Linseed Mucilage and Chitosan composite films - 11th International ...

Linseed Mucilage and Chitosan composite films: Preparation, physical, mechanical and
microstructure properties
Laura Esther Latorre Salamanca a , Laura Eugenia Pérez Cabrera a , Gloria Cristina Díaz Nárvaez a , Liliana Raquel
Barba de Alba b
a Department of Food Technology, Universidad Autónoma de Aguascalientes, Aguascalientes, Mexico.
(leperez@correo.uaa.mx)
b Department of Agriculture, Universidad Autónoma de Aguascalientes, Aguascalientes, Mexico.
ABSTRACT
Films based on biopolymers can be used to reduce water vapour, oxygen, lipid, and flavour migration between
components of multi-component food products, and between food and the surroundings. Linseed mucilage
contain substantial amounts (5–8%) of soluble fibre mucilaginous material and it has a high water holding
capacity and shows similar functional properties to those of gum arabic, since this characteristic is its interest in
its application as a coating. The objective of the present work was to develop composite films based on linseed
mucilage polymer and chitosan, and to evaluate optical, barrier and microstructure properties of these films.
Films were prepared using chitosan (1%) and linseed mucilage in different ratios. The concentration linseed
mucilage polymer ranged from 2.0, 1.5 and 1.0% w/v. The optical properties such as transparency, opacity and
colour were measured. Water vapour transmission rate of the films was also investigated. Films were evaluated
for microstructure. Addition of linseed mucilage polymer in varied proportions to chitosan led to changes in
transparency and opacity of films. The water vapour transmission rate change significantly upon addition of
linseed mucilage polymer. Composite films obtained from linseed mucilage polymer and chitosan may reduce
environmental problems associated with synthetic packaging.
Keywords: linseed mucilage; chitosan; film; water vapour permeability; microestructure
INTRODUCTION
Shelf life of food is governed by its numerous interactions with the surroundings and can be extended using
proper packaging material. The deterioration of packaged foodstuffs largely depends on the transfers that may
occur between the internal environment of the packaged food and the external environment. Films based on
biopolymers can be used to reduce water vapour, oxygen, lipid, and flavour migration between components of
multi-component food products, and between food and the surroundings. The film properties depend on the type
of material used and the process conditions employed which in turn determine their applications [1]. Biological
materials used to prepare packaging material include polysaccharides, proteins, lipids and their derivatives.
Specifically, within polysaccharides, cellulose derivatives, chitosan, starch, alginate, carrageenan and pectin are
preferred because of their high film forming ability. Polymer blending is one of the useful methods to obtain new
materials with desired functional properties and there has been great scientific and commercial progress made in
the area of food applications [2].
Chitin and its deacetylated product, chitosan, have received much interest for their application in agriculture,
biomedicine, biotechnology and food industry due to their biocompatibility, biodegradability and bioactivity [3].
Due to its antimicrobial activity [4], chitosan film is a promising packaging material that can be included in the
active film category [5]. However, chitosan is expensive and functional properties of chitosan films can be
improved by combining it with other hydrocolloids [6]. Thus importance is attached to the research on the
combination of chitosan with other macromolecules [2].

Flaxseed gum is commercially feasible only as a by-product of the linseed oil industry therefore preparation
methods of gum are based on oil meal or oil meal cake [7]. Flaxseed gum is a heterogeneous polysaccharide
composed of xylose, arabinose, glucose, galactose, galacturonic acid, rhamnose and fucose [8]. Flaxseed gum is a
hydrocolloid with good water-holding capacities, owing to its marked swelling capacity and high viscosity in
aqueous solution [8]. Functionally, flaxseed gum resembles gum arabic more closely than the other common
gums, so that it has been suggested to replace gum arabic in emulsions [7]. Flaxseed gum also exhibits ‘‘weak
gel’’-like properties that can be used to replace most of the non-gelling gums for food and non-food applications
[9].
MATERIALS & METHODS
Mucilage was extracted from linseed in a proportion 1:5 with deionized water at 40°C for 1h and 1400 rpm.
Formulations, FA, FB and FC, were made by 100, 70 and 80 mL of mucilage and they were solubilized in
distilled water to complete 100 mL. Lactic acid was added at 0.5% (v/v) and agitated for 30 minutes, chitosan at
1% (w/v) and after 24 hours, glycerol at 0.3% (v/v). pH’s formulations (FA, FB and FC) were: 4.5, 4.3 and 4.4
and water activity: 0.9945, 0.9965 and 0.9970. Formulations were pasteurized and filtered. Each formulation was
poured in Petri dishes completing 20 g and dried in a stove at 40°C during 24 hours. Solids films were set with
silica gel for a day.
Optical properties
Each film specimen was cut into a rectangular piece, thickness was measured in three points of the films and
these were equilibrated at 50% RH for a day before placing them in a spectrophotometer test cell. Measurements
were performed using air as the reference. The light transmittance of the films was scanned from wavelength of
300 to 700nm using a GBC spectrophotometer. The measurement was done in triplicate and the average of three
spectra was calculated. The transparency at 600nm (T 600 ) was obtained from the following equation [10]:
T 600 =(log %T)/b (1)
where %T is percentage transmittance and b is the film thickness (mm). The opacity of the films was calculated
by the following equation according to the method described by [11]: Opacity = absorbance at 500nm × film
thickness
The color of the film was assessed using a colorimeter (Minolta, CR-400). A white standard color plate (L =
96.9379, a = -0.1121, b = 2.3085) for the instrument calibration was used as a background for color
measurements of the films. The system provides the values of three color components; L* (black-white
component, luminosity), and the chromaticness coordinates, a* (+red to −green component) and b* (+yellow to
−blue component). Hunter L*, a*, and b* values were averaged from six readings across for each film, and then
the total color difference (∆E*) was calculated using the following equation [12]: ∆E* = [(∆L*) 2 + (∆a*) 2 +
(∆b*) 2 ] 0.5 where ∆L*=L*−L 0 *, ∆a*=a*−a 0 *, ∆b*=b*−b 0 *, where L 0 *, a 0 * and b 0 * are color values for control
films and L*, a* and b* are color values for FA, FB and FC films containing chitosan. Films were equilibrated at
75% HR.
A modification of the ASTM E96-95 gravimetric method for measuring water vapour permeability (WVP) of
flexible films was employed, using Payne permeability cups (Elcometer SPRL). Deionised water was used inside
the testing cup to achieve 100% relative humidity on one side of the film through a circular opening of 3.5 cm in
diameter. Once the films were placed in the cups. The environment within the cabinets was held at constant RH
using over-saturated NaCl solution. The cabinets were placed at controlled temperature of 20ºC. During WVP
testing, the side of the film in contact with the PTFE plate was placed in contact with that part of the test cup
having the highest relative humidity. The cups were weighed periodically after steady state was reached using an
analytical balance (±0.0001 g). Water vapour permeability was determined from the slope obtained from the
regression analysis of weight loss data as a function of time, once the steady state was reached. The method

proposed by [13] to correct the effect of concentration gradients established in the stagnant air gap inside the cup
was used.
Microstructural analysis of cross-sections of the dry films (previously conditioned in desiccators with P 2 O 5 for at
least 15 days) was carried out using SEM technique in a JEOLJFM-59LV electron microscope. Pieces of 6 x 1
mm were cut from films and mounted in copper stubs. Samples were gold coated and observed using an
accelerating voltage of 10 kV.
RESULTS & DISCUSSION
Homogeneous, thin and flexible films were obtained from linseed mucilage and chitosan mixture solutions. Films
formed could be easily removed from the petri dishes and had an average thickness of 0.05mm. The films were
free standing as they did not roll over or break. Visually, all the films were colorless and translucent.
Films made from linseed mucilage and chitosan transmitted 40% (Figure 1.) of incident visible light. All films
showed similar transmittance. Highest transmittance in visible region was found for FA films containing 1%
chitosan (w/v) and 100 mL of linseed mucilage.
Figure 1. Transmittance of films as affected by the different
formulation. FA, FB and FC
Addition of linseed mucilage and chitosan films also led to changes in transparency and opacity of films (Table
1). It can be seen that, opacity. The films did not significantly differences for transparency, the interaction with
different concentrate of linseed mucilage polymer (FA, FB, & FC), chitosan (1% for all formulations) and water
molecules not modifies the refractive index of thus affecting the film transparency. The opacities of films varied
with linseed mucilage polymer cocentration. FC films with 70% (v/v) of mucilage were most opaque, followed
by FB (Table 2). These findings are important since film transparency or opacity are critical properties in various
film applications, particularly if the film will be used as a surface food coating or for improving product
appearance.
Table 1. Transparency and opacity of FA, FB and, FC films
FILM SAMPLE TRANSPARENCY OPACITY
FA 32.02 ± 4.69 1.12x10 -2 ± 2.59x10 -3
FB 32.43 ± 3.79 1.16x10 -2 ± 2.53x10 -3
FC 33.66 ± 4.81 8.22x10 -3 ± 1.87x10 -3
Color attributes are of prime importance because they directly influence consumer acceptability. The results of
evaluation of color of the linseed mucilage-chitosan based films are shown in Figure 2 and Table 2. It can be seen
that there was no significant change in L* value for all films, whereas b* value increased significantly upon

addition of less polymer (FC), these findings suggest a net increase in yellow-brown color due to incorporation of
water level. Negative values of a* suggest the films had a green tint.
Color
20.00
18.00
16.00
14.00
b*
12.00
10.00
8.00
FA
FB
FC
Control
6.00
4.00
2.00
0.00
-3.00 -2.00 -1.00 0.00
a*
Figure 2. Color parameters of FA, FB and FC films.
The color index (∆E*) (Table 2) is influenced by L*, a* and b* values and could describe how far apart two
colors are in the color space. It was seen that ∆E* values changed upon addition of linseed mucilage polymer due
to alterations in b* and a* values of film.
Table 2. Color parameters of FA, FB and FC films
Film sample L* a* b* ∆E
FA 97.01±1.02 (-)1.54±0.49 10.55±3.22 5.06±1.64
FB 97.52±0.93 (-)1.71±0.28 9.88±2.33 5.06±0.81
FC 96.08±1.26 (-)2.20±0.51 15.18±3.89 7.53±2.47
The water vapor transmission rate of films plays an important role in deteriorative reactions of food; therefore, it
is the most extensively studied property of films. Water vapor permeability is assumed to be independent of the
water vapor pressure gradient applied across the films. However, hydrophilic materials, such as polysaccharide
films, deviate from this ideal behavior due to interactions of permeating water molecules with polar groups in the
film’s structure [14]. The WVTR values showed in Table 3. change significantly with varying concentrations of
linseed mucilage polymer. In order hand the chitosan films have relatively poor water vapor barrier
characteristics, which result from their hydrophilicity. Glycerol, through its plasticizing action, changes the
polymer network creating mobile regions with larger interchain distances, promoting water clustering
by competing with water at active sites of the polymer matrix and the formation of micro cavities in the polymer
network structure. Water sorption by biopolymers often results in swelling and conformational changes. The
absorbed water plasticizes the film matrix, leading to a less dense structure where chain ends are more mobile,
thus increasing transmission rate [15].
Table 3. WVT of films
Film WVT (g Pa -1 s -1 m -1 ) x 10 -10

FA 18.79±0.382
FB 19.80±0.517
FC 15.59±0.322
SEM micrographs of the cross-sections of the films, which show not differences, a continuous structure was
observed for all films. The films’ microstructure is affected by the organization of the different components of the
film and by how they interact during the drying process. Their microstructure provides information about the
arrangement of the ingredients of the film-forming dispersions and allows us a better understanding of water
vapour transmission mechanisms and mechanical properties. Fig. 3 shows the cross-sections of linseed mucilagechitosan
films where the differing formutations gave rise to no observed differences. In FC film lipid particles (or
their voids) that are embedded in the polymer matrix are observed. These particles (or voids) interrupt the
chitosan matrix producing discontinuities in the polymer network.
FA
FB
FC
CONCLUSION
Figure 3. SEM micrographs of the cross-sections of the films
Composite films obtained from linseed mucilage-chitosan based may reduce environmental problems associated
with synthetic packaging. Further studies would be required to determine the use of these films in commercial
food systems.
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