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

Abstract

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.

Isolation and Characterization of Starch from Pearl Millet (Pennisetum typhoidium) Flours

“…In the x-ray diffractogram, the sharp peaks are associated with the crystalline region while the diffused peaks with the amorphous region of the samples. [31] Corn starch (control) exhibited singlet and sharper peaks at 2θ values of 15 and 23º and a double or diffused peak at 2θ of 17 and 18º which is a characteristic of A-type crystallinity (Fig. 5).…”

Structuring of indirectly expanded snacks based on potato ingredients: A review

“…The crust has a structure normally found in the bulk of expanded snacks. Such an inhomogenous cell size distribution is obtained via preprocessing where the pellet contains a large air pocket in the middle of the pellet -acting as nucleation site for the large bubble (Dharmaraj et al, 2011). From a textural point of view such inhomogeneous structures are quite intriguing.…”

Finger millet porridges subjected to different processing conditions showed low glycemic index and variable efficacy on plasma antioxidant capacity of healthy adults

“…Parboiling process involved steeping the grains for equilibrium moisture content, steaming or boiling to gelatinize the starch and finally dehydrating the grains to remove the moisture to a safe level appropriate for storage. Previous studies have shown an optimum steaming time of 30 min for finger millets (Dharmaraj et al 2011). In the present study two time periods (15 and 30 min) were used for the steaming of grains.…”

“…Parboiling is a popular hydrothermal tratment used for paddy to improve its milling yield and nutritional quality. However, limited published information is available for finger millet parboiling (Dharmaraj et al 2011;Bora et al 2018). The use of different processing methods may help improve the quality of FMP for rendering health benifits.…”