Physicochemical, antimicrobial, and cytotoxic characteristics of a chitosan film cross-linked by a naturally occurring cross-linking agent, aglycone geniposidic acid

Article abstract of DOI:10.1021/jf0529868

The purpose of this study was to evaluate the characteristics of a chitosan film cross-linked by a naturally occurring compound, aglycone geniposidic acid (aGSA). This newly developed aGSA-cross-linked chitosan film may be used as an edible film. The chitosan film without cross-linking (fresh) and the glutaraldehyde-cross-linked chitosan film were used as controls. The characteristics of test chitosan films evaluated were their degree of cross-linking, swelling ratio, mechanical properties, water vapor permeability, antimicrobial capability, cytotoxicity, and enzymatic degradability. It was found that cross-linking of chitosan films by aGSA (at a concentration up to 0.8 mM) significantly increased its ultimate tensile strength but reduced its strain at fracture and swelling ratio. There was no significant difference in the antimicrobial capability between the cross-linked chitosan films and their fresh counterpart. However, the aGSA-cross-linked chitosan film had a lower cytotoxicity, a slower degradation rate, and a relatively lower water vapor permeability as compared to the glutaraldehyde-cross-linked film. These results suggested that the aGSA-cross-linked chitosan film may be a promising material as an edible film.

Full text of DOI:10.1021/jf0529868

3290 J. Agric. Food Chem. 2006, 54, 3290−3296
Physicochemical, Antimicrobial, and Cytotoxic Characteristics
of a Chitosan Film Cross-Linked by a Naturally Occurring
Cross-Linking Agent, Aglycone Geniposidic Acid
FWU-LONG MI,† CHIN-TSUNG HUANG,‡ HSIANG-FA LIANG,‡ MEI-CHIN CHEN,‡
YA-LING CHIU,‡ CHUN-HUNG CHEN,‡ AND HSING-WEN SUNG*,‡
Applied Chemistry Division, Department of Applied Science, Chinese Naval Academy, Kaohsiung,
and Department of Chemical Engineering, National Tsing Hua University,
Hsinchu, Taiwan, Republic of China
The purpose of this study was to evaluate the characteristics of a chitosan film cross-linked by a
naturally occurring compound, aglycone geniposidic acid (aGSA). This newly developed aGSA-cross-
linked chitosan film may be used as an edible film. The chitosan film without cross-linking (fresh) and
the glutaraldehyde-cross-linked chitosan film were used as controls. The characteristics of test chitosan
films evaluated were their degree of cross-linking, swelling ratio, mechanical properties, water vapor
permeability, antimicrobial capability, cytotoxicity, and enzymatic degradability. It was found that cross-
linking of chitosan films by aGSA (at a concentration up to 0.8 mM) significantly increased its ultimate
tensile strength but reduced its strain at fracture and swelling ratio. There was no significant difference
in the antimicrobial capability between the cross-linked chitosan films and their fresh counterpart.
However, the aGSA-cross-linked chitosan film had a lower cytotoxicity, a slower degradation rate,
and a relatively lower water vapor permeability as compared to the glutaraldehyde-cross-linked film.
These results suggested that the aGSA-cross-linked chitosan film may be a promising material as
an edible film.
KEYWORDS: Chitosan; glutaraldehyde; aglycone geniposidic acid; edible film
INTRODUCTION
In this study, a naturally occurring cross-linking agent,
aglycone geniposidic acid (aGSA), was produced from the fruits
of Gardenia jasminoides ELLIS using an enzyme-immobilized
method and identified by HPLC and NMR spectral analyses.
The obtained aGSA was used to cross-link chitosan for the
development of edible films. The chemical characteristics,
mechanical properties, water vapor permeability, antibacterial
capability, cytotoxicity, and enzymatic degradability of the
aGSA-cross-linked chitosan film were investigated. Fresh and
glutaraldehyde-cross-linked chitosan films were used as controls.
Edible films have been widely used to cover food surfaces,
separate different components, or act as casings, pouches, or
wraps (1). The advantages of edible films include extending
the shelf life and the quality of food by forming barriers to
oxygen, aroma, oil, or moisture, carrying functional ingredients
such as antioxidants or antimicrobials, and improving appear-
ance and handling characteristics (2). Chitosan, derived from
the deacetylation of chitin, can be formed into fibers, films,
beads, or nanoparticles for different applications (3-6). As
compared with other biobased food-packaging materials, chi-
tosan has the advantage of being able to incorporate functional
substances such as minerals or vitamins and possesses antibacte-
rial activity (7-9). Therefore, chitosan films have been used
as a packaging material for the quality preservation of a variety
of food (10-13).
MATERIALS AND METHODS
Materials. Dried fruits of G. jasminoides ELLIS were acquired from
a local herbal-medicine store. Chitosan (MW ≈ 2.5 × 105) with a degree
of deacetylation of approximately 85% was purchased from Fluka
Chemical Co. (Switzerland). Cellulase (1.92 units/mg) and lysozyme
(1000 units/mg) were obtained from Sigma Chemical Co. All other
reagents and solvents were reagent grade.
Production of aGSA. Geniposide (GS) was isolated from dried fruits
of G. jasminoides ELLIS using a method reported by Paik et al. (19,
20). 13C NMR (500 MHz, D2O): δ 172.9 (-CO2-), 155.2 (C-3), 144.0
(C-8), 131.8 (C-7), 114.4 (C-4), 101.5 (C-G1), 99.8 (C-1), 78.9 (C-
G5), 78.3 (C-G3), 75.4 (C-G2), 72.2 (C-G4), 63.3 (C-G6), 62.4
(C-10), 54.5 (-OCH3), 48.4 (C-9), 40.7 (C-6), 36.9 (C-5). The isolated
GS (0.5 mmol) was added to 1 mL of NaOH aqueous solution (1 mmol)
at 60 °C and the resulting solution stirred for 1 h. After being reacted
The water vapor permeability of chitosan films may be
moderated by chemical modification with a cross-linking agent
(11, 12, 14-16). However, currently available cross-linking
agents such as glutaraldehyde and diepoxy compounds are all
synthetic compounds and highly cytotoxic (17, 18).
* To whom correspondence should be addressed. Phone: 886-3-574-
2504. Fax: 886-3-572-6832. E-mail: hwsung@che.nthu.edu.tw.
† Chinese Naval Academy.
‡ National Tsing Hua University.
10.1021/jf0529868 CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/06/2006

aGSA-Cross-Linked Chitosan Film
J. Agric. Food Chem., Vol. 54, No. 9, 2006 3291
Figure 2. Time courses of hydrolysis of GSA using (a) a free form of
cellulase and (b) an immobilized cellulase to obtain aGSA.
(m, 1, H-5), 2.81 (m, 2, H-6), 2.51 (m, 1, H-9). 13C NMR (500 MHz,
CD3COCD3): δ 168.73 (-CO2-), 153.33 (C-3), 145.79 (C-8), 127.31
(C-7), 111.40 (C-4), 97.21 (C-1), 61.36 (C-10), 48.27 (C-9), 39.53 (C-
6), 37.28 (C-5).
Preparation of Test Chitosan Films. The chitosan films used in
the study were fabricated by means of a casting/solvent evaporation
technique. Chitosan solution (1.5% w/v) was prepared by dissolving
chitosan powder (3 g) in 200 mL of deionized water containing 1.0%
(v/v) acetic acid at room temperature. The prepared chitosan solution
was sonicated for 5 min and allowed to stand overnight to remove the
trapped air bubbles. The air-bubble-free chitosan solution was poured
into a glass disk in a dust-free environment and dried in air. The dried
chitosan films were neutralized by an aqueous NaOH solution (1 N)
and then thoroughly washed with phosphate-buffered saline (PBS).
Aqueous glutaraldehyde and aGSA solutions (with a concentration of
0.4-6.4 mM) were prepared. Subsequently, the prepared chitosan films
were immersed in the aqueous glutaraldehyde (glutaraldehyde-cross-
linked chitosan film) or aGSA (aGSA-cross-linked chitosan film)
solution for cross-linking. After 6 h, the cross-linked chitosan films
were thoroughly washed with deionized water to remove the excess
glutaraldehyde or aGSA and dried in air.
Degree of Cross-Linking. The degree of cross-linking of the
chitosan film, using the fixation index determined by the ninhydrin
assay, was defined as the percentage of free amino groups in the test
chitosan film reacted with glutaraldehyde or aGSA after reaction. In
the ninhydrin assay, the test sample first was lyophilized for 24 h and
then weighed. Subsequently, the lyophilized sample was heated with a
ninhydrin solution for 20 min. After heating with ninhydrin, the optical
absorbance of the solution (at 570 nm) was recorded with a spectro-
phometer (model UV-150-02, Shimadzu Corp., Kyoto, Japan) using
glucosamine at various known concentrations as a standard.
Figure 1. HPLC chromatograms of (a) GS isolated from dried fruits of G.
jasminoides ELLIS, (b) GSA, and (c) aGSA.
with the alkaline solution, GS was converted to geniposidic acid (GSA).
Subsequently, the obtained GSA was hydrolyzed to aGSA using an
enzyme (cellulase)-immobilized method as described below. A free
form of the enzyme was used as a control.
To prepare the immobilized enzyme, sodium alginate (800 mg) and
cellulase (120 units) were dissolved in 40 mL of distilled water and
the resulting solution stirred thoroughly. The mixed alginate/cellulase
was then added dropwise to a 1.0% (by w/v) CaCl2 aqueous solution
under continuous stirring for the formation of gel beads. The gel beads
immobilized with cellulase were washed with 200 mL of acetate buffer
(0.1 M, pH 4.5). The prepared gel beads were then added to the GSA
solution (pH 4.0), and the enzymatic reaction was carried out at 50 °C
for up to 18 h. The obtained crude aGSA (5 mL, ∼0.2 mol) was
extracted by 50 mL of ethyl acetate and subsequently purified using a
silica gel column. The column (40 × 3 cm) was eluted with chloroform/
acetone gradients of 200 mL/0 mL, 70 mL/30 mL, and 100 mL/0 mL.
The concentration of aGSA was measured by high-performance liquid
chromatography (HPLC). The mobile phase was acetonitrile-water-
perchloric acid (17:83:0.1 by volume) at a flow rate of 1.0 mL/min.
1H NMR (500 MHz, CD3COCD3): δ 7.48 (s, 1, H-3), 5.79 (t, 1, H-7),
4.85 (d, 1, J ) 8 Hz, H-1), 4.25 (dd, 2, J ) 1.5, 1.5 Hz, H-10), 3.10
Swelling Ratio. The swelling ratios of the fresh chitosan film (the
film without cross-linking) and the glutaraldehyde- and aGSA-cross-
linked chitosan films were determined by soaking each test film (200

3292 J. Agric. Food Chem., Vol. 54, No. 9, 2006
Mi et al.
Figure 3. Presumed cross-linking structures of (a) glutaraldehyde-cross-linked chitosan and (b) aGSA-cross-linked chitosan.
mg) in deionized water at room temperature. Subsequently, the swollen
test films were taken out, blotted with a filter paper, and then weighed
immediately (We). The swelling ratio of each test film in the medium
was calculated as follows:
diameter) cut from the sterilized films were placed at the bottom of
each well in a 24-well plate. Subsequently, a 50 µL bacterial broth
(Escherichia coli or Staphylococcus aureus) was seeded onto each test
film (105 colony-forming units (CFUs)/mL). The bacterial broth cultured
in the well without any test film was used as a control. Subsequently,
the 24-well plate was placed in a moisture incubator at 37 °C. After 4
h of incubation, each test film was transferred to a test tube containing
1 mL of PBS and sonicated for 75 s. A 50 µL sample of the solution
was then taken from each test tube, seeded on an agar plate containing
nutrient broth, and incubated at 37 °C for 24 h. Finally, the CFUs in
each agar plate were counted.
Cytotoxicity Study. The cytotoxicity of the test films was evaluated
using an in vitro cell-culture assay. Each test film (2 × 1 cm) cut from
the sterilized films was glued to the center of a cultural dish (60 mm
in diameter) using a sterilized collagen solution. Subsequently, human
foreskin fibroblasts (HFFs) at 1 × 105 cells/well were seeded evenly
onto the surface of each test sample in 1 mL of Dulbecco’s modified
Eagle’s medium (DMEM; Gibco 430-2800EG, Grand Island, NY) with
10% fetal calf serum (FCS; Hyclone Laboratories, Logan, UT). The
cell cultures were maintained in a humidified incubator at 37 °C with
5% CO2 in air. After 1, 2, or 4 days, the media were removed, and the
cells cultured on the surface of each test film were photographed using
an inverted light microscope (Olympus Optical Co., Ltd., IX70, Tokyo,
Japan).
Esw (%) ) [(We - W0)/W0] × 100
where Esw is the swelling ratio of the test film at equilibrium and W0
is the weight of the dried test film.
Mechanical Properties. Stress-strain curves of each test film (in
a dumbbell shape) were determined by uniaxial measurements using
an Instron material testing machine (Mini 44, Canton, MA) at a constant
speed of 50 mm/min. The strain at fracture was taken as the percent
strain at the point of fracture, while the ultimate tensile strength was
taken as the force at which fracture occurred divided by the initial cross-
sectional area.
Enzymatic Degradability. Test films were immersed in a 1000 units/
mL lysozyme solution (pH 7.4) and incubated at 37 °C for up to 8
weeks. After degradation, the formation of oligomers containing
N-glucosamine units, due to the cleaved â-glycosidic bonds of chitosan,
induced an increment in the content of free amino groups in the
incubation medium which can be determined by the ninhydrin assay.
The degradation of each studied group was examined by analyzing the
increased N-glucosamine units in the incubation medium (21). The
medium was heated with a ninhydrin solution for 20 min. After heating
with ninhydrin, the optical absorbance of the medium (at 570 nm) was
recorded with a spectrophometer (model UV-150-02, Shimadzu Corp.)
using glucosamine at various known concentrations as a standard to
determine the amount of N-glucosamine degraded from chitosan.
Water Vapor Permeability. The water vapor permeability of each
test film was determined using the ASTM method (E96-14) in a
controlled chamber conditioned at 25 °C with a 50% relative humidity.
A cylinder (3 cm in diameter and 5 cm in height) filled with 10 g of
deionized water was placed in the closed chamber. The test film was
fixed on the opening of the cylinder. Evaporation of water through the
test film was monitored by measuring the weight of water remaining
in the cylinder.
Statistical Analysis. Statistical analysis for the determination of
differences in the measured properties between groups was ac-
complished using one-way analysis of variance and determination of
confidence intervals, performed with a computer statistical program
(Statistical Analysis System, Version 6.08, SAS Institute Inc., Cary,
NC). All data are presented as a mean value with its standard deviation
indicated (mean ( SD).
RESULTS AND DISCUSSION
Production of aGSA. Figure 1a presents an HPLC chro-
matogram of GS isolated from dried fruits of G. jasminoides
ELLIS. The obtained GS was converted to GSA after being
treated with an alkaline solution (Figure 1b). Parts a and b of
Figure 2 show the time courses of hydrolysis of GSA using a
free form of cellulase and an immobilized cellulase, respectively.
As indicated, the concentrations of aGSA obtained by both
Antibacterial Capability. The antibacterial capability of test films
was studied per a method described by Grzybowski et al. (22). Test
films were sterilized in a graded series of ethanol solutions with a
gradual increase in concentration from 20% to 75% over a period of 4
h and subsequently rinsed in sterilized PBS. Test samples (16 mm in

aGSA-Cross-Linked Chitosan Film
J. Agric. Food Chem., Vol. 54, No. 9, 2006 3293
Table 1. Degree of Cross-Linking, Swelling Ratio, Ultimate Tensile Strength, and Strain at Fracture of Chitosan Films without Cross-Linking (Fresh)
and Those Cross-Linked with GA or aGSA at Various Known Concentrations (n 5)
)
test sample
fresh
0.4 mM
0.8 mM
Degree of Cross-Linking (%)
1.6 mM
3.2 mM
6.4 mM
GA
aGSA
0.0
0.0
±
±
0
0
7.3
17.0
±
±
0.6
2.7
7.4
17.5
±
±
2.7
1.9
14.0
25.1
±
±
3.0
2.5
34.1
42.1
±
±
3.1
2.9
63.4
70.8
±
±
1.0
1.7
Swelling Ratio (%)
GA
aGSA
101.4
101.4
±
±
7.7
7.7
92.1
71.2
±
±
2.5
7.5
84.3
68.2
±
±
4.2
6.2
74.8
65.6
±
±
4.3
5.0
65.7
56.7
±
±
3.7
5.0
57.2
51.1
±
±
4.5
3.0
Ultimate Tensile Strength (MPa)
GA
AGSA
18.2
18.2
±
±
1.1
1.1
22.1
24.4
±
±
0.8
1.0
24.9
28.5
±
±
1.1
1.8
26.9
21.1
±
±
2.1
1.5
18.9
13.8
±
±
1.1
1.4
9.5
7.1
±
±
1.0
2.0
Strain at Fracture (%)
GA
aGSA
25.9
25.9
±
±
0.5
0.5
21.5
19.5
±
±
0.9
1.3
19.8
16.9
±
±
1.1
0.5
16.7
10.5
±
±
0.9
1.2
9.1
7.8
±
±
0.7
1.0
7.5
5.9
±
±
0.9
0.6
methods decreased significantly after 8 h of hydrolysis. There-
fore, an 8 h duration was chosen for the hydrolysis of GSA by
cellulase to obtain aGSA in the study. It was found that the
amount of aGSA obtained using the immobilized cellulase was
greater than that of the free form of cellulase. This can be
attributed to the fact that the obtained aGSA can react directly
with the free amino groups of the free form of cellulase (a
protein-type enzyme), and thus, the activity of cellulase is
decreased significantly. The decrease in the activity of cellulase
may be limited by encapsulating the enzyme in the alginate
beads. Finally, the obtained aGSA was purified using a silica
gel column (Figure 1c). As shown in the HPLC chromatograms
(Figure 1), the retention times of GS, GSA, and aGSA were
4.3, 3.2, and 3.5 min, respectively.
Degree of Cross-Linking. Chitosan, containing hydroxyl and
amino groups, is readily hydrated in water. To reduce its degree
of hydration, chemical modification or cross-linking of chitosan
is needed. In the study, glutaraldehyde, a commonly used cross-
linking agent, and aGSA were used to cross-link chitosan films.
After cross-linking, the glutaraldehyde-cross-linked chitosan film
turned yellow, while the aGSA-cross-linked film became brown.
The mechanism of cross-linking of chitosan with glutaraldehyde
was discussed in detail previously (21). The bifunctional
glutaraldehyde reacts with the free amino groups on chitosan
to form Schiff bases (-CdN- linkage). Furthermore, glutaral-
dehyde may undergo an aldol condensation to polymerize in
an aqueous environment. With the polymerization of glutaral-
dehyde molecules, a network cross-linking structure can be
created between chitosan molecules.
Figure 4. Degradation profiles of the fresh chitosan film and GA- and
aGSA-cross-linked chitosan films with time incubated in a lysozyme
solution.
Table 2. Number of CFUs of E. coli or S. aureus Growing on Fresh
and GA- and aGSA-Cross-Linked Chitosan Films (n
)
5)a
no. of CFUs
test sample
E. coli (
×
105)
S. aureus (×
105)
control
fresh
GA
576
108
134
125
±
75
15
56
39
258
49
58
±
±
±
±
34
12
16
19
±
±
±
aGSA
63
a The bacterial broth cultured in the well without any test film was used as a
control.
It is known that aGSA can spontaneously react with the free
amino groups of amino acids or proteins to form red pigments
(23, 24). These red pigments have been used in the fabrication
of food dyes. The probable mechanism for the formation of
red pigments is due to a nucleophilic attack by the primary
amino group of amino acids on the third carbon of aGSA. This
followed by the opening of the aGSA ring formed an intermedi-
ate aldehyde group. The resulting aldehyde group is subse-
quently attacked by the attached secondary amino group.
Dimerization occurs at the second stage, perhaps by radical
reaction, to form a heterocyclic cross-linking structure (24, 25).
Accordingly, both glutaraldehyde and aGSA can intramolecu-
larly and intermolecularly cross-link chitosan (Figure 3).
cross-linked film, at the same concentration, was significantly
greater than that of its glutaraldehyde-fixed counterpart (p <
0.05).
Swelling Ratio. Both the glutaraldehyde- and aGSA-cross-
linked chitosan films showed a significant decrease in the
swelling ratio as compared to their fresh counterpart (p < 0.05,
Table 1). With increasing degree of cross-linking, the swelling
ratios of both studied groups decreased. The swelling ratio of
the aGSA-cross-linked chitosan film, due to a higher degree of
cross-linking, was relatively lower than that of its glutaralde-
hyde-cross-linked counterpart.
Mechanical Properties. It was found that the values of the
ultimate tensile strength of the cross-linked films increased
significantly over that of the fresh counterpart and with
increasing concentration of glutaraldehyde or aGSA up to 0.8
mM (p < 0.05, Table 1). With a further increase of the
As shown in Table 1, the degrees of cross-linking (the
fixation indices) of both the glutaraldehyde- and aGSA-cross-
linked chitosan films increased with increasing concentration
of the cross-linking agent. The fixation index of the aGSA-

3294 J. Agric. Food Chem., Vol. 54, No. 9, 2006
Mi et al.
Figure 5. Photomicrographs (original magnification 40×; reproduced here at 80% of original size) of HFFs cultured on the surface and its vicinity of the
(a) fresh chitosan film, (b) GA-cross-linked chitosan film, and (c) aGSA-cross-linked chitosan film after 1, 2, or 4 days of cell culture. The test sample
was placed on the right bottom corner of the cell-culture well in each photomicrograph.
concentration of the cross-linking agent, the values of the
ultimate tensile strength of the cross-linked films decreased
significantly (p < 0.05). The amino and hydroxyl groups present
in each repeat unit of the N-glucosamine on chitosan can readily
lead to intermolecular hydrogen bonds between chitosan mol-
ecules. A high degree of cross-linking may disrupt the inter-
molecular hydrogen bonds and reduce the crystallinity of the
chitosan film. As a result, a decrease in the value of the ultimate
tensile strength was observed for the chitosan film cross-linked
with a relatively high concentration of glutaraldehyde or aGSA.
The values of the strain at fracture for the cross-linked chitosan
films decreased significantly with increasing concentration of
glutaraldehyde or aGSA (p < 0.05, Table 1). This is because
cross-linking of chitosan films led to a decrease in their
elongation (Figure 3).
greatest degradability among all studied groups. Due to a higher
degree of cross-linking, the degradability of the aGSA-cross-
linked chitosan film was lower than that of its glutaraldehyde-
cross-linked counterpart (p < 0.05). Additionally, the bulky
heterocycle-cross-linking structure of the aGSA-cross-linked
chitosan film may have a greater stereohindrance for the
penetration of lysozyme than the network-cross-linking structure
of the glutaraldehyde-cross-linked chitosan film (Figure 3). The
structure of stereohindrance may prevent lysomyze from binding
the N-acetylglucosamine residues on chitosan.
Water Vapor Permeability. The fresh chitosan film had a
higher value of water vapor permeability (835 ( 69 g‚m-2
‚
day-1‚atm-1) than the glutaraldehyde-cross-linked (724 ( 38
g‚m-2‚day-1‚atm-1) and aGSA-cross-linked (684 ( 56 g‚m-2
‚
day-1‚atm-1) chitosan films (p < 0.05). It is known that the
free hydroxyl and amino groups on chitosan are hydrophilic.
The decrease in the water vapor permeability for the cross-linked
chitosan films may possibly be due to the consumption of the
free amino groups on chitosan after cross-linking. The water
vapor permeability of the aGSA-cross-linked film was relatively
lower than that of its glutaraldehyde-cross-linked counterpart,
again due to its higher degree of cross-linking.
As discussed above (Table 1), the chitosan films cross-linked
with 0.8 mM glutaraldehyde or aGSA had the highest values
of the ultimate tensile strength among their counterparts cross-
linked at different concentrations. Therefore, these samples were
chosen for the rest of the study.
Enzymatic Degradability. Figure 4 presents the degrad-
ability of each test film with time incubated in a lysozyme
solution. It was observed that the increment in the free amino
group content in the medium incubated with the fresh chitosan
film was significantly greater than those of the media incubated
with the glutaraldehyde- and aGSA-cross-linked chitosan films
(p < 0.05). This indicated that the fresh chitosan film had the
Antibacterial Capability. As compared with the control
group, the numbers of colony-forming units (E. coli or S. aureus)
observed on fresh and glutaraldehyde- and aGSA-cross-linked
chitosan films were significantly inhibited (p < 0.05, Table
2). The antibacterial activity of chitosan against a broad spectrum
of bacteria has been documented in the literature (26-28). It

aGSA-Cross-Linked Chitosan Film
J. Agric. Food Chem., Vol. 54, No. 9, 2006 3295
(6) Geng, X.; Kwon, O. H.; Jang, J. Electrospinning of chitosan
dissolved in concentrated acetic acid solution. Biomaterials 2005,
26, 5427-5432.
(7) Jeon, Y. J.; Kamil, J. Y. V. A.; Shahidi, F. Chitosan as an edible
invisible film for quality preservation of herring and Atlantic
cod. J. Agric. Food Chem. 2002, 50, 5167-5178.
(8) Mo¨ller, H.; Grelier, S.; Pardon, P.; Coma, V. Antimicrobial and
physicochemical properties of chitosan-HPMC-based films. J.
Agric. Food Chem. 2004, 52, 6585-6591.
(9) Chen, X. G.; Zheng, L.; Wang, Z.; Lee, C. Y.; Park, H. J.
Molecular affinity and permeability of different molecular weight
chitosan membranes. J. Agric. Food Chem. 2002, 50, 5915-
5918.
was proposed that the interaction between the polycationic
chitosan (NH3 on glucosamine) and the negatively charged
+
surface of bacteria may alter the permeability of the bacterial
wall and lead to the leakage of intracellular electrolytes and
proteins (29). However, the differences in the numbers of
colony-forming units seen on all test films were insignificant
(p > 0.05). These results suggested that cross-linking of chitosan
films did not alter their antibacterial capability. This may be
due to the fact that the cross-linking degrees of the glutaralde-
hyde- and aGSA-cross-linked chitosan films used in this part
of the study were relatively low (<18%, with a concentration
of cross-linking agent of 0.8 mM, Table 1).
(10) Suyatma, N. E.; Tighzert, L.; Copinet, A. Effects of hydrophilic
plasticizers on mechanical, thermal, and surface properties of
chitosan films. J. Agric. Food Chem. 2005, 53, 3950-3957.
(11) Wu, T.; Zivanovic, S.; Draughon, F. A.; Conway, W. S.; Sams,
C. E. Physicochemical properties and bioactivity of fungal chitin
and chitosan. J. Agric. Food Chem. 2005, 53, 3888-3894.
(12) Tsai, G. J.; Su, W. H. Antibacterial activity of shrimp chitosan
aganist Escherichia coli. J. Food Prot. 1999, 62, 239-243.
(13) Park, S. I.; Zhao, Y. Incorporation of a high concentration of
mineral or vitamin into chitosan-based films. J. Agric. Food
Chem. 2004, 52, 1933-1939.
(14) Zeng, X.; Ruckenstein, E. Cross-linked macroporous chitosan
anion-exchange membranes for protein separations. J. Membr.
Sci. 1998, 148, 195-205.
(15) Devi, D. A.; Smitha, B.; Sridhar, S.; Aminabhavi, T. M.
Pervaporation separation of isopropanol/water mixtures through
crosslinked chitosan membranes. J. Membr. Sci. 2005, 262, 91-
99.
(16) Liu, Y. L.; Su, Y. H.; Lee, K. R.; Lai, J. Y. Crosslinked organic-
inorganic hybrid chitosan membranes for pervaporation dehydra-
tion of isopropanol-water mixtures with a long-term stability. J.
Membr. Sci. 2005, 251, 233-238.
(17) Nishi, C.; Nakajima, N.; Ikada, Y. In vitro evaluation of
cytotoxicity of diepoxy compounds used for biomaterial modi-
fication. J. Biomed. Mater. Res. 1995, 29, 829-834.
(18) Sung, H. W.; Huang, R. N.; Huang, L. L. H.; Tasi, C. C. In
vitro evaluation of cytotoxicity of a naturally occurring crosslink-
ing reagent for biological tissue fixation. J. Biomater. Sci., Polym.
Ed. 1999, 10, 63-78.
Cytotoxicity Study. As shown in Figure 5a,c, after a 4 day
culture, the surfaces of fresh and aGSA-cross-linked chitosan
films and their vicinity were filled with HFF cells. However,
only a few cells were observed on the surface of the glutaral-
dehyde-cross-linked film (Figure 5b). These results suggested
that the cytotoxicity of the aGSA-cross-linked chitosan film was
less than that of its glutaraldehyde-cross-linked counterpart. It
is known that glutaraldehyde is highly cytotoxic and may impair
the biocompatibility of its cross-linked products (30).
Interestingly, the transparent chitosan biobased films became
brown after being cross-linked with aGSA, without addition of
any pigments. The aGSA-cross-linked chitosan film demon-
strated a lower water vapor permeability, a superior antibacterial
capability, and a lower cytotoxicity, as compared with those
cross-linked with traditional cross-linking agents. These results
suggested that the aGSA-cross-linked chitosan film may rep-
resent a promising and new type of edible films for packaging
of foods.
Conclusion. There was no significant difference in the
antimicrobial capability between the cross-linked chitosan films
and their fresh counterpart. The aGSA-cross-linked chitosan film
had a relatively lower water vapor permeability, a lower
cytotoxicity, and a slower degradation rate than the glutaral-
dehyde-cross-linked film. These results suggested that the
aGSA-cross-linked chitosan film may be a promising material
as an edible film.
(19) Paik, Y. S.; Lee, C. M.; Cho, M. H.; Hahn, T. R. Physical stability
of the blue pigments formed from geniposide of Gardenia
fruits: effects of pH, temperature, and light. J. Agric. Food Chem.
2001, 49, 430-432.
(20) Park, J. E.; Lee, J. Y.; Kim, H. G.; Hahn, T. R.; Paik, Y. S.
Isolation and characterization of water-soluble intermediates of
blue pigments transformed from geniposide of Gardenia jasmi-
noides. J. Agric. Food Chem. 2002, 50, 6511-6514.
(21) Mi, F. L.; Tan, Y. C.; Liang, H. C.; Huang, R. N.; Sung, H. W.
In vitro evaluation of a chitosan membrane cross-linked with
genipin. J. Biomater. Sci., Polym. Ed. 2001, 12, 835-850.
(22) Grzybowski, J.; Antos, M.; Trafny, E. A. A simple in vitro model
to test the efficacy of antimicrobial agents aeleased from
dressings. J. Pharmacol. Toxicol. 1996, 36, 73-76.
(23) Moritome, N.; Inoue, K. Effects of acid and amine on the
formation of red pigment from geniposidic acid. J. Food Sci.
Technol. 2000, 37, 139-143.
(24) Moritome, N.; Nakashima, K.; Inoue, K.; Shingu, T. Formation
of red pigment produced from geniposidic acid and amino
compound. J. Food Sci. Technol. 2002, 39, 345-352.
(25) Mi, F. L.; Peng, C. K.; Shyu, S. S. Characterization of ring-
opening polymerization of genipin and pH-dependent cross-
linking reactions between chitosan and genipin. J. Polym. Sci.,
Part A: Polym. Chem. 2005, 43, 1985-2000.
ABBREVIATIONS USED
GS, geniposide; GSA, geniposidic acid; aGSA, aglycone
geniposidic acid; HFFs, human foreskin fibroblasts; PBS,
phosphate-buffered saline.
LITERATURE CITED
(1) Miller, K. S.; Krochta, J. M. Oxygen and aroma barrier properties
of edible films: A review. Trends Food Sci. Technol. 1997, 8,
228-236.
(2) Siew, D. C. W.; Heilmann, C.; Easteal, A. J.; Cooney, R. P.
Solution and film properties of sodium caseinate/glycerol and
sodium caseinate/poly(ethylene glycol) edible coating systems.
J. Agric. Food Chem. 1999, 47, 3432-3440.
(3) Ogawa, S.; Decker, E. A.; McClements, D. J. Production and
characterization of O/W emulsions containing droplets stabilized
by lecithin-chitosan-pectin mutilayered membranes. J. Agric.
Food Chem. 2004, 52, 3595-3600.
(4) Liu, C. G.; Desai, G. H.; Chen, X. G.; Park, H. J. Preparation
and characterization of nanoparticles containing trypsin based
on hydrophobically modified chitosan. J. Agric. Food Chem.
2005, 53, 1728-1733.
(26) Ouattara, B.; Simard, R. E.; Piette, G.; Be´gin, A.; Holley, R. A.
Inhibition of surface spoilage bacteria in processed meats by
application of antimicrobial films prepared with chitosan. Int.
J. Food Microbiol. 2000, 62, 139-148.
(5) Mi, F. L.; Peng C. K.; Lo, S. H. Preparation and characterization
of N-acetylchitosan, N-propionylchitosan and N-butyrylchitosan
microspheres for controlled release of 6-mercaptourine. Carbo-
hydr. Polym. 2005, 60, 219-227.

3296 J. Agric. Food Chem., Vol. 54, No. 9, 2006
Mi et al.
(27) Coma, V.; Martial-Gros, A.; Garreau, S.; Copinet, A.; Salin, F.;
Deschamps, A. Edible anti-microbial films based on chitosan
matrix. J. Food Sci. 2002, 67, 1162-1169.
modified collagenous tissues. In Collagen; Nimni, M. E., Ed.;
CRC Press: Boca Raton, FL, 1988; Vol. 3, pp 1-38.
(28) Be´gin, A.; Van Calsteren, M. R. Antimicrobial films produced
from chitosan. Int. J. Biol. Macromol. 1999, 26, 63-67.
(29) Muzzarelli, R.; Tarsi, R.; Filippini, O.; Giovanetti, E.; Biagini,
G.; Varaldo, P. E. Antimicrobial properties of N-carboxybutyl
chitosan. Antimicrob. Agents Chemother. 1990, 34, 2019-2023.
(30) Nimni, M. E.; Cheung, D. T.; Strates, B.; Kodama, M.; Sheikh,
K. Bioprosthesis derived from cross-linked and chemically
Received for review November 29, 2005. Revised manuscript received
March 5, 2006. Accepted March 16, 2006. This work was supported
by a grant from the Veterans General Hospitals and the University
System of Taiwan Joint Research Program (VGHUST93-P6-24),
Republic of China.
JF0529868