MINISTRY OF EDUCATION AND TRAININGNONG LAM UNIVERSITY - HO CHI MINH CITYFaculty of Chemical Engineering and Food Technology DEVELOPMENT OF BIODEGRADABLE FILM FROM SODIUM ALGINATE, KONJAC
Characteristics of edible packaging, advantages and limitations
Edible polymers offer significant market advantages, including biocompatibility, moisture and gas barrier properties, non-toxicity, and environmental friendliness (Mellinas et al., 2016) Consequently, active, biodegradable, and edible packaging materials have become a top priority in the food industry, driven by the growing demand for renewable, recyclable, and easily degradable packaging solutions that minimize disposal needs (Jeevahan et al., 2020).
In today's market, consumers increasingly prefer products that are natural, safe, and hygienic, along with packaging that is biodegradable, recyclable, and environmentally friendly (Dirpan et al., 2023) Biodegradable packaging serves as a sustainable alternative to conventional plastics, addressing the growing demand for eco-conscious options Unlike traditional plastics, which are made from fossil fuels like petroleum and natural gas, biodegradable plastics are sourced from renewable materials such as plant and microbial biomass The benefits of using biodegradable packaging, including edible films, are illustrated in the accompanying image (Figure 2.1).
Figure 2.1 Benefits of edible food packaging (Petkoska et al., 2021)
Biodegradable films for food packaging offer significant environmental benefits but face challenges that need addressing for widespread adoption High production costs hinder commercial viability, necessitating advancements in industrial-scale edible film production Additionally, these films may not match the durability and barrier properties of conventional plastics, highlighting the need for further research to enhance their mechanical, physical, and barrier characteristics Despite these challenges, recent technological advancements present a promising future for biodegradable food packaging, which is poised to play a crucial role in sustainable development within the food industry.
Plasticizers play a crucial role in enhancing the flexibility of polymer matrices by reducing intermolecular forces, which consequently increases water and oxygen permeability (Kumar et al., 2022) They are essential for the formulation of edible films and coatings, particularly those made from polysaccharides and proteins, which tend to be brittle and stiff due to strong polymer interactions (Krochta and coatings, 2002) The incorporation of plasticizers not only improves the flexibility and processability of these films but also influences their elastic modulus and overall mechanical properties, enhancing their resistance to vapor and gas permeation.
Sorbitol, a soluble and stable polyol, is effective as a plasticizer for polymers rich in hydroxyl (-OH) or amine (-NH) groups, including plant proteins and polysaccharides (Mohsin et al., 2011) Its nontoxic nature makes sorbitol suitable for food-contact materials, positioning it as an excellent option for food packaging applications (Tian et al., 2017).
Sorbitol plays a crucial role in the production of edible films by reducing internal hydrogen bonds in intermolecular interactions Its plasticizing effect significantly influences the mechanical properties of these films, as the amount of sorbitol added is directly proportional to the percentage of elongation or strain Consequently, higher concentrations of sorbitol lead to increased elongation values, enhancing the flexibility and performance of the edible films.
Sorbitol, used as a plasticizer in bioplastics, significantly reduces internal hydrogen bonds, enhancing flexibility while decreasing tensile strength (Sanyang et al., 2015) Additionally, higher concentrations of sorbitol can accelerate the degradation process of bioplastics, which relies on the presence of microbes, moisture, and soil chemistry (Tian et al., 2017) This means that the incorporation of sorbitol not only improves the mechanical properties of bioplastics but also influences their biodegradability.
Sodium alginate
Alginate, derived from brown seaweed of the Pheophyceae family, is a linear chain copolymer consisting of B-D-mannuronic acid and ơ-L-guluronic acid monomers, with the chemical formula (C6H8O6)n Typically found in a white, yellow, or fibrous powder form, it is primarily utilized as sodium alginate extracted from brown algae This versatile substance serves as a stabilizer in ice cream, yogurt, cream, and cheese, while also functioning as a thickener and emulsifier in salad dressings, puddings, jams, and canned goods Additionally, alginate acts as a hydration agent for noodles, bread, and frozen products Its benefits include low toxicity, slow release of active ingredients within the gel, tolerance to acidic environments, and cost-effectiveness (Yan et al., 2023).
Figure 2.3 Chemical structure of sodium alginate (Badita et al., 2020)
Sodium alginate is a non-toxic, long-chain polysaccharide known for its excellent moisture and water vapor barrier properties Despite its brittleness, alginate offers several advantages, such as reducing shrinkage, maintaining food color and odor, and retaining moisture While strong edible coatings made from alginate typically exhibit poor water resistance due to their hydrophilic nature, they remain a valuable option for enhancing food preservation.
Alginate can be combined with synthetic polymers like polyphenol or gelatin to enhance their tensile strength, water resistance, and thermal properties, tailored for specific packaging applications (Yan et al., 2023) Additionally, alginate can react with natural biopolymers to create fully biodegradable green packaging films Notably, alginate interacts effectively with cellulose (Pranoto et al., 2005) and oil (Sirviử et al.,).
Recent studies have demonstrated that edible films made from SA/Starch/CMC/PEG 200, enhanced with varying concentrations of sorbitol, outperform commercial alternatives in tensile strength, water barrier, and grease resistance, while also degrading within 14 days in simulated compost (Mohammed et al., 2023) Additionally, the incorporation of essential oils can enhance the antimicrobial properties of alginate, making it a crucial factor for food packaging applications Innovations in alginate-based composites are paving the way for their effective use in both food and industrial packaging solutions.
Konjac glucomannan (KGM) is a dietary fiber extracted from the tubers of the Amorphophallus konjac plant, known for its ability to solidify into jelly As a safe and edible polysaccharide, KGM is a promising candidate for biopolymer-based active packaging films due to its biocompatibility, degradability, and excellent film-forming properties Historically used as a key food ingredient in China and Japan, KGM is recognized as a generally safe (GRAS) food additive in many countries and offers various health benefits (Tester et al., 2016).
KGM is a high molecular weight, neutral heteropolysaccharide primarily composed of D-mannose and D-glucose, connected by B-1,4 glycosidic bonds This white powder is hydrophilic but needs to be heated for rapid dissolution Its molecular structure features numerous hydroxyl and carbonyl groups.
Nine groups readily form hydrogen bonds, and KGM can also bind through hydrogen bonds, molecular dipoles, induced dipoles, and instantaneous dipoles This ability allows KGM to immobilize water molecules, resulting in a strong and stable network structure Consequently, KGM exhibits outstanding gelling and film-forming properties, as illustrated in Figure 2.4 (Zhang and Yang, 2014; Zhang and Rhim, 2022).
Recent studies have explored various combinations of konjac glucomannan (KGM) with different biopolymers to create biodegradable films with enhanced mechanical and water vapor barrier properties Notably, Chambi et al (2011) developed a four-component edible film incorporating methylcellulose, glucomannan, pectin, and gelatin Additionally, KGM has been successfully combined with keratin (Strnad et al., 2019), zein (Wang et al., 2017), carrageenan, and agar (Ploypetchara et al., 2022), demonstrating its ability to improve the mechanical and barrier characteristics of the resulting films.
Figure 2.4 Chemical structure of konjac glucomannan (Xu et al., 2008)
The research was conducted from December 2023 to February 2024 at the
Laboratory of the Faculty of Food Science and Technology, Universitas Jenderal
Soedirman, and continued from February to March at the Biochemistry Laboratory of Nong Lam University
Sodium alginate and konjac glucomannan, both in 500g powder form, were sourced from PT Samiraschem Indonesia and Chengdu Root Industry Co., LTD, respectively, and stored at a controlled temperature of 25 ± 2 °C and relative humidity of 55 ± 1% Additionally, sorbitol and NaCl were obtained from Prima Chemical Store in Purwokerto, Indonesia, while distilled water was utilized consistently throughout the study.
The general experiment of this study was demonstrated in Figure 3.2
Magnetic stirrer (500 rpm, heat 80°C + 2, 40 minutes)
Sodium alginate powder Konjac glucomannan powder Sorbitrol plasticizer Distiled water
Experiment 1: Determine suitable concentration of sorbitol for casting film
Experiment 2: Study on the ratio of SA and KGM on the ability of the film casting XN
Figure 3.2 Flow diagram of biodegradable film production.
3.3 Determine a suitable concentration of sorbitol for casting film
In this study, the film casting technique was adapted from Duan et al (2021), utilizing a blend of sodium alginate (SA), konjac glucomannan (KGM), and varying concentrations of sorbitol as a plasticizer Both SA and KGM were maintained at a concentration of 0.5%, while three different levels of sorbitol (0.5%, 1%, and 1.5%) were evaluated for their impact on film properties The preparation involved mixing 1.25 g of SA with 1.25 g of KGM in a glass beaker, followed by the addition of water to create a 250 mL slurry This mixture was stirred at 500 rpm and heated to 80°C for 20 minutes before incorporating the sorbitol After an additional 20 minutes of stirring under the same conditions, the homogenous casting solution was cooled to 45°C and poured into molding dishes These dishes were then placed in an oven at 35°C for 20 hours, after which the films were removed and stored on baking paper under ambient conditions of 25°C.
55 + 1% RH) The physicochemical properties of the films including thickness, tensile strength, elongation, and colors were measured For each of the films, the experiment was done in triplicates.
3.4 Study on the ratio of SA and KGM on the ability of the film-casting
The method of film casting also followed the method described by Duan et al.
In 2021, a film was composed of sodium alginate (SA), konjac glucomannan (KGM), and a constant concentration of sorbitol The formulation included 1% SA and KGM, with varying ratios of SA to KGM tested at 9:1, 7:3, 5:5, 3:7, and 1:9 for film casting The specific amounts of SA and KGM were weighed and combined with water to create a total solution of 250 mL This mixture was stirred at 500 rpm on a heating magnetic stirrer set to 80°C for 20 minutes Subsequently, the previously determined sorbitol concentration was added to the hot mixture, which was stirred for an additional 20 minutes under the same conditions to ensure a homogeneous casting solution.
To create a thin film, a mixture was cooled to 45°C ± 2, then 100 mL was poured into 16 cm x 12 cm x 1 cm plastic molding dishes, resulting in an excellent appearance The films were dried in an oven with air circulation at 35°C ± 2 for 20 hours and then allowed to rest at room temperature for 24 hours After drying, the films were carefully peeled off, placed on baking paper, and stored in a plastic bag with silica gel under ambient conditions (25 ± 2 °C and 55 ± 1% RH) for one week prior to characterization The physicochemical properties of the films, including thickness, tensile strength, elongation, color, opacity, moisture content, water vapor transmission rate (WVTR), water solubility, and biodegradability, were measured, with each property tested in four replicates Figure 3.2 illustrates the film preparation process.
The thickness of the edible film was assessed using a handheld micrometer (0 — 25 mm) as outlined by Singha et al (2023) Measurements were taken at ten random locations across the film, with evaluations conducted at three specific points: the upper, middle, and bottom ends The final thickness value represents the average of these measurements.
Tensile strength (TS) and elongation at break (%E) were assessed using the method established by Singha et al (2023) with a Texture Analyzer from Stable Microsystem, UK The films were prepared by cutting them into thin strips measuring 80 mm x 20 mm, which facilitated the evaluation of their textural properties The testing procedure involved applying tension to the samples to determine their mechanical performance.
! and parameters The pre-test speed was adjusted to 5 mm s", the test speed to 1 mm s” the post-test speed to 5 mm s-! with a distance of 150 mm and a trigger force of 5 g A
5 kg load cell was linked to the probe The calculation of tensile strength was calculated using equation (1) and elongation at break using equation (2)
14 maximum tensile strength when sample breaks (F) Tensile strength (MPas) = : : cross — sectional area of specimen
; tension at rupture of the film
EEBDplp[UH.RUC.NESRLE II = the initial length of the film Scie lệ
Color analysis was conducted using a calibrated color reader instrument, following the methodology outlined by Bhatia et al (2023) with some modifications Prior to use, the instrument was calibrated with a black and white panel The analysis involved placing the optic probe on a biodegradable film sheet, with measurements taken at 10 different points to ensure accuracy The results were averaged and displayed on the screen, indicating values for L (lightness/brightness) and a*.
(redness/greenness), and b* (yellowness/blueness) values.
Study on the ratio of SA and KGM on the ability of the film-casting
The method of film casting also followed the method described by Duan et al.
In 2021, a film was composed of sodium alginate (SA), konjac glucomannan (KGM), and a constant concentration of sorbitol The formulation included 1% SA and KGM, with varying ratios of SA to KGM tested at 9:1, 7:3, 5:5, 3:7, and 1:9 for film casting The specific amounts of SA and KGM were weighed and mixed with water to create a total solution of 250 mL This mixture was stirred at 500 rpm using a heating magnetic stirrer at 80°C for 20 minutes Following this, the previously determined sorbitol concentration was added to the hot mixture, which was then stirred under the same conditions for an additional 20 minutes to achieve a homogeneous casting solution.
The mixture was allowed to cool to 45°C ± 2 before being poured into plastic molding dishes (16 cm x 12 cm x 1 cm) to create a thin layer with an excellent appearance The film solution was then placed in an oven with air circulation at 35°C ± 2 for 20 hours to ensure proper drying Afterward, the dishes were kept at room temperature for 24 hours, and the dry films were carefully peeled off and stored on baking paper in a plastic bag with silica gel at ambient conditions (25 ± 2°C and 55 ± 1% RH) for one week prior to characterization The physicochemical properties of the films, including thickness, tensile strength, elongation, color, opacity, moisture content, water vapor transmission rate (WVTR), water solubility, and biodegradability, were measured, with each film tested in four replicates.
The thickness of the edible film was assessed using a handheld micrometer (0 — 25 mm) following the method outlined by Singha et al (2023) Measurements were taken at random lengths across the film, with the final thickness value determined as the average of ten measurement sites Assessments were conducted at three key locations: the upper, middle, and bottom ends of the film.
The tensile strength (TS) and elongation at break (%E) of the films were evaluated using the procedure established by Singha et al (2023) with a Texture Analyzer (Stable Microsystem, UK) Thin pieces measuring 80 mm x 20 mm were cut from each film to assess their textural features, and the tests were conducted in tension mode.
! and parameters The pre-test speed was adjusted to 5 mm s", the test speed to 1 mm s” the post-test speed to 5 mm s-! with a distance of 150 mm and a trigger force of 5 g A
5 kg load cell was linked to the probe The calculation of tensile strength was calculated using equation (1) and elongation at break using equation (2)
14 maximum tensile strength when sample breaks (F) Tensile strength (MPas) = : : cross — sectional area of specimen
; tension at rupture of the film
EEBDplp[UH.RUC.NESRLE II = the initial length of the film Scie lệ
Color analysis was performed using a calibrated color reader instrument, following the modified methods of Bhatia et al (2023) The calibration involved a black and white panel provided with the device The analysis was conducted by placing the optic probe on a biodegradable film sheet, with measurements taken at ten different points to ensure accuracy The results were presented in terms of L (lightness/brightness) and a* values, representing the average of these replications.
(redness/greenness), and b* (yellowness/blueness) values.
Opacity measurements were conducted using a UV-Vis spectrophotometer, following the methodology established by Zhao et al (2022) Samples, measuring 4 x 1 cm, were prepared in cuvette form to maintain a consistent light path for accurate absorbance readings at a wavelength of 600 nm (A600) The opacity was calculated using the specified equation (3).
Opacity = — (3) where A600 is the absorbance of light at 600 nm and x is the thickness of the film
WVTR tests were conducted following the methodology of Behera et al (2022), with some modifications The study utilized cups measuring 4 x 1 cm in diameter, with a capacity of 70 mL, to assess the WVTR of the films Each cup was sealed with a film using adhesive tape, and 2 grams of silica gel were placed in a desiccator containing a saturated NaCl solution (RH = 75%) at a controlled temperature of 25.0 ± 2 °C The cups were weighed at 30-minute intervals, totaling eight measurements, to determine the water vapor transmission rate (WVTR).
() calculated from the slope of increased weight divided by the exposed film area (m7) according to equation (4)
WVTR |“, | = A x 10000 where W¡ = initial weight, W¿ = final weight, and A = area of the films
The moisture content of films was assessed using the gravimetric method, as described by Junior et al (2021) Initially, the films were cut into small pieces and weighed to determine their initial weight (Wi) Subsequently, the samples were dried in an oven at 105°C ± 2 until a constant weight (Ws) was achieved The moisture content (MC %) was then calculated using the specified equation.
Where Wi and W are the initial and final masses of the biodegradable films, respectively.
Water solubility was assessed using a modified method based on Behera et al (2022) Initially, film samples were cut into 2 cm x 2 cm squares and dried in an oven at 105°C for 24 hours to determine their initial dry weight (Wi, grams) Each sample was then immersed in 100 mL of distilled water with constant magnetic stirring at 500 rpm for 2 hours The insoluble residues were filtered using qualitative filter paper with a maximum pore size of 15-20 µm and subsequently dried in an oven at 105°C for 3 hours to measure the weight of the non-solubilized film (Ws, grams) The water solubility value of the samples was calculated using the specified equation.
1 where W; = initial mass of the film, Wr = final mass of the non-solubilized film.
The biodegradability test assesses the aerobic biodegradation of bioplastics under controlled composting conditions, following a modified method by Beghetto et al (2020) This evaluation involved a soil burial degradation test, where biodegradable films, cut into 2 x 2 cm pieces, were buried in garden soil (Tribat soil) at intervals of 5, 15, and 30 days Daily observations were conducted to monitor the degradation of the samples until they were fully decomposed.
Table 3.1: Composition of soil Composition Percentage Organic matter 64%
Total KaO 0.4% pH: 5 - 6.5 Magnesium (Mg) Manganese (Mn) Zine (Zn) 733mg/kg Copper (Cu) 20.3mg/kg
The data are expressed as mean ± standard deviation, and the experimental results were analyzed using Minitab software version 17.1 (Minitab Pty Ltd, Sydney, Australia) A one-way analysis of variance (ANOVA) was conducted at a significance level of 5% to identify significant differences between the mean values, with a p-value threshold set at less than 0.05.
4.1 Investigating the optimal sorbitol concentration for film samples
4.1.1 Thickness and mechanical properties at different concentrations of sorbitol
Data analysis revealed that sorbitol concentration significantly influenced the thickness and mechanical properties of the produced biodegradable film, with the average values presented in Table 4.1.
Table 4.1 Thickness, tensile strength, and elongation at break at different concentrations of sorbitol
Sorbitol added Thickness Tensile strength Elongation at break
Values given are mean + standard deviation (n = 3) Values with different superscripts in the same column are significantly different (p < 0.05).
The study found that film thickness increased with higher sorbitol concentrations, with the thickest film measuring 0.083 mm at 1.5% sorbitol, compared to the thinnest at 0.053 mm with 0.5% sorbitol This trend aligns with findings by Zhang et al (2016), who reported a similar increase in thickness of sorbitol-GG films, noting a rise from 0.060 mm to 0.068 mm as sorbitol concentration increased.
The thickness of biodegradable films can range from 15% to 45% and is significantly influenced by the concentration of plasticizers used Sorbitol, a commonly used plasticizer, enhances the film's flexibility, strength, and thickness by penetrating the polymer network more efficiently (Sanyang et al., 2015) Additionally, increasing the plasticizer concentration can elevate the polymer content within the film matrix, leading to a rise in total dissolved solids in the solution and consequently increasing the overall film thickness (Rahmawati et al., 2019) Notably, the film thickness achieved in this study aligns with the Japanese Industrial Standard.
The thickness of films produced with 1.0% and 1.5% sorbitol was not significantly different, remaining within a maximum of 0.25 mm (p