Effect of processing on the microstructure of finger millet by X-ray diffraction and scanning electron microscopy.

Finger millet is one of the important minor
cereals, and carbohydrates form its major chemical constituent.
Recently, the millet is processed to prepare hydrothermally
treated (HM), decorticated (DM), expanded (EM) and
popped (PM) products. The present research aims to study the
changes in the microstructure of carbohydrates using X-ray
diffraction and scanning electron microscopy. Processing the
millet brought in significant changes in the carbohydrates. The
native millet exhibited A-type pattern of X-ray diffraction
with major peaks at 2θ values of 15.3, 17.86 and 23.15°,
whereas, all other products showed V-type pattern with
single major peak at 2θ values ranging from 19.39 to 19.81°.
The corresponding lattice spacing and the number of unit
cells in a particular direction of reflection also reduced
revealing that crystallinity of starch has been decreased
depending upon the processing conditions. Scanning electron
microscopic studies also revealed that the orderly pattern of
starch granules changed into a coherent mass due to
hydrothermal treatment, while high temperature short time
treatment rendered a honey-comb like structure to the
product. However, the total carbohydrates and non-starch
polysaccharide contents almost remained the same in all the
products except for DM and EM, but the individual
carbohydrate components changed significantly depending
on the type of processing.