Agriculture Reference
In-Depth Information
The Peleg equation was used to predict kinetics of osmotic dehydration process. It is
suitable for describing kinetics of various processes, such as water transfer in foods during
soaking or osmotic dehydration (Ganjloo, 2012). Peleg (1988) proposed a two-parameter
sorption equation and tested its prediction accuracy during water vapor adsorption of milk
powder and whole rice, and soaking of whole rice and this equation has since been known as
the Peleg model. In this chapter Peleg equation was adapted to represent water loss (WL) and
solids gain (SG):
t
WL
WL
WL
k
k
t
(3)
1
2
t
SG
SG
SG
k
k
t
(4)
1
2
WL
WL
SG
SG
k
1
k
2
k
1
k
2
where:
i
- represents model parameters for water loss,
i
- represents
model parameters for solids gain and
t
- time in minutes.
This kinetic model offers the advantage that by calculating the inverse of the two
constants (
k
1
and
k
2
) it is possible to obtain the initial rate of mass transfer parameters and the
mass transfer parameters values at the equilibrium. The rate of osmotic dehydration process
specific parameters (WL and SG) can be obtained from the first derivative of the Peleg
equation. The Peleg rate constant
k
1
(its reciprocal value) relates to osmotic dehydration rate
at the very beginning in the case of water loss or in the case of solid gain it refers to rate of
solid gain at the very beginning of osmotic dehydration process, i.e., t = t
0
. Correspondingly
to that, the Peleg capacity constant
k
2
relates to a maximum attainable dependent variable. In
this study inverse values of the secound Peleg parameter can be related to equilibrium water
loss or solid gain.
Experimental Design and Statistical Analysis
Response surface methodology (RSM) is useful model for studying the effect of
several factors influencing the responses by varying them simultaneously and carrying out
limited number of experiments (Morgan, 1991). The best combination of process parameters
(solute concentration and temperature) was investigated. For the description of the responses
Y (inverse values of
k
1
and
k
2
for water loss as well as solid gain) a second-degree
polynomial model was fitted to data:
2
ii
Y
b
X
b
X
b
X
X
i
i
ii
ij
i
j
(5)
where b
i
represents the linear, b
ii
the quadratic and b
ij
the interaction effect of the factors.
In the case of sucrose solution, full factorial experimental design was used and the factor
variables and their range are: X1 - sucrose concentration (30 - 70%, w/w) and X2 -
temperature (30 - 50
o
C). When combined solutions of sucrose and sodium chloride were used
as osmotic medium central composite experimental design was applied. It comprises of 17
