Effect of Temperature on Sorption Isotherm of Instant Noodles from Rice Flour

Effect of Temperature on Sorption Isotherm of Instant Noodles from Rice Flour

Mana Suriya, Tassaneeyaporn Satmak, Kanitta Nakprasert, Yongyut Chalermchat, Rattana Muangrat

Food Engineering Department, Faculty of Agro-Industry, Chiangmai University


Abstract

Moisture sorption isotherms for instant noodles with rice flour were determined at 15,
35 and 60oC using a gravimetric technique. Samples were equilibrated in hygrostats
containing saturated salt solution of known water activity (0.11-0.92) and placed in
temperature-controlled cabinets for approximately 21-24 days. The experimental data were
fitted to six models (Modified Henderson, Modified Chung-Pfost, Modified Oswin, Modified
Halsey, Guggenheim-Anderson-de Boer (GAB) and Modified Brunauer-Emmett-Teller
(Modified BET)). The Modified Henderson and Modified Oswin models were found to be
good models for prediction of experimental data. The Modified Henderson and Modified
Oswin models give mean relative error ( P,% ) of 25.82 and 28.05 and Standard Error of
Moisture (SEM) of 2.76 and 2.51, respectively.

Keywords: Sorption isotherm, Instant noodles, Rice flour

Introduction
HOM MALI RICE 105 is an extremely popular rice and is increasingly being
manufactured as flour to substitute wheat flour having highly cost. Then HOM MALI RICE
105 flour was developed and used in instant noodles (Suwannapat et al., 2006). The quality of
most instant noodles depends to a great upon their physical, chemical and microbiological
stability. This stability is mainly a consequence of the relationship between the equilibrium
moisture content (EMC) of instant noodles and its correspondence water activity ( a ), at a
w
given temperature. Most of instant noodles products have low moisture resulting that they can
adsorb moisture from ambient during storage process. The water activity ( a ) of the flour
w
exerts a strong influence on its quality properties. A number of models have been studied and
suggested for moisture adsorption isotherms of flour. Moisture adsorption isotherms exhibit
the equilibrium relationship between the moisture content of flour and the water activity at a
given temperature. The Modified Henderson, Modified Chung-Pfost, Modified Oswin,
Modified Halsey, Guggenheim-Anderson-de Boer (GAB) and Modified Brunauer-Emmett-
Teller (Modified BET) models have been adopted and used for mathematically describing
moisture adsorption isotherms (Sukumar et al., 2002, Jasmin et al., 2004).
The objective of this research was to determine the suitable model describing the
equilibrium moisture content of the data variety given the water activity and temperature.

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Material and Methods
Material
Instant noodles with rice flour (70% wheat flour, 30% HOM MALI Rice 105 flour)
(Benjamaporn, 2006) was dried in oven 60 ± 1oC for 24 hr. Then the dried instant noodles
were milled to pass mesh. (Endecotts, Octagon 200, Test Sieve Shaker, UK) and placed in a
desiccator at a room temperature for 3 days prior to the beginning of the experiment for the
adsorption process.
Methods
The equilibrium moisture content (EMC) of instant noodles with rice flour was
determined at 15, 35 and 60oC. The statistic gravimetric method was applied. Samples of 6 ±
0.5 g were weighed in weighing bottles. The weighing bottles were then put in hygrostats
with five saturated salt solution (LiCl, MgCl ?
?
?
2 6H2O, Mg(NO3)2 6H2O, NaCl and BaCl2 2H2O)
used to obtain water activity range (0.11-0.92) and placed in temperature-controlled cabinets.
Samples were weighed every three days. Equilibrium was acknowledged when three
consecutive weight measurements showed a difference less than 0.001 g, this took between
21-24 days. The experimental EMC data were processed and analyzed using the nonlinear
regression program. The following six mathematical models describing the relationship
between EMC of flour and a were statistically investigated and reviewed (Menkov et al.,
w
2005) :
Modified Henderson equation :
a = 1? exp ?? (
A T + B)
C
M ?
w
?
?
(1)
Modified Chung – Pfost equation :
?
A
?
a = exp ?
exp(?BM )
(2)
w
?
?
? T + C
?
Modified Halsey equation :
? exp(A + BT ) ?
a = exp ?

(3)
w
?
C
?
?
M
?
Modified Oswin equation :
?1
C
?? A+ BT
?
?
a = ?
+1
?
?
?
(4)
w
??
M
?
?
?
?
GAB equation :
A B
? C
? a
?

w
M = (

(5)
1? B a
?
? B a
? + B C
? a
?
w ) (1
w
w )
Modified BET equation :
(A + BT )Ca

w
M = (
(6)
1 ? a
1 ? a
+ Ca
w ) (
w )
w )

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where a is water activity, M is the equilibrium moisture content (% dry basis), T is the
w
temperature (oC) and ,
A A ,
? B, B ,?C,C? are constants.

The suitability of the equations was evaluated and compared using the mean relative
error ( P ,%) and standard error of moisture (SEM) :
100
M
? M
Mean relative error :
exp
P =
?
(7)
N
M exp

?(M ? M
exp
)2
Standard error of moisture : SEM =
(8)
df

where M
and M are experimentally observed and predicted by the model value of the
exp
equilibrium moisture content (EMC), respectively. N is the number of data points and df is
the degree of freedom (number of data points minus number of constants in the model).

Results and Discussion
The obtained mean values of EMC for respective water activity and temperature are
presented in Figure 1 for adsorption. The EMC values increased with an increase water
activity at constant temperature and decreased with an increase in the temperature at constant
water activity.


t

25.00

t
e
n
n
o
20.00

r
e

C
b
d
15.00
i
s
t
u

o
)
,
%
C


M
M
10.00
m

(
E
r
i
u
5.00

i
l
i
b
u
q

E
0.00

0.00
0.20
0.40
0.60
0.80
1.00
Water activity (a w )

Figure 1. Equilibrium moisture content of instant noodles with rice flour at 15, 35 and 60oC

The constants for the three-parameter models, P and SEM values are presented in
Table 1 and the constants for GAB model, P and SEM values are presented in Table 2. The
modified Henderson and modified Oswin models have the smallest mean relative error ( P ,%)
and the smallest standard error of moisture (SEM) for moisture adsorption. Therefore we

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recommend the modified Henderson and modified Oswin models for description of the
instant noodles with rice flour equilibrium isotherms. Theoretical values of Henderson and
modified Oswin models gave the best fit for data at different temperature (Figure 2(a)-(c)).

Table 1. Constants ( ,
A B,C ), mean relative error ( P ,%) and Standard Error of Moisture
(SEM) of Modified Henderson, Modified Chung – Pfost, Modified Oswin, Modified Halsey
and Modified BET
Model
A
B
C
P
SEM
Modified Henderson
0.00015
29.1623
1.9258
25.72
2.76
Modified Chung - Pfost
267.5725
0.2249
15.4750
29.34
2.72
Modified Oswin
11.7850
-0.0800
3.1202
28.05
2.51
Modified Halsey
5.6869
-0.0218
2.4745
32.09
2.58
Modified BET
2.6351
-0.0162
-2.955x1012
36.24
4.87
Table 2. Constants ( A ,
? B ,?C? ), mean relative error ( P ,%) and Standard Error of Moisture
(SEM) of GAB model
Model
A?
B?
C?
P
SEM
Guggenheim-Anderson-de Boer (GAB)
4.8520
0.8161
3.927x1011 37.67
3.32
25.0
25.0
d
b
b
d
20.0
20.0
t
e
n
t
,
%
o
n
t
e
n
t
,
%
o
n
15.0
Chung-Phost
15.0
Chung-Phost
Oswin
r
e

C
Oswin
o
i
s
t
u
r
e

C
Halsey
Halsey
10.0
o
i
s
t
u
10.0

M
Henderson

M
Henderson
GAB
GAB
5.0
BET
5.0
i
l
i
b
r
i
u
m
BET
q
u
i
l
i
b
r
i
u
m
Sample
q
u
Sample
E
0.0
E
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
water activity (a )
water activity (a )
w
w


(a) (b)
25.0
d
b
20.0
o
n
t
e
n
t
,
%
15.0
Chung-Phost
Oswin
o
i
s
t
u
r
e

C
Halsey
10.0

M
Henderson
m
GAB
r
i
u
5.0
BET
q
u
i
l
i
b
Sample
E
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
water activity (a )
w

(c)
Figure 2. Experiment EMC - water activity data compared with the predicted by the
modified Henderson, modified Chung-Pfost, modified Oswin, modified Halsey, GAB and
modified BET models at (a) 15oC (b) 35oC (c) 60oC

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Conclusions
The moisture adsorption capacity of instant noodles with rice flour decreased with an
increase in temperature at constant water activity. The modified Henderson and modified
Oswin models are suitable for describing the relation between the equilibrium moisture
content, the water activity and the temperature for the instant noodles with rice flour. The
Modified Henderson and Modified Oswin models give mean relative error ( P,% ) of 25.82
and 28.05 and Standard Error of Moisture (SEM) of 2.76 and 2.51, respectively.

References
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