Effect of power level on aromatic compound (2-Acetyl-
1-pyrroline) and sensory evaluation
From Table 5 it was observed that the 2-acetyl-
1-pyrroline content decreased with increase in
microwave output powers because of its temperature
sensitivity. The retention of 2-acetyl-1-pyrroline
content was more and not significantly different in
samples dried at 540 and 360 W output power. But
2-acetyl-1-pyrroline content of samples dried at 180 W
was found to be less than that obtained at 360 W. This
may be due to the relatively long drying time (14 min)
requirement, which facilitated for removal of volatile
compounds. The mean sensory scores for different
quality attributes of dried leaves are also presented in
Table 5. The sensory attributes were almost same for
aromatic rice and non aromatic rice when cooked with
fresh leaves. The color of microwave dried samples
was observed to be significantly better as compared
to that of the shade dried samples. The microwave
output power level except 180 W did not have any
significant effect on color of the dried products.
These results are consistent with those of Ozkan et
al. (2007). They investigated the colour change in
spinach leaves at microwave powers of 90 to 1000
W and determined the lowest colour change at 750
W microwave powers. According to Schiffmann
(1995), high moisture bio-products undergoing
microwave drying have the advantage. Microwave
drying pushes liquid into the surface and the liquid
is usually converted into the vapour. This process
results in drying without causing surface overheating
phenomena. Therefore, in terms of surface colour
degradation, preservation of the product colour was
good. It is estimated that the products are subjected
to high temperature with the increasing power levels
during microwave drying. Therefore, the product
colour is adversely affected in the drying processes
at very high microwave powers (Ozkan et al., 2007).
In the present study, the relatively low sensory scores
in colour at 720 and 900 W microwave power are
supported by the results obtained in the previous
research above. From the organoleptic evaluation
(aroma, and overall acceptability score) of dried
samples, it was observed that the samples at lower
microwave output powers were preferable product.
However, it was also observed that the samples dried
at 540 W, fetched highest sensory score and there
was no significant difference in all these quality
parameters obtained at 360 W. But the drying rates
achieved at 360 W is less and hence the drying time
requirement is more. On the contrary, though the
drying rates achieved at 540 and 720 W are very close,
there was a significant reduction in quality parameters
in samples dried at 720 W. Hence, considering the