BÁO CÁO KHOA HỌC " Changes in microbial and postharvest quality of shiitake mushroom (Lentinus edodes) treated with chitosan–glucose complex coating under cold storage " pptx

Changes in microbial and postharvest quality of shiitake
mushroom (Lentinus edodes) treated with chitosan–glucose
complex coating under cold storage
Tianjia Jiang, Lifang Feng, Jianrong Li
⇑
College of Food Science and Biotechnology, Zhejiang Gongshang University, Food Safety Key Lab of Zhejiang Province, Hangzhou 310035, PR China
article info
Article history:
Received 13 July 2011
Received in revised form 23 August 2011
Accepted 23 August 2011
Available online 19 September 2011
Keywords:
Chitosan-glucose complex
Shiitake mushroom
Microbiological quality
Sensory evaluation
Storage life
abstract
The effect of chitosan, glucose and chitosan–glucose complex (CGC) on the microbial and postharvest
quality of shiitake (Lentinus edodes) mushroom stored at 4 ± 1 °C for 16 days was investigated. Mushroom
weight loss, respiration rate, firmness, ascorbic acid, total soluble solids, microbial and sensory quality
were measured. The results indicate that treatment with CGC coating maintained tissue firmness, inhib-
ited increase of respiration rate, reduced microorganism counts, e.g., pseudomonads, yeasts and moulds,
compared to uncoated control mushroom. The efficiency was better than that of chitosan or glucose coat-
ing treatment. In addition, CGC coating also delayed changes in the ascorbic acid and soluble solids con-
centration. Sensory evaluation proved the efficacy of CGC coating by maintaining the overall quality of
shiitake mushroom during the storage period. Our study suggests that CGC coating might be a promising
candidate for maintaining shiitake mushroom quality and extending its postharvest life.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction

Shiitake (Lentinus edodes) mushroom is highly perishable and
tends to lose quality immediately after harvest. Its shelf life is short
because of its high respiration rate, tendency to turn brown and
having no physical protection to avoid water loss or microbial at-
tack (Simón, González-Fandos, & Tobar, 2005). Bacteria, moulds,
enzymatic activity and biochemical changes can cause spoilage
during storage. Gram-negative microorganisms, such as Pseudomo-
nas tolaasii, Pseudomonas fluorescens and yeasts, such as Candida
sake, have been associated with mushroom spoilage (Masson,
Ainsworth, Fuller, Bozkurt, & Ibanoglu, 2002). The short shelf-life
of mushroom is an impediment to the distribution and marketing
of the fresh product.
The use of modified atmosphere packaging as an adjunct to low
temperature storage has been extensively reported to extend the
shelf-life of shiitake mushrooms (Ares, Parentelli, Gámbaro, Lareo,
& Lema, 2006; Jiang, Wang, Xu, Jahangir, & Ying, 2010). Jiang, Luo,
Chen, Shen, and Ying (2010) also reported application of gamma-
irradiation in combination with MAP can extend the storage life
of shiitake mushroom up to 20 days.
Chitosan [b-(1,4)-2-amino-2-deoxy-
D
-glucopyranose], which is
mainly made from crustacean shells, is the second most abundant
natural polymer in nature after cellulose (Shahidi, Arachchi, & Jeon,
1999). Due to its non-toxic nature, antioxidative and antibacterial
activity, film-forming property, biocompatibility and biodegrad-
ability, chitosan has attracted much attention as a natural food
additive (Majeti & Ravi, 2000). Chitosan has been used in foods,
as a clarifying agent in apple juice, and antimicrobial and
antioxidant in muscle foods (Gómez-Estaca, Montero, Giménez, &

Gómez-Guillén, 2007; Kim & Thomas, 2007). Furthermore, chito-
san also has potential for food packaging, especially as edible films
and coatings (Tual, Espuche, Escoubes, & Domard, 2000). It has
been used to maintain the quality of postharvest fruits and
vegetables, such as citrus (Chien, Sheu, & Lin, 2007), tomatoes (El
Ghaouth, Ponnampalam, Castaigne, & Arul, 1992), apples (Ippolito,
El Ghaouth, Wilson, & Wisniewski, 2000), longan fruit (Jiang & Li,
2001), peach, pear and kiwifruit (Du, Gemma, & Iwahori, 1997).
Several researchers have developed methods to improve the
properties of chitosan using chemical and enzymatic modifica-
tions. However, chemical modifications are generally not preferred
for food applications because of the formation of potential
detrimental products. Chitosan–lysozyme conjugates have been
reported to have better emulsifying properties and bactericidal
action (Song, Babiker, Usui, Saito, & Kato, 2002).
The Maillard reaction, resulting from condensation between the
carbonyl group of reducing sugars, aldehydes or ketones and an
amine group of amino acids, proteins or any nitrogenous
compound, is one of the main reactions taking place in food. Mail-
lard reaction compounds contribute to flavour formation, antioxi-
dative and antimicrobial effects and improvement of functional
0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.foodchem.2011.08.087
⇑
Corresponding author. Tel./fax: +86 571 88071024.
E-mail address: (J. Li).
Food Chemistry 131 (2012) 780–786
Contents lists available at SciVerse ScienceDirect
Food Chemistry
journal homepage: www.elsevier.com/locate/foodchem

properties (Chevalier, Chobert, Genot, & Haertle, 2001). It is desir-
able to modify chitosan so that it attains excellent antioxidant
activity without affecting its antimicrobial activity. Chitosan has
an amino group which can react with the carbonyl group of a
reducing sugar. Hence, chitosan was heated with glucose to form
a Maillard reaction product. Kanatt, Chander, and Sharma (2008)
found that chitosan–glucose complex (CGC), a modified form of
chitosan prepared by heating chitosan with glucose, showed excel-
lent antioxidant activity, while chitosan or glucose alone did not
have any significant activity. On the other hand, the antimicrobial
activity of CGC was similar to chitosan against Escherichia coli,
Pseudomonas, Staphylococcus aureus and Bacillus cereus, and it can
increase the shelf life of pork cocktail salami to 28 days.
However, research on the application of CGC to fruits and veg-
etables is limited. The objectives of this work were to evaluate
the effect of CGC on the microbiological and postharvest quality
of shiitake mushrooms during cold storage.
2. Materials and methods
2.1. Materials
Shiitake (Lentinula edodes) mushrooms used in this study were
harvested from a local farm in Hangzhou, China. Mushrooms were
picked from the same flower and from the same area of the shed so
as to reduce possible variations caused by cultivation and environ-
mental conditions. The mushrooms were transported to the labo-
ratory within one hour of picking, under refrigerated conditions,
then stored in darkness at 1 ± 1 °C and 95% relative humidity (RH).
2.2. Preparation of chitosan–glucose complex (CGC) solutions and
application of treatments
Chitosan (deacetylated P95%, and viscosity 630 mPa s) was
purchased from Zhejiang Xuefeng Calcium Carbonate Co., Ltd.

(Zhejiang, China). One percentage of chitosan was prepared in 1%
glacial acetic acid. Chitosan glucose complex (CGC) was prepared
by autoclaving chitosan (1%) and glucose (1%) for 15 min. Mush-
rooms were divided into four samples of 60 each. Four different
treatments were used: (1) control; (2) 1% glucose coating; (3) 1%
chitosan coating, and (4) CGC coating. Mushrooms were dipped
into the solution for 5 min. Samples dipped in distilled water were
used as control. Treated samples were kept over a plastic sieve for
30 min and a fan generating low-speed air was used to hasten dry-
ing. Then a tissue paper was used to absorb excess solution from
the surface. The treated samples were placed and sealed in
18 cm  20 cm bags of low density polyethylene (PE) (0.04 mm
thickness) in the laboratory; the PE gas transmission rates were
1078 Â 10
À18
mol m
À1
s
À1
Pa
À1
for O
2
, 4134 Â 10
À18
mol m
À1
s
À1
Pa

À1
for CO
2
(both at 20 °C and 100% RH) and 2.8 Â 10
À5
–6.5
 10
À5
gm
À2
s
À1
for H
2
O (at 37 °C and 90% RH). They were then
stored for 16 days at 4 ± 1 °C and 95% relative humidity (RH).
Fifteen replicates were included in each treatment group, and sub-
sequently every 4 days, three replicates from each treatment group
were analysed.
2.3. Respiration rate
Respiration rate was determined according to the method of Li,
Zhang, and Yu (2006). A closed system was chosen to measure res-
piration rate of the product. At each storage time, approximately
50 g of mushrooms from the four groups were placed under nor-
mal air for 1 h. Then, mushrooms were stored at 20 °C for 1 h in
a closed container, which contained 15 mL 0.05 M Ba(OH)
2
. Then,
2 drops of phenolphthalein were added, and titrated with 1/44 M
oxalate. Measurements were replicated three times. Respiration

rates of samples were (expressed as CO
2
production rate) calcu-
lated with the following formula:
RI ¼
ðV
1
À V
2
ÞÂc  44
W Â t
In the formula, V
1
is the volume of oxalate titrated for the control
(mL); V
2
is the volume of oxalate titrated for the samples (mL); c
is the concentration of oxalate (M); 44 is the molecular weight of
CO
2
; W is the weight of samples (g); t is the test time (h).
2.4. Weight loss
Weight loss was determined by weighing the whole mushroom
before and after the storage period. Weight loss was expressed as
the percentage of loss of weight with respect to the initial weight.
2.5. Texture measurement
A penetration test was performed on the shiitake mushroom
cap using a TA.XT Express-v3.1 texture analyser (Stable Micro Sys-
tems, Godalming, UK), with a 5 mm diameter cylindrical probe.
Samples were penetrated 5 mm in depth. The speed of the probe

was 2.0 mm s
À1
during the pretest as well as during penetration.
Force and time data were recorded with Texture Expert (Version
1.0) from Stable Micro Systems. From the force vs time curves,
firmness was defined as the maximum force used.
2.6. Total soluble solids and ascorbic acid content
Mushrooms were ground in a mortar and squeezed with a hand
press, and the juice was analysed for total soluble solids (TSS). TSS
was measured at 25 °C with a digital refractometer (Atago, Tokyo,
Japan). The determination of total ascorbic acid was carried out as
described by Hanson et al. (2004), on the basis of coupling 2,
4-dinitrophenylhydrazine (DNPH) with the ketonic groups of dehy-
droascorbic acid through the oxidation of ascorbic acid by 2,6-
dichlorophenolindophenol (DCPIP) to give a yellow/orange colour
in acidic conditions. Mushroom tissues (10 g) were blended with
80 mL of 5% metaphosphoric acid in a homogeniser and centri-
fuged. After centrifuging, 2 mL of the supernatant were poured into
a 20 mL test tube containing 0.1 mL of 0.2% 2,6-DCIP sodium salt in
water, 2 mL of 2% thiourea in 5% metaphosphoric acid and 1 mL of
4% 2,4-DNPH in 9 N sulphuric acid. The mixtures were kept in a
water bath at 37 °C for 3 h followed by an ice bath for 10 min. Five
millilitres of 85% sulphuric acid were added and the mixtures were
kept at room temperature for 30 min before reading at 520 nm.
2.7. Microbiological analysis
All samples were analysed for the mesophilic, psychrophilic,
pseudomonad, and yeasts and moulds bacteria counts. Twenty-five
grams of mushrooms were removed aseptically from each pack
and diluted with 225 mL 0.1% peptone water. The samples were
homogenised by a stomacher at high speed for 2 min. Serial dilu-

tions (10
À1
–10
v9
) were made in serial dilution tubes by taking
1.0 mL with 9.0 mL of 0.1% peptone water. Aerobic counts were
determined on plate count agar (PCA; Merck, Darmstadt, Germany)
following incubation at 35 °C for 2 days for mesophilic bacteria,
and at 4 °C for 7 days for psychrophilic bacteria. Pseudomonas
was counted on cephaloridin fucidin cetrimide agar (CFC; Difco;
BD, Franklin Lakes, NJ), with selective supplement SR 103 (Oxoid,
Basingstoke, UK). The incubation temperature was 25 °C and plates
were examined after 48 h. Yeasts and moulds were estimated on
T. Jiang et al. /Food Chemistry 131 (2012) 780–786
781
potato dextrose agar (PDA; Merck) and incubation conditions were
28 ± 1 °C for 5–7 days.
2.8. Sensory evaluation
The sensory attributes that characterised mushroom deteriora-
tion were determined. These attributes were: off-odour, gill colour,
gill uniformity, cap surface uniformity, and presence of dark zones
on the cap (Ares et al., 2006). Samples were evaluated by a sensory
panel of 10 trained assessors. Mushrooms were served in closed,
odourless plastic containers at room temperature. After opening
polyethylene bags, mushrooms were placed in plastic containers
and evaluations were performed within 2 h, in order to avoid loss
of off-odours. A balanced complete block design was carried out for
duplicate evaluation of the samples. For scoring, 10 cm unstruc-
tured scales anchored with ‘‘nil’’ for zero and ‘‘high’’ for 10 were
used, except for the gill colour descriptor, for which the anchors

were ‘‘white’’ and ‘‘brown’’.
2.9. Statistical analysis
Experiments were performed using a completely randomised
design. Data were subjected to one-way analysis of variance (ANO-
VA). Mean separations were performed by Tukey’s multiple range
test (DPS Version 6.55). Differences at p < 0.05 were considered
significant.
3. Results and discussion
3.1. Effect of CGC coating on respiration rate
The main characteristics of the respiration rates of the shiitake
mushrooms treated with different kinds of coatings are shown in
Fig. 1. According to the results, throughout the storage period,
the respiration rates of coated mushrooms significantly decreased
(p < 0.05). These values were 78.2–92.6% of those of the control
samples at the beginning of the cold storage period. By Day 16,
the respiration rates of the control samples were 1.23–1.37 times
higher than those of the coated mushrooms. Internal gas atmo-
sphere modification has been suggested to be the cause of reduced
CO
2
production by coated fruits and vegetables. In this regard the
gas barrier properties and permselectivity of the edible coating ap-
plied to the skin surface and their dependence on relative humidity
and temperature will play an important role in the changes in
endogenous O
2
and CO
2
levels. It is well known that excessive
restriction of gas exchange can lead to anaerobiosis and the devel-

opment of off-flavour. Chitosan coating has been reported to
modify the internal atmosphere of tomatoes (El Ghaouth et al.,
1992), Japanese pear (Du et al., 1997) and apples (Gemma & Du,
1998) by depletion of endogenous O
2
and a rise in CO
2
, without
achieving anaerobiosis. In our study, CGC coating is more effective
in reducing the respiration rates of shiitake mushroom although
the difference between the three coating treatments was not sig-
nificant (p > 0.05). This could be because CGC coating is more effi-
cient in restricting the gas exchange between mushroom and the
atmosphere during storage.
3.2. Effect of CGC coating on weight loss
Compared with the control samples, the coated mushrooms
showed a significantly (p < 0.05) reduced weight loss during stor-
age (Fig. 2). After 16 days of storage, the mushrooms coated with
CGC and chitosan showed 2.41% and 2.71% weight loss, respec-
tively, as compared to 3.71% and 3.13% weight loss in control and
glucose-coated mushroom. Mushroom weight loss is mainly cause
by water transpiration and CO
2
loss during respiration. The thin
skin of shiitake mushrooms makes them susceptible to rapid water
loss, resulting in shrivelling and deterioration. The rate at which
water is lost depends on the water pressure gradient between
the mushroom tissue and the surrounding atmosphere and the
storage temperature. Low vapour pressure differences between
the mushroom and its surroundings and low temperature are rec-

ommended for the storage of mushrooms. Edible coatings act as
barriers, thereby restricting water transfer and protecting mush-
room epidermis from mechanical injuries, as well as sealing small
wounds and thus delaying dehydration. Chitosan coatings have
been effective at controlling water loss from some commodities,
including cucumber, pepper and longan fruit (El Ghaouth, Arul,
Ponnampalam, & Boulet, 1991; Jiang et al., 2001). Clearly, relatively
lower weight loss in CGC coated mushrooms contributed to main-
taining better quality of mushroom during cold storage.
3.3. Effect of CGC coating on texture
The texture of shiitake mushroom is often the first of many
quality attributes judged by the consumer and is, therefore,
extremely important in overall product acceptance. Shiitake mush-
room suffers a rapid loss of firmness during senescence which con-
tributes greatly to its short postharvest life and susceptibility to
fungal contamination. Fig. 3 shows that CGC and chitosan coatings
significantly (p < 0.05) reduced the loss in firmness of shiitake
mushroom during storage. There was no significant (p > 0.05)
difference in the firmness of the control mushrooms and those
60
80
100
120
140
160
180
200
0481216
Stora
g

e time (da
y
s)
Respiration rate
(mg CO
2
kg
1
h
1
)
Control
Glucose
Chitosan
CGC
Fig. 1. Effect of CGC coating on respiration rate changes of shiitake mushrooms
stored at 4 °C for 16 days. Each data point is the mean of three replicate samples.
Vertical bars represent standard errors of means.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0481216
Stora

g
e time (da
y
s)
Weight loss (%)
Control
Glucose
Chitosan
CGC
Fig. 2. Effect of CGC coating on weight loss changes of shiitake mushrooms stored
at 4 °C for 16 days. Each data point is the mean of three replicate samples. Vertical
bars represent standard errors of means.
782 T. Jiang et al. /Food Chemistry 131 (2012) 780–786
glucose coated. The maximum retention in firmness was obtained
by CGC and chitosan coating, with 2.80 N and 2.76 N firmness
values, respectively, at the end of storage. Softening can occur be-
cause of the degradation of cell walls in postharvest mushrooms by
bacterial enzymes and increased activity of endogenous autolysins
(Zivanovic, Buescher, & Kim, 2000). Microorganisms such as
Pseudomonas degrade mushrooms by breaking down the intracel-
lular matrix and reducing the central vacuole, resulting in partially
collapsed cells and a loss of turgor. This kind of bacterial-induced
softening was observed in control samples but was inhibited by
chitosan and CGC coating treatments. The maintenance of firmness
in the mushrooms treated with CGC and chitosan coatings could be
due to their higher antifungal activity, and covering of the cuticle
and lenticels, thereby reducing infection, respiration and other
senescence processes during storage, according to previous reports
in sweet cherry coated with aloe vera gel (Martínez-Romero et al.,
2006).

3.4. Effect of CGC coating on total soluble solids and ascorbic acid
content
Changes in the soluble solids content (SSC) of shiitake mush-
rooms over storage are shown in Fig. 4A. The SSC of control mush-
rooms increased after 4 days of storage whilst coated mushrooms
experienced a slight increase during the same period. The lowest
levels of SSC were recorded in CGC and chitosan-coated mushroom
at end of the storage. Tao, Zhang, Yu, and Sun (2006) have reported
an increase in SSC in button mushrooms stored at 4 ± 1 °C and 75%
RH. The effect of chitosan in reducing the increase in SSC during
storage of shiitake mushroom was probably due to the slowing
down of respiration and metabolic activity, hence retarding the
senescence process. Indeed, the greater changes in SSC occurred
in those mushrooms which suffered the greatest water loss. The
solubilisation of the cell wall polysaccharides and hemicelluloses
in senescent mushroom might also contribute to the increase in
SSC. It is well documented that the filmogenic property of chitosan
results in an excellent semi-permeable film around the vegetable
and fruit, modifying the internal atmosphere by reducing O
2
and/
or elevating CO
2
, and suppressing ethylene evolution (Dong, Cheng,
Tan, Zheng, & Jiang, 2004). A suppressed respiration rate also slows
down the synthesis and the use of metabolites, resulting in lower
SSC, due to the slower hydrolysis of carbohydrates to sugars (Roh-
ani, Zaipun, & Norhayati, 1997). Our results are in line with those of
Kittur, Saroja, Habibunnisa, and Tharanathan (2001), where a slow
rise in SSC was recorded in mango and banana treated with chito-

san. However, other studies have indicated that the SSC of chitosan
dipped papaya and zucchini were the same as in the untreated
fruits (Bautista-Baños, Hernández-López, Bosquez-Molina, & Wil-
son, 2003).
Fig. 4B shows changes in ascorbic acid content of coated and un-
coated shiitake mushrooms during 16 days storage. The initial
ascorbic acid content of shiitake mushrooms was 41.6 mg/kg.
Although ascorbic acid of both coated and uncoated samples de-
creased throughout storage, the use of CGC coating significantly re-
duced the loss of ascorbic acid in mushroom samples. After 16 days
of storage, ascorbic acid retention of mushroom treated with glu-
cose, chitosan and CGC coating was 19.3, 23.5 and 25.9 mg/kg,
respectively, whereas control samples maintained 17.7 mg/kg of
initial ascorbic acid content. Since ascorbic acid loss can be greatly
favoured by the presence of O
2
, the incorporation of chitosan to
coating formulations may reduce O
2
diffusion, slow down the res-
piration rate and consequently better preserve ascorbic acid con-
tent and delay senescence of shiitake mushroom. Similar results
were obtained by Ayranci and Tunc (2003), who reported that
methylcellulose-based edible coating reduced ascorbic acid loss
in both button mushrooms and cauliflower. The ascorbic acid con-
tent in the CGC coated samples was higher than that in the samples
coated with chitosan. It has been suggested that edible coatings
containing chitosan promote ascorbic acid loss by acting as an abi-
otic elicitor, generating reactive oxygen species (ROS), which are
scavenged by antioxidant compounds, such as ascorbic acid. CGC

coating could inhibit ascorbic acid loss, due to the protection ef-
fected by its superior antioxidant activity, as compared to chitosan
or glucose (Kanatt et al., 2008).
0
0.5
1
1.5
2
2.5
3
3.5
4
Stora
g
e time (da
y
s)
Firmness (N)
Control
Glucose
Chitosan
CGC
Fig. 3. Effect of CGC coating on firmness changes of shiitake mushrooms stored at
4 °C for 16 days. Each data point is the mean of three replicate samples. Vertical
bars represent standard errors of means.
0
1
2
3
4

5
6
7
8
9
0481216
Storage time (days)
Soluble solids concentration (%)
Control
Glu co s e
Chitos an
CGC
0
5
10
15
20
25
30
35
40
45
0481216
Stora
g
e time (da
y
s)
Ascorbic acid (mg •kg
)

Control
Glu co s e
Chitos an
CGC
A
B
Fig. 4. Effect of CGC coating on total soluble solids (A) and ascorbic acid (B) change
of shiitake mushrooms stored at 4 °C for 16 days. Each data point is the mean of
three replicate samples. Vertical bars represent standard errors of means.
T. Jiang et al. /Food Chemistry 131 (2012) 780–786
783
3.5. Effect of CGC coating on microbiological quality
Mesophilic bacteria, pseudomonads, yeasts and moulds pre-
dominated during storage in all the analysed samples. It is evident
from this study that CGC coating was more effective in reducing
microbial counts than other treatments (Table 1). In any of the
studied treatments, the psychrophilic bacteria counts increased
less than two orders during the entire storage period. All samples
Table 1
Effect of CGC coating on microbial counts (log
10
cfu g
À1
) change of shiitake mushrooms stored at 4 °C for 16 days.
a,b,c
Days at 4 °C Control Glucose Chitosan CGC
Mesophilic
0 4.12 ± 0.06
aE
4.10 ± 0.08

aE
4.16 ± 0.04
aE
4.13 ± 0.11
aD
4 4.54 ± 0.12
aD
4.38 ± 0.20
aD
4.43 ± 0.02
aD
4.45 ± 0.14
aC
8 5.30 ± 0.08
aC
5.25 ± 0.17
aC
4.76 ± 0.16
bC
4.57 ± 0.08
cC
12 5.83 ± 0.20
bB
6.10 ± 0.05
aB
5.12 ± 0.07
cB
4.84 ± 0.14
dB
16 6.61 ± 0.17

bA
6.82 ± 0.13
aA
5.47 ± 0.14
cA
5.22 ± 0.24
dA
Psychrophilic
0 1.64 ± 0.12
aD
1.62 ± 0.11
aD
1.60 ± 0.05
aC
1.61 ± 0.12
aD
4 2.24 ± 0.17
aC
2.12 ± 0.05
abC
2.27 ± 0.16
aBC
1.98 ± 0.18
bC
8 2.67 ± 0.06
aB
2.59 ± 0.09
aB
2.58 ± 0.12
aB

2.47 ± 0.09
aB
12 2.89 ± 0.02
aAB
2.92 ± 0.14
aAB
2.90 ± 0.09
aAB
2.87 ± 0.10
aAB
16 3.25 ± 0.24
aA
3.20 ± 0.24
aA
3.17 ± 0.14
aA
3.18 ± 0.17
aA
Pseudomonad
0 5.37 ± 0.16
aE
5.35 ± 0.06
aE
5.34 ± 0.13
aE
5.38 ± 0.07
aE
4 6.46 ± 0.09
aD
6.11 ± 0.08

bD
5.75 ± 0.22
bD
5.57 ± 0.14
cD
8 6.90 ± 0.27
bC
7.21 ± 0.10
aC
6.34 ± 0.18
cC
5.74 ± 0.27
dC
12 7.87 ± 0.35
aB
7.90 ± 0.07
aB
6.68 ± 0.27
bB
6.12 ± 0.24
cB
16 8.46 ± 0.21
aA
8.55 ± 0.16
aA
7.36 ± 0.15
bA
6.35 ± 0.28
cA
Yeasts and moulds

0 3.81 ± 0.11
aE
3.82 ± 0.07
aE
3.86 ± 0.05
aE
3.80 ± 0.13
aE
4 4.55 ± 0.06
aD
4.36 ± 0.13
aD
4.11 ± 0.09
bD
4.15 ± 0.06
bD
8 5.62 ± 0.04
aC
5.58 ± 0.18
aC
4.87 ± 0.16
bC
4.50 ± 0.09
cC
12 5.97 ± 0.15
aB
6.04 ± 0.27
aB
5.32 ± 0.22
bB

4.82 ± 0.18
cB
16 6.60 ± 0.22
aA
6.68 ± 0.14
aA
5.76 ± 0.21
bA
5.05 ± 0.26
cA
a
Mean of three replications ± standard deviation.
b
Means in same row with different small letters are significantly different (p < 0.05).
c
Means in same column with different capital letters are significantly different (p < 0.05).
Table 2
Effect of CGC coating on sensory attributes change of shiitake mushrooms stored at 4 °C for 16 days.
a,b,c
Days at 4 °C Control Glucose Chitosan CGC
Off-odour
00 0 0 0
4 1.62 ± 0.04
aD
1.51 ± 0.06
abD
1.54 ± 0.03
abD
1.41 ± 0.05
bD

8 2.51 ± 0.06
aC
2.20 ± 0.11
bC
2.16 ± 0.07
bC
2.19 ± 0.08
bC
12 5.35 ± 0.12
aB
5.05 ± 0.07
bB
4.22 ± 0.08
cB
3.83 ± 0.12
dB
16 7.12 ± 0.15
aA
6.93 ± 0.15
bA
5.82 ± 0.05
cA
5.52 ± 0.16
dA
Gills colour
00 0 0 0
4 1.32 ± 0.05
abD
1.23 ± 0.05
bcD

1.10 ± 0.06
cD
1.87 ± 0.11
aD
8 2.93 ± 0.09
aC
2.81 ± 0.12
abC
2.55 ± 0.06
cC
2.63 ± 0.08
bcC
12 5.41 ± 0.24
aB
5.18 ± 0.26
bB
4.17 ± 0.12
cB
5.21 ± 0.16
bB
16 7.85 ± 0.20
aA
6.73 ± 0.14
cA
5.04 ± 0.16
dA
7.37 ± 0.19
bA
Gill uniformity
010101010

4 8.47 ± 0.20
aA
8.36 ± 0.24
aA
8.12 ± 0.31
bA
8.03 ± 0.16
bA
8 6.62 ± 0.13
bB
6.53 ± 0.07
bB
7.46 ± 0.16
aB
7.34 ± 0.05
aB
12 4.95 ± 0.14
cC
5.17 ± 0.12
bC
5.72 ± 0.12
aC
5.87 ± 0.08
aC
16 4.11 ± 0.04
dD
4.32 ± 0.10
cD
5.08 ± 0.05
bD

5.32 ± 0.13
aD
Cap uniformity
010101010
4 8.53 ± 0.14
bA
8.44 ± 0.26
bA
8.60 ± 0.07
bA
8.85 ± 0.30
aA
8 7.56 ± 0.17
bB
7.42 ± 0.20
bB
7.83 ± 0.21
aB
7.91 ± 0.21
aB
12 6.20 ± 0.07
cC
6.57 ± 0.27
bC
7.21 ± 0.14
aC
7.16 ± 0.17
aC
16 5.12 ± 0.27
bD

5.22 ± 0.16
bD
6.21 ± 0.15
aD
6.11 ± 0.15
aD
Dark zones
00 0 0 0
4 1.25 ± 0.04
aD
1.17 ± 0.04
aD
0.88 ± 0.07
bD
1.07 ± 0.02
aD
8 2.32 ± 0.05
aC
2.22 ± 0.07
aC
1.73 ± 0.11
bC
1.53 ± 0.04
cC
12 3.59 ± 0.08
aB
3.33 ± 0.12
bB
2.55 ± 0.02
cB

2.12 ± 0.10
dB
16 5.72 ± 0.14
aA
4.36 ± 0.21
bA
3.12 ± 0.10
cA
2.87 ± 0.08
dA
a
Mean of three replications ± standard deviation.
b
Means in same row with different small letters are significantly different (p < 0.05).
c
Means in same column with different capital letters are significantly different (p < 0.05).
784 T. Jiang et al. /Food Chemistry 131 (2012) 780–786
had counts below 10
4
cfu g
À1
. This contamination level suggests
that shiitake mushrooms in the studied coating conditions did
not favour the development of this type of bacteria. Mushrooms
from the control treatment exhibited tiny brown spots on Day 4
that developed into dark zones, characteristic of Pseudomonas
spoilage by Day 8. Mushrooms were highly decayed at this point
and the end of shelf-life was due to microbial spoilage. The CGC-
coated samples did not exhibit these characteristics of microbial
degradation even on Day 12. The organisms usually responsible

for spoilage of mushrooms are gram-negative, psychrotrophic bac-
teria, particularly belonging to the Pseudomonadacae family, be-
cause of contamination of the product from compost. Kanatt
et al. (2008) have reported the antimicrobial activity of CGC was
similar to chitosan against E. coli, Pseudomonas, S. aureus and B. cer-
eus, the common food spoilage and pathogenic bacteria. However,
in our experiment, we found that CGC exhibited superior antimi-
crobial activity to chitosan in coating shiitake mushrooms during
storage. Therefore, microbial degradation resulting in changes such
as browning and softening was clearly delayed in CGC-coated
samples.
3.6. Effect of CGC coating on sensory attributes
As expected, mushroom off-odour, gill colour, gill uniformity,
cap uniformity and dark zones significantly (p < 0.05) changed with
storage time, supporting the validity of using these parameters as
indicators of mushroom deterioration. Average values for the sen-
sory attributes are shown in Table 2. Off-odour intensity signifi-
cantly increased after 8 days of storage in control samples. The
colour of mushroom gills gradually became browner and less uni-
form with time for all the evaluated conditions. The gills of control
mushrooms showed a colour intensity of 5.4 and uniformity near to
5.0 at the 12th day of storage. However, the gills of chitosan coated
mushrooms reached these intensities after 4 days of storage. A bet-
ter trend was observed for the uniformity of the cap surface and the
presence of dark stains on the cap in CGC-coated samples. These re-
sults suggest that CGC and chitosan coating were more effective in
retarding mushroom sensory deterioration. The browning of mush-
rooms is attributed to the action of polyphenol oxidase (PPO) and
the action of bacteria and mould on the mushroom tissue. CGC
and chitosan coating cause reduction of spoilage organisms, such

as Pseudomonas, responsible for oxidation of phenolic compounds
to form brown-coloured melanins, and thus prevent the formation
of brown patches, hence improving the appearance and colour.
Considering the development of the evaluated sensory attributes,
mushrooms coated with CGC showed the lowest deterioration rate,
followed by those coated with chitosan and finally those coated
with glucose and the control treatment. Although CGC coating
showed negative effect on gills colour because of the browning col-
our itself, it could maintain sensory characteristics of shiitake
mushrooms for the longest time. This could be related to the fact
that CGC had superior antioxidant and antimicrobial activity as
compared to chitosan or glucose.
4. Conclusions
Our research showed that the senescence inhibition of cold-
stored shiitake mushroom by the CGC coating treatment involved
the maintenance of tissue firmness and sensory quality, inhibition
of respiration rate, and reduction of microbial counts compared
with the control. In addition, CGC coating also delayed changes
in the ascorbic acid and soluble solids concentration during the
storage period. These results suggest that CGC is promising as an
edible coating to be used for maintaining shiitake mushroom
quality and extending its postharvest life.
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