was lightly taped with filter paper in order to remove the excess water and then reweighed.
The final value of swelling capacity (SR) was calculated with the formula: where W 0 represent the initial mass (g) and W t is the sample mass after the time t, (g). The water activity index (a w ) is an important parameter, especially if we take into account that its low value, in the case of tested samples, also highlights the ability to provide protection against microbial contamination. The water activity index was determined using Aqua Lab equipment (ICT International, Armidale, NSW 2350, Australia), and the determinations were performed at a temperature of 23 ± 2 • C. The value noted represent the sum of least five determinations made in different areas of the film surface.

•
The microbiological assessments As the films developed are intended for the packaging of food supplements and consumed with them, it is imperative to be safe from this point of view. Thus, the incidence of microorganisms was tested using Compact Dry TC/CF/ETC/ETB/EC/XSA/LM/YM dehydrated specific culture media plates (NISSUI Pharma).
For these determinations, saline was used to hydrate the medium. Thus, 1 g of sample was homogenized with 9 mL of saline. From the solution, 1 mL was poured onto the culture media. After hydration, the plates with culture media were maintained at 72 • C for 24-36 h for TC/CF/ETC/ETB/EC/XSA/LM/YM determinations and 72 h for plates with Polymers 2021, 13, 3779 6 of 16 specific yeast and mold culture media. In order to obtain precise results, for each sample tested, we performed three dilutions.

• Statistical analysis
The purpose of the statistical determinations was to optimize the composition for the development of materials with improved properties. For this purpose, the Design Expert 12 (State Ease) program was used, generating SRM responses. Significant differences were evaluated by carrying out one-way analysis of variance (ANOVA) and Tukey's test at p < 0.05. Data analysis was performed using MiniTAB statistics software (MiniTAB Ltd., Coventry, UK).

Results
For drying, the film-forming solutions were maintained for about 48 h at a temperature of 24 ± 0.5 • C and 39 ± 1% relative humidity. The composition of the films and their physical characteristics can be found in Table 1. In order to establish the conditions for maintaining the solutions until complete drying and film development, as well as to establish the characteristics necessary for future industrial use, the adhesiveness, the appearance of the films, and possible mixtures with other biopolymers were evaluated. The results are useful for improving the characteristics and obtaining industrial performances. According to Table 1, the compositions most suitable for packaging materials are those of samples B2, B3, B10, and B13-B16. Their common feature is the increase in the plasticizer content in the composition. The exception is sample B3, which, however, contains a higher amount of sodium alginate. Other studies have reported the ability of agar to form hard films and alginate to facilitate the development of glossy and flexible films [27]. The films were kept at constant temperature and rH. Samples B1-B16 showed different characteristics and behavior (Table 2), a beneficial aspect if we take into account that they can be used later for packaging products with different properties.
The difference between B3 and B14 is represented by the decrease in the agar mass and the increase in the plasticizer mass. According to the results (Table 3), the best characteristics for use as packaging materials are those of the last sample.
According to the images in Figure 2, the samples with higher content of plasticizer in the composition (B13-B16) show a more homogeneous and compact structure, but also a lower roughness. The reduced roughness may be due to the glycerol molecules which, due to the reduced formations, have the possibility to integrate much more easily in the film matrix. Reduced roughness is observed in the samples with higher agar content in the composition, as evidenced by the low standard deviations, with values of 0.19 (B13), 0.41 (B1), 0.74 (B6), 0.81 (B12), and 0.96 (B7).
The retraction ratio is an important and useful determination for the manufacturer, because, depending on the thickness of the film-forming solution and the value of the retraction ratio, the final thickness of the foil can be determined in advance and accurately. In this way, the manufacturer has the ability to determine the thickness of the material obtained. As can be seen from Table 2, the lowest values of the retraction ratio are observed in the samples with the highest values of thickness, namely B1 and B4. The retraction ratio is inversely proportional to the thickness; thus, where the thickness has low values, the shrinkage ratio has high values (B5, B10, B2, B13).
The lowest thickness can be seen in sample B5, with an equal content of biopolymers in composites, although the amount of plasticizer is small. Studies have presented that a high amount of plasticizer in the composition leads to thin and flexible films [28]. According to the microstructure presented in the images in Figure 2, the plasticizer used, which was glycerol in this case, is compatible with the biopolymers used. When the plasticizer is not used in the right amount or is not compatible with the other substances, visible visual defects can be observed: cracks, the tendency to break, white color, and high opacity, properties that can be attributed to phase separations [29]. The values obtained after evaluating the moisture content, water solubility, and water activity index are presented in Table 4.      According to the images in Figure 2, the samples with higher content of plasticizer in the composition (B13-B16) show a more homogeneous and compact structure, but also a lower roughness. The reduced roughness may be due to the glycerol molecules which, due to the reduced formations, have the possibility to integrate much more easily in the film matrix. Reduced roughness is observed in the samples with higher agar content in the composition, as evidenced by the low standard deviations, with values of 0.19 (B13), 0.41 (B1), 0.74 (B6), 0.81 (B12), and 0.96 (B7).
The retraction ratio is an important and useful determination for the manufacturer, because, depending on the thickness of the film-forming solution and the value of the retraction ratio, the final thickness of the foil can be determined in advance and accurately. In this way, the manufacturer has the ability to determine the thickness of the material obtained. As can be seen from Table 2, the lowest values of the retraction ratio are observed in the samples with the highest values of thickness, namely B1 and B4. The retraction ratio is inversely proportional to the thickness; thus, where the thickness has low values, the shrinkage ratio has high values (B5, B10, B2, B13).
The lowest thickness can be seen in sample B5, with an equal content of biopolymers in composites, although the amount of plasticizer is small. Studies have presented that a high amount of plasticizer in the composition leads to thin and flexible films [28]. According to the microstructure presented in the images in Figure 2, the plasticizer used, which was glycerol in this case, is compatible with the biopolymers used. When the plasticizer The solubility of new materials is of interest due to their subsequent applicability. As the study aimed to develop films that can be used for food packaging and food supplements, the films can be consumed with the product when it is immersed in liquids with temperatures above 45 • C.
The high agar content of the composition facilitated the decrease in luminosity (the lowest in the case of sample B1-86,221, where the mass of agar is 3 g). The highest value of luminosity-92,772-was found in sample B10, which, although there are no large variations between the masses of the two biopolymers, contains a higher amount of plasticizer in the composition (0.75 g).
After testing the selling ratio capacity, according to the graph in Figure 3, samples B2 and B4 could not be evaluated, as they disintegrated in the first 30 s of water immersion. Sample B4 showed a tendency to flake off and disintegrated immediately. According to these determinations, these foils can be used for the packaging of products with low humidity (such as powders, tablets, instant drinks, powdered milk, etc., which require solubilization before consumption). The films B1, B3, B6, and B9 kept their shape very well, even 20 min after immersion in water. According to the graph, samples B1 and B9 had a low water retention capacity, demonstrated by the low values of the swelling ratio of 157.43% and 949%, respectively, after 20 days of immersion. According to Table 1, film B1 has only agar and glycerol in its composition, unlike film B9, which contains equal masses of biopolymers, but less glycerol. Film B3, with a higher agar content in composition, and film B6, with more sodium alginate, although they had high values of rehydration capacity (2292.27% and 2650.28%, respectively), kept their shape and did not solubilize. These materials can be used for packaging products with higher moisture content, such as fruits and vegetables, meat and meat products, or other products with similar characteristics. Samples B10, B11, and B12, although they had low values of hydration capacity (1183.45%, 1008.05%, and 980%) and did not disintegrate after 20 min of immersion, did not keep their uniformity, like the other films.
The high alginate content resulted in films with high transmittance values ( Figure 4). Thus, according to the obtained results, samples B2 (3 g alginate, T-81.10%) and B7 (2.5 g alginate, T-63.79%) showed higher transmittance as opposed to those with higher agar content. Exceptions are samples B3 and B14; although the amount of agar was higher, the films showed high values of the transmitter (67.17% and 51.70%, respectively). This behavior could be attributed to the higher mass of plasticizer in the film composition or due to the synergistic effect between the compounds used.
Conversely, samples with low values other than transmittance showed high opacity. For example, the opacity of sample B1, with 3 g of agar and without sodium alginate in the composition, was 18.33 A*mm −1 , followed by sample B8, with 15.56 A*mm −1 , and then B11, with 13.94 A*mm −1 . According to the obtained results, it is possible to identify a wellestablished correlation between the composition of the films and the opacity, since the three samples with high values show different proportions of biopolymers.
The applicability of these foils is intensively studied, especially due to the common properties with those of conventional packaging materials. In the images in Figure 5, various applications of the new materials can be observed. Depending on the results obtained, samples B14, B15, and B16 were used. They can be intended for the packaging of food products and supplements that require solubilization in water with a temperature above 40 °C, before consumption. These packaging materials can be used for a wide range of foods, especially those with low moisture content. According to results presented in Table 4, the increase in the agar mass in the film composition facilitates the obtaining of The films B1, B3, B6, and B9 kept their shape very well, even 20 min after immersion in water. According to the graph, samples B1 and B9 had a low water retention capacity, demonstrated by the low values of the swelling ratio of 157.43% and 949%, respectively, after 20 days of immersion. According to Table 1, film B1 has only agar and glycerol in its composition, unlike film B9, which contains equal masses of biopolymers, but less glycerol. Film B3, with a higher agar content in composition, and film B6, with more sodium alginate, although they had high values of rehydration capacity (2292.27% and 2650.28%, respectively), kept their shape and did not solubilize. These materials can be used for packaging products with higher moisture content, such as fruits and vegetables, meat and meat products, or other products with similar characteristics. Samples B10, B11, and B12, although they had low values of hydration capacity (1183.45%, 1008.05%, and 980%) and did not disintegrate after 20 min of immersion, did not keep their uniformity, like the other films.
The high alginate content resulted in films with high transmittance values ( Figure 4). Thus, according to the obtained results, samples B2 (3 g alginate, T-81.10%) and B7 (2.5 g alginate, T-63.79%) showed higher transmittance as opposed to those with higher agar content. Exceptions are samples B3 and B14; although the amount of agar was higher, the films showed high values of the transmitter (67.17% and 51.70%, respectively). This behavior could be attributed to the higher mass of plasticizer in the film composition or due to the synergistic effect between the compounds used.
Conversely, samples with low values other than transmittance showed high opacity. For example, the opacity of sample B1, with 3 g of agar and without sodium alginate in the composition, was 18.33 A* mm −1 , followed by sample B8, with 15.56 A* mm −1 , and then B11, with 13.94 A* mm −1 . According to the obtained results, it is possible to identify a well-established correlation between the composition of the films and the opacity, since the three samples with high values show different proportions of biopolymers.
The applicability of these foils is intensively studied, especially due to the common properties with those of conventional packaging materials. In the images in Figure 5, various applications of the new materials can be observed. Depending on the results obtained, samples B14, B15, and B16 were used. They can be intended for the packaging of food products and supplements that require solubilization in water with a temperature above 40 • C, before consumption. These packaging materials can be used for a wide range of foods, especially those with low moisture content. According to results presented in Table 4, the increase in the agar mass in the film composition facilitates the obtaining of biopolymer materials with low solubility, which can be used for the packaging of products with higher moisture content.
None of the microorganisms tested, such as coliforms, enterococci, enterobacteria, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, or yeasts and molds, developed on the culture medium. The incidence and proliferation of microorganisms was also hampered by the low values of the water activity index. Following the determinations, its values varied between 0.414 and 0.457, being small enough to prevent microbial contamination. This feature is extremely important because the preservation of nutritional and sensory characteristics, but also the preservation of the product's dependence depends on the presence of spoilage microorganisms. Additionally, the incidence of pathogenic microorganisms endangers the health of the consumer, which is excluded in this case.

Statistical Analysis
According to the images presented in Figure 6 and the statistical analysis, agar, alginate and glycerol can be used to obtain films that can be used as packaging materials in the food industry and beyond.. The influence of their content on water solubility, thickness, opacity, and roughness was evaluated. Thus, for an average value of water solubility, the amounts of biopolymers are 1.24 g agar and 0.98 g alginate (Figure 6a), and the ratio of biopolymers:glycerol should be 3:1 (Figure 6b). The increase in solubility is directly proportional to the increase in alginate content, an aspect also found in the specialized literature [30,31,32]. Thickness is strongly influenced by the content in biopolymers. A higher agar content in the composition will facilitate the obtaining of The evaluation of the microbiological characteristics highlighted the safety of inges-tion of these films when they are consumed together with the packaged product. None of the microorganisms tested, such as coliforms, enterococci, enterobacteria, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, or yeasts and molds, developed on the culture medium. The incidence and proliferation of microorganisms was also hampered by the low values of the water activity index. Following the determinations, its values varied between 0.414 and 0.457, being small enough to prevent microbial contamination. This feature is extremely important because the preservation of nutritional and sensory characteristics, but also the preservation of the product's dependence depends on the presence of spoilage microorganisms. Additionally, the incidence of pathogenic microorganisms endangers the health of the consumer, which is excluded in this case.

Statistical Analysis
According to the images presented in Figure 6 and the statistical analysis, agar, alginate and glycerol can be used to obtain films that can be used as packaging materials in the food industry and beyond.. The influence of their content on water solubility, thickness, opacity, and roughness was evaluated. Thus, for an average value of water solubility, the amounts of biopolymers are 1.24 g agar and 0.98 g alginate (Figure 6a), and the ratio of biopolymers:glycerol should be 3:1 (Figure 6b). The increase in solubility is directly proportional to the increase in alginate content, an aspect also found in the specialized literature [30][31][32]. Thickness is strongly influenced by the content in biopolymers. A higher agar content in the composition will facilitate the obtaining of materials with higher thickness, while the increase in the alginate mass will favor the development of thinner The evaluation of the microbiological characteristics highlighted the safety of ingestion of these films when they are consumed together with the packaged product. None of the microorganisms tested, such as coliforms, enterococci, enterobacteria, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, or yeasts and molds, developed on the culture medium. The incidence and proliferation of microorganisms was also hampered by the low values of the water activity index. Following the determinations, its values varied between 0.414 and 0.457, being small enough to prevent microbial contamination. This feature is extremely important because the preservation of nutritional and sensory characteristics, but also the preservation of the product's dependence depends on the presence of spoilage microorganisms. Additionally, the incidence of pathogenic microorganisms endangers the health of the consumer, which is excluded in this case.

Statistical Analysis
According to the images presented in Figure 6 and the statistical analysis, agar, alginate and glycerol can be used to obtain films that can be used as packaging materials in the food industry and beyond. The influence of their content on water solubility, thickness, opacity, and roughness was evaluated. Thus, for an average value of water solubility, the amounts of biopolymers are 1.24 g agar and 0.98 g alginate (Figure 6a), and the ratio of biopolymers:glycerol should be 3:1 (Figure 6b). The increase in solubility is directly proportional to the increase in alginate content, an aspect also found in the specialized literature [30][31][32]. Thickness is strongly influenced by the content in biopolymers. A higher agar content in the composition will facilitate the obtaining of materials with higher thickness, while the increase in the alginate mass will favor the development of thinner ones. According to the optimization, for the development of a thin film, it is necessary for the composition of biopolymers (agar:alginate) to maintain a ratio of 3:1.5 (Figure 6c). Similarly, increasing the glycerol content of the composition will favor the development of thinner films. To obtain medium-thick materials, the optimization results indicate a ratio of 3:0.5 biopolymer content:plasticizer (Figure 6d). The opacity is directly correlated with the addition of agar in the composition, as the films with a high addition of alginates are more transparent (Table 1, Figure 3). To obtain films with low opacity, the biopolymer:glycerol ratio must be maintained at 3.5:1 (Figure 6e). The increase in the mass of alginate and glycerol will favor the development of materials with low opacity and, implicitly, high transmittance (Figure 6f).
Polymers 2021, 13, x FOR PEER REVIEW 13 of 16 materials with higher thickness, while the increase in the alginate mass will favor the development of thinner ones. According to the optimization, for the development of a thin film, it is necessary for the composition of biopolymers (agar:alginate) to maintain a ratio of 3:1.5 (Figure 6c). Similarly, increasing the glycerol content of the composition will favor the development of thinner films. To obtain medium-thick materials, the optimization results indicate a ratio of 3:0.5 biopolymer content:plasticizer (Figure 6d). The opacity is directly correlated with the addition of agar in the composition, as the films with a high addition of alginates are more transparent (Table 1, Figure 3). To obtain films with low opacity, the biopolymer:glycerol ratio must be maintained at 3.5:1 (Figure 6e). The increase in the mass of alginate and glycerol will favor the development of materials with low opacity and, implicitly, high transmittance (Figure 6f).
Water solubility Depending on the use of the developed materials, the content in biopolymers can be modified, so as to finally obtain the product with the desired characteristics. In the case of packaging products with a higher content of lipids or compounds that can degrade in the presence of light, such as vitamins, the agar content of the composition will be higher, unlike that of alginate or plasticizer. If it is desired to obtain transparent foils, which better present the product contained, the amounts of alginate and glycerol in the composition of the material should be increased. The roughness of the materials is strongly influenced by the addition of biopolymers in the composition. In order to develop a material with low roughness, it is recommended to use biopolymers in a ratio of 3:1 agar:alginate ( Figure  5g) and plasticizer in a ratio of 3.5:0.5 (Figure 6h).

Conclusions
The present study investigated the development and testing of new potential materials used for food packaging that require solubilization before consumption. The Depending on the use of the developed materials, the content in biopolymers can be modified, so as to finally obtain the product with the desired characteristics. In the case of packaging products with a higher content of lipids or compounds that can degrade in the presence of light, such as vitamins, the agar content of the composition will be higher, unlike that of alginate or plasticizer. If it is desired to obtain transparent foils, which better present the product contained, the amounts of alginate and glycerol in the composition of the material should be increased. The roughness of the materials is strongly influenced by the addition of biopolymers in the composition. In order to develop a material with low roughness, it is recommended to use biopolymers in a ratio of 3:1 agar:alginate ( Figure 5g) and plasticizer in a ratio of 3.5:0.5 (Figure 6h).

Conclusions
The present study investigated the development and testing of new potential materials used for food packaging that require solubilization before consumption. The idea of obtaining such films arose in response to authorities' concern about the intensive pollution of the environment due to conventional, oil-based packaging that is largely single-use and difficult to sort and recycle. The films were obtained from biopolymers, such as agar and alginate, being completely natural and edible. The sample with the most suitable characteristics was obtained from agar:alginate:glycerol in a ratio of 2:1:1. According to the tests performed, a higher amount of plasticizer in the composition was responsible for the improvement of the physical characteristics and solubility of the films. The results obtained indicate the possibility of using these foils as packaging material. To improve their properties, they can be enriched by the addition of natural compounds in the form of powders, purees, extracts, or essential oils, or in combination with other biopolymers, when their use is intended for packaging other categories of food. Although biopolymer films can be a substitute for plastics, there are still some issues that need to be addressed. First, since biopolymers are natural substances, influenced by the growing environment, climatic conditions, and extraction methods, there is the possibility that the reproducibility of the method does not ensure the development of the same product with identical characteristics, unlike synthetic materials. At the moment, production costs are higher than those for plastics, but as the demand and need for these biomaterials increase, costs can be mitigated. Besides this, the obtaining technology is easy and does not involve qualified personnel or special equipment.