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Journal of Ready to Eat Food | January-March, 2016 | Volume 03 | Issue 01 | Pages 01-05
© 2016 Jakraya
JOURNAL OF READY TO EAT FOOD
Journal homepage: www.jakraya.com/journal/jref
ORIGINAL ARTICLE
Optimization of Process Parameters for Drying of Button Mushroom (Agaricus
bisporous) Using Response Surface Methodology (RSM)
Jyotsna Raj
1
, Md I. A. Ansari
1
* and Pramod Rai
1
1
Department of Agricultural Engineering, Birsa Agricultural University, Kanke, Ranchi - 834006, India.
*Corresponding Author:
Md I. A. Ansari
Email: irfan26200@yahoo.com
Received: 10/01/2016
Accepted: 25/03/2016
Abstract
Drying is used to increase the shelf life of mushroom by reducing
moisture. Drying experiments were conducted using Rotatable Central
Composite Design (RCCD) technique based on Response Surface
Methodology (RSM). The slice thickness and air temperature were taken as
independent variables. The dependent variables taken were drying time
(T
d
), rehydration ratio (RR) and visual colour (VC). Blanched mushroom
samples of slice thickness (6-14 mm) were dehydrated in a tray dryer at air
temperature range of 50-70 ºC. The optimum values of drying air
temperature and slice thickness were found to be 67 ºC and 11.78 mm
respectively at desirability value of 0.654. The optimized drying conditions
can be utilized in mushroom dehydration industry.
Keywords:
Button mushroom, Optimization, Response surface
methodology, Rehydration ratio, Visual colour.
1. Introduction
Mushroom is a highly perishable commodity
and has a shelf life of only about 24 hrs at ambient
conditions and 7-10 days even with refrigerated storage
because of its high moisture content and rich nutrients
that spoil easily and quickly. Therefore, mushroom is
dried to more stable forms that can be stored for
extended period thereby reducing losses and making
them available round the year. Dehydration combined
with some pre-treatments appears to be a cost effective
method of preservation (Rama and John, 2000). The
most common method used in dehydration of
mushrooms is hot air convective drying. Mechanical
drying speeds up the drying process, prevents losses,
ensures use of safer drying temperatures and produces
superior product compared to sun drying (Mudahar and
Bains, 1982). Zhuk and Tsapalova (1973) have
recommended the hot air temperature of 50-60
º
C for
conventional tray drying of mushrooms. Giri and
Prasad (2007) studied the drying kinetics and
rehydration characteristics of microwave-vacuum and
convective hot-air dried mushrooms. They used slices
of 6-14 mm thickness and air temperature of 50, 60 and
70
º
C. Dehydrated mushrooms are used as an important
ingredient in several food formulations including
instant soups, pasta salads, snack seasonings, stuffing,
casseroles, and meat and rice dishes (Tuley, 1996). The
main objective of the study was to determine optimum
drying conditions of button mushroom.
2. Material and Methods
2.1 Raw Material and Sample Preparation
Fresh edible button mushroom were obtained
from mushroom production unit, BAU, Kanke and
stored at 4 to 5
º
C temperature. Prior to experiments,
mushrooms were thoroughly washed and graded. The
samples were prepared by cutting the mushrooms
vertically with a vegetable slicer. The slice thickness
was kept between 6 to 14 mm.
2.2 Determination of Moisture Content
Moisture content of the fresh mushroom
samples was determined by drying the samples in an
oven at 104
º
C for 24 hours. The amount of moisture
evaporated was calculated and moisture content was
expressed as % (w. b.). The initial moisture content of
the mushrooms used for this study was in range of 87-
90 % (w. b.).
2.3 Experimental Procedure for Drying
About 50 g of mushrooms samples were taken
and desired thickness were obtained by cutting them
vertically with a vegetable slicer. The mushroom
samples of 50 g was taken for blanching treatment with
citric acid (1.4 %), sodium metabisulphite (1.4 %) and
blanching time (5.2 min) (Raj et al., 2012). Drying was
carried out in a tray drier at different temperatures as
per experimental conditions given in Table 1.
Raj et al…Optimization of Process Parameters for Drying of Button Mushroom (Agaricus bisporous) using
Response Surface Methodology (RSM)
Journal of Ready to Eat Food | January-March, 2016 | Volume 03 | Issue 01 | Pages 01-05
© 2016 Jakraya 2
Table 1: The experimental data of various parameters and their responses
Experiment No. Level of variable [(code) actual] Actual value of responses
T
a
(
⁰
C) d(mm) T
d
(hr.) RR VC
1 -1(53) -1(7.17) 2.6 1.42 2.3
2 1(67) -1(7.17) 3.3 1.54 1.2
3 -1(53) 1(12.83) 4.3 2.09 4.2
4 1(67) 1(12.83) 3.1 2.22 2.6
5 -1.414(50) 0(10) 3.25 1.24 3.2
6 1.414(70) 0(10) 3.45 2.17 2.6
7 0(60) -1.414(6) 2.72 1.34 2.6
8 0(60) 1.414(14) 3.8 2.3 3.8
9 0(60) 0(10) 3.1 1.83 2.72
10 0(60) 0(10) 3.52 1.85 2.83
11 0(60) 0(10) 3.55 2 2.7
12 0(60) 0(10) 3.53 1.9 2.75
13 0(60) 0(10) 3.51 2.1 2.8
The dryer was run for at least half an hour to stabilize
the temperature of the drying air to the pre-set desired
value. The water loss was determined done by
weighing the sample outside the drying chamber, using
the digital top pan balance (± 0.1 g). Drying was
conducted till constant weight was achieved.
2.4 Visual Colour (VC)
The visual color evaluations of dried samples
were carried out by a 10 untrained panelists. They were
given a proforma for color evaluation of each sample.
The evaluation was performed using 5-point Hedonic
scale with 10 panel members. The Hedonic scale rating
used are as follows: Excellent: 1, Good: 2, Fair: 3,
Poor: 4 and Very poor: 5.
2.5 Calculation of Rehydration Ratio (RR)
The rehydration experiments were carried out
for dried samples (2 g) by soaking in boiling water.
The samples were weighed at every 15 min intervals
after draining excess water until constant weight was
attained. The rehydration ratio was calculated by
following equation:
Rehydration ratio = weight after rehydration
weight before rehydration
2.6 Experimental Plan and Design
Drying time, rehydration ratio and color are the
important qualities attributes of dehydrated mushroom
which depends on slice thickness and drying air
temperature. For optimization of drying conditions, the
independent variables taken were slice thickness and
hot air temperature. The dependent variables taken
were drying time (T
d
), rehydration ratio (RR) and
visual colour (VC). Thirteen experiments were
conducted according to second order central composite
rotatable design with two variables and five levels of
each variable. Levels of independent variables are
coded using following equations:
levelssuccessivebetweenerval valuecentral
x
i
i
int
−
=
ε
… (1)
Where,
x
i
= Coded value of the independent variable
ε
i
= Actual value of the factor
313221
2
3
2
2
2
1321
xkxxjxxhxgxfxexdxcxbxay +++++++++=
… (2)
The independent variables, coded variables and their
levels combinations for a 2-factor CCRD are presented
in Table 1. The experimental data were fitted in second
order regression equation as given in equation 2.
2.7 Analysis of Data and Response Surface
Analysis of variance (ANOVA) was conducted
to examine the statistical significance of the model
terms (Montgomery, 1984). The adequacies of the
models were determined using model analysis, lack - of
fit test and R
2
(coefficient of determination). The R
2
is
defined as the ratio of the explained variation to the
total variation, and is a measure of the degree of fit of
the model (Haber and Runyon, 1977). Coefficient of
variation (CV) indicates the relative dispersion of the
experimental points from the prediction of the model.
The response surface plot was plotted for response
variables T
d
, RR and VC against independent variables
slice thickness and air temperature using regression
equation after deleting the non significant terms.
Raj et al…Optimization of Process Parameters for Drying of Button Mushroom (Agaricus bisporous) using
Response Surface Methodology (RSM)
Journal of Ready to Eat Food | January-March, 2016 | Volume 03 | Issue 01 | Pages 01-05
© 2016 Jakraya 3
Fig 1: Effect of air temperature and slice thickness on drying time.
2.8 Optimization
Numerical optimization technique of the
Design-Expert 8.01 software was used for
simultaneous optimization of the multiple responses.
The desired goals for each factor and response
were chosen. All the independents factors were kept
within range while the responses were either
maximized or minimized.
3. Results and Discussion
3.1 Effect of Process Parameters on Drying
Time (T
d
)
The experimental values of T
d
, RR and VC for
various experimental conditions are presented in Table
1. Multiple regression co-efficient were predicted using
least square technique to predict quadratic polynomial
model for drying time (T
d
). The model was tested for
adequacy by analysis of variance. The regression
model for drying time was found to be highly
significant with a coefficient of determination as
0.8792 and F value of 21.83. The equation developed
for drying time in term of air temperature and slice
thickness is given in equation 3.
T
d
= -11.993+0.234*T
a
+1.55*d-0.023*T
a
*d … (3)
Effect of independent variables (T
a
, d) on drying
time (T
d
) predicted from regression model is shown in
Fig 1 in the form of 3-D plot. It is clear Fig 1 that by
increasing the value of slice thickness (d) drying time
(T
d
) increases. The value of drying time also increased
with combined effect of slice thickness (d) and air –
Raj et al…Optimization of Process Parameters for Drying of Button Mushroom (Agaricus bisporous) using
Response Surface Methodology (RSM)
Journal of Ready to Eat Food | January-March, 2016 | Volume 03 | Issue 01 | Pages 01-05
© 2016 Jakraya 4
Fig 2: Effect of air temperature and slice thickness on rehydration ratio.
Fig 3: Effect of air temperature and slice thickness on visual colour.
temperature (T
a
) and it is affected more by slice
thickness (d) because of very high F-value (36.52).
3.2 Effect of Process Parameters on
Rehydration Ratio (RR)
The regression model for rehydration ratio (RR)
was found to be highly significant with a coefficient of
determination as 0.8149 and F value of 22.02. The
equation developed for rehydration ratio in term of air
temperature and slice thickness is given by equation 4.
RR = -1.01063 + 0.0276*T
a
+ 0.1196*d … (4)
Effect of independent variables (T
a
, d) on
rehydration ratio (RR) predicted from regression model
is shown in Fig 2 in the form of 3-D plot. It is clear
Raj et al…Optimization of Process Parameters for Drying of Button Mushroom (Agaricus bisporous) using
Response Surface Methodology (RSM)
Journal of Ready to Eat Food | January-March, 2016 | Volume 03 | Issue 01 | Pages 01-05
© 2016 Jakraya 5
from Fig 2 that by increasing the value of slice
thickness (d), rehydration ratio (RR) increases. The
rehydration ratio increases slightly with increase in air
temperature. This could be due to larger vapour
pressure difference. The effect of slice thickness on
rehydration ratio was found to be more than that the
effect of air temperature.
3.3 Effect of Process Parameters on Visual
Colour (VC)
The regression model for visual colour (VC)
was found to be highly significant with a coefficient of
determination as 0.7737 and F value of 17.09. The
equation developed for visual colour in term of air
temperature and slice thickness is given in equation 5.
VC = 4.3476 - 0.0627*T
a
+ 0.22084*d … (5)
Effect of independent variables on visual colour
(VC) predicted from regression model is shown in Fig.
3 in the form of 3-D plot. It is clear from Fig 3 that
with increase in the value of slice thickness, the value
of visual colour (VC) increases. The value of visual
colour was slightly increased with increase in air
temperature.
3.4 Optimization of Process Parameters
The numerical optimization technique (Design-
Expert 8.01 software) was used to get the optimum
values of the independent variables i.e. air temperature
and slice thickness. The response variables selected for
optimization were drying time, rehydration ratio and
visual colour. The optimum condition was found by
minimizing drying time, maximizing the rehydration
ratio, and minimizing visual colour.
The optimum drying air temperature and slice
thickness was found to be 67
º
C and 11.78 mm
respectively at desirability value of 0.654. At this
optimum condition, the drying time, rehydration ratio
and visual colour were found to be 3.27 hours, 2.25 and
2.74 respectively. These optimum drying conditions can
be used for drying of button mushroom with retention of
desired quality attributes.
4. Conclusion
Drying is an important unit operation to extend
shelf life of mushroom by reducing moisture. Drying
experiments were conducted using Rotatable Central
Composite Design (RCCD) technique based on
Response Surface Methodology (RSM). The slice
thickness and air temperature were taken as
independent variables. The response variables taken for
optimization were drying time (T
d
), rehydration ratio
(RR) and visual colour (VC). The optimum value of
drying air temperature and slice thickness were found to
be 67 ºC and 11.78 mm respectively at desirability value
of 0.654.
References
Giri KS and Prasad S (2007). Studied drying kinetics and
rehydration characteristics of microwave-vacuum and
convective hot-air dried mushrooms. Journal of Food
Engineering, 78(2): 512-521.
Haber A and Runyon R (1977). General statistics, (3
rd
Eds.)
reading, MA: Addison-Wesley Publishing Company.
Montgomery DC (1984). Design and analysis of experiments.
(2
nd
Eds). New York: John Wiley and Sons.
Mudahar GS and Bains GS (1982). Pretreatment effect on
quality of dehydrated Agaricus bisporus mushroom.
Indian Food Packer, 28: 19-22.
Raj J, Ansari IA, Rai P and Prasad G (2012). Optimization of
blanching treatments of button mushroom. Journal of
Research, 24(2): 165-169.
Rama V and John PJ (2000). Effects of methods of drying
and pre-treatments on quality of dehydrated mushroom.
Indian Food Packer, 54: 59-64.
Tuley L (1996). Swell time of dehydrated vegetables.
International Food Ingredients, 4(1): 23-27.
Zhuk YUT and Tsapalova IE (1973). Effect of heat drying on
the quality of dried mushroom. Konservnaya -i-
Ovoshchesushil ‘naya-Promyshlennost, No., 12: 30-31.
