Journal
Journal of Applied Horticulture, 14(2): 110-113, 2012
Appl
Effect of dehydration on keeping quality of white button
mushroom, Agaricus bisporus Lange (Sing.)
M.P. Singh, H.S. Sodhi, A. Singh* and P.K. Khanna
Department of Microbiology, Punjab Agricultural University, Ludhiana, *Department of Processing and Food Engineering,
Punjab Agricultural University, Ludhiana-141004, India. E-mail: elektra803@yahoo.co.in, drhssodhig@rediffmail.com
Abstract
Key words: Agaricus bisporus, cabinet drying, microwave-oven drying, color index, texture index, carbohydrates, proteins, lipids
Introduction
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White button mushrooms, Agaricus bisporus (strains U3 and S11) were dried in cabinet at two temperatures (45 and 55°C) and
microwave oven at 380W for 30 minutes. Dried mushrooms were subjected to physical (color, texture, rehydration ratio, dehydration
ratio), biochemical (carbohydrates, proteins and lipids) and microbiological (total bacterial count) parameters after three months of
storage period. In strain U3, carbohydrate content was highest in 0.1% KMS treated mushrooms dried at 45˚C, protein ranged between
3.43 to 3.89 g/100 g of fresh mushrooms, lipid content ranged between 0.06 to 0.30 g/100 g of mushrooms and the total bacterial count
ranged between 1.48 to 2.07 log cfu/g which was within the permissible limits of dried fruit products while in microwave oven dried
mushrooms there was no significant difference in two strains in terms of carbohydrate, protein and lipid contents. Bacterial count
was found to be within the permissible limit of dried fruit products (1.85-2.17 log cfu/g). The weight of dried mushrooms remained
almost constant throughout the storage period of 3 months. However, cabinet drying was preferred for most of the color and texture
index parameters. Springiness was maximum for microwave oven dried mushrooms of S11 strain treated with 0.1% KMS, followed
by the unwashed mushrooms. Resilience ranged between 0.23 to 0.33 in all the treatments. Cohesiveness was maximum in unwashed
mushrooms of U3 dried at 55˚C, followed by cabinet dried mushrooms of S11 strain (55˚C) both unwashed and 0.1% KMS treated.
Chewiness and gumminess were also maximum for cabinet dried unwashed mushrooms of U3, followed by microwave oven dried
0.1% KMS treated mushrooms. A. bisporus was most acceptable in cabinet drying for 0.1% KMS treated U3 strain at both 45˚C and
55˚C while in case of microwave oven drying, total color difference (2.88 for U3 and 2.58 in S11) was minimum and rehydration ratio
(1.91 to 3.06) was found to be maximum for U3 strain.
drying had been combined with conventional hot air drying to
reduce the drying time, optimize energy efficiency and improve
product quality (Zhang et al., 2006). Pretreatments of mushrooms
before drying by, washing in water, KMS, sugar, salt either
alone or in combination help in checking enzymatic browning,
stabilizing color, enhancing flavor retention and maintaining
textural properties (Singh et al., 2001). The optimum conditions
of drying were established by Kar et al. (2004) on the basis of
rehydration ratio and sensory evaluation. Drying at microwave
intensity of 400 W with pretreatment of blanching in boiling
water for 3 min., followed by steeping in solution of 0.1% KMS
+ 0.2% CA + 6% sugar + 3% NaCl at room temperature for 15
min. yielded an acceptable dehydrated product in about 45 min.
The rehydration ability of the dried product is a critical parameter
indicating the degree of damage caused by physiochemical
treatments (Krokida and Marinos, 2003). Present investigation
was undertaken to study the effect of drying by different methods
on color, texture, biochemical and microbiological quality
parameters of the dehydrated white button mushrooms.
White button mushroom (Agaricus bisporus) is devoured by
mankind for its characteristic aroma, texture and nutritional
value (Arumuganathan et al., 2003). Dehydration appears to be
a promising and cost effective method of mushroom preservation
for the Indian conditions as it is easy to transport the dried product
compared to canned, pickled and frozen products. The dehydrated
products, apart from the increased shelf life, offer an advantage of
decreased weight and volume with a potential for saving the cost
of packaging, handling, storage and transport (Amuthan et al.,
1999). Dried mushrooms, packed in airtight containers can have
a shelf life of above one year (Bano et al., 1992). Mushrooms
could be dried to a moisture level down below 10% at drying
temperature of 55˚C to give the end product with the desired
qualities of texture, color and rehydration. At a drying temperature
of 55-60˚C, the insects and microbes on the mushrooms would
be killed in a few hours, which give the dehydrated final product
of lower moisture content with longer shelf life. A cabinet drier
with proper air circulation has been reported to be superior by
Mudahar and Bains (1982).
Materials and methods
Microwave oven drying is an alternative way which generates
very rapid heat and mass transfer resulting in quick drying of
mushrooms. It offers the product with good organoleptic and
nutritional values (Sahni et al., 1997). Heating of foods by
microwave energy sources are instantaneous. Microwave-vacuum
Two strains S11 and U3 of A. bisporus, were harvested from the
Mushroom Research Farm, PAU, Ludhiana. Half the sample of
mushrooms (500g) from each strain was treated with 1% KMS
for 10 minutes in order to inactivate the enzymes and improve
its color characteristics while other half was left untreated as
Effect of dehydration on keeping quality of white button mushrooms
Cabinet drying: Mushrooms were dried in cabinet tray drier
(Kilbron Oven, Macneil and Magor Ltd.) where mushrooms were
kept in series of trays and warm air temperature of 45oC and 55oC
was passed with air velocity of approximately 1m / sec. Weight
of tray was noted regularly. Readings were taken at an interval
of 2 hours till 7-8% constant moisture was achieved.
Microwave drying: Mushrooms were dried in microwave
[Electrolux (250-700)] at 380W for 30 minutes. The dried
mushrooms were packed in airtight polyethylene bags of 150
gauze. The observations were made on wt. loss (%), appearance,
color, optical density, dehydration ratio, rehydration ratio,
biochemical and microbiological properties in comparison to
the unwashed mushrooms as control. Rehydration was done by
dipping weighed sample (5g) of dried mushroom in distilled
water. Dehydration and rehydration ratio was calculated using
the formula of Ranganna (1986).
Color and texture analysis: The color of freshly harvested and
stored samples was measured by using Miniscan XE plus Hunter
Lab Colorimeter (Burton et al., 1987; Gormley, 1974). L, a, b
values for samples were obtained in triplicate. From these values
of ‘L’, ‘a’ and ‘b’ total color difference was obtained using the
formula:
ΔE =√ΔL2 + Δa2 +Δb2
Where, ΔL, Δa and Δb are deviations from L, a and b values of the
fresh sample.
ΔL = L sample - L standard; + ΔL means sample was lighter than
standard, -ΔL means sample was darker than standard.
Δa = a sample - a standard; +Δ a means sample was redder than standard,
-Δa means sample was greener than standard.
Δb = b sample - b standard, + Δb means sample was yellower than
standard, -Δb means sample was bluer than standard.
The hue (H), chroma (C) and browning index (BI), which represented
the purity of brown color (Polou et al., 1999), were also calculated
according to the given equation:
Hue= tan-1 (b/a), Chroma = (a2 + b2)1/2
BI= 100(x - 0.31) /0.172,
Where, x= (a + 1.75L) / (5.645 + a-3.012b)
The textural behavior of the whole mushroom was estimated in
terms of the texture profile analysis (TPA) curve. The parameters
of brittleness, hardness, cohesiveness, adhesiveness, chewiness,
springiness and gumminess were calculated from the plot of
two cyclic compression text performed on mushroom sample
of about 5 mm thickness using an aluminium cylinder known as
P/75 cylindrical probe having 75 mm diameter. The conditions
set for TPA were: Load cell: 50 kg, Test mode: measure force
in compression, Pretest speed: 10 mm/s, Test speed: 5 mm/s,
Post test speed: 10 mm/s, Time lag between 2 compressions: 2s,
Test strain: 75% of sample height, Trigger force: 0.05 N, Data
acquisition rate: 200 pps, Probe: SMS P/75 cylindrical probe,
75 mm diameter.
Total bacterial count: Total bacterial count (cfu/ g fresh
mushrooms) was determined by standard method of serial dilution
and plating.
Biochemical analysis: Estimation of total sugars was done by
Dubois et al. (1956) method. Extraction was done by taking
carbohydrates from dried samples of A. bisporus. Estimation of
proteins was done by method given by Lowry et al. (1951) and
extraction and estimation of total lipids was done by Folsch et
al. (1957) method.
Results and discussion
Biochemical and microbiological analysis: Fruit bodies of A.
bisporus strains S11 and U3 were subjected to cabinet drying
(45˚C and 55˚C) and microwave oven drying (380W, 30 minutes)
followed by their biochemical and microbiological analysis. In
strain U3, carbohydrate content was highest in 0.1% KMS washed
and mushrooms dried at 45˚C followed by mushrooms received
same pretreatment and dried at 55˚C. The protein content ranged
between 3.43 to 3.89 g/100 g of fresh mushrooms whereas lipid
content was 0.06 to 0.30 g/100 g of mushrooms (Table 1). The
total bacterial count ranged between 1.48 to 2.07 log cfu/g which
was within the permissible limits of dried fruit products (less
than 2.7 log cfu/g, non pathogenic). In microwave oven dried
mushrooms, there was no significant difference in two strains in
terms of carbohydrates, proteins and lipids contents and bacterial
count was found to be within the permissible limits of dried fruit
products (1.85-2.17 log cfu/g) (Table 1). The weight of dried
mushrooms remained almost constant throughout the storage
period of 3 months. Dehydration ratio for all the treatments
ranged between 9.25 to 13.78 with lowest for 0.1% KMS
treated mushrooms (S11 and U3) dried in microwave oven. The
rehydration ratio for all the treatments ranged between 1.91 to
3.06 with highest in 0.1% KMS treated U3 mushrooms dried in
microwave oven (Table 1).
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control. The mushrooms were then cut longitudinally into pieces,
blanched and dried in cabinet drier and in microwave. Five
replicates for each set of experiment were observed and analyzed
statistically for ANOVA at P= 0.05.
111
Color index: The mushrooms from two different strains received
different pretreatments and dried by two different methods along
with control were compared for color index for L, a, b, ΔE, hue,
chroma, browning index. In each treatment, L value for 0.1%
KMS treated mushrooms was better with highest value of 41.45
L for U3 strain. There were no significant differences in a value
for different treatments. ΔE value was lowest for microwave oven
dried mushrooms in comparison to cabinet dried mushrooms. The
hue index showed increased value from 0.1% KMS pretreated to
unwashed mushrooms of S11 strain in cabinet drying whereas
contrast was true for mushrooms of U3 in cabinet drying and both
S11 and U3 for microwave oven dried mushrooms. The browning
index for cabinet dried unwashed mushrooms of S11 was higher
whereas it was low for unwashed U3 mushrooms. However, there
was no significant difference in browning index in microwave
oven dried mushrooms (Table 2).
Texture profile: The texture profile of dried mushrooms indicated
adhesiveness ranging from -1.57 to -6.98 for all treatments. In
cabinet dried mushrooms, maximum hardness (texture) was in
0.1% KMS treated mushrooms from U3 strain. In microwave
oven dried mushrooms, maximum hardness for both 0.1%KMS
treated and unwashed mushrooms was in U3 strain. Springiness
was maximum for microwave oven dried mushrooms of S11 strain
treated with 0.1% KMS, followed by the unwashed mushrooms.
112
Effect of dehydration on keeping quality of white button mushrooms
Table 1. Physico-chemical and microbiological properties of dried A. bisporus using different techniques
Drying
Strain Treatment Temperature Carbohydrate Proteins
Lipids
Bacterial
Change in Dehydration Rehydration
type
(g/100g of
(g/100g of
(g/100g of
count
wt. during
ratio (x)
ratio (x)
mushrooms) mushrooms) mushrooms) (log cfu/g) storage (%)
Cabinet
S11 0.1%KMS
45˚C
2.04
3.79
0.06
1.70
7.24
13.47
2.39
Unwashed
2.89
3.58
0.12
2.07
6.66
9.93
2.22
drying
0.1%KMS
55˚C
2.47
3.61
0.21
1.61
15.75
13.78
2.76
Unwashed
2.50
3.52
0.30
2.0
5.5
12.63
2.56
U3 0.1%KMS
Unwashed
0.1%KMS
Unwashed
45˚C
55˚C
CD (P=0.05)
Microwave S11 Unwashed 380W(30min)
oven drying
0.1%KMS
U3 Unwashed 380W(30min)
0.1%KMS
CD (P=0.05)
4.39
2.17
3.02
2.01
0.73
2.48
3.64
3.89
3.43
3.77
NS
3.80
0.06
0.09
0.08
0.07
0.35
0.10
1.48
2.07
1.31
2.0
0.17
2.17
4.32
6.20
4.51
12.61
0.34
-13.0
11.32
11.42
11.80
12.13
0.34
10.22
2.48
3.03
2.25
1.91
0.35
2.41
2.50
2.13
2.14
NS
3.63
3.50
3.43
0.38
0.13
0.10
0.08
NS
1.91
2.07
1.85
0.12
-.0015
12.01
-28.70
1.63
9.25
11.12
9.25
0.37
2.61
2.70
3.06
0.18
NS= Non Significant in all the three table
Resilience ranged between 0.23 to 0.33 in all the treatments.
Cohesiveness was maximum in unwashed mushrooms of U3 dried
at 55˚C, followed by cabinet dried mushrooms of S11 strain (55˚C)
both unwashed and 0.1% KMS treated. Chewiness was also
maximum for cabinet dried unwashed mushrooms of U3, followed
by microwave oven dried 0.1% KMS treated mushrooms. This
lot also indicated maximum gumminess (Table 3).
level of moisture content in the end product (Table 2 & 3).
Observations after three months of storage indicated that
cabinet drying at temperatures of 45 and 55˚C gave best results
particularly in 0.1% KMS treated mushrooms of U3 strain. The
drying temperature of 55˚C in the plenum chamber gave the end
product with the desired qualities of texture, color and rehydration
(NRCM, 2008). Pre-drying treatments had a significant effect
on whiteness and color change of the dried mushroom slices.
Whiteness is reported to be high in blanched mushrooms
compared to other treatments but it gave very low rehydration
ratio (Nour et al., 2011). In present study, cabinet drying gave
superior results with respect to color and texture index, while
microwave drying required lesser time for drying to achieve same
Table 2. Color index of dried A. bisporus using different techniques
Drying type
Strain Treatment Temperature
L
Cabinet drying S11 0.1%KMS
0.1%KMS
Unwashed
U3 0.1%KMS
Unwashed
0.1%KMS
Unwashed
C.D (P=0.05)
Microwave
oven drying
b
5.27±0.22
-1.10±0.96
22.04±0.68
4.27±0.16
6.18±0.64
55˚C
34.99±0.61
6.41±0.13
5.20±0.25
30.02±0.62
39.47±0.47
32.02±0.15
41.45±1.16
34.46±0.39
3.13
28.80±1.67
30.49±1.67
5.41±0.12
7.27±0.18
5.81±0.07
8.00±0.34
6.59±0.01
NS
6.5±0.12
8.18±0.14
6.20±0.21
8.42±1.06
2.51±0.16
6.39±0.59
3.49±0.21
0.94
4.53±0.15
3.53±0.15
45˚C
55˚C
U3 Unwashed 380W (30 min)
CD (P=0.05)
Color index
ΔE
a
28.66±0.83
S11 Unwashed 380W (30 min)
0.1%KMS
0.1%KMS
Use of cabinet and microwave-oven drying for the dehydration
of A.bisporus (strains U3 and S11) suggested that, in cabinet
drying, out of two strains, 0.1% KMS treated mushrooms of U3
strain gave good results for most of the parameters at both drying
temperature of 45˚C and 55˚C while in case of microwave oven
45˚C
Unwashed
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Singh et al. (2007) also showed that button mushroom samples
dehydrated at 50˚C gave better quality. They reported diffusivity
of 1.05x10-08 to 7.48x10-09 m2/s and it increased with drying air
temperature. Drying using microwave oven has been reported as
non satisfactory mainly because of lack of temperature control
and high time of exposure resulting in charring of mushrooms
particularly at the edges (Walde et al., 1997). However, the time
taken for drying from 7.5% (db) moisture to 2% (db) has been
reported more for cabinet than for microwave oven drying (Walde
et al., 2006). A comparative new technique ‘Microwave-vacuum
drying’ had resulted in 70-90% reduction in the drying time with
better rehydration characteristics as compared to convective air
drying (Giri and Prasad, 2007).
HUE
CHROMA
BI
9.890
-11.79
5.38
8.91
55.35
7.51
46.05
5.16
39.09
8.25
28.64
48.89
49.19
23.37
38.62
27.91
0.47
34.87
23.34
8.22
11.12
6.33
10.24
7.46
0.57
7.92
8.91
35.45
36.58
20.64
29.99
23.81
0.19
32.60
30.64
9.62
7.69
2.58
30.15±0.04
6.7±0.02
5.68±0.09
40.28
8.78
36.12
32.15±0.02
8.53±0.05
4.68±0.09
2.88
28.75
9.73
33.90
NS
NS
NS
0.20
NS
0.77
Effect of dehydration on keeping quality of white button mushrooms
Table 3. Texture profile of dried A. bisporus by different techniques
Drying type
Strain Treatment Temperature Adhesiveness Hardness
(g x mm)
(g)
S11 0.1%KMS
U3
C.D (P=0.05)
Microwave
oven drying
Unwashed
0.1%KMS
Unwashed
0.1%KMS
Unwashed
0.1%KMS
Unwashed
45˚C
55˚C
45˚C
55˚C
S11 Unwashed 380W (30
min)
0.1%KMS
U3 Unwashed 380W (30
min)
0.1%KMS
CD (P=0.05)
Resilience Cohesiveness Chewiness Gumminess
(g x mm)
(g)
-3.89
10562
0.68
0.27
0.03
281
411
-5.00
-5.33
-5.30
-6.98
-2.08
-6.79
-3.42
0.36
-1.57
-1.99
-4.93
-4.02
0.19
12274
14487
14400
197140
35485
170870
88010
628626.0
44550
44965
109876
103921
47.64
0.78
0.94
0.90
0.42
0.61
0.001
0.40
0.16
1.00
1.10
0.14
0.15
0.22
0.29
0.31
0.25
0.33
0.24
0.32
0.28
0.37
0.23
0.24
0.29
0.30
NS
0.02
1.96
1.80
0.07
0.75
0.80
2.18
0.17
0.57
0.75
0.07
0.09
0.19
195
26851
23509
6044
16450
226
77033
13.84
25616
37657
1239
1573
0.60
250
28396
25920
14391
26862
137550
191863
3531.0
25393
34039
8438
9997
0.60
drying, L Value and rehydration ratio were highest for mushrooms
of U3 strain (0.1% KMS treated and untreated) as compared to
S11 (0.1% KMS treated and untreated). Among the two drying
methods, cabinet drying should be preferred for texture and
whiteness index (L value) while to save time, microwave drying
should be preferred for lower ΔE value and better rehydration
ratio of the product.
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Complementary Copy
Cabinet drying
Springiness
(mm)
113
Received: April, 2012; Revised: October, 2012; Accepted: October, 2012