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

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