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Chitosan as A Preservative for Fruits and Vegetables: A Review on Chemistry and Antimicrobial Properties



Chitosan, derived from chitin, a major constituent (in quantity) of crustaceans, is a unique aminopolysaccharide with emerging commercial potential in agriculture, food, pharmaceuticals and nutraceuticals due to its nontoxic, biodegradable and biocompatable properties. Chitosan coating on fruits and vegetables has been found to be effective for the reduction of a variety of harmful micro-organims and extend the shelf-life of these products. In this review, our focus is on the antimicrobial properties of chitosan and its application as a natural preservative for fresh products. We detailed the key properties that are related to food preservation, the molecular mechanism of the antimicrobial activity of chitosan on fungi, gram-positive and gram-negative bacteria, coating methods for using chitosan and its formulation for preserving fruits and vegetables, as well as the radiation method of producing chitosan from chitin. Understanding the economic and scientific factors of chitosan's production and efficiency as a preservative will open its practical application for fruits and vegetable preservation.
Journal of Bioresources and Bioproducts. 2019, 4(1): 1121 11
DOI: 10.21967/jbb.v4i1.189
Chitosan as A Preservative for Fruits and Vegetables: A Review on Chemistry
and Antimicrobial Properties
Chao DUAN1, Xin MENG1, Jingru MENG1, Md. Iqbal Hassan KHAN2, Lei DAI1, Avik KHAN2, Xingye AN2, 3,
Junhua ZHANG2, 4, Tanzina HUQ2, Yonghao NI1, 2*
1 College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi’an 710021,
2 Department of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada;
3 Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and Technology, Tianjin 300457, China;
4 Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming 650500, China
*Corresponding author: Yonghao NI,
Received 21 October 2018; Accepted 10 December 2018
Abstract: Chitosan, derived from chitin, a major constituent (in quantity) of crustaceans, is a unique aminopolysaccharide
with emerging commercial potential in agriculture, food, pharmaceuticals and nutraceuticals due to its nontoxic,
biodegradable and biocompatable properties. Chitosan coating on fruits and vegetables has been found to be effective for
the reduction of a variety of harmful micro-organims and extend the shelf-life of these products. In this review, our focus
is on the antimicrobial properties of chitosan and its application as a natural preservative for fresh products. We detailed
the key properties that are related to food preservation, the molecular mechanism of the antimicrobial activity of chitosan
on fungi, gram-positive and gram-negative bacteria, coating methods for using chitosan and its formulation for preserving
fruits and vegetables, as well as the radiation method of producing chitosan from chitin. Understanding the economic and
scientific factors of chitosan’s production and efficiency as a preservative will open its practical application for fruits and
vegetable preservation.
Keywords: chitosan; food preservative; oligochitosan; coating; antimicrobial property
Citation: Duan Chao, Xin Meng, Jingru Meng, et al., 2019. Chitosan as a preservative for fruits and vegetables: a review
on chemistry and antimicrobial properties. Journal of Bioresources and Bioproducts, 4(1): 11–21.
1 Introduction
Freshness of fruits and vegetables (F&V) is an important
criterion that dictates which product a consumer prefers
to buy in the market. Supermarkets face challenges to
keep the F&V fresh and offer consumers better quality
products. The F&V are biodegradable and prone to
microbial attack. Challenges involving natural rippening
and the degradation process of the F&V, mainly through
enzymatic reaction, are an important concern for food
industries. The F&V are sensitive to decay and perish,
due to rapid ripening and softening, which limits their
storage, handling and transport potential (Hu et al., 2017).
Characteristics that lower the products quality, such as
browning, off-flavour deve l o pme nt an d tex t ur e
breakdown, are commonly seen on microbiologically
sp oiled food. Therefore, accep t able met hod s of
preservation are top priority in the food industry. Coating
the F&V with biocompatable nonallergic polymers is a
good choice for preservation. Inadequate and costly
solutions for food preservation has led scientists to create
natural preservatives which are safe, effective, and
acceptable (Huq et al., 2015). Keeping in mind relatively
long time storage and transportation, use of biologically
d e r i v e d p r e s e r v a t i v e s
with compliance to health and safety regulations can
bring a great solution for preservation of the F&V
(Romanazzi et al., 2017).
One such strategy that has been of recent interest is the
edible coatings in the fresh fruit industry to reduce the
deleterious effects that could take place on intact
vegetable tissues which are usually subject to minimal
processing. Preservatives, either chemically synthesized
or originating from nature, should meet the following
criterion: 1) efficient against a broad range of spoilage
organisms; 2) tasteless and odorless; 3) non-toxic; 4) safe;
and 5) inexpensive. The general perishability of the F&V,
varying from their sensitivity to decay induced by
enzymatic actions, is mainly due to the rapid ripening
process thus limiting the storage, handling and transport
potential of the F&V (Lee et al., 2015).
Edible coating, an innovative method of food
preservation, produces physical barriers on the surface of
the F&V that cause moisture and solute to migration, gas
exchange, respiration and oxidative reaction rates reduced
for extending the shelf-life (Arnon et al., 2014).
Biopolymer coating materials are formulated to carry
active ingredients such as antibrowning agents, colorants,
This is an Open Access article under the CC-BY-NC license.
Journal of Bioresources and Bioproducts, 2019, 4(1): 1121
flavours, nutrients, spices and antimicrobial compounds
to extend product shelf life and reduce the risk of
pathogen growth on food surfaces (Pranoto et al., 2005).
Chitosan, a partially deacetylated derivative of chitin,
is a hetero-polysaccharide composed of 2-amino-deoxy-
β-D-glucopyranose and 2-acetamido-deoxy-β-D-glu-
copyranose (chitin) residue (Khan et al., 2014). The major
property of chitosan is dictated by the presence of three
different functional groups (primary —OH, secondary
—OH and —NH2) and its water solubility in acidic pH.
Due to the presence of reactive groups, it inhibits
the growth of a wide variety of bacteria and fungi
(Hosseinnejad and Jafari, 2016). Chitosan has many
different applications and can be utilized for developing
various formulations (Fatehi et al., 2010). Chitosan-based
edible coatings can also be used as carriers of food
ingredients (antimicrobials, texture enhancers and
nutraceuticals) to improve the safety, quality and
functionality of the F&V. Edible coating without
disturbing sensory quality and nutritional value of the
F&V needs further scientific research (Martins et al.,
Chitosan/chitin refers to one of the most abundant
natural polysaccharides in nature (Lavall et al., 2007). It
can be obtained from several different sources, but the
main source of chitosan is usually marine crustacean’s
shells (Arbia et al., 2013). Atlantic Canada, with its long
coastline, offers a great source of different marine crusta-
ceans, i.e., shrimp, lobster, crab, etc. that can be utilized
for the extraction of chitosan. Aquaculture industries in
Atlantic Canada are growing fast to meet current demand.
However, disposal of crustacian shells is an environ-
mental concern for aquaculture industries and recovery of
these shells from various sources can leverage industries for
producing chitosan and its derivatives at competitive costs.
2 Properties of Chitosan
2.1 Solubility and deacetylation of chitosan
Chitosan is derived by modifying chitin structure through
removal of the acetyl groups, which are bonded to amine
radicals in the C2 position on the glucan ring (Fig. 1).
Chemical hydrolysis in concentrated alkaline solution is
performed at elevated temperatures to produce a partially
deacetylated form of chitin referred to as chitosan. Chito-
san preparations differ by the degree of deacetylation.
While chitin is insoluble in most organic solvents,
chitosan is readily soluble in diluted acidic solutions
below pH 6.0. This is because chitosan can be considered
a strong base as it possesses primary amino groups with a
pKa value of 6.3. The presence of the amino groups
indicates that pH substantially alters the charged state and
Chao DUAN et al.: Chitosan as A Preservative for Fruits and Vegetables: A Review on Chemistry and Antimicrobial Properties 13
Fig. 1 Schematic flow chart of conventional process for chitosan production from shellfish
properties of chitosan (Elsabee and Abdou, 2013). At low
pH, these amines get protonated and become positively
charged and that makes chitosan a water-soluble cationic
polyelectrolyte. On the other hand, as the pH increases
above 6, chitosan’s amines become deprotonated and the
polymer loses its charge and becomes insoluble. The
soluble-insoluble transition occurs at its pKa value around
pH between 6.0 and 6.5. The solubility of chitosan is
dependent on the degree of deacetylation and the method
of deacetylation used (Cho et al., 2000). Whereas the
degree of ionization depends on the pH and the pKa of
the acid (acetic acid and hydrochloric acid) which causes
protonation of chitosan in the presence of acetic acid and
hydrochloric acid. Chitosan can easily form quaternary
ammonium salts at low pH values. So, organic acids such
as acetic, formic, and lactic acids can dissolve chitosan
(Cruz-Romero et al., 2013). The best solvent for chitosan
was found to be formic acid although the most commonly
used solvent is 1% acetic acid (as a reference) at about pH
4.0. Chitosan is also soluble in 1% hydrochloric acid and
dilute nitric acid but insoluble in sulfuric and phosphoric
acids. Concentrated acetic acid solutions at high
temperatures can cause depolymerization of chitosan
(Pillai et al., 2009). Combination of studies on intrinsic
viscosity, Fourier transform infrared spectroscopy (FT-IR),
and powder X-ray diffraction (XRD) showed that the
molecular weight and degree of deacetylation are
collectively responsible for the solubility which could be
due to intermolecular force (Shrinivas et al., 2007). It was
concluded that the solution properties of chitosan depend
not only on its average deacetylation, but also on the
distribution of the acetyl groups in the main chain
(Younes and Rinaudo, 2015). However, apart from the
deacetylation, the molecular weight is also an important
parameter that significantly controls the solubility and
antimicrobial properties of chitosan (Chang et al., 2015).
2.2 Molecular weight and depolymerization of chitosan
Although the chemical and physical processes control
some of the applications of chitosan and its derivatives,
considerable evidence has been gathered indicating that
most of their physiological activities and functional
properties depend on their molecular weight (MW) (Cota-
Arriola et al., 2013). It has been reported that the
distribution of chitosan prepar ations of different
molecular weight is influenced by the conditions
employed in the deacetylation process. The molecular
weight ranges from several hundred to over one million
Dalton (Mu) are common, with a mean molecular mass of
up to 1 Mu, corresponding to a chain length of
approximately 5000 U (Rhoades and Roller, 2000). There
are methods for determining the MW of chitosan such as
light scattering spectrophotometry, gel permeation
c h r o m a t o g r a p h y a n d
viscometry, and gel permeation chromatography is the
most widely used method (Niebel et al., 2014).
Depolymerization of chitosan using gamma irradiation is
a recent and useful approach. However, high doses of
gamma irradiation cause degradation of chitosan and
produces chitosan with relatively lower molecular weight
(Martínez- Morlanes et al., 2011). Degradation of chitosan
due to main-chain scission leads to the opposite effect on
the mechanical properties, and eventually produces soft,
gummy or tar like materials. When chitosan is irradiated,
both crosslinking and degradation often occur
simultaneously. Irradiation also brings about significant
changes in physicochemical, thermal and morphological
properties of chitosan which provides great potential for
many applications (Rashid et al., 2012). Among various
techniques used for the modification of polymer
properties, the use of ionizing radiation either in photonic
(gamma radiation, X-rays) or particulate forms
(accelerated electrons, ion beams) has proven to be a very
convenient technique (Senna et al., 2010). Since
molecular weight dictates physicochemical properties of
polymers, the control of molecular weight and its
distribution are of great importance in determining the
technical specifications required for an end-use (Huq et
al., 2012). Low MW chitosan is degraded at lower
temperatures than the higher MW. The interactions
between the molecules become weaker due to irradiation
and less energy is required for the thermal movement
(García et al., 2015). Irradiation also has an effect on
mechanical properties of chitosan films. It has been
reported that decreasing the MW increased the tensile
properties whereas the elongation breaks decreased
(García et al., 2015). Extensive study on the relationship
among molecular weight, water-solubility and
antimicrobial activity of chitosan is lacking until now.
Though it has been reported that molecular weight could
affect the antimicrobial properties of chitosan (Kim et al.,
2011; Wang et al., 2017).
3 Mechanism of Antimicrobial Activity of Chitosan
Chitosan is cationic biopolymer, having antimicrobial
properties which can be affected by pH, concentration,
molecular weight, degree of polymerization and cross-
linking (Elsabee and Abdou, 2013). Chitosan solution is
highly stable over a long period of time, however its
stability in neutral pH is highly important for exhibiting
antimicrobial activity against a wide variety of foodborne
Journal of Bioresources and Bioproducts, 2019, 4(1): 1121
pathogens (Alishahi and Aïder, 2012). The major
mechanism of action in antimicrobial activity involves
interaction with bacterial cell wall, cell membrane and
cytoplasmic constituents via electrostatic interactions.
Chitosan has been found to be effective against both
gram-positive and gram-negative bacteria. The outer
membrane (OM) of gram-negative bacteria such as,
Escherichia coli, is composed of an asymmetric lipid-
protein bilayer (lipopolysaccharide, LPS). The divalent
cations (i.e., Ca2+, Mg2+) present in the OM play an
important role in the stabilization of the core anionic
charges of the LPS molecules (Terry, 1999; Khan et al.,
2015). It can be hypothesized that chitosan replaces the
divalent cations from their binding sites and reduces the
interaction between the LPS molecules, causing
membrane disruption and cell lysis due to penetration
(through electrostatic interaction) of positively charged
chitosan through cell membrane of gram-negative
bacteria (Fig. 2). Unlike gram-negative bacteria, the
gram-positive bacteria do not have an outer membrane.
Hence, chitosan as a poly- cationic long chain molecule
can adhere better with gram-positive bacterial members
such as Staphylococcus aureus. For this reason, the
inhibition effort from chitosan is more effective against
gram-positive bacteria than gram-negative bacteria (Fig.
3). In the literature, it was reported that gram-positive
bacteria containing teichoic acid and lipoteichoic acid that
are poly-anionic surface polymers, interact with
intracellular substances, so that the vital bacterial
activities are impaired (Aranda-Martinez et al., 2016).
Fig. 2 Cell wall architecture and antibacterial activity of
chitosan against gram-negative bacteria
Chao DUAN et al.: Chitosan as A Preservative for Fruits and Vegetables: A Review on Chemistry and Antimicrobial Properties 15
Fig. 3 Cell wall architecture and antibacterial activity of
chitosan against gram-positive bacteria
Raafat et al. (2008) reported simultaneous permeation
of the cell membrane to small cellular components,
coupled to a significant membrane depolarization. No
concomitant cell wall biosynthesis was observed. Later
they analyzed multiple changes in the expression profile
of S. aureus SG11 genes which are involved with the
regulation of stress and autolysis and the genes involved
with energy metabolism and postulated a possible
mechanism for chitosan’s activity. Chung and Chen (2008)
found that the removal ratios of chitosan for S. aureus
protoplasts and E. coli spheroplasts were significantly
higher than those for intact cells during the first 3–4 h of
contact time, indicating chitosan-cell wall interaction is
more intense than other cell membranes.
In another study, chitosan in gel form was used in the
antibacterial tests carried out by turbidity and well
inhibition zone showing chitosan consistently more active
against the gram-positive S. aureus than gram-negative E.
coli (Goy et al., 2016). Morimoto et al. (2001) reported
that chitosan derivatives have better specific binding
activity on the cell wall of Pseudomonas aerogenosa. Lal
et al. (2013) reported the interaction of chitosan with cell
surface polymers such as teichoic acid of gram-positive
bacteria, which is consistent with the fact that binding of
chitosan with the lipopolysaccharide layer of a gram-
negative bacterial cell wall, would not significantly affect
the susceptibility. However, adherence due to electrostatic
interaction may cause secondary effects on cytoplasmic
membrane such as disruption of cell membrane, which
finally results in leakage of small cellular components.
The similarity between the antibacterial profiles and
patterns of chitosan and those of two other control
substances, polymyxin and ethylene diamine tetraacetic
acid (EDTA), verified amino group assisted mechanism
of chitosan. Helande et al. (2001) detailed the specific
binding mechanism of chitosan on gram-negative bacteria
that relates weakening of barrier function of outer
membrane. Chemical and electrophoretic analyses of free
cell supernatants of chitosan-treated cell suspensions
showed that interaction of chitosan with E. coli and S.
typhimurioum involved no release of the LPS or other
membrane lipids. This was further evidenced by using
highly cationic mutants of S. typhimurioum which was
more resistant to chitosan than parent strains. In the same
study, they found chitosan caused extensive cell surface
alterations and covered the outer membrane with
vesicular structures as shown in their electron microscopy
study (Helander et al., 2001). The activity of chitosan on
gram-positive and gram-negative bacteria was again
evidenced, and established that chitosan in acid pH is
extensively protonated and bound with carboxyl and
phosphate groups of the bacterial surface which offers
potential sites for electrostatic binding of chitosan (Li et
al., 2016). It should be noted that chitosan shows broad
spectrum activity on microorganisms except the fungi
which contain chitosan as wall constituent. Chitosan’s
antimicrobial activity (as preservative) is often limited to
food, such as the F&V products with low protein and
NaCl content (Roller and Covill, 1999).
4 Application of Chitosan as a Food Preservative
4.1 Edible coatings and films
The use of chitosan is widely investigated as an edible
coating, which is defined as the formation of a thin film
directly on the surface of the product they are intended to
protect. Edible coatings/films form a protective barrier
around the F&V and can be consumed along with the
coated product (Kerch, 2015). In the F&V preservative
applications, the creation of a moisture and gas barrier may
lead to weight loss and respiration rate reductions with a
consequent general delay in spoilage, which will extend
the shelf-life of the product (Chien et al., 2007). Water
vapor permeability (WVP) and oxygen permeability (OP)
are the barrier properties commonly studied to determine
the ability to protect foods from the environment
(Valencia-Chamorro et al., 2011). Edible chitosan films
are extremely good barriers for permeation of oxygen,
while exhibiting relatively low water vapor barrier
characteristics (Khan et al., 2012). Films and coatings
develop selective permeability characteristics, especially
to O2, CO2 and ethylene and allow some control of fruits
respiration and reduce growth of microorganisms
(Dominguez-Martinez et al., 2017). Coating practice has
long been followed for preservation of citrus, apples
(shellac and carnauba wax), tomatoes (mineral oil) and
cucumbers (various waxes). Schematic diagram of the
effect of chitosan coating on the physiological properties
of fruits and vegetables is shown in Fig. 4.
According to El Ghaouth et al. (1992), chitosan coated
tomatoes were prevented from attacks of Penicillium spp.,
Aspergillus spp., Rhizopus stolonifer and Botrytis cinerea.
Moreover, Chitosan has itself, the ability to control some
fungal diseases, which deteriorate fruits quality during
storage (Romanazzi et al., 2013). Studies were also carried
out on papaya (Carica papaya L.), which incur 20%–30%
loss post-harvest stage (Romanazzi et al., 2017). Post-
harvest deterioration of papaya is a microbiological
process; the fruits become a target of several pathogens in
the market thus decreasing its acceptability and shelf life.
The storage life of papaya was extended up to 33 through
the use of calcium chloride (2%) with chitosan coatings on
fruits. Kim et al. (2011) reported that low MW chitosan
Journal of Bioresources and Bioproducts, 2019, 4(1): 1121
showed better antimicrobial activity against E. coli
whereas chitosan samples with broad MW range (1–1671 ku)
were effective to inhibit Listeria monocytogenes. Wang
et al. (2017) also reported strong in vitro and in vivo
antifungal activity of chitosan samples with low MW (50
ku). The in vivo antifungal activity was tested on pear
fruits. It was reported that the fungal proliferation was
much lower for the pear fruits coated with chitosan. The
coating also reduced the rate of browning and
demonstrated a dose dependent reduction in browning
incidence over a 34-day storage. Similarly, chitosan
coating was found to be effective to enhance the firmness,
delay ripening and reduce browning of peach fruits (Ma
et al., 2013).
Raafat et al. (2008) demonstrated and performed
challenge tests to establish chitosan’s activity against
potential bacterial contaminants for up to 28 d. Another
good example of chitosan’s use in coating application is in
the preservation of mango (Abbasi et al., 2009).
Biochemical reactions are involved with the ripening
process and softening of mango texture which results in a
series of consequences such as increased respiration,
ethylene production, change in structural polysaccharides
causing softening, degradation of chlorophyll, developing
pigments by carotenoids biosynthesis, change in
carbohydrates or starch conversion into sugars, organic
acids, lipids, phenolics and volatile compounds (Abbasi et
al., 2009). The chitosan-based coating can effectively slow
down these processes.
As discussed, coating and film are the most popular
Fig. 4 Effect chitosan coating on fruits and vegetables
methods of using chitosan for food/fruit preservation.
With the continuing increased demands of using natural
preservatives, chitosan may be added as an ingredient to
food/fruits. Literature review on this topic is available.
For example, Sharif et al. (2017) published an excellent
review with detailed preservation methods, focusing on
the use of natural preservatives as alternative to artificial
4.2 Chitosan derivatives
Amino groups of chitosan could be suitably modified to
impart desired properties and distinctive biological
Chao DUAN et al.: Chitosan as A Preservative for Fruits and Vegetables: A Review on Chemistry and Antimicrobial Properties 17
functions to chitosan. Chemical modification of chitosan
has been discussed in the context of functionality (Islam
et al., 2017). The unique amino group’s functionality
involves chemical reactions such as acetylation,
quaternization, reactions with aldehydes and ketones,
alkylation, grafting, chelation of metals, etc. resulting in a
variety of products exhibiting the properties such as
antibacterial, anti-fungal, anti-viral, anti-acid, non-toxic,
non-allergenic, biocompatibility and biodegradability, etc.
On the other hand, the hydroxyl functional groups also
give various reactions such as O-acetylation, H-bonding
with polar atoms, grafting, etc. (Oyervides-Muñoz et al.,
One such chitosan derivative, carboxymethyl chitosan,
of different molecular weights was prepared and was
applied on peaches using a dipping treatment. The authors
found that low molecular weight chitosan has better
preservative and antioxidant activity than that of high
molecular weight (Elbarbary and Mostafa, 2014). Since
chitosan and its derivatives have solubility in acetic acid
which has inherent antimicrobial activity, it is important
to determine the allowable concentration of acetic acid.
Liu et al. (2006) determined that acetic acid concentration
more than 0.02% (i.e., 0.05%–0.10%) is bactericidal
against E. coli whereas at low concentrations below
0.02% acetic acid had no antibacterial activities. The low
molecular weight chitosan concentration (more than
0.005%) showed exceeding activity over acetic acid and
chitosan’s concentration over 0.02%, and it killed almost
all bacteria.
Water soluble chitosan derivatives such as ethylamine
hydroxyethyl chitosan, chitosan lactate, chitosan hyd-
roglutamate were prepared and their activity was tested
against S. aureus, Listeria monocytogenes, Bacillus
cereus, E. coli, Shigella dysenteriae and Salomonella
typhimurium (Chung et al., 2011). The authors found that
chitosan-glucosamine derivative showed relatively higher
activity than the acid soluble chitosan. Their results
showed that these derivatives may be a promising
commercial substitute for acid-soluble chitosan. Schiff
base types of chitosan-saccharide derivatives, were
identified as good performers against various bacteria
(Ying et al., 2011). Benhabiles et al. (2013) developed N,
O-carboxymethyl chitosan (NOCC), and found that
tomatoes coated with the NOCC solutions had extended
shelf life. Several oligochitosan based formulations have
shown potential antimicrobial activity. Essential oils,
organic acids, inorganic compounds, inorganic
nanoparticles and composites enhance the antimicrobial
activity of chitosan. Lemon essential oils enhanced
chitosan’s activity against fungi on strawberries
inoculated with a spore suspension of Botrytis cinerea
(Perdones et al., 2012).
4.3 Chitosan Based Formulations
Chitosan was used to determine the synergistic activity
with sulfamethoxazole, a sulfonamide antimicrobial agent
(Lal et al., 2013). They used and compared wild and
mutant P. aeruginosa to unveil the efflux mechanism of
chitosan in combination with Sulphamethoxazole. Other
than benzoate, Chitosan has been reported to potentiate
the antimicrobial activity for a number of other
preservatives such as phenethyl alcohol, benzoic acid and
phenylmercuric acetate against a number of test strains
(Lei et al., 2014).
The effect of chitosan coating in combination with
phytic acid in fresh cut lotus root preservation has been
investigated and the results showed decreased weight loss,
postponed browning, restrained activities of peroxidase
(POD), polyp h enol oxidas e , an d phe n yl alanine
ammonia-lysae and increased content of vitamin C and
polyphenol (Yu, 2012a). Romanazzi et al. (2017) reported
that chitosan mixed with ethanol, wax and similar types
of organic materials, improved the protecting effect on
grapes from gray mold compared to the application
chitosan alone. Inorganic compounds such as calcium
ions (calcium gluconate) in combination with chitosan
helped the structural integrity of fruits and vegetable
membranes thus maintaining firmness of fruits skin in
addition to reducing fungal incidences (Kou et al., 2014).
Calcium gluconate at concentration of 0.5% with 1.5% or
1.0% with chitosan showed better antifungal activity than
chitosan only. The incorporation of calcium ions in fruits
tissue promo tes new crosslinks between anionic
homo-galacturonans, strengthening the cell wall and
particularly the middle lamella. The complex of zinc and
cerium in combination with chitosan was used for shelf
life extension of Chinese jejube fruits (Wu et al., 2010).
Addition of nano-silicon dioxide (0.04%) in 1%
chitosan solution decreased weight loss and respiration
rates, indicating that chitosan’s filmogenic property was
increased (Yu et al., 2012b). Reports are available on
combination treatment i.e., chitosan-heat, chitosan-1-met-
hylcycloprpene (1-MCP, ethylene inhibitor), chitosan and
modified packaging etc. (Zhong and Xia, 2007). In all
these cases, chitosan’s activity was increased compared to
the activity of chitosan alone. Coating on citrus fruits
following a layer by layer approach such as using
cellulose derivatives, methylcellulose, hydroxypropyl
cellulose, carboxymethyl cellulose and chitosan coatings,
were investigated, and the results showed that
carboxymethyl cellulose as internal layer and chitosan as
external layer gave the best performance for keeping
mandarins unaffected (Arnon et al., 2015). They also used
several formulations of carboxymethyl cellulose, with
steric acid, oleic acid, glycerol, and the results were
Journal of Bioresources and Bioproducts, 2019, 4(1): 1121
compared with commercial wax. Several parameters of
fruits such as firmness, weight loss, ethanol concentration,
external appearance, ripening progression, sensory
evaluations, disease incidence etc. were considered and
they found the presence of chitosan coating contributed to
fruits preservation very effectively (Zhong and Xia, 2007).
The antimicrobial activity and minimum inhibitory
concentration of chitosan glucose complex as a novel
preservative was estimated and found effective against
common spoilage microorganisms for fruits and
vegetables such as E. coli, Psudomonas, S. aureus and B.
cereus (Jiang et al., 2012). Chitosan-glucose complex was
found to have both antioxidant and antimicrobial activity
and thus a promising novel preservative for various fruits.
Combined treatment of UV and coating with 1.5%
Chitosan resulted in decrease of decay for Jejubes and
restrained increased respiration rate, weight loss,
malonaldehyde content and electrolyte leakage (Zhang et
al., 2014).
4.4 Irradiated chitosan
Different types of irradiated chitosan coatings were
studied for enhancing the shelf life and improving quality
of mangos. The effect of coating with irradiated crab and
shrimp chitosan (MW=5.14×104) and un-irradiated crab
chitosan (MW=2.61×105) on postharvest preservation of
mangos (Mangifera indica L.) was studied (Abbasi, 2009)
and results showed effectiveness at an appreciable level.
The effect of both control and irradiated chitosan was
observed on the fruits-spoiling fungi (Colletotrichum
gleosporioides). The percentages of spoiled fruits were
13.3% and 6.9% respectively, for untreated and treated
mangoes after 14 d of storage. At the end of storage, the
control fruits were fully spoiled. However, 75% of
irradiated chitosan coated fruits were not attacked by
diseases. In another study (Oyervides-Muñoz et al., 2017),
it was reported that the application of irradiated chitosan
was effective on preservation of fresh fruits, as well as
limiting the growth of fungi without affecting ripening
characteristics of fruits. In a recent study, the use of a
150ku MW chitosan for coating over papaya was
compared to chitosan of 300ku MW (Dotto et al., 2015)
and an increased shelf life of papayas at ambient storage
temperatures was found and the count of mesophilic
bacteria, yeasts and molds were substantially decreased.
They explained that chitosan of 150 ku has less organized
structure with lower crystallinity and a rough surface with
protuberances and cavities which improved its solubility
in acid solvent, forming a more homogeneous solution
and consequently a more homogeneous coating was
4.5 Toxicity of chitosan
The toxicity of chitosan and its derivatives has been a
well- studied subject, and a thorough review paper on the
topic was competed by Kean and Thanou (2010).
Chitosan is a non-toxic, biologically compatible polymer.
Its use for dietary applications is well known in many
different countries and it has been approved by the Food
and Drug Administration for use in wound dressings.
5 Summary
Chitosan, due to having amino groups available to
interact with microbial cell walls when applied to fruits
and vegetables, causes ultimate death of bacteria and
fungi through cell lysis mechanisms. Chitosan can have
interactions with selective microorganisms, and the
chitosan based formulations have been studied for
augmenting the activity of chitosan for fruits and
vegetable preservation. In many reports, chitosan has
shown to be an effective natural antimicrobial agent based
on the electrostatic mechanism, and control of respiration
rate, weight loss and water loss, without affecting taste,
odor and palatability of skinned and fresh cut fruits and
vegetables. The polymeric nature of chitosan is
structurally tuned in utilizing antimicrobial properties
against microorganisms, it can also produce a protective
barrier on fruits and vegetables. Although both
gram-positive and gram-negative bacteria are sensitive to
the antimicrobial activity of chitosan, the former is more
sensitive than the latter due to the difference of molecular
architectural features in cell walls (negative charge
distribution and availability). Optimization of molecular
weight in relation to antimicrobial activity and further
understanding molecular mechanisms may pave the way
for commercial technologies to use chitosan for
preservation of fruits and vegetables. Irradiation is a good
choice for producing low MW chitosan that not only
gives oligo-chitosan, but also influences deacetylation
without leaving any chemical residues. Radiation has a
good sterilization effect as well. In this way, chitosan can
be produced cost effectively with a high degree of
deacetylation using green technology. Technological
parameters, costs, environmental impact or details about
producing of chitosan are presented in this review,
especially industrial methods or with radiation
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... It has been shown that an edible chitosan coating maintained the post-harvest quality of strawberries [19,20], ber fruit [21], apples, tomatoes, cucumbers [22] and figs [16]. Dam et al. [23] found that the combined application of calcium gluconate and chitosan maintained the quality of strawberries for up to 10 days, while more than 60% of untreated fruit turned rotten. ...
... After 12 days, the control treatment had the highest percentage of weight loss (16%), and strawberries treated with CTS had the lowest (8%). The 0.1% CTS and CTS-Pro NP coatings formed a smooth, semi-permeable layer on the fruit surface and served as a protective barrier to reduce transpiration [22]. ...
Full-text available
Edible coatings are an appropriate way to preserve the quality of horticultural crops and reduce post-harvest losses. In this study, treatments with proline (Pro), chitosan (CTS) and proline-coated chitosan nanoparticles (CTS-Pro NPs) to maintain quality and reduce the decay of strawberry fruit were examined during storage at 4 °C for 12 days. The strawberries were treated with Pro 1 and 5 mM, CTS at 0.1% (w/v), CTS-Pro NPs at 0.1% (w/v) and distilled water (control) at 20 °C for 5 min. Following 3, 6, 9 and 12 days of cold storage, the fruits were removed from refrigeration, and some traits were evaluated one day after storage under shelf-life conditions. The results indicated that the fruit coated with CTS and CTS-Pro NPs showed reduced malondialdehyde and hydrogen peroxide content and less decay and weight loss compared to control and proline. CTS-Pro NPs also preserved fruit quality by conserving higher levels of ascorbic acid, total soluble solids, total phenolic content, and antioxidant capacity and enzymes. These results confirmed the benefit of using chitosan and CTS-Pro NP coatings to maintain fruit quality and increase the shelf life of strawberries by enhancing their antioxidant system and their ability to eliminate free radicals under cold storage.
... The results of the antimicrobial activity tests of CH-based films are shown in Tables 5a and 5b. The antimicrobial activity of T 16 chitosan film against bacteria, yeast, and molds was the highest because of the binding of positively charged amino groups of chitosan to the primarily anionic components of the bacteria surface [72]. Chitosan has an inherent antimicrobial capability [73]. ...
Full-text available
This study includes development of chitosan-based films with incorporated essential thyme oil and different combinations of cross-linkers viz., ZnO, CaCl2, NC, and PEG for the safe storage of sweet cherries. The resulting films stored with sweet cherries were analyzed for different physicochemical and antimicrobial properties. Incorporation of ZnO, CaCl2, NC, and PEG in chitosan-based films maintained fruit quality by conserving higher total soluble solids, titratable acidity, and reduced weight loss. The combined ZnO + CaCl2 + NC + PEG in chitosan-based films also suppressed microbial activity. The sensorial quality of fruits stored with CH + ZnO + CaCl2 + NC + PEG treatment was also stable during storage. In conclusion, the combined CH + ZnO + CaCl2 + NC + PEG with added thyme oil application is an effective approach to maintain the postharvest quality and could be an alternative to increase the shelf life of sweet cherries, besides decreasing environmental impacts of non-biodegradable packages.
... TiO2-NTs continuously release CIP in an aqueous microenvironment. However, Cs, which helps to maintain the release of CIP, also has an antibacterial effect [54]. The other reason for this antibacterial effect is the large surface area of TiO2-NTs, which leads to higher adhesion to bacteria cells [55,56]. ...
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Due to their high entrapment efficiency, anodized titanium nanotubes (TiO2-NTs) are considered effective reservoirs for loading/releasing strong antibiotics whose systemic administration is associated with diverse and severe side-effects. In this study, TiO2-NTs were synthesized by anodic oxidation of titanium foils, and the effects of electrolyte percentage and viscosity on their dimensions were evaluated. It was found that as the water content increased from 15 to 30%, the wall thickness, length, and inner diameter of the NTs increase from 5.9 to 15.8 nm, 1.56 to 3.21 µm, and 59 to 84 nm, respectively. Ciprofloxacin, a highly potent antibiotic, was loaded into TiO2-NTs with a high encapsulation efficiency of 93%, followed by coating with different chitosan layers to achieve a sustained release profile. The prepared formulations were characterized by various techniques, such as scanning electron microscopy, differential scanning calorimetry, and contact measurement. In vitro release studies showed that the higher the chitosan layer count, the more sustained the release. Evaluation of antimicrobial activity of the formulation against two endodontic species from Peptostreptococcus and Fusobacterium revealed minimum inhibitory concentrations (MICs) of 1 µg/mL for the former and the latter. To summarize, this study demonstrated that TiO2-NTs are promising reservoirs for drug loading, and that the chitosan coating provides not only a sustained release profile, but also a synergistic antibacterial effect.
... The mechanical and the preservation properties of gelatin based packaging can be improved by the incorporation of other polymers such as CS and metallic NPs [10]. CS is a non-toxic polysaccharide which exhibits good film forming capacity, biodegradability and mechanical and barrier properties [11]. The addition of silver NPs to gelatin composite films has been reported to improve the barrier properties [12]. ...
Full-text available
Synthetic plastics are causing serious environmental and health problems due to which the concept of developing biodegradable food packaging has gained considerable attention. In this study, extraction of gelatin from chicken feet was optimized followed by characterization of gelatin. Chicken feet gelatin was used to develop biodegradable nanocomposite films by the incorporation of chitosan (CS) and zinc oxide (ZnO) nanoparticles (NPs). Gelatin nanocomposite films were used to increase the shelf-life of fresh grapes by determining the browning index, weight loss, and microbial profile of fresh grapes. A high yield (7.5%) of gelatin and Bloom strength (186 g) were obtained at optimized extraction conditions (pretreatment with 4.2% acetic acid and extraction at 66 ◦C for 4.2 h). Electrophoretic analysis of gelatin revealed the presence of α (130–140 kDa) and β chains (195–200 kDa), whereas a Fourier transformed infrared (FTIR) spectrometer confirmed the presence of amide A and B and amide I, II, and III. Incorporation of ZnO NPs in a gelatin–CS matrix improved the barrier and the mechanical and the thermal properties of films. Gelatin nanocomposite films with 0.3% ZnO NPs significantly reduced the weight loss (23.88%) and the browning index (53.33%) of grapes in comparison to control treatments. The microbial count in artificially inoculated grapes wrapped in gelatin nanocomposite films remained below 4 log CFU/mL until the fifth storage day in comparison to control treatments. The gelatin from poultry byproducts such as chicken feet can serve as an efficient biopolymer to develop biodegradable food packaging to enhance the shelf-life of perishable food products.
... CHNPs had inhibitory zones ranging from 20.0 to 25.5 mm for bacterial strains, while for fungi strains were 17.3 to 19.0 mm. According to Duan [28], this strong bactericidal activity is due to a change in the cell permeability barrier caused by interactions between the positively charged chitosan and the negatively charged bacteria cell membranes. ...
Full-text available
Apricots are a fragile fruit that rots quickly after harvest. Therefore, they have a short shelf-life. The purpose of this work is to determine the effect of coatings containing chitosan (CH) as well as its nanoparticles (CHNPs) as thin films on the quality and shelf-life of apricots stored at room (25 ± 3 °C) and cold (5 ± 1 °C) temperatures. The physical, chemical, and sensorial changes that occurred during storage were assessed, and the shelf-life was estimated. Transmission electron microscopy was used to examine the size and shape of the nanoparticle. The nanoparticles had a spherical shape with an average diameter of 16.4 nm. During the storage of the apricots, those treated with CHNPs showed an obvious decrease in weight loss, decay percent, total soluble solids, and lipid peroxidation, whereas total acidity, ascorbic acid, and carotenoid content were higher than those in the fruits treated with CH and the untreated fruits (control). The findings of the sensory evaluation revealed a significant difference in the overall acceptability scores between the samples treated with CHNPs and the other samples. Finally, it was found that CHNP coatings improved the qualitative features of the apricots and extended their shelf-life for up to 9 days at room temperature storage and for 30 days in cold storage.
... To broaden its range of application, chitin is deacetylated into chitosan, its more soluble derivative. Due to their properties, like biodegradability, biocompatibility, non-toxicity, adsorption, antioxidant, humectant and antimicrobial activity 18,33,34 , chitin, chitosan and their derivatives are used in industrial and biomedical applications, such as agriculture, food and nutrition, tissue engineering, wastewater treatment, drug delivery, wound healing and cosmetics 19,[35][36][37][38][39] . Structurally, chitosan is a cationic polysaccharide consisting of D-glucosamine and N-acetyl D-glucosamine units. ...
Full-text available
Growing antimicrobial resistance has prompted researchers to identify new natural molecules with antimicrobial potential. In this perspective, attention has been focused on biopolymers that could also be functional in the medical field. Chitin is the second most abundant biopolymer on Earth and with its deacetylated derivative, chitosan, has several applications in biomedical and pharmaceutical fields. Currently, the main source of chitin is the crustacean exoskeleton, but the growing demand for these polymers on the market has led to search for alternative sources. Among these, insects, and in particular the bioconverter Hermetia illucens , is one of the most bred. Chitin can be extracted from larvae, pupal exuviae and dead adults of H. illucens , by applying chemical methods, and converted into chitosan. Fourier-transformed infrared spectroscopy confirmed the identity of the chitosan produced from H. illucens and its structural similarity to commercial polymer. Recently, studies showed that chitosan has intrinsic antimicrobial activity. This is the first research that investigated the antibacterial activity of chitosan produced from the three developmental stages of H. illucens through qualitative and quantitative analysis, agar diffusion tests and microdilution assays, respectively. Our results showed the antimicrobial capacity of chitosan of H. illucens, opening new perspectives for its use in the biological area.
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Mechanical wound on fruit triggers the formation of reactive oxygen species (ROS) that weaken cell walls, resulting in post-harvest losses. This mechanism can be controlled by using fruit preservatives to stimulate fruit antioxidant enzyme activities for the detoxification of ROS. Chitosan is a safe and environmentally friendly preservative that modulates ROS in whole fruits and plant cells, but the effects of chitosan on the ROS metabolism of mechanically wounded apples during storage are unknown. Our study focused on exploring the effects of post-harvest chitosan treatment on ROS production, cell membrane integrity, and enzymatic and non-enzymatic antioxidant systems at fruit wounds during storage. Apple fruits (cv. Fuji) were artificially wounded, treated with 2.5% (w/v) chitosan, and stored at room temperature (21–25°C, RH = 81–85%) for 7 days. Non-wounded apples were used as healthy controls. The results showed that chitosan treatment stimulated the activities of NADPH oxidase and superoxide dismutase and increased the formation of superoxide anions and hydrogen peroxide in fruit wounds. However, malondialdehyde, lipoxygenase, and membrane permeability, which are direct biomarkers to evaluate lipid peroxidation and membrane integrity, were significantly decreased in the wounded fruits after chitosan treatment compared to the wounded control fruits. Antioxidant enzymes, such as peroxidase and catalase activities, were induced by chitosan at fruit wounds. In addition, ascorbate-glutathione cycle-related enzymes; ascorbate peroxide, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and the content of substrates, mainly ascorbic acid, dehydroascorbate, reduced glutathione, and glutathione, were increased at fruit wounds by chitosan compared to the wounded control fruits. Our results show that wounding stimulated the production of ROS or oxidative stress. However, treatment with chitosan triggered antioxidant systems to scavenge ROS and prevent loss of fruit membrane integrity. Therefore, chitosan promises to be a favorable preservative in inducing tolerance to stress and maintaining fruit quality.
Despite decades of development of biomaterials, hemorrhage remains a primary cause of death in surgeries and accidents. Effective hemostatic agents that induce hemostasis and rapid coagulation are needed by surgeons and in daily life. Here, we report on the application of hemostatic agents by studying mesoporous bioglass (MBG) doped with bismuth oxide via a two-step acid-catalyzed self-assembly (TSACSA) process. The results show that all the samples have an ordered mesoporous structure and a large surface area, especially MBG doped with 2 mol% Bi2O3 has the highest specific surface area (704.06 m²/g). MBG doped with different proportions of Bi accelerated the intrinsic coagulation pathway and was not found to exhibit severe erythrocyte cytotoxicity. It is worth noting that MBG added with 1 and 2 mol% Bi2O3 had higher thrombus formation, fibrin polymerization rates, and platelet adhesion; however, higher content of Bi2O3 (3 mol%) may affect the consequence of coagulation. These results of our investigation suggest that MBG doped with a low range of Bi is a potential hemostatic biomaterial for clinical applications.
Chitosan is a type of biopolymer that can be obtained from animal/marine sources, and it can also be extracted or produced from agriculture waste products like mushroom or different fungal sources after the chitin deacetylation. Depending on the size of mushroom farm, the amount of waste ranges between 5% and 20% of the production volume. The cell wall of the filamentous fungi, a good source of chitin, offers an easy way to extract chitin. The physicochemical characteristics such as molecular weight and degree of deacetylation of fungal chitosan can be controlled compared to chitosan obtained from crustacean sources. Fungal sourced chitosan can be used in food, pharmaceutical or biomedical applications for different applications, for example, as an antimicrobial agent, coating material, water purification or bio-pesticide. This review mainly focused on the extraction of chitin from mushroom or different fungal sources and also showed some applications of commercial chitosan products.
There are significant incentives/pressures on decreasing the use of plastics and their related products in the packaging industry, correspondingly, strong demands are emerging for clean, renewable, recyclable/ biodegradable packaging products. In this context, molded fiber/pulp products have attracted increasing attention, due to their green/sustainable advantages, simply because the raw materials used are plant-based and/or recycled fibers. Many companies have switched their packing practices from plastics to more environmentally friendly products, such as molded fiber products, which already have had and will continue to have obvious effect on packaging industries. This paper initially provides an overview on the general concept of molded pulp products, and further summarizes the different types of molded fiber products in terms of natural fiber sources, manufacturing processes, current and emerging applications as well as the environmental sustainability of molded products.
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Chemical, enzymatic or microbial activities from the surrounding environment and the food itself can cause spoilage to food products. In the meantime, the recent surge in world population, calls for food products to be stored and delivered from one place to another place. During delivery, food products will start to deteriorate, lose their appearance and decrease in nutritional values. Thus, the presence of food preservation methods such as heating, pickling, edible coating, drying, freezing and high-pressure processing can solve this problem by extending the food products‟ shelf life, stabilize their quality, maintaining their appearance and their taste. There are two categories of food preservations, the modern technology preservation method and the conventional preservation method. In the meantime, conventional food preservations usually use natural food preservatives. Meanwhile, the use of the synthetic preservative such as sulphites, benzoates, sorbates etc. for food preservation can cause certain health problems. In this light, replacing these synthetic preservatives with natural preservatives such as salt, vinegar, honey, etc. are much safer for human and environment. Furthermore, natural preservatives are easy to obtain since the sources are from plant, animal and microbes origin. This review paper focuses on preservation methods and the natural preservatives that are suitable to be used for food preservation. Chemical Engineering Research Bulletin 19(2017) 145-153
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Chitin and its deacetylated derivative chitosan are natural polymers composed of randomly distributed β-(1-4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit). Biopolymers like chitin and chitosan exhibit diverse properties that open up a wide-ranging of applications in various sectors especially in biomedical science. The latest advances in the biomedical research are important emerging trends that hold a great promise in wound-healing management products. Chitin and chitosan are considered as useful biocompatible materials to be used in a medical device to treat, augment or replace any tissue, organ, or function of the body. A body of recent studies suggests that chitosan and its derivatives are promising candidates for supporting materials in tissue engineering applications. This review article is mainly focused on the contemporary research on chitin and chitosan towards their applications in numerous biomedical fields namely tissue engineering, artificial kidney, skin, bone, cartilage, liver, nerve, tendon, wound-healing, burn treatment and some other useful purposes.
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This study aimed to develop and characterize biodegradable films containing mucilage, chitosan and polyvinyl alcohol (PVA) in different concentrations. The films were prepared by casting on glass plates using glycerol as plasticizer. Mechanical properties, water vapor and oxygen barrier, as well as the interaction with water, were measured. The compatibility of the film-forming components and the uniformity of the films were determined by zeta potential and SEM, respectively. The glycerol and mucilage allowed obtaining more hydrophilic films. The barrier properties of the films made from 100 % chitosan were similar to composed films containing PVA up to 40 %. The results of this study suggest that the interaction between chitosan and mucilage could increase water vapor permeability. The films prepared from either 100 % chitosan or PVA showed a more hydrophobic behavior as compared to the composed films. The films were homogenous since no boundary or separation of components was observed, indicating a good compatibility of the components in the films.
The freshness and safety of fruits and vegetables is important in our daily life. Paper products are often used for shipping, wrapping, and decoration in the retail for fruits and vegetables. When these paper products are modified with active substances, they can offer additional functions other than just packaging. Thus, introducing 1-methylcyclopropene (1-MCP) into paper products can impart a preservation function for fruits and vegetables. 1-MCP is an excellent and eco-friendly inhibitor of ethylene that can effectively retard the ripening of fruits and vegetables. This article reviews the ripening process induced by ethylene, the inhibition mechanism of 1-MCP, and the existing technologies and products for 1-MCP utilization. Novel active paper packaging products via the use of encapsulated 1-MCP complexes may have a great potential for commercialization. Such packaging containing 1-MCP active paper could be effective in prolonging the shelf-life and improving the quality of the product during the storage, shipping process, and retail market, and can be attractive economically, socially, and environmentally.
Functionalized high molar mass chitosan derivatives with increased antibacterial properties were prepared by the reaction of chitosan with different quaternary ammonium salts. Benzalkonium bromide, pyridinium bromide and triethyl ammonium bromide were synthesized by a quaternization reaction between 1,4-dibromobutane and the respective tertiary amines (N, N-dimethylbenzylamine, triethylamine and pyridine) to obtain three ammonium salts with a bromide end-group capable of reacting with a functional group from the chitosan backbone. The ammonium salts were chemically grafted along the chitosan macromolecular chains. Four different chitosan derivatives were obtained and their chemical structures analyzed and confirmed by ¹H NMR and FT-IR. The corresponding thermal stability was analyzed by TGA. Antibacterial activity has been assessed by determining their minimal inhibitory concentration upon Escherichia coli and Staphylococcus aureus. Furthermore, the antibiogram method was used to complement the antibacterial analysis. The bacteria inhibitory property of the chitosan derivatives exhibited a remarkable improvement compared to unmodified chitosan.
Chitosan antifungal activity has been reported for both filamentous fungi and yeast. Previous studies have shown fungal plasma membrane as main chitosan target. However, the role of the fungal cell wall (CW) in their response to chitosan is unknown. We show that cell wall regeneration in Neurospora crassa (chitosan sensitive) protoplasts protects them from chitosan damage. Caspofungin, a β-1,3-glucan synthase inhibitor, showed a synergistic antifungal effect with chitosan for N. crassa but not for Pochonia chlamydosporia, a biocontrol fungus resistant to chitosan. Chitosan significantly repressed N. crassa genes involved in β-1,3-glucan synthesis (fks) and elongation (gel-1) but the chitin synthase gene (chs-1) did not present changes in its expression. N. crassa cell wall deletion strains related to β-1,3-glucan elongation (Δgel-1 and Δgel-2) were more sensitive to chitosan than wild type (wt). On the contrary, chitin synthase deletion strain (Δchs-1) showed the same sensitivity to chitosan than wt. The mycelium of P. chlamydosporia showed a higher (ca. twofold) β-1,3-glucan/chitin ratio than that of N. crassa. Taken together, our results indicate that cell wall composition plays an important role on -sensitivity of filamentous fungi to chitosan.
Chitosan with different degree of deacetylation (DD) and ultra high molecular weight (MW >106) was prepared from β-chitin by mild deacetylation. The effects of DD of chitosan and pH value of its solution/suspension on its antibacterial activity were investigated. The results showed that the optimal pH value was 6.0 for the highest bactericidal activity. The antibacterial activity against Escherichia coli and Staphylococcus aureus of chitosan solution at pH 6.0 enhanced as the DD of chitosan increased. Same as chitosan with low MW, the antibacterial activity of chitosan with high MW in acidic solution was also due to the amino protonation and subsequently cationic formation. Its ultra long molecular chain was propitious to coat and bind the E. coli and S. aureus, and highly enhanced its antibacterial activity. E. coli and S. aureus were at first restrained and then killed by chitosan and the cells were ruptured and decomposed gradually.
Chitosan as one of the natural biopolymers with antimicrobial activities could be a good choice to be applied in many areas including pharmaceuticals, foods, cosmetics, chemicals, agricultural crops, etc. There have been many studies in the literature which show this superb polymer is dependent on many factors to display its antimicrobial properties including the environmental conditions such as pH, type of microorganism, and neighbouring components; and its structural conditions such as molecular weight, degree of deacetylation, derivative form, its concentration, and original source. In this review, after a brief explanation of antimicrobial activity of chitosan and its importance, we will discuss the factors affecting the antimicrobial properties of this biopolymer based on recent studies.