Agriculture Reference
In-Depth Information
Table 3. Analysis of variance (ANOVA) of the microwave dried sugar beet pulp
Rezi
d
ual
Model
Response
R
2
SS
DF
MS
SS
DF
MS
F
p-value
UT 1/k
1
0.568
3
0.189
42.434
6
7.072
37.368
0.006533
0.904
UT 1/k
2
0.064
3
0.021
148.598
6
24.766
1154.963
0.000039
0.964
CT 1/k
1
0.102
3
0.034
8.067
6
1.344
39.373
0.006052
0.867
CT 1/k
2
1.819
3
0.606
714.516
6
119.086
196.374
0.000558
0.904
UT - untreated (plain dried sugar beet pulp); CT - chemically treated sugar beet pulp
Microwave Dried Sugar Beet Pulp
In the case of rehydration data for the microwave dried untreated and treated sugar beet
pulp the coefficient of determination (R
2
) was within the limits of 0.985 to 0.999 for Peleg
equation while the Weibull equation within the limits of 0.986 to 0.999. Both equations are
adequate for representation of rehydration data, but Peleg equation was chosen for further
analysis for the same reasons mentioned earlier. In Tables 3. and 4. results of fitting the
experimental data of microwave dried sugar beet pulp to the polynomial model are given.
All polynomial models tested for the selected responses for microwave dried sugar beet
pulp were significant at 95% confidence level (p-value; 0.05, Table 3). Second-order
polynomial is fitted well the experimental results for both the rehydration initial rate as well
as the equilibrium moisture content of untreated and treated sugar beet pulp subjected to
microwave drying.
The results of the statistical analysis according to the experimental plan are presented in
Table 4. The significance of each coefficient was determined by Student‟s t-test. The highest
linear effect on the rehydration initial rate has rehydration temperature, while its square
influence even more significant. For the equilibrium moisture content of untreated sugar beet
pulp the most important factor is the strength of microwave power during drying. In fact,
looking at the t-values of regression coefficients it can be concluded that the influence of
microwave power more pronounce for equilibrium moisture content than for rehydration
initial rate. In the case of treated sugar beet pulp for rehydration initial rate the most important
effect is linear influence of rehydration temperature followed by quadratic influence of the
power of microwave drying. The most important factor for the equilibrium moisture content
is b
0
which indicates that the calculated value of the equilibrium moisture content are close to
the calculated values of b
0
(Djuric et al. 2004).
The rise in power of microwave drying leads to an increase in the rehydration initial rate
due to the formation of porous structure of the tissue fibers during drying at higher
microwave powers (Figure 5.). On the other hand, the same effect has the rise in rehydration
temperature during process, i.e., with increasing rehydration temperature rehydration initial
rate is increasing due to reduced water viscosity at higher temperatures.
The equilibrium moisture content increases with rehydration temperature increase, while
the influence of microwave power is more complex. In fact, with the increase in power from
150W to 250W there is a drop in the equilibrium moisture content. The reason for this is
likely a higher temperature of the sample during drying at higher microwave power, and the
consequent disruption of the tissue structure at these higher temperatures (Figure 6.). On the
