Agriculture Reference
In-Depth Information
M). Chemical treatment lasts for 24 hours at room temperature. After completing the
chemical treatment decolorized sugar beet pulp were neutralized (pH 6-7) with hydrochloric
acid (36.2%). After separation of the liquid phase pulp was pressed. After pressing beet pulp
was dried and in order to investigate process of beet fiber rehydration two types of drying
were selected: convective and microwave drying.
Convective drying: sugar beet pulp was placed in tray dryer (Iskraterm 2K, manufacturer
Iskra Kranj, Slovenia). Samples of beet pulp were put into the chamber of the trey drier and
the thickness of the layer was about 1 cm. Before drying chamber was warmed up to selected
temperature, after which the samples are placed into it. Drying of dietary fiber was performed
at temperatures of 65
o
C, 85
o
C and 105
o
C. This temperature range was chosen to minimize
changes in the dietary fibers properties during drying (Thibault 2000). Air velocity was set to
1 m s
-1
.
Microwave drying: for microwaving drying domestic microwave oven was used. It
possesses a regulatory circuit for defining the energy of microwave radiation as well as a
timer to control the length of the process. Inside the dryer is located in the sample holder
which rotates during the drying process. The presence of the rotating carrier is necessary to
achieve optimum operation of the dryer and reduce reflections of microwaves (Khraisheh et
al. 1997). Sample preparation for microwaving dry counterparts is preparing for convective
drying. Drying in a microwave oven was carried out at three different powers 150 W, 250 W
and 350 W.
Rehydration of sugar beet pulp at atmospheric pressure was performed in a thermostat.
Plain and treated sugar beet cossettes are immersed in a laboratory jars (150ml) at
temperatures of 20, 40 and 60°C. In each jar 3g sample (accuracy ± 0.01g) was placed.
During the process of rehydration the samples were completely immersed in distilled water,
which was heated at the proper temperature. The samples were then taken out at
predetermined time intervals, ranged from 5 to 90 min. After the excess water was removed
the weight of rehydrated samples was measured on a technical scale (accuracy ± 0.01g).
Moisture content of the samples at each time step was calculated based on the increase in
sample mass at corresponding times. Dry basis (d.b.) moisture content was used in
calculations. The results were fitted to the selected mathematical models.
Calculations
Mathematical models for explanation of rehydration process can be divided into three
groups: diffusion models, empirical and semi-empirical models and multidisciplinary models.
Empirical models because of their simplicity are greatly used in the modeling of rehydration
process. The most commonly used models of this type are Peleg and Weibull model. Peleg
equation is two-parametric empirical equation proposed to describe the rehydration of dried
food products (Peleg 1988), but it found its application to describe other processes as well.
The Peleg equation is characterized by the existence of a dynamic period after which follows
the equilibrium period, i.e., asymptotic convergence to the equilibrium values:
t
M
t
M
(1)
0
k
k
t
1
2
