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.
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Adebowale KO, Afolabi TA, Olu-Owolab BI (2005) Hydrothermal treatment of finger millet (Eleusine coracana) starch. Food Hydrocolloids 19:974–983
Ali SZ, Bhattacharya KR (1972) Hydration and amylose-solubility behaviour of parboiled rice. Lebensmittel-Wissenschaft und Technologie 5(6):207–212
Balzar D (2002) Report on the size-strain Round Robin. IUCr-Newsletter 14:228
Cheetham NWH, Tao L (1998) Variation in crystalline type with amylose content in maize starch granules: an X-ray powder diffraction study. Carb Poly 36:277–284
Dharmaraj U, Malleshi NG (2011) Changes in carbohydrates, proteins and lipids of finger millet after hydrothermal processing. LWT 44:1636–1642
Feign LA, Svergun DI (1987) Structure analysis by small-angle x-ray and neutron scattering. Plenum, New York
Ford CW (1981) Estimation of hexose:pentose ratios in solution using the phenol-sulphuric acid method. J Sci Food Agri 32:153–156
Frost K, Kaminski D, Kirwan G, Lascaris E, Shanks R (2009) Crystallinity and structure of starch using wide angle X-ray scattering. Carbohydr Polym 78:543–548
Holm J, Bjorck I, Drews A, Asp NG (1986) A rapid method for the analysis of starch. Starch-Starke 38:224–226
Hoover R, Vasanthan T (1994) Effect of heat moisture treatment on the structure and physicochemical properties of cereal, legume and tuber starches. Carbohydrate Res 252:33–53
Lakshmi Kumari P, Sumathi S (2002) Effect of consumption of finger millet on hyperglycemia in non-insulin dependent diabetes mellitus (NIDDM) subjects. Plant Foods Hum Nutr 57:205–213
Lopez-Rubio A, Htoon A, Gilbert EP (2007) Influence of extrusion and digestion on the nanostructure of high amylose maize starch. Biomacromolecules 8:1564–1572
Lopez-Rubio A, Clarke JM, Scherer B, Topping DL, Gilbert EP (2009) Structural modifications of granular starch after acylation with short chain fatty acids. Food Hydrocolloids 23:1940–1946
Maache-Rezzoug Z, Zarguili I, Loisel C, Queveau D, Buleon A (2008) Structural modifications and thermal transitions of standard maize starch after DIC hydrothermal treatment. Carbohydr Polym 74:802–812
Mahanta C, Ali SZ, Bhattacharya KR, Mukherjee PS (1989) Nature of starch crystallinity in parboiled rice. Starch 41:171–176
Malleshi NG (2006) A process for the preparation of decorticated finger millet. US Patent No. 2003/0185951 A1
Malleshi NG, Desikachar HSR (1981) Varietal differences in puffing quality of ragi (Eleusine coracana). J Food Sci Tech 18:30–32
Malleshi NG, Desikachar HSR, Tharanathan RN (1986) Free sugars and non-starchy polysaccharides of finger millet (Eleusine coracana), pearl millet (Pennisetum typhoideum), foxtail millet (Setaria italica) and their malts. Food Chem 20:253–261
Meek GA (1976) Practical electron microscopy for biologists, 2nd edn. Wiley, London
Mohan BH, Gopal A, Malleshi NG, Tharanathan RN (2005) Characteristics of native and enzymatically hydrolysed ragi (Eleusine coracana) and rice (Oryza sativa) starches. Carbohydr Polym 59:43–50
Ong MH, Blanshard JMV (1995) The significance of starch polymorphism in commercially produced parboiled rice. Starch 47:7–13
Priestly RJ (1976) Studies on parboiled rice: part I-comparison of the characteristics of raw and parboiled rice. Food Chem 1:5–14
Singh V, Ali SZ (2008) Properties of starches modified by different acids. Intl J Food Prop 11:495–507
Singh V, Ali SZ, Somashekar R, Mukherjee PS (2006) Nature of crystallinity in native and acid modified starches. Intl J Food Prop 9(4):845–854
Smitha VK, Malleshi NG, Samir OM, Urs G, Mahesh SS, Somashekar R (2008) The application of WAXS data to the nanosized crystallites of hydrolysis of finger millet and barley malts. Intl J Food Prop 11:781–790
Somashekarappa H, Somashekar R, Singh V, Ali SZ (1999) Microcrystalline parameters in native and acid-modified starches. Bull Mat Sci 22(4):805–810
Sowbhagya CM, Bhattacharya KR (1971) A simplified colorimetric method for determination of amylose content in rice. Starch 23(2):53–56
Ushakumari SR, Rastogi NK, Malleshi NG (2007) Optimization of process variables for the preparation of expanded finger millet using response surface methodology. J Food Eng 82:35–42
Warren BE, Averbach BL (1952) The separation of cold-work distortion and particle size broadening in X-ray patterns. J App Phy 23(4):497
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The authors acknowledge with thanks Mr. Anbalagan, CIFS department for scanning electron microscopy.
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Dharmaraj, U., Parameswara, P., Somashekar, R. et al. Effect of processing on the microstructure of finger millet by X-ray diffraction and scanning electron microscopy. J Food Sci Technol 51, 494–502 (2014). https://doi.org/10.1007/s13197-011-0536-4
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DOI: https://doi.org/10.1007/s13197-011-0536-4