Microsoft Word - ETASR_V11_N4_pp7489-7494
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7489
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
Preparation and Characterization of Gelatin-Based
Films Cross-Linked by Two Essential Oils at
Different Concentrations and Plasticized with
Glycerol
Hayet El Kolli
Multiphase Polymeric Materials Laboratory
University of Ferhat Abbas Setif 1
Setif, Algeria
Meriem El Kolli
Laboratory for the Valorization of Biological Natural Resources
University of Ferhat Abbas Setif 1
Setif, Algeria
Abstract-Gelatin cross-linking has recently been discovered to be
a very appealing production method. The current research looks
at various commercial gelatin (type B) films to improve their
physical qualities. Bunium alpinum and bunium incrassatum
Essential Oils (EOs) in two quantities (5% and 25%) were added
to the films, which showed substantial biological activity
(antibacterial, antioxidant, antihemolytic, and anti-
inflammatory). According to electronic scanning microscopy
results, the basic gelatin matrix had changed and there were
multiple dense spots on the cross-linked films. The particles
appear to be more bonded in an isotropic form. Infrared
spectroscopy cannot provide substantial accuracy on the new
characteristics and chemical interactions formed due to the
complex system of gelatin and EOs. According to the UV
transmission test results, adding EOs to gelatin films improves
the barrier properties against UV rays and prevents UV light
transmission. Finally, the swelling water test revealed that
included EOs in the film composition reduce the film's swelling.
Keywords-gelatin; bunium alpinum; bunium incrassatum;
crosslinking; barrier property against UV; food packaging
I. INTRODUCTION
Polymeric materials are required in a variety of routine
applications, from food packaging to cosmetics and other
specialized sectors, e.g. the biopharmaceutical and
pharmaceutical sectors [1]. For more than 20 years researchers
try to improve conventional polymers by adding particles into
the polymer matrix, thus changing its properties [2]. The
agriculture and food sectors are increasingly concerned about
the preservation of commonly consumed items against
deterioration caused by environmental (heat, sunlight) or
biological (bacterial and fungal) factors [3]. Bio-packaging is
currently being researched as a healthy and environmentally
friendly option [4]. Traditional polymers used in the product
packaging are being replaced with healthier, less toxic and
biodegradable alternatives in the agri-food, pharmaceutical, and
cosmetic industries through technological procedures. As a
result, biopolymers like gelatin are gaining popularity in this
sector. Film-making gelatin is a form of gelatin. It becomes
more stable and manageable when mixed with other substances
[5]. In innovative packaging applications, biopolymers are
coupled with natural products such as medical plant extracts
(essential oils and plant powders) and pure or semi-purified
natural components (polyphenols, flavonoids, pigments, etc.)
[6]. This link bestows all of the qualities and benefits
associated with natural items on the designed bundle. The use
of essential oils in packaging systems, imparts the flavors of
the essential oils used and the antibacterial and antifungal
properties that characterize them [3, 7]. Phenolic compounds
protect packaged commodities from degradation caused by
external conditions and bacteria by acting as antioxidants [8].
This study aims to develop a novel type of gelatin
packaging that is cross-linked with glycerol. This polymer
contains antibacterial, antifungal, and antioxidant Essential Oils
(EOs) from bunium incrassatum and bunium alpinum [9].
II. MATHERIALS AND METHODS
A. Chemicals
Hydro-distillation in a Clevenger-style device was used to
extract the volatile EOs, and each separated oil was kept at 4°C
in a refrigerator. The EOs were analyzed using Gas
Chromatography-Mass Spectrometry (GC-MS). The contents
of the EOs were determined by comparing the mass spectral
pattern and Retention Indices (RIs) of the EOs to those of pure
compounds available in the literature as well as a laboratory-
built database of authentic chemicals [10]. Fluka and
Biochemika synthetized gelatin powder from porcine skin
(with a medium gel strength 180 blooms) was utilized.
B. Preparation of Biofilms
The methodology defined in [11] is employed in this work
with minor modifications. To make the film-forming solution,
3.5g gelatin powder (180 bloom porcine skin gelatin) was
mixed with 100ml distilled water for 30min, then 2ml glycerol
(plasticizer) were added. This mixture was heated at 70°C for
30min and was constantly stirred. At the same time, a 3:1 (v/v)
mixture of EOs and Tween-20 (emulsifier) was prepared. The
Corresponding author: Meriem El Kolli (elkollim@yahoo.fr)
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7490
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
combination was added to the initial solution in percentages of
5% and 25%. A vortex mixer (3500rpm) was used to
homogenize the generated solution for 3min. The dissolved air
in the films was then extracted with a vacuum pump. Finally,
13ml of liquid were placed in plastic Petri dishes and were
allowed to air dry for 4 days at room temperature. The films
were then carefully peeled and assessed. Control films were
made using the same procedure as the test films but without the
EOs.
C. Characterization
• Thickness
In compliance with the French standard NF Q 03-016, the
film thickness (e) was measured with a foot electronic slide-
type Mitutoyo DIGIMATIC 500-123U. Three discs were cut
from each formulation (each measuring 4.5cm). Each disc was
measured for thickness in 5 different spots at random [12].
• Areal density
The film's mass determines the areal density in g/m
2
based
on a unit area. The French standard NF Q 03-019 was used to
determine it. Each formulation was sliced into 3 discs (each
measuring 4.5cm) and was weighed precisely. The film density
(D) was calculated using the equation D=AD/e from the
thickness and basis weight [13].
• Scanning Electronic Microscopy (SEM)
SEM was used to evaluate sample films' morphology or
surface topography (a JEOL JSM 6360LV scanning electron
microscope was utilized). To make them conductive a 25 to
30nm thickness layer was placed to the surface and the samples
were first metalized with gold in a Cressington Sputter Coater
metallizer. Electron acceleration voltages ranging from 3 to
10kV were used to obtain the photos [12].
• Fourier Transform-Infrared (FT-IR)
Infrared spectroscopy was used to determine the physical
states of organic and inorganic molecules based on their
vibrational properties. Chemical bonds do vibrate in specific
modes as a result of infrared light (deformation, stretching). As
a result, comparing the sample's incidence and transmission is
sufficient to disclose the sample's fundamental chemical
functions [14]. The FTIR-8400S device was used (Fourier
Transform Infra-Red Spectrophotometer, SHIMADZU). The
data were read using IR-SOLUTION software.
• Transparency and light transmission
The film's light transmission in ultraviolet and visible light
was measured using a UV-visible spectrophotometer
(UNICAM UV 300 type 200-800nm). VISION32 Software
V1.10 was used to read the data. The film's Transparency
Value (TV) is calculated by [14]:
�� = ��� (�
)/
(1)
where �
: 600nm transmission fraction,
: the thickness of
the film (mm).
A high �� value is indicative of low film transparency.
• Swelling test
The film samples (40mm/30mm) were dried for 24h at
104°C in an air-circulating oven until they were consistent in
weight. The initial weight (�� ) was measured. The film
samples were immersed in a 100ml Erlenmeyer flask with
50mL distilled water for 24h at room temperature. After
removing from the flask and rubbing it between filter papers to
remove any residual surface water, each sample was weighed
and the ultimate weight (��) was calculated. Equation (2) [15]
was used to compute the weight gain or swelling percentage
(S %):
� (%) = ( −�� / ��) 100 (2)
At least three measurements were taken in each test.
III. RESULTS AND DISCUSSION
This is a new line of research which aims to synthesize
biodegradable matrices, based on gelatin or another
biopolymer, with new formulations by adding safe to use and
low cost natural metabolites such as EOs, known for their
broad antimicrobial spectrum with the aim of using them in
packaging, as patches for the release of drugs, or in the case of
the encapsulation of active ingredients. Table I shows the
thickness, areal density, and density of the several gelatin films
supplemented with varying concentrations of EOs, as well as
the control film.
• Training films
The chains of gelatin unfold during the solubilization of
gelatin in water, generating the polymer network. The viscosity
of the film-forming fluids increases substantially as the gelatin
molecules flocculate and transform into a gel at temperatures
above the gelling temperature (60°C). Reduced hydration
layers around polymer chains increase hydrophobic
interactions, resulting in increased hydrophobic interactions
[16]. Gelatin's methyl groups interact with the molecules
around them, forming intermolecular connections. The
hydrogen-type intermolecular bonds are formed by isolating
the hydration solvent (water) from the polymer chains.
Glycerol is a low-molecular-weight (92g/mol) hydrophilic
molecule that can readily be placed between gelatin segments.
Hydrogen bonds arise between the hydroxyl groups of the
glycerol and gelatin during the gelling or evaporation of the
solvent.
• Look and Flexibility
Control films and films with EOs and have a smooth,
continuous appearance with no surface imperfections. It is
worth noting that the flexibility of the films is proportional to
the amount of EO used [16, 12]. The film that contained the
most bunium incrassatum EO (25%) was the most flexible and
yellow-tinted (since this EO is darker than the other). Based on
this finding, the films developed a stable emulsion system.
There is no emulsion breakdown or change during the
dehydration process, and no bubbles or cracks appear.
• Thickness
The EO-enhanced films were all thicker in consistency than
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7491
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
the control film (0.22mm). Droplets of EOs can be
incorporated into the film network, obstructing the link
between gelatin chains, lowering network compactness, and
obstructing orderly alignment. The formation of gelatin chains
might increase density. This can be controlled by surface
tension and/or changes in the size of the oil droplets.
Furthermore, EOs are available in various formulations, each of
which interacts with the gelatin chain in the film matrix in a
distinct way [10]. As a result, the gelatin molecules'
arrangement in the film matrix can shift, resulting in changes in
film thickness [17]. As a consequence, adding glycerol to the
control film enhanced dramatically the surface density.
Combining glycerol and EOs increases the film thickness, but
has a significant impact on the density. This is because glycerol
has a density of only 1257kg m
-3
.
TABLE I. THICKNESS, AREAL DENSITY, AND VOLUME MASS OF
THE FILMS
Sample
Thickness
(mm)
Areal
density
(g m
-2
)
Volume
mass
(kg m
-3
)
Control 0.22 ± 0.004 72.705 3304.802
Film with 25% of
bunium incrassatum
0.36 ± 0.005 70.651 1962.547
Film with 25% of
bunium alpinum
0.32 ± 0.008 64.846 2026.441
Film with 5% of
bunium incrassatum
0.34 ± 0.005 69.268 2037.306
Film with 5% of
bunium alpinum
0.24 ± 0.008 63.861 2660.878
• SEM and determination of the morphology
According to SEM, the control film has a smooth,
continuous, compact, and completely transparent surface
(Figure 1). For films having varying concentrations of EOs,
several dense zones develop on the same sample, where the
particles appear more bound with anisotropic structure, without
pores, and without micro-fractures (Figure 1). The most
densely built-up areas are those with the highest percentage of
EOs, meaning that EOs' droplets modify the transverse
distribution of protein-protein inside the film matrix
(improving roughness), most likely within the film network.
Because of the EO droplets, water molecules will not travel
through the film network [18]. Terpene compounds make up
many EO compositions [29, 20]. These molecules can combine
with different proteins or amino acids in gelatin to form
"Protein Cross-links," which change the gelatin's underlying
matrix and give rise to various morphologies [21].
• FT-IR
The FTIR spectra of gelatin and gelatin / EO films are
shown in Figures 2 and 3. The purpose of this classification
was to determine how various functional groups interacted with
each another. Because each film has a large number of
functional groups, the FTIR spectra generated from each film
include a large number of overlapping absorption bands,
offering more information than all of the chemical components
analyzed independently. The distinction was made using
proteins and polypeptides, which are the essential components
that determine function in food systems. The infrared spectra of
nearby peptide groups are affected by vibrational coupling.
Film without EO
Film enriched with 5% of bunium
incrassatum
Film enriched with 25% of bunium
incrassatuum
Film enriched with 5% of bunium
alpinuum
Film enriched with 25% of bunium
alpinuum
Fig. 1. SEM micrographs of the gelatin and gelatin/EO films.
Fig. 2. FT-IR spectra of gelatin films with bunium alpinum and bunium
incrassatum EOs at various concentrations (4000-500cm
-1
)
The vibratory features of FT-IR can be used to show the
presence of species adsorbed and/or grafted to the surface of
the film. FT-IR does not provide considerable precision on the
features and newly developed connections due to the various
activities of gelatin and EO, and glycerol in all films [12]. The
same prominent peaks with various amplitudes appeared in all
FT-IR spectra (Figure 2).
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7492
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
Fig. 3. FT-IR spectra of control and modified films with EOs (1500-
500cm
-1
)
The notable peaks in both films with and without EOs were
nearly identical: both film samples contained a band with a
wavenumber of 1165.32cm
-1
. It refers to an amine having a
short C-N chain that can be used as a primary, secondary, or
tertiary amine [12]. Several bands in the 1940–1847cm
-1
range
are also found in gelatin and EOs and are linked to NH2
bending vibrations and C=O, C=C, and C=N stretching
vibrations. At 3826 cm
-1
, an amide-A band and an amide-B
band with NH-stretching combined with hydrogen-bonding and
CH stretching were identified.
• Transparency and light transmission
The spectrum in Figure 4 depicts the transmittance of UV
rays and visible light in the wavelength range of 200-800nm of
gelatin films enhanced with various EOs. There was no UV
transmission in any of the films at 200nm, including control.
They had all started transmitting light at wavelengths less than
300nm. The use of EOs in gelatin films has been suggested as a
means to improve UV barrier properties. These coatings
effectively reduce UV light transmission. It can generally bind
excellent UV barrier qualities and absorb UV radiation because
of the rich amino acid content that produces the amino acids'
gelatin and interactions with the EO's diverse components [22,
16]. The control film transmission ranged from 52, 61 to 86,
and 51% for visible light (300-800nm). The lowest values were
seen in the films enriched with EOs (independent of EO type
but proportionate to their concentration) (Table II).
Fig. 4. Transmittance of films at 200-800nm wavelengths.
These data suggest that adding EOs to the films lowered
light transmission considerably. The EO droplets in the matrix
may be able to block UV and visible light from going through.
In the visible range, the film containing 25% EO of B.
incrassatum had the lowest light transmission (from 10.65 to
78.64%), followed by the film containing the same proportion
of EO of bunium alpinum. The film with 5% of the EO of
bunium incrassatum comes third, whereas the film with 5% of
bunium alpinum comes fourth. The presence of EOs in the
films might cause light scattering in variable degrees. For light
transmission through the films, the arrangement or alignment
of the polymer chains in the film network is crucial. When
considering the maximum transparency, the lowest
transmittance value is employed [23]. Authors in [24]
demonstrated their hypothesis by using lemon EO to lower the
opacity of chitosan films. They discovered that the size and
placement of EO droplets in the film network can influence the
occurrence of this event. The findings in [25] are consistent
with this discovery.
TABLE II. TRANSPARENCY VALUES OF THE FILMS
Glycerol (%) EO Light transmission (%) at different wavelengths Transparency value
20%
200 300 350 400 500 600 700 800
Control 0 52.617 71.836 78.456 82.189 83.635 85.26 86.513 3.579
Bunium incrassatum 25% 0 10.651 36.241 52.243 65.958 71.917 76.027 78.645 3.300
Bunium incrassatum 5% 0 33.435 59.623 70.344 78.329 81.302 83.582 85.003 3.378
Bunium alpinum 25% 0 29.315 55.122 69.077 78.231 81.163 83.052 84.304 3.404
Bunium alpinum 5% 0 43.050 65.850 74.586 80.858 82.887 84.718 85.911 3.538
• Swelling test
When EOs were introduced, the swelling of gelatin films
was considerably reduced (Table III). Gelatin is a hydrophilic
substance, which means it soaks up water molecules. Porous
gelatin films have a higher swelling capacity due to their
network architecture, allowing more water to pass. Because
EOs are hydrophobic, it is possible that adding them to gelatin
films reduces their swelling potential. Hydrophobic contact
between gelatin's hydrophobic domains and EOs improves the
interfacial interaction between matrix (gelatin) and filler (EOs)
[26]. This causes the EOs to saturate the gelatin network,
preventing water molecules from migrating into the gelatin and
reducing swelling [27]. These findings show that gelatin sheets
containing EOs could be promising liquid-absorbing packaging
materials.
TABLE III. SWELLING VALUES
Sample Swelling (%)
Control 542 ± 7
Film with 5% of bunium alpinum 530± 3
Film with 5% of bunium incrassatum 547±3
Film with 25% of bunium alpinum 527±12
Film with 25% of bunium incrassatum 512±4
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7493
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
IV. CONCLUSION
Plastic packaging has many drawbacks, one of which being
its negative influence on the environment. Biodegradable films
and coatings made from natural bio-based polymers can be
promoted as a viable plastic substitute. In the current study, the
EOs of bunium alpinum and bunium incrassatum were shown
to be very compatible with gelatin, resulting in flexible and
easy-to-handle films in the studied concentration range.
Including EOs in the gelatin films resulted in a significant
reduction in edema, depending on the dose. According to the
SEM results, the EOs were well dispersed in the film matrix,
and good adhesion was attained. The addition of EOs to gelatin
films on a dose-by-dose basis has improved the UV barrier
qualities of gelatin/EO films. These findings suggest that the
selected EOs could be helpful as cross-linking agents in several
applications, such as food packaging and pharmaceuticals.
More research and applications are required to complete the
assessment of possible applications.
ACKNOWLEDGMENT
The authors acknowledge the help in SEM technique of
Doctor Abdelyamine Bouda from CDTA (Centre de
Développement des Technologies Avancées), Algeria.
REFERENCES
[1] J. Wroblewska-Krepsztul, T. Rydzkowski, I. Michalska-Pozoga, and V.
K. Thakur, "Biopolymers for Biomedical and Pharmaceutical
Applications: Recent Advances and Overview of Alginate
Electrospinning," Nanomaterials, vol. 9, no. 3, Mar. 2019, Art. no. 404,
https://doi.org/10.3390/nano9030404.
[2] M. Danikas, Α. Bairaktari, R. Sarathi, and A. B. B. A. Ghani, "A Review
of Two Nanocomposite Insulating Materials Models: Lewis’
Contribution in the Development of the Models, their Differences, their
Similarities and Future Challenges," Engineering, Technology & Applied
Science Research, vol. 4, no. 3, pp. 636–643, Jun. 2014,
https://doi.org/10.48084/etasr.441.
[3] K. Oudjedi, S. Manso, C. Nerin, N. Hassissen, and F. Zaidi, "New active
antioxidant multilayer food packaging films containing Algerian Sage
and Bay leaves extracts and their application for oxidative stability of
fried potatoes," Food Control, vol. 98, pp. 216–226, Apr. 2019,
https://doi.org/10.1016/j.foodcont.2018.11.018.
[4] E. Basiak, A. Lenart, and F. Debeaufort, "How Glycerol and Water
Contents Affect the Structural and Functional Properties of Starch-Based
Edible Films," Polymers, vol. 10, no. 4, Apr. 2018, Art. no. 412,
https://doi.org/10.3390/polym10040412.
[5] M. C. Gomez-Guillen, J. Turnay, M. D. Fernandez-Diaz, N. Ulmo, M.
A. Lizarbe, and P. Montero, "Structural and physical properties of
gelatin extracted from different marine species: a comparative study,"
Food Hydrocolloids, vol. 16, no. 1, pp. 25–34, Jan. 2002, https://doi.org/
10.1016/S0268-005X(01)00035-2.
[6] D. Carrizo, G. Taborda, C. Nerin, and O. Bosetti, "Extension of shelf life
of two fatty foods using a new antioxidant multilayer packaging
containing green tea extract," Innovative Food Science & Emerging
Technologies, vol. 33, pp. 534–541, Feb. 2016, https://doi.org/
10.1016/j.ifset.2015.10.018.
[7] M. Carpena, B. Nunez-Estevez, A. Soria-Lopez, P. Garcia-Oliveira, and
M. A. Prieto, "Essential Oils and Their Application on Active Packaging
Systems: A Review," Resources, vol. 10, no. 1, Jan. 2021, Art. no. 7,
https://doi.org/10.3390/resources10010007.
[8] D. Carrizo, G. Gullo, O. Bosetti, and C. Nerin, "Development of an
active food packaging system with antioxidant properties based on green
tea extract," Food Additives & Contaminants: Part A, vol. 31, no. 3, pp.
364–373, Mar. 2014, https://doi.org/10.1080/19440049.2013.869361.
[9] C. Pena, G. Mondragon, I. Algar, I. Mondragon, J. Martucci, and R.
Ruseckaite, "Gelatin Films: Renewable Resource for Food Packaging,"
in Gelatin: Production, Applications and Health Implications, New
York, NY, USA: Nova Science, 2013, pp. 71–86.
[10] E. K. Hayet, L. Hocine, and E. K. Meriem, "Chemical Composition And
Biological Activities Of The Essential Oils And The Methanolic
Extracts Of Bunium Incrassatum And Bunium Alpinum From Algeria,"
Journal of the Chilean Chemical Society, vol. 62, no. 1, pp. 3335–3341,
Mar. 2017, https://doi.org/10.4067/S0717-97072017000100006.
[11] P. Tongnuanchan, S. Benjakul, and T. Prodpran, "Properties and
antioxidant activity of fish skin gelatin film incorporated with citrus
essential oils," Food Chemistry, vol. 134, no. 3, pp. 1571–1579, Oct.
2012, https://doi.org/10.1016/j.foodchem.2012.03.094.
[12] J. Wu, X. Sun, X. Guo, S. Ge, and Q. Zhang, "Physicochemical
properties, antimicrobial activity and oil release of fish gelatin films
incorporated with cinnamon essential oil," Aquaculture and Fisheries,
vol. 2, no. 4, pp. 185–192, Jul. 2017, https://doi.org/10.1016/
j.aaf.2017.06.004.
[13] L. Scartazzini et al., "Gelatin edible coatings with mint essential oil
(Mentha arvensis): film characterization and antifungal properties,"
Journal of Food Science and Technology, vol. 56, no. 9, pp. 4045–4056,
Sep. 2019, https://doi.org/10.1007/s13197-019-03873-9.
[14] P. Tongnuanchan, S. Benjakul, and T. Prodpran, "Comparative studies
on properties and antioxidative activity of fish skin gelatin films
incorporated with essential oils from various sources," International
Aquatic Research, vol. 6, no. 2, Jul. 2014, Art. no. 62, https://doi.org/
10.1007/s40071-014-0062-x.
[15] G. Kavoosi, A. Rahmatollahi, S. Mohammad Mahdi Dadfar, and A.
Mohammadi Purfard, "Effects of essential oil on the water binding
capacity, physico-mechanical properties, antioxidant and antibacterial
activity of gelatin films," LWT - Food Science and Technology, vol. 57,
no. 2, pp. 556–561, Jul. 2014, https://doi.org/10.1016/j.lwt.2014.02.008.
[16] M. Aitboulahsen et al., "Gelatin/pectin-based film incorporated with
essential oils: Functional characteristics and shelf life extension of
tilapia fillets under refrigeration," Journal of Food Safety, vol. 40, no. 3,
2020, Art. no. e12774, https://doi.org/10.1111/jfs.12774.
[17] J. Xiao et al., "Impact of melting point of palm oil on mechanical and
water barrier properties of gelatin-palm oil emulsion film," Food
Hydrocolloids, vol. 60, pp. 243–251, Oct. 2016, https://doi.org/
10.1016/j.foodhyd.2016.03.042.
[18] S. Jahani, A. Shakiba, and L. Jahani, "Fabrication of Gelatin Nano-
Capsules Incorporate Ferula assa-foetida Essential Oil With
Antibacterial and Antioxidant," Zahedan Journal of Research in Medical
Sciences, vol. 17, no. 7, Jul. 2015, Art. no. e1018,
https://doi.org/10.17795/zjrms1018.
[19] J. Bruneton, Pharmacognosie: Phytochimie, plantes medicinales, 3rd ed.
Paris, France: Technique et Documentation Lavoisier, 1999.
[20] S. Burt, "Essential oils: their antibacterial properties and potential
applications in foods—a review," International Journal of Food
Microbiology, vol. 94, no. 3, pp. 223–253, Aug. 2004, https://doi.org/
10.1016/j.ijfoodmicro.2004.03.022.
[21] S. D. Sarkar, B. L. Farrugia, T. R. Dargaville, and S. Dhara, "Physico-
chemical/biological properties of tripolyphosphate cross-linked chitosan
based nanofibers," Materials Science and Engineering: C, vol. 33, no. 3,
pp. 1446–1454, Apr. 2013, https://doi.org/10.1016/j.msec.2012.12.066.
[22] A. Jongjareonrak, S. Benjakul, W. Visessanguan, T. Prodpran, and M.
Tanaka, "Characterization of edible films from skin gelatin of
brownstripe red snapper and bigeye snapper," Food Hydrocolloids, vol.
20, no. 4, pp. 492–501, Jun. 2006, https://doi.org/10.1016/
j.foodhyd.2005.04.007.
[23] M. Cofelice, F. Cuomo, and A. Chiralt, "Alginate Films Encapsulating
Lemongrass Essential Oil as Affected by Spray Calcium Application,"
Colloids and Interfaces, vol. 3, no. 3, Sep. 2019, Art. no. 58,
https://doi.org/10.3390/colloids3030058.
[24] Y. Peng and Y. Li, "Combined effects of two kinds of essential oils on
physical, mechanical and structural properties of chitosan films," Food
Hydrocolloids, vol. 36, pp. 287–293, May 2014, https://doi.org/10.1016/
j.foodhyd.2013.10.013.
Engineering, Technology & Applied Science Research Vol. 11, No. 4, 2021, 7489-7494 7494
www.etasr.com El Kolli & El Kolli: Preparation and Characterization of Gelatin-Based Films Cross-Linked by Two …
[25] S. Shojaee-Aliabadi et al., "Characterization of antioxidant-antimicrobial
κ-carrageenan films containing Satureja hortensis essential oil,"
International Journal of Biological Macromolecules, vol. 52, pp. 116–
124, Jan. 2013, https://doi.org/10.1016/j.ijbiomac.2012.08.026.
[26] Y.-H. Hong, G.-O. Lim, and K. B. Song, "Physical Properties of
Gelidium corneum–Gelatin Blend Films Containing Grapefruit Seed
Extract or Green Tea Extract and Its Application in the Packaging of
Pork Loins," Journal of Food Science, vol. 74, no. 1, pp. C6–C10, 2009,
https://doi.org/10.1111/j.1750-3841.2008.00987.x.
[27] S. Chaoui, D. Smail, A. Hellati, and D. Benachour, "Effect of Starch
Nanocrystals on the Properties of Low Density Polyethylene/
Thermoplastic Starch Blends," Engineering, Technology & Applied
Science Research, vol. 10, no. 4, pp. 5875–5881, Aug. 2020,
https://doi.org/10.48084/etasr.3608.