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Drying Technology
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Influence of Drying Techniques on the Characteristics
of Chitosan and the Quality of Biopolymer Films
Guilherme Luiz Dotto
a
, Vanderlei Constantino de Souza
a
, Jaqueline Motta de Moura
a
,
Catarina Motta de Moura
a
& Luiz Antonio de Almeida Pinto
a
a
Unit Operation Laboratory, School of Chemistry and Food, Federal University of Rio
Grande, Rio Grande, RS, Brazil
Available online: 03 Oct 2011
To cite this article: Guilherme Luiz Dotto, Vanderlei Constantino de Souza, Jaqueline Motta de Moura, Catarina Motta de
Moura & Luiz Antonio de Almeida Pinto (2011): Influence of Drying Techniques on the Characteristics of Chitosan and the
Quality of Biopolymer Films, Drying Technology, 29:15, 1784-1791
To link to this article: http://dx.doi.org/10.1080/07373937.2011.602812
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Influence of Drying Techniques on the Characteristics of
Chitosan and the Quality of Biopolymer Films
Guilherme Luiz Dotto, Vanderlei Constantino de Souza, Jaqueline Motta de Moura,
Catarina Motta de Moura, and Luiz Antonio de Almeida Pinto
Unit Operation Laboratory, School of Chemistry and Food, Federal University of Rio Grande,
Rio Grande, RS, Brazil
In this work, spouted bed and tray-drying techniques were
employed at different drying air temperatures to produce dried
chitosan, and the chitosan powder was used to produce biofilms.
The products obtained from each drying technique were compared
in relation to quality aspects (molecular weight, lightness, and hue
angle). The results found for chitosan in spouted bed drying
(90
C) showed lower alteration and best quality aspects in relation
to the chitosan powder. However, in tray drying under the best con-
dition (60
C) the chitosan molecular weight increased about 50% in
relation to the initial value and browning was observed. The biofilms
produced from chitosan dried in the spouted bed showed the best
mechanical properties (tensile strength of 42 MPa and elongation
of 29%) and lower water vapor permeability (3.95 g mm m
2
kPa
1
day
1
).
Keywords Drying technique; Molecular weight; Spouted bed;
Water vapor permeability
INTRODUCTION
Chitin is usually isolated from the exoskeletons of crus-
taceans, more particularly from shrimp and crabs.
[1]
Chitosan is obtained from partially N-acetylated chitin
by alkaline
D-N-acetylation, a family of linear binary
copolymers of (1 ! 4)-linked 2-acetoamido-2-deoxy-b-
D-
glucopyranose (GlcNAc; A-unit) and 2-amino-2-deoxy-b-
D-glucopyranose (GlcN; D-unit), where the A- and D-uni ts
have been shown to be randomly distributed along the
chains.
[2,3]
Chitosan has characteristics of biocompatibility,
nontoxicity, antibacterial and antifungal propert ies, and
wide applicability; for example, in the food industry, agri-
culture, medicine, wastewater treatment, and for use in
edible films.
[4]
The important parameters regarding the quality of chit-
osan and its application are the degree of deacetylation,
molecular weight, and color determined from the methods
used in the production and drying process.
[5,6]
Chitosan
produced by alkali deacetylation usually occurs only par-
tially and is necessary in the purificat ion process, where it
is obtained in paste form,
[7]
making it necessary for
dehydration, stora ge, marketing, volume decrease, and
preservation of its characteristics.
[8]
Generally, chitosan is dried in a spray dryer.
[9,10]
Some
researchers have presented alternatives to spray drying,
such as sun drying,
[6]
tray drying,
[8]
oven drying, and infra-
red drying.
[11]
The study of new drying alternatives, such
as spouted bed drying, in order to obtain chitosan
with high quality and appropriate to produce edible films
with good characteristics is desirable. In a spouted
bed, some charact eristics contribute to the drying of
heat-sensitive materials, such as good solids mixing
coupled with satisfactory gas–particle contact and short
residence time.
[12]
Tray dryers can be employed to dry heat-sensitive mate-
rials under controlled conditions and are the simplest ba tch
dryers.
[13]
In spouted bed and tray dryers, the product
properties and dryer performance are dependent on the
operating conditions and the system confi guration.
[13,14]
The main problem in chitosan drying is polymerization,
so it is necessary to control the different parameters that
influence its characteristics, con sequently modifying its
chemical–physical properties. However, the different
drying methods and conditions affect the properties and
functionalities of chitosan and, consequently, its
application.
[6,8,9,11]
According to Vargas et al.
[15]
good quality edible film
needs to have low water vapor permeability and good
mechanical properties, preventing loss of moisture or water
absorption by the food matrix, loss of odor, and preventing
solute transport. The present study aimed at investigating
the effe cts of drying techniques (spouted bed drying and
tray drying) and temperature on the quality aspects of chit-
osan. The dried chitosan obtained from each technique was
used for production of biofilms, and mechanical properties
(water vapor permeability, tensile strength, and elongation)
of the biofilms were evaluated.
Correspondence: Luiz Antonio de Almeida Pinto, FURG, 475
Engenheiro Alfredo Huch Street, 96201-900, Rio Grande, RS,
Brazil; E-mail: dqmpinto@furg.br
Drying Technology, 29: 1784–1791, 2011
Copyright # 2011 Taylor & Francis Group, LLC
ISSN: 0737-3937 print=1532-2300 online
DOI: 10.1080/07373937.2011.602812
1784
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MATERIAL AND METHODS
Raw Material
Chitin was obtained from shrimp (Farfantepenaeus
brasiliensis) wastes, and shrimp wastes were submitted to
demineralization, deproteinization, and deodorization.
Chitosan was obtained from alkaline deacetylation of
chitin with sodium hydroxide solution (421 g L
1
)at
130 2
C under constant agitation at 50 rpm.
[5]
Chitosan
was purified through dissolution in dilute acetic acid (1%
v=v). The solutions were then centrifuged at 6,650 g in
a centrifuge (model Sigma 6–15, D-37520, Osterode,
Germany) for 30 min to remove insoluble material. Total
precipitation of chitosan occurred by addition of sodium
hydroxide until pH 12.5, followed by neutralization until
pH 7.0. The chitosan suspension was centrifuged for separ-
ation of the supernatant.
[7]
The purified chitosan in paste
form was characterized according to ashes, moisture
content,
[16]
color,
[6]
molecular weight,
[17]
and degree of
deacetylation.
[3,18]
Spouted Bed Drying
Drying experiments were carried out in a conventional
spouted bed (CSB) dryer consisting of a stainless steel cyl-
indrical cone column with cones of glass. The conical base
with an enclosed angle of 60
had a height of 0.15 m and
the cylindrical column had a diameter of 0.175 m and
height of 0.75 m. The dryer had a ratio of 1:6 between
the column diameter and the air inlet diameter. The air
was supplied to the system through a radial blower
(NBR7094, Weg, Sa˜o Paulo, Brazil) with power of 6 kW
and maximum outflow of 0.1 m
3
s
1
, and it was heated in
a system composed of three electric resistance heaters of
800 W each. Temperature control of the exit air stream
was carried out by a temperature controller (IDO2B,
Contemp, Sa˜o Caetanedo Sul, Brazil). The drying air velo-
city was measured by an orifice meter and the pressure
drop through the bed by a U-tube manometer. The tem-
perature readings were carried out using K-type copper-
constantan thermocouples. The dried chitosan was col-
lected in a lapple cyclone. The inert particles used in the
spouted bed were polyethylene pellets (diam eter 0.003 m,
sphericity 0.7, density 960 kg m
3
) with particle loading
of 2.5 kg.
[19]
Drying experiments were carried out as follows. In order
to guarantee spouted bed stability in all experiments, press-
ure drop velocity curves (figures not shown) were
developed to determine the minimum spouting air drying
velocity. The pressure drop velocity curves obtained were
similar to the generic pressure drop velocity curve shown
in Mathur and Epstein.
[20]
The minimum spouting veloci-
ties obtained in this work ranged from 0.62 to 0.66 m s
1
.
The air circulation rate used in experiments was 100%
higher than the minimum spouting velocity.
[20]
When a
steady velocity regime was established, the chitosan paste
was fed into the cell (0.18 kg
paste
kg
1
inert
h
1
according to
preliminary tests) through atomization with a peristaltic
pump and air comp ressed at 10
5
Pa. Dried chitosan was
transported pneumatically by the drying air stream and
collected in a cyclone. The dried product was collected
for analysis. Inlet air drying temperatures of 90, 100, and
110
C were used in order to verify the temperature effect.
All experiments were carried out in three replicates.
The spouted bed dryer performance was evaluated
through determination of mass accumulation rate in the
bed (Ac) and product recovery rate (R)
[19]
using Eqs. (1)
and (2):
Ac ¼
ðm
FB
m
IB
Þð1 X
FB
Þ
m
I
100 ð1Þ
R ¼
m
c
ð1 X
F
Þ
m
I
100 ð2Þ
where m
FB
is total bed mass at the end of the operation (g),
m
IB
is total bed mass before the operation (g), m
I
is total
solid mass introduced into the dryer (g),
X
FB
is the final
moisture content of powder in the bed (% wb), R is the pro-
duct recovery rate (%), m
C
is the colle cted mass in the cyc-
lone (g), and
X
F
is the final moisture content of the powder
product (% wb).
Tray Drying
Chitosan in paste form was dried in a discontinuous tray
dryer with perforated recta ngular trays (0.25 m height and
0.2 m width) and a perforated screen (mesh 10) in constant
air conditions. The air temperature was measured by
K-type copper-constantan thermocouples and air velocity
was measured using an anemometer (TFA, Windmesser
MIT, Sanitz, Germany) with precision of 0.1 m s
1
.An
electronic scale (AS2000C, Marte, Sa˜o Paulo, Brazil) with
0.01 g precision was used to measure sample weight. The
sample thicknesses were measured with a digital caliper
(CD-6CS, Mitutoyo, New Hudson, NH) with 0.0001 m
precision. The air relative humidity was measured with a
thermohygrometer (3310–00, Cole Parmer, Vernon Hills,
IL) with 0.1% precision.
Drying experiments were carried out with a material
load in the tray of 4 kg m
2
; the air drying velocity was
1.5 m s
1
and absolute humidity was approximately
0.010 kg kg
1
.
[8]
The air temperatures used in order to ver-
ify the temperature effect were 60, 70, and 80
C. Samples
were dried until they reached the commercial moisture
content (lower than 10% wb). The dried samples were
ground by using a mill (Wiley Mill Standard model no. 3,
Swedesboro, NJ) and sieved until the discrete particle size
ranged from 0.26 0.02 mm. All experiments were carried
out in replicate.
INFLUENCE OF DRYING ON CHITOSAN
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Chitosan Powder Characterization
The moisture content of dried samples was determined
using the standard vacuum oven method.
[16]
Grain size
analysis of the spouted bed–dried chitosan was carried
out in a standardized mesh screen. The average diameter
was calculated as the Sauter mean diameter, as shown in
Eq. (3)
[21]
:
D
sauter
¼
1
P
DX
i
D
mi
ð3Þ
where D
Sauter
is the Sauter mean diameter (m), D
mi
is the
arithmetic average diameter between two screens (m), and
X
i
is weight fraction of particle size D
mi
(%).
The chitosan color was determined using the Minolta
system (CR-300, Minolta Corporation, Osaka, Japan).
Color was measured from three-dimensional color diagram
(L
,a
,b
), and numerical values (a
,b
) were converted in
hue angle a ccording Eq. (4)
[6]
:
H
ab
¼ tan
1
b
a
ð4Þ
where H
ab
is the hue angle (
).
The degree of chitosan deacetylation (Eq. (5)) was deter-
mined through Fourier transform infrared (FTIR) analy-
sis. Chitosan powder was macerated and submitted to
spectroscopic determination in the region of the infrared
ray (210045, Prestige, Kyoto, Japan), using the diffuse
reflectance technique in potassium bromide.
[18]
%DD ¼ 87:8 3ðA
C¼O
=A
OH
Þ½ð5Þ
where A
C¼O
is the absorbance of the C¼O group, A
-OH
is
the absorbance of the -OH group, and %DD is the degree
of deacetylation (%).
[18]
The chitosan molecular weight was determined by visco-
simetric method (Cannon-Fenske capillary viscometer,
model GMBH – D65719, Schott Gerate, Mainz,
Germany). Reduced viscosity was determined by the
Huggins equation, and converted to molecular weight
using the Mark-Houwink-Sakurada equation (Eq. (6)).
[17]
g ¼ KM
a
w
ð6Þ
where g is intrinsic viscosity (mL g
1
), M
w
is molecular
weight (Da), K ¼ 1.81 10
3
mL g
1
,anda ¼ 0.93.
[5]
The chitosan surface was characterized by scanning elec-
tronic microscopy (SEM; JEOL, JSM-6060, Tokyo,
Japan).
[9]
SEM is one of the most widely used surface
diagnostic tools.
Biofilms Preparation and Characterization
The chitosan powder obtained in the best condition from
spouted bed and tray dryers was used to produce biofilm.
One gram (db) of chitosan powder was dissolved in
0.1 mol L
1
acetic acid solution using moderate magnetic
stirring (MAG-01H, Marte) at room temperature for
120 min. Then the film-forming solution was centrifuged
(Centrifugal Baby I, model 206 BL, Fanem, Sa˜o Paulo,
Brazil) at 5,000 g for 15 min. An appropriate volume
(50 mL) of the film-forming solution was poured onto a level
Plexiglas plate in order to keep the total amount of polymer
deposited constant. The films were obtained by solvent
evaporation in an oven with air circulation at 40 2
Cfor
about 24 h. Finally, the film samples were removed from
plates and conditioned in desiccators with relative humidity
of 55% at 25 1
C for at least 48 h prior to testing. The
thickness of the film samples was measured using a digital
micrometer (model INSIZE IP54, Series 3103–25,
Sa˜o Paulo, Brazil) of 0.0010 mm resolution. Mean thickness
was calculated from 10 measurements taken at different
locations on film sample, according to Ferreira et al.
[22]
The biofilm was characterized in relation to water vapor
permeability,
[23]
mechanical properties (tensile strength and
percentage of elongation),
[24]
and SEM.
[9]
The water vapor
permeability was measured under controlled conditions
(temperature 25
C, relative humidity 75%, pressure vari-
ation 3.16 kPa) using a desiccator. Mechanical properties
were measured using a Texture Analyzer TA-XT-2i (Stable
Micro Systems, Surrey, UK) with a 50 N load cell equipped
with tensile grips (A=TG model). The testing speed for
texture analysis was 2 mm s
1
. Sample biofilms were cut
into 25-mm (width) 100-mm (length) strips.
[24]
Statistical Analysis
Tukey’s test was used to determine significant differ-
ences (p 0.05)
[25]
between chitosan obtained through the
different drying techniques in relation to quality aspects
(molecular weight, lightness, and hue angle). Also, biofilms
were co mpared in relation to water vapor permeability and
mechanical properties (tensile strength and percentage of
elongation).
RESULTS AND DISCUSSION
Raw Material Characterization
The chitosan obtained in paste form from shrimp wastes
had a moisture content of 94 1% (wb), ash content of
0.10 0.01%, molecular weight value of 140 5 kDa, light-
ness value of 81.0 1.2, hue angle value of 62.5 1.2, and
%DD value of 85 1%.
Spouted Bed Drying
With regard to process characteristics and chitosan
quality aspects in spouted bed drying (Table 1), it was
1786
DOTTO ET AL.
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observed that in all inlet air drying temperatures, high
values of product recovery and low values of accumulated
mass were reached. In addition, Table 1 shows that the
increase in inlet air drying temperature led to an increase
in outlet air drying temperature. According to Benali and
Amazouz,
[26]
outlet air drying temperature is a key para-
meter in order to guarantee product quality, and tempera-
tures below 75
C are desirable. Another important
parameter in order to guarantee product quality is the resi-
dence time.
[12]
Chitosan paste residence time in spouted bed
drying was around 15 min. This time was determined when
the outlet air temperature reached a constant value. Similar
values were reported by Peixoto et al.,
[27]
who found a
range of 10–17 min for the spouted bed drying of organic
pastes, without modification of product characteristics.
It can be observed in Table 1 that the commer cial moist-
ure content (less than 10% wb) of chitosan was reached in
all experiments. The chitosan particle size was not
influenced by temperature (p > 0.05). The hue angle of
chitosan was not modified by the different drying con-
ditions (p > 0.05), indicating a faint yellow coloration.
The increase in inlet air temperature from 90 to 110
C
led to an increase of 70% in chitosan molecular weight
and a decrease in chitosan lightness (Table 1). This beha-
vior can be explained because the temperature increase
causes more water removal and closer packing of chitosan
polymeric chains, increasing the molecular weight of the
biopolymer and consequently decreas ing the lightness. In
addition, an increase in inlet air temperature caused an
increase in outlet air temperature; because chitosan is a
carbohydrate, polymerizat ion and browning occurred. A
similar effect was obtained by Srinivasa et al.
[11]
in the con-
vective drying of chitosan at various temperatures. For
spouted bed drying of okara, Wachiraphansakul and
Devahastin
[28]
showed that a temperature increase from
90 to 130
C caused a decreas e in urease index.
TABLE 2
Process characteristics and chitosan quality aspects in tray drying
Air drying temperature (
C)
Characteristics 60 70 80
Process characteristics Total drying time (min) 145 4
a
105 3
b
85 3
c
Production capacity (kg h
1
m
2
) 1.6 0.1
a
2.3 0.2
b
2.8 0.2
c
Chitosan quality aspects Molecular weight (kDa) 210 4
a
248 2
b
322 4
c
a
5.4 0.1
a
5.3 0.2
a
5.5 0.2
a
b
4.8 0.1
a
5.0 0.2
a
4.9 0.2
a
Hue angle (
) 41.5 1.0
a
42.1 1.0
a
41.7 1.0
a
Lightness 63.7 0.3
a
50.5 0.5
b
20.7 0.5
c
Moisture content (% wb) 8.5 0.5
a
8.7 0.5
a
8.6 0.5
a
Mean values standard error. Same letters in same line indicate p > 0.05. Different letters in same line indicate p < 0.05.
TABLE 1
Process characteristics and chitosan quality aspects in spouted bed drying
Inlet air drying temperature (
C)
Characteristics 90 100 110
Process characteristics Product recovery (%) 95 3
a
93 4
a
94 2
a
Mass accumulated (%) 3 1
a
4 1
a
4 1
a
Outlet air temperature (
C) 72 1
a
85 1
b
94 1
c
Chitosan quality aspects Molecular weight (kDa) 142 3
a
200 2
b
245 2
c
a
1.2 0.2
a
1.3 0.1
a
1.5 0.3
a
b
2.2 0.2
a
2.8 0.5
a
2.4 0.3
a
Hue angle (
)61.8 2.0
a
62.1 1.8
a
61.5 1.5
a
Lightness 80.5 0.3
a
60.5 0.3
b
41.3 0.2
c
Moisture content (% w.b.) 7.5 0.5
a
7.2 0.7
a
7.4 0.5
a
Particle size (mm) 100 20
a
100 20
a
100 20
a
Mean values standard error. Same letters in same line indicate p > 0.05. Different letters in same line indicate p < 0.05.
INFLUENCE OF DRYING ON CHITOSAN
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The best inlet air drying temperature in the spouted bed
was 90
C. In this condition, modifications in chitos an mol-
ecular weight and lightness were not found, and the
commercial moisture content was obtained (10% wet
basis).
Tray Drying
Table 2 shows the process characteristics and chitosan
quality aspects in tray drying. It can be observed in
Table 2 that the temperature increase caused a decrease
in total drying time and consequently an increase in pro-
duction capacity. In tray drying, the commercial moisture
content was reached in all experiments; in addition, the
drying did not modify the degree of chitosan deacetylation
which remained at 85 1%. The hue angle value of chito-
san paste (62.5 1.2) decreased for chitosan dried at all
temperatures (41.5 2.0), and the product showed a dark
yellow coloration. Table 2 shows that the increase in air
temperature led to an increase in molecular weight and,
consequently, a decrease in chitosan lightness. This
occurred because chitosan is a heat-sensitive material, so
the temperature increase causes a decrease in its quality
aspects. In tray drying of tomato pulp at 50, 60, and
70
C, Chawla et al.
[29]
verified that the lycopene content
decreased with an increase in temperature. The quality of
dried potato cubes was evaluated by Iciek and Krysiak.
[30]
They found that a temperature increase from 60 to 90
C
caused a decrease in potato quality aspects. In this work
the best condition for tray drying was at a air drying
temperature of 60
C.
Chitosan Powder Comparison
The chitosan powder obtained in the best cond ition for
each drying technique was compared according to the final
moisture content, molecular weight, and color (lightness
and hue angle).
Table 3 shows that the final moisture content was not
significantly different (p > 0.05), and the commercial
values were reached using both drying techniques. In
spouted bed drying, chitosan molecular weight, lightness,
and hue angle were not modified in relation to initial
value (p > 0.05), indicating that this process preserves chit-
osan. This occurred because a short residence time was
observed (15 min), and good conditions for heat and mass
transfer in the spouted bed were maintained.
[31]
On the
other hand, in tray drying, chitosan molecular weight
increased about 50% compared with the initial value,
TABLE 3
Comparison of chitosan products in spouted bed and tray drying
Characteristics Chitosan paste Chitosan dried in a spouted bed Chitosan dried in a tray dryer
Final moisture content (%) — 7.5 0.5
a
8.5 0.5
a
Molecular weight (kDa) 140 5
a
142 3
a
210 4
b
a
1.1 0.2
a
1.2 0.2
a
5.4 0.1
b
b
2.1 0.2
a
2.2 0.2
a
4.8 0.1
b
Lightness 81.0 1.2
a
80.5 0.3
a
63.7 0.3
b
Hue angle (
) 62.5 1.2
a
61.8 2.0
a
41.5 1.0
b
Mean values standard error. Same letters in same line indicate p > 0.05. Different letters in same line indicate p < 0.05.
FIG. 1. SEM photographs: (a) powder chitosan in spouted bed drying
and (b) powder chitosan in tray drying.
1788 DOTTO ET AL.
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and a decrease in lightness and hue angle was observed.
This indicates the polymerization and browning of chito-
san, decreasing the final product’s quality. This likely
occurred because the residence time in tray drying
(145 min) was about nine times greater in relation to the
residence time in a spouted bed. The residence time is
important because it determines the relation between
material degradation and drying conditions.
[13]
In spouted
bed drying of paddy, Madhiyanon et al.
[32]
showed
that although the inlet air temperature (130–1 60
C) was
high, no significant changes in the whiteness were
observed, because the grain was exposed to the hot air
in the spouting region within a very short time (from
1.5 to 10.2 min).
The surface and physical structure of chitosan dried
using both techniques were evaluated according to SEM
photographs (Fig. 1). In Fig. 1a it can be observed that
spouted bed–dried chitosan has a rough surface area and
porous internal structure with irregular pores; however,
in tray-dried chitosan (Fig. 1b), a rigid, compact, and non-
porous surface can be observed. The resul ts showed that
the spouted bed preserves chitosan characteristics, leading
to a high-quality product with applications in food a nd
pharmaceutical areas.
[4]
On the other hand, chitosan
obtained by tray drying was of lower quality and is
recommended for industrial application.
[33]
Biofilms Comparison
The SEM images of chitosan films are shown in Fig. 2.
It can be observed in Figs. 2a and 2b that the biofilm
obtained from chitosan dried in a spouted bed has a
homogeneous and continuous surface. On the other hand,
the biofilm obtained from chitosan dried in a tray dryer
has a heterogeneous and irregular surface (Figs. 2c and
2d). According to Yang et al.
[34]
the neat chitosan
film must exhibit a smooth and compact surface to obtain
a biofilm with characteristics required for specific
application.
FIG. 2. SEM photographs: (a), (b) biofilm obtained from chitosan produced in spouted bed drying and (c), (d) biofilm obtained from chitosan
produced in tray drying.
INFLUENCE OF DRYING ON CHITOSAN
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The chitosan films obtained from chitosan dried in
spouted bed and tray dryers were compared in relation to
water vapor permeability (WVP), tensile strength, percent-
age of elongation, and SEM micrographs. These results are
shown in Table 4.
Table 4 shows that the best mechanical properties and
lower WVP were observed in the biofilm obtained from
chitosan dried in a spouted bed due to the smooth and con-
tinuous surface obtained using this method (Figs. 2a and
2b). These characteristics cause a decrease in the preferen-
tial paths and make water vapor diffusion difficult, conse-
quently decreasing WVP. In addition, chitosan dried in a
spouted bed has an internal porous structure and lower
molecular weight in relation to chitosan dried in a tray
dryer, facilitating its solubilization. According to Bout-
room and Chinnan,
[35]
an increase in molecular weight pro-
vides changes in edible film hydrophilicity (increased
molecular weight causes a decrease in chitosan solub ility
and, consequently, the film hydrophilicity is decreased)
and has a negative impact on WVP and mechanical
properties of dried chitosan.
CONCLUSION
In this research, spouted bed and tray drying of chitosan
were studied at different temperatures. The results showed
that in a spouted bed, the best inlet air drying temperature
was 90
C. In this condition, the color and molecular weight
of dried chitosan were not significantly different (p 0.05)
in relation to chitosan paste, and the commercial moisture
content was obtained. In tray dry ing, the best air tempera-
ture was 60
C; however, in this condition, the molecular
weight increased about 50% compared to chitosan paste
and browning was observed.
The biofilms produced from chitosan dried in a
spouted bed presented the best mechanical properties
(tensile strength of 42 MPa an d elongation of 29%)
and lower water vapor permeability (3.95 g mm m
2
kPa
1
day
1
) in relation to biofilms produced from chito-
san dried in a tray dryer (tensile strength (TS) ¼ 23 MPa,
elongation (E) ¼ 14%, WVP ¼ 6.83 g mm m
2
kPa
1
day
1
).
Thus, chitosan obtained from spouted bed drying was more
appropriate for producing biofilms.
NOMENCLATURE
A
C
Accumulation rate in the bed (%)
A
C¼O
Amide band absorbance
A
-OH
Hydroxyl band absorbance
a Redness
b Yellowness
%DD Degree of chitosan deacetylation (%)
D
mi
Arithmetic average diameter between two screens
(mm)
D
sauter
Sauter mean diameter of (mm)
H
ab
Hue angle (
)
K Constant for chitosan in system of acetic acid=
sodium chloride at 25
C
L Lightness
M
W
Chitosan molecular weight (Da)
m
c
Collected mass in the cyclone (g)
m
FB
Total bed mass at the end of the operation (g)
m
i
Total solid mass introduced into the dryer (g)
m
iB
Total bed mass before the operation (g)
R Product recovery rate (%)
X
F
Final moisture content of powder (% wb)
X
FB
Final moisture content of powder in the bed
(% wb)
DX
i
Weight fraction of particles size D
mi
(%)
Greek Symbols
a Constant for chitosan in system of acetic acid=
sodium chloride at 25
C
g Intrinsic viscosity (m L g
1
)
ACKNOWLEDGMENTS
The authors than k CAPES (Brazilian Agency for
Improvement of Graduate Personnel) and CNPq (the
National Council of Science and Technological
Development) for the financial support.
TABLE 4
Chitosan film comparison
Characteristics
Film from chitosan dried
in a spouted bed
Film from chitosan dried
in a tray dryer
Water vapor permeability
(g mm m
2
kPa
1
day
1
)
3.95 0.05
a
6.83 0.05
b
Tensile strength (MPa) 42 1
a
23 1
b
Elongation (%) 29 1
a
14 1
b
Mean values standard error. Same letters in same line indicate p > 0.05. Different letters in same line indi-
cate p < 0.05.
1790 DOTTO ET AL.
Downloaded by [Luiz Pinto] at 16:19 03 October 2011
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