Turmeric essential oil infused pectin blended sodium alginate polymer as sustainable food packaging material

Abstract

Eco-friendly, renewable materials have been pushed in many applications to replace non-renewable resources in recent years. In the present work, a similar attempt was made to replace synthetic polymer-based food packaging films with films made out of waste-derived renewable materials. In this study, pectin (P) and sodium alginate (SA) polymers were blended with turmeric essential oil (O) to increase the functionality of the film. Turmeric essential oil was chosen over other plant based essential oils due to its potential antioxidant, antifungal and broad-spectrum antimicrobial activity. Calcium ions were used to crosslink the films with glycerol as the plasticizer in order to increase their potential usefulness. The prepared films were characterised to ascertain their performance for practical applications. Tensile strength, tear resistance, percent elongation, water contact angle, thermal stability, degree of crystallinity and FTIR analysis were undertaken to evaluate the suitability of the prepared films for intended usage. The elongation at break for P/SA film was 79.96% and that of P/SA/O film was 91.08%. Also, the ultimate modulus of P/SA film was 1.58 MPa and that of P/SA/O film was 9.49 MPa. So, it was found that the P/SA/O films have higher modulus than that of neat blend films, which indicates that oil addition did not have any negative impact on the strength of the film. The biodegradation investigations on prepared films showed that films will break down under ambient conditions over a notable period of time, indicating that they would be a better option as an environmentally benign food packaging and edible coating material. The uniqueness is in the combination of sustainable polymers selected to produce the stable antimicrobial films with essential oil extracted from the matured leaves of the plant. Most of the studies focus on use of essential oil extracted from rhizome, but in the present study, the essential oil extracted from the waste source (matured leaf) is used. Henceforth it is a value addition to the waste.

Introduction

Biopolymers are organic materials derived from living things. The Greek terms for nature and living things, “bio” and “polymer,” are the origin of the word “biopolymer”. Biopolymers are large macromolecules made up of a number of repeating units. The biopolymers can be used in a variety of applications because of their biocompatible and biodegradable nature. Applications includes edible films, emulsions, packaging materials and medical implants, wound patches, tissue scaffolds and dressing materials in the pharmaceutical industry^1–8. The majority of biopolymers can be degraded by bacteria under ambient conditions. Biopolymers are fascinating materials because of their availability, biocompatibility and distinctive characteristics, including non-toxicity⁹. For effective usage in variety of applications, nanoscale reinforcements are being added into biopolymer in order to enhance their properties and usefulness^10,11. Natural abundant polymers include starch, cellulose and pectin. Polysaccharides and proteins are the most often employed natural polymers in biological applications.

Pectin and gelatine are two examples of natural polymers that can be used to create biocompatible and biodegradable materials^12,13. Any potential toxicity or degradability issues brought on by the use of synthetic materials can be removed by utilising these materials. Pectin in particular has been used for the development of pharmaceutical formulations designed for regulated drug delivery because of its interesting properties. Pectin is widely distributed in fruits and vegetables of terrestrial plants. It is widely added to dishes and promotes better digestion and health by lowering cholesterol levels. The peels of citrus fruits contain the majority of pectin. Pectin is a heterogeneous polymer because each pectin molecule contains a linear chain of (1,4)-d-galacturonic acid^14–16.

Another significant biodegradable polymer is sodium alginate, commonly referred to as alginic acid, is a substance found in the cell walls of brown algae. A sticky paste made of alginate and water is widely used to make moulds of small items like hands, feet or other body parts^17,18. Alginate naturally gels because of its extraordinary capacity to store 200–300 times of its weight of water. Alginate is a versatile ingredient for casting, thickening or medicinal applications since it may be formulated to the thickness required to finish the casting for use. It is widely used in the food, paper and cosmetic sectors due to its thickening, suspending, emulsifying, stabilising and capacity to generate gels, films and fibres^19–22. Alginic acid has been shown to have anti-anaphylaxis, immunomodulatory and antioxidant activities in recent pharmacological research. Alginate, also known as polyuronide, is a well-known example of a natural ion exchange^21,23. Alginate’s in charged condition is advantageous for the production of films. Pectin and sodium alginate combine to generate miscible mixture at all concentrations. Pectin and Sodium alginate both undergo gelation, enabling them to dissolve in water and produce films. Temperature, pH, and the presence of ions (calcium ions for sodium alginate, for example) can all have an impact on this gelation process.

Films made of pectin and alginate are used for packaging, wound care and water-soluble medication delivery systems. Using pectin, alginate and whey protein concentrate edible films were reported^24,25. In order to increase the shelf life of bakery products such as buns, bread, biscuits as well as different fruits and vegetables these compositions were examined as prospective matrices for adding functional components such as probiotics, antimicrobials or antioxidants²⁶. Alginate and pectin have gathered the most interest among the numerous components that could be included in the edible coating formulation too. Both of them are hydrocolloid substances created from extracts of brown algal seaweed and plant tissue. Both are ionic polysaccharides that fall under the category of polyuronates and have the capacity to form hydrogels. The mechanical strength and barrier qualities of films made entirely of sodium alginate and pure pectin may be limited^27–30.

Several studies have reported that chitosan, gelatin, and starch-based films also possess significant film-forming and antimicrobial properties. For instance, chitosan films have been widely studied for their intrinsic antimicrobial activity and strong barrier properties, while gelatin and starch-based films have been explored for their biodegradability and mechanical properties. Although, chitosan, gelatin, and starch-based films offer unique advantages, the choice of polymer matrix depends on the intended application^31–36. Pectin and sodium alginate, being plant-derived polysaccharides, offer excellent biocompatibility, flexibility, mechanical strength and environmental safety, making them suitable for sustainable packaging and edible coatings.

However, the practical application of these films in food packaging is often limited due to their susceptibility to microbial contamination. To address these challenges, active packaging approaches incorporating natural antimicrobial agents, such as essential oils, have been explored³⁷. Various studies have explored the antibacterial properties of essential oils, such as thyme, clove, and cinnamon, in biopolymer films. For instance, cinnamon oil exhibited strong antimicrobial properties due to its high cinnamaldehyde content, while clove oil, rich in eugenol, was effective against a broad spectrum of bacteria and fungi. Thyme oil, primarily composed of thymol and carvacrol, also showed significant antibacterial activity^38–41. In comparison, turmeric oil contains curcumin and turmerone, which exhibit significant antimicrobial activity, showing effectiveness against various bacteria, fungi, and viruses, and even against antibiotic-resistant strains⁴². Based on the literature survey turmeric oil as essential oil was selected as filler for the development of polymer film.

In the current study, pectin, sodium alginate, P/SA and P/SA/EO films having nearly equivalent mechanical strengths as synthetic plastic materials were developed and characterised to see if they were a superior substitute for the synthetic food packaging made from petro-based materials.

Experimental

Chemicals and reagents

Citrus pectin and sodium alginate were purchased from Merck chemicals (Bengaluru, India). Glycerol and calcium chloride of analytical grade were purchased from SD Fine chemicals Ltd (Mumbai, India). Turmeric oil was extracted from the matured leaves of the plant by hydrothermal distillation. The matured turmeric leaves were identified and collected by obtaining the permission from the concerned authorities and with the assistance of a taxonomist (Dr. Murali, University of Mysore), from the botanical garden situated at the University of Mysore (deposited in the Herbarium lab, University of Mysore with voucher number 12/295). The matured leaves were thoroughly washed using double-distilled water and the extraction of turmeric oil was carried out using Clevenger apparatus in hot water. The boiling mixture was then condensed, separating the oil from water.

Preparation of pectin/sodium alginate (P/SA) and pectin/sodium alginate/ turmeric essential oil (P/SA/O) films

About 2 g of citrus pectin was dissolved in 70 mL of distilled water with continuous stirring at 4 °C for 30 min. In another beaker, 2 g of sodium alginate was dissolved in 70 mL of distilled water with continuous stirring at 40 °C for 30 min. The homogeneous pectin solution and sodium alginate solutions were mixed with each other in 1:1 ratio with constant stirring at 800 rpm at 70 °C for about 30 min. Then to the same solution, about 1.2 g of glycerol was added and stirred for 2 h. Later, 60 mL of CaCl₂.2H₂O solution (0.08 g of CaCl₂.2H₂O dissolved in 60 mL of water) was added dropwise at a rate of 1 mL/min with constant stirring for 1 h. The resultant solution was transferred onto a Teflon tray and dried by placing it in a hot air oven set at 45 °C for 48 h. The dried P/SA film was obtained as shown in Fig. 1(a). To prepare the P/SA/O film, the same steps were followed with additional 100 µl of extracted turmeric oil addition to the final solution and stirring well before casting the film and dried in hot air oven to get the film as shown in the Fig. 1(b). The neat Pectin (P) and Sodium alginate (SA) films as control were also prepared by following same steps taking the respective solution (Fig. 1c and d) without essential oil. The calcium chloride is added as a crosslinking agent, the Ca²⁺ ion react with -COO- groups of pectin and sodium alginate to form ionic crosslinks, this helps in uniform stable film formation with improved mechanical strength. Before fixing the amount of individual polymer to be blended, preliminary studies were undertaken wherein different weight ratio of polymers were tried, which gave better compatibility and good mechanical strength were selected for further studies.

Fig. 1.

Images of prepared (a) P/SA film, (b) P/SA/O film, (c) P film and (d) SA film.

Film thickness

A screw gauge was used to measure the P, SA, P/SA, and P/SA/O film’s thickness with an accuracy of 0.01 mm. Four random spots were chosen to measure the thickness of each film, and an average value is reported.

Water contact angle

The water contact angle of prepared films was measured using a contact angle metre (HO-IAD-CAM-01 A, Holmarc Opto-Mechanic Pvt. Ltd., Kochi). Water was dropped onto the surface of the prepared films and photos were captured at the instant of dropping. The contact angle of each film was measured at different spots and an average value is reported.

Tensile test

The most common testing equipment used for tensile testing is the universal testing machine and procedure followed was as per ASTM D 882 standard. The machine has two crossheads; one is adjusted for the length of the specimen and the other is driven to apply tension to the test specimen at a particular strain rate with a specified load (International Equipment’s, Mumbai, India). Tensile tests measure the force required to break the specimen and the extent to which the specimen stretches or elongates before breaking. Tensile tests provide a stress-strain diagram, which is used to determine tensile modulus. The three trials were taken for each composition of film and the average test value is reported in Table 1 along with standard deviation (SD).

Table 1.

The tensile properties of P, SA, P/SA and P/SA/O films.

Film composition	Tensile strength (MPa)	Elongation at break (%)	Modulus (MPa)
P	5.40 ± 0.8	45.64 ± 2.2	23.53 ± 1.3
SA	7.13 ± 1.0	72.96 ± 3.8	7.84 ± 0.9
P/SA	2.48 ± 0.3	79.76 ± 4.1	1.58 ± 0.2
P/SA/O	0.82 ± 0.04	91.08 ± 2.6	9.49 ± 1.1

Tear test

The ASTM D 1938 covers the determination of the force required to propagate a tear in plastic film and thin sheeting by a single-tear method. The tear-propagation resistance of slightly extensible or non-extensible film or sheeting is distinguished by the load-time or load-displacement data. The force required to tear the film apart is recorded by the instrument. The three trials were taken for each composition of film and the average test value is shown in Fig. 3.

Fig. 3.

Tear strength results of the studied films.

FT-IR spectra

The FTIR spectra of the films were recorded using a JASCO FTIR-4100 spectrometer (Japan) operating in transmittance mode. Measurements were carried out at room temperature over a wavenumber range of 4000–400 cm⁻¹. The recorded spectra were then analysed using Spectra Manager software (https://jascoinc.com/products/spectroscopy/ftir-spectrometers/ftir-software/).

XRD spectra

In order to find the structural characteristics such as the degree of crystallinity of the prepared films X-ray diffraction (XRD) is used. X-ray diffraction (XRD) analysis was carried out using a Proto-AXRD benchtop diffractometer (Proto, Canada) equipped with a CuKα radiation source, operated at a tube voltage of 40 kV and a tube current of 35 mA. The diffraction patterns were recorded over a 2θ range of 5° to 80°. XRD spectra were recorded using XRDwinPD software (https://www.protoxrd.com/products/xrd-software).

Thermal analysis

The thermal degradation behaviour of P/SA and P/SA/O films were studied using Q50, TA Instruments, USA, at a heating rate of 10 °C/min between 30 and 900 °C.

Biodegradation studies

The biodegradation studies in soil were carried out to assess the degradation behaviour of the prepared film. The P, SA, P/SA and P/SA/O films were cut into small pieces of dimension of 2 cm × 2 cm and their original weights are recorded. Six different sets were prepared for the study, and they were set aside undisturbed inside the soil taken in a tray for the defined period. About 10 mL of water is sprinkled to the soil every two days to keep the moisture. Every seven days, the films were removed from the buried soil and their weight was noted. This procedure was repeated for about six weeks to monitor the weight loss¹⁰.

Bread packaging

Bread is a short shelf-life commodity and is vulnerable to fungal attack, primarily due to Pichia anomala commonly known as bread mould. To study the developed food packaging film capability to protect the packed food, a case study of bread packing was undertaken. Further the commercial LDPE film was chosen as the control film for the study. The films were cut into the desired dimensions, and they were heat sealed on all sides with a slice (2 cm × 2 cm) of bread piece packed inside. The bread sample without any packing and bread packed pouches were kept at room temperature and they were monitored for any morphological changes and possible fungal growth over a period of 30 days^27,43.

Results and discussion

Film thickness

The thickens of the films prepared was measure using a screw gauge with an accuracy of 0.01 mm at random spots of each film. The average thickness of the prepared film was in the range of 100–105 µM.

Water contact angle

The most common way to characterize how hydrophilic of hydrophobic a film surface is by measuring its water contact angle (θ). The assessment typically involves measuring the contact angle that forms between the film surface and the water droplet. Hydrophilic materials have a contact angle between 0° and 90°, while hydrophobic materials have a contact angle between 90° and 180°. The water contact angle picture of P, SA, P/SA and P/SA/O films were shown in Fig. 2a, b, c and d respectively.

Fig. 2.

Water contact angle of (a) P film (b) SA film (c) P/SA film and (d) P/SA/O film.

The measured contact angles of pectin and alginate films were 54.56° and 63.74° respectively. The P/SA blend film exhibited a contact angle of 24.54°, indicating higher hydrophilicity. Additional incorporation of essential oil into P/SA film increased the contact angle to 34.12°, reflecting the reduced surface wettability^24,44. The increased hydrophilicity of blend film can be attributed to disruption of internal networking, increased exposure of hydrophilic groups and less dense packing upon blending due to disturbed original packing. Most of the essential oils are hydrophobic and their addition into the polymer matrix decreases the accessibility of the hydroxyl groups on the film surface, making the film less prone to interact with water. The other possible reason can be formation of compact structure that makes it further difficult for water molecules to infuse.

Tensile testing

Food packaging applications of films anticipates materials to possess sufficient mechanical strength, otherwise it may cause the accidental failure of material during handling and processing condition⁴⁵. The tensile testing of films was carried out according to ASTM D 638. The results of the test were shown in Table 1. The addition of essential oil into the blend improved the elasticity of the film, making it easier for processing. The modulus of the film with oil is higher than neat blend film, which indicates that oil addition did not have any negative impact on the strength of the film. The tensile strength, percentage elongation and ultimate modulus were directly given by the software (https://www.shimadzu.com/an/products/software-informatics/index.html). It is observed from the data that the percent elongation of the prepared film is superior compared control films and the pectin blend film^10,46–48.

The blend film tensile strength was lower than individual polymer film, but elongation was more, it suggests that the film became more flexible upon blending. But the addition of essential oil increased the modulus, this may be attributed to reaction between oil and polymers leading to cross-links or hydrogen bonding. Similar studies were reported showing that the tensile strength of the polymer matrix decrease with the incorporation of essential oil, which is agreeing with our studies^38,49. The tensile properties are crucial for understanding how a food packaging film will perform in real-life applications. It reveals material’s ability to withstand load and deformation. Higher tensile strength provides better protection against mechanical damage during handling, transportation and storage, crucial for maintaining food integrity during transit. Elongation at break indicates the film’s stretchability and flexibility. A more flexible and ductile film can conform to the shape of the food product, enabling a secure seal and wrap thus minimizing packaging failures. Films with good elongation can also absorb impacts/shocks without damage. Modulus of elasticity represents the stiffness of film, which is very much essential for maintaining package integrity, particularly in automatic packaging lines.

Tear strength

Tear test measures the tear propagation resistance of the film. The neat pectin was very weak in terms of tear strength but upon addition of sodium alginate, the overall tear strength was increased. The addition of essential oil further improved the tear strength of the film. The tear strength was measured in triplicates and an average value is reported in N/mm. The result of the test is shown in Fig. 3 below. The P/SA/O film showed the better tear strength than the blend of P/SA, which can be attributed to rough surface morphology as evident from the SEM images. The roughness of the film hinders the easy propagation of tearing crack though the thickness of the film.

Addition of essential oil can enhance the tear strength of film may be due to rearrangement of the polymer network. Sometimes the essential oils can act as plasticizer thus increasing the flexibility of the film. This enhanced flexibility can lead to a reorganization of the polymer chains to slide past each other more easily, allowing them to better distribute stress and resist tear spread. Certain compounds in essential oil like phenols, may be able to react with the polymer matrix, leading to cross-linking of polymer chains. This creates interconnected and more robust network, making the film tougher and less prone to tearing.

Spectral analysis

FTIR analysis

Films made of pectin, alginate, P/SA and P/SA/O were subjected for FTIR analysis. The FTIR spectra of prepared films were recorded between 4000 –400 cm^{− 1} wavenumber as shown in the Fig. 4. In the FTIR spectrum of pectin film, Fig. 4a, the broad absorbance band at 3300 cm^{− 1} is due to the presence of OH group. The absorbance bands at 2930 cm^{− 1}, 1738 cm^{− 1} and 1402 cm^{− 1} corresponds to -CH₃ stretching, C = O of carbomethoxy group and COO- asymmetric stretching of pectin, respectively⁵⁰. FTIR spectrum of sodium alginate film, as shown in Fig. 4b, exhibited a broad band at 3355 cm^{− 1} corresponding to hydrogen bonding of -OH group. Bands at 2944 cm^{− 1} can be attributed to the C-H stretching, and another band at 1608 cm^{− 1} is due to the presence of COO⁻ stretching⁵¹. In the FTIR spectrum of pectin/sodium alginate film as in Fig. 4c, a broad band at 3342 cm^{− 1} is due to the stretching vibration of hydroxyl group. The absorbance band at 2944 cm^{− 1} correspond to C-H stretching, 1629 cm^{− 1,} which is a characteristic band of C = O stretching/hydrogen bonding coupled with a COO⁻ group of P and SA. The absorbance bands at 1402 cm^{− 1} correspond to COO⁻ groups. Thus, the bands present in FTIR spectrum confirms the presence of pectin and alginate in the film^52,53. Pectin/Sodium alginate/essential oil FTIR spectrum, as shown in the Fig. 4d, shows slight shift in the band position, which is due to an addition of essential oil. The 3376 cm^{− 1} stretching frequency is due to -OH group, and the C-H stretching of CH₃ and C-OH vibrations are observed at 2937 cm^{− 1} and 1039 cm^{− 1} respectively. The band intensity variations in the range of 1350 –1250 cm^{− 1} in the blend clearly indicates the interaction between pectin and sodium alginate. The ether groups interaction in blend around 1050 cm^{− 1} also evident from the spectra. Further, it is evident that the presence of turmeric oil is revealed by the stretching vibration at 1601 cm^{− 1} due to C = C and at 1224 cm^{− 1} due to its ring structure. The results are in par with the studies reported previously⁵⁴. The presence of curcuminoids of essential oil resulted in C = C stretching vibrations around 1490 cm^{− 1}. The interaction between the blend components was slightly modified by the presence of essential oil as indicated by the FTIR spectra, which can be attributed to C-O stretching vibrations.

Fig. 4.

FT-IR spectra of (a) P film (b) SA film (c) P/SA film and (d) P/SA/O film.

X-ray diffraction analysis

In order to find the structural characteristics such as the degree of crystallinity of the prepared films X-ray diffraction (XRD) is used. The XRD analysis gave an insight into the composition and crystallinity of pectin, alginate, P/SA and P/SA/O films. The crystallinity percentage was evaluated using crystallinity tool available on XRDWIN^® 2.0 software (https://www.protoxrd.com/products/xrd-software). The XRD profiles of pectin, alginate, P/SA and P/SA/O film is shown in Fig. 5. In the diffractogram pattern of pure pectin film the peaks at 2θ value of 21.6° and 29.4° was observed with 65.36% crystallinity as shown in Fig. 5a. In the diffractogram pattern of sodium alginate film, the peaks at 2θ value of 32.25°, 46.19°, 57° and 75.78° were prominent, the crystallinity was around 98.85% as shown in Fig. 5b, it is in par with the literature⁵². The diffractogram pattern of pectin/sodium alginate film the diffused peaks at 2θ value of 9.88°, 21.96°, 29.59°, 35.37°, 41.88° and 47.45° was observed (Fig. 5c). From the data, it confirms that pectin/alginate film as about 77.52% of crystallinity. The diffractogram pattern of pectin/alginate/essential oil film, Fig. 5d shows diffused peaks in the 2θ range of 20.07° to 44.11° which confirms the presence of pectin and alginate and in addition to the peaks of pectin and alginate, the 2θ diffraction peak at 39.46° indicates the presence of turmeric essential oil. As a result, the P/SA/O film pattern differs from both of its parent polymers and exhibits 73.80% of crystallinity⁵⁵. Though there is change in crystallinity of the film with the addition of essential oil, it did not adversely affect the film mechanical properties as evident from the tensile and tear test results. This may be due to very less concentration of the oil used in the study.

Fig. 5.

XRD spectra of (a) P film (b) SA film (c) P/SA film and (d) P/SA/O film.

SEM analysis

By using scanning electron microscope, the surface morphology of the films was studied. Pectin film shows a homogeneous and smooth surface morphology, as shown in above Fig. 6a, b. Because of this property, pectin can be used as a matrix. Through SEM analysis it is observed that even sodium alginate film (Fig. 6c and d) has a very smooth surface and can also act as a matrix. The SEM micrograph of P/SA (Fig. 6e and f) blend film shows roughness on the surface. Further the surface roughness with well-defined cubes in P/SA/O film (Fig. 6g and h) has increased due to the presence of turmeric oil. The change in the morphology of the films clearly indicates the incorporation of essential oil into the polymer matrix, with the similar biphasic microstructure as reported in the literatures for the citrus pectin and sodium alginate blend^56,57.

Fig. 6.

SEM analysis of (a, b) P film (c, d) SA film (e, f) P/SA film and (g, h) P/SA/O film.

TGA analysis

Thermogravimetry is a widely used technique for the analysis of polymer’s thermal stability. The percent weight loss and DTG curves of P/SA and P/SA/O films are shown in Fig. 7a and b respectively. The first major weight loss of P/SA film is at 186 °C (2.48 mg, 15.59%), which is due to the moisture loss while the second minor weight loss step is at 538.82 °C (8.11 mg) was due to thermal degradation of pectin and sodium alginate films. The blend of P/SA/O film has shown first minor weight loss at 142.06 °C (2.86 mg, 16.95%) which can be attributed to moisture loss. The second major weight loss occurs at 483.04 °C (8.78 mg) which is the result of thermal degradation of polymeric molecules. With the incorporation of oil to the polymer blend, there is not much variation in thermal stability. Thus, change in thermal property with the addition of oil to the polymer matrix is minimal. The similar weight degradation stages were reported in the literature survey^58,59.

Fig. 7.

TGA plots of (a) P/SA film (b) P/SA/O film.

Biodegradation studies

Films were cut into pieces (2 cm × 2 cm), their initial weight was recorded and then buried in soil at room temperature. The degradation study of the films was conducted for 6 weeks. Throughout the degradation investigations, the soil was watered once in every two days. During the experimental period the weight loss was monitored carefully. The degradation percentage of P, SA, P/SA and P/SA/O blended films were calculated and are summarized in Table 2. During the biodegradation study, there were no changes in the weight of sample for the initial 24 h. One factor that contributes to this degradation is the activity of soil-resident bacteria. Bacteria and fungi are the microorganisms responsible for biodegradation of the films in soil. After one week there was about 24.58% reduction in the weight of P film and about 48.45% reduction in the weight of SA film. The P/SA and P/SA/O film showed 30.57% and 40.49% reduction in weight, respectively. After a time period of 14 days, 33.72%, 51.37%, 54.43% and 43.68% weight reduction are exhibited by P, SA, P/SA and P/SA/O films, respectively. Neat films of P and SA degraded slowly over 21 days and then entered into a steady-state degradation mode despite the presence of glycerol and calcium chloride. Near to 28th day, the films degradation rate was substantially increased. The changes observed in the films during the degradation is shown in Fig. 8. The degradation process in soil depends upon the amount of water absorbed by the films and also on the susceptibility of components towards the microorganism/enzymatic attack. Since alginate and pectin are the naturally derived polymers, their susceptibility toward attack by microorganisms is high and thus the degradation percentage of blend films is lower than neat P and SA film. The reported degradation percentage is the sum of completely/partially degraded products and the polymer chains that are dissolved/disrupted from the sample. The percentage degradation of blend films is lower than expected. Depolymerization of films may occur, wherein the extracellular enzymes from the microorganisms can break down the polymer to produce short chain smaller molecules such as oligomers, dimers and monomers, which are small enough to pass through the semipermeable outer bacterial membranes. The biodegradation end products of these short-chain molecules are CO₂, H₂O and biomass. Finally at the end of seventh week, weight reduction of pectin film was around 78.98% and that of SA film was 76.58%, whereas that of blended P/SA film and P/SA/O film was about 69.12% and 63.43%, respectively. Biopolymer degradation by microorganisms leads to an increase in water diffusion and consequently an increase in cleavage of molecules by hydrolysis. The presence of essential oil may act as antimicrobial agent thus retarding the degradation^60–63.

Table 2.

Summarizes the biodegradation test results of films in soil.

Time period	% Weight loss of pectin film	% Weight loss of SA film	% Weight loss of P/SA film	% Weight loss of P/SA/O film
1st week 2nd week 3rd week 4th week 5th week 6th week	28.42 36.29 45.07 57.98 62.29 78.97	13.64 47.29 50.70 57.97 63.43 73.65	30.68 43.98 54.43 55.63 61.09 69.12	40.49 43.68 47.56 51.96 57.01 63.43

Fig. 8.

Photographs of biodegraded P, SA, P/SA and P/SA/O films.

Bread packaging: a case study

Among edible items, bread holds significant cultural, religious and even social value. As society evolved, bread production, consumption, storage and purchases have changed significantly. As a result, there is a growing need to prolong the shelf life of this highly perishable product. Bread staling is the term for a set of physicochemical alterations that occur during its storage and lead to a slow decrease in consumer acceptance. Structural modifications, such as increased crumb stiffness and crumbliness due to moisture loss and starch retrogradation, as well as flavour and fragrance changes from oxidative processes are characteristics of bread staling. In addition to altering the recipe, there are other ways to extend the shelf life of bread, such as using different packaging options that primarily work to delay oxidation and moulding. Food shelf-life is determined by the packaging, which is the amount of time that allows for a tolerable degree of microbiological and sensory quality deterioration. The perception of bread as “daily and fresh” can be manipulated by combining formulation modifications with suitable packaging solutions. The main aim of packaging is protecting food from degradative factors such as light, oxygen, water vapor, molds, yeasts, bacteria and insects. Active packaging strategy has the ability to release or absorb gas. Specifically, these packaging systems have the ability to chemically eliminate unwanted gases from the headspace, like ethylene, oxygen or water vapour, or they can progressively release volatile antioxidants, preservatives and antimicrobials, like ethanol, sulphur dioxide or essential vegetable oils into the headspace to prolong the shelf-life⁶⁴. In the case study of the packed and unpacked bread samples, it is observed that the unpacked bread sample started to show fungal deterioration on the 7th day and even the polythene pouch could not protect the bread against fungal deterioration and the bread packed inside the polythene pouch showed substantial fungal growth on the 14th day. No fungal growth was observed on bread samples packed in P/SA and P/SA/O films up to 21st day showing their good protection against fungal attack. At 30th day there was fungal growth seen on P/SA and P/SA/O packed bread samples too. But the percentage of growth on bread sample packed using P/SA/O was too less compared to the sample packed with P/SA film. The unpacked bread showed complete degradation and became hard around 30th day. The changes observed during the study is shown in the Fig. 9. The presence of essential oil may act as antimicrobial agent, thus retarding the spoilage of bread sample. This indicates that the developed films are good at food protection even at room condition for extended period. Hence, they can be a good replacement for the commercial films available in the market with an additional benefit of renewable source based and biodegradation^65,66.

Fig. 9.

The visual appearances of bread slice with Polythene, P/SA and P/SA/O film compared to control sample during the study.

The future studies may focus on fresh produce packaging like fruits, vegetables, red meat and study the efficacy of the developed film for selective permeation of ethylene gas and carbon dioxide. The film barrier properties and strength can be further enhanced by adding nanofillers like silver nanoparticle, ZnO, MgO, TiO₂ etc., which renders film inherent antimicrobial properties.

Conclusion

In the present study, pectin and sodium alginate derived biodegradable food packaging films were developed with turmeric essential oil as an active ingredient. The prepared films were characterised to ascertain their performance for practical applications. Tensile strength, tear resistance, water contact angle and thermal stability of the prepared films were encouraging. The P/SA/O film exhibited an elongation at break of 91.08% and an ultimate modulus of 9.49 MPa, indicating that the addition of turmeric essential oil did not compromise film strength. However, the antimicrobial efficacy of the oil enhanced the shelf-life of the product packed. The biodegradation studies revealed that films will break down under ambient conditions over a notable period of time, indicating that they would be a better option as an environmentally benign food packaging material. The shelf-life study showed that the prepared films were good enough to protect the food items packed within it for the extended period than the presently used packaging material like polythene. The film can be suitably finetuned in their properties to use for bakery products like bread packaging, which is the highest sold baked item purchased on regular basis. So, its packaging has frequent disposal. Hence the developed films can be a better option for the packaging industries to switch from long lasting landfilling materials to eco-friendly packaging materials.

Author contributions

S.B.S., R.K.M., B.S., H.A.B. K.M.L., L.S.: Conceptualization, Methodology, Investigation, Formal analysis; P.S., C.S., R.K.M., K.S.A., V.S., E.S.: Data curation, Investigations, Formal analysis, Writing- Original draft preparation. B.S., E.S., S.P.K.: Visualization, Project administration, validation. B.S., S.P.K.: Resources, Supervision, Writing- Reviewing and Editing.

Data availability

All the data generated or analyzed during this study are included within the article.

Declarations

Competing interests

The authors declare no competing interests.