Preparation and functional properties of decorticated finger millet ( Eleusine coracana

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Journal of Food Engineering 79 (2007) 529–538

Preparation and functional properties of decorticatedfinger millet (Eleusine coracana)

S. Shobana, N.G. Malleshi *

Department of Grain Science and Technology, Central Food Technological Research Institute, Mysore 570 020, India

Received 6 October 2004; received in revised form 31 August 2005; accepted 17 January 2006Available online 18 April 2006

Abstract

The food uses of finger millet are confined to flour based products because, it has not been possible to decorticate the millet similar toother cereals. This is mainly due to the highly floury endosperm. But, it was observed that, the hydrothermal treatment to the millethardens the endosperm texture and enables its decortication. Accordingly, the optimal conditions for the hydrothermal treatmentand also for decortication of the millet were determined. Equilibrating the millet to 33 ± 2% moisture content and steaming the samefor about 20 min at atmospheric pressure followed by drying to 12 ± 2% moisture content enhanced the hardness of the millet kernelfrom 1.1 ± 0.2 to 7.1 ± 0.5 kg/cm2 and enabled its decortication. Among the various cereal pearlers and decorticators, horizontal car-borundum disc mill was most suitable and incipient moist conditioning the millet improved the decortication efficiency. The decorticatedmillet contained 6.3 ± 0.6 g protein, 0.9 ± 0.2% fat, 14.7 ± 1.8% dietary fibre, 0.180 ± 0.015% calcium and 0.109 ± 0.01% phosphorus.The polyphenols and phytate phosphorus content of the decorticated millets were lower by 74.7% and 39.8%, respectively, as comparedto the native millet. The decorticated millet could be cooked as discrete grains similar to rice to soft edible texture within 5 min which wasnot possible hitherto. The pasting and the dough properties and also some of the functional characteristics of the product indicated itsversatility for diversified food uses.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Cooking characteristics; Decortication; Endosperm texture; Finger millet; Hydrothermal treatment

1. Introduction

Finger millet or Ragi (Eleusine coracana) is an impor-tant staple food for the traditional consumers and the peo-ple belonging to the lower socio-economic strata in theIndian subcontinent and also in some of the African coun-tries. It is a small seeded (1.2–1.8 mm diameter) minor cer-eal having, light brown to brick red coloured seed coat withminutely undulated surface. Its pericarp is membranous,thin layered and loosely attached tissue covering the entireseed and generally detaches during harvesting or by simpleabrasion. On the other hand, the seed coat or the bran con-sisting of highly pigmented testa fused with the aleuronelayer, is rigidly attached to the endosperm (McDonough,

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doi:10.1016/j.jfoodeng.2006.01.076

* Corresponding author. Tel.: +91 821 2510843; fax: +91 821 2517233.E-mail address: [email protected] (N.G. Malleshi).

Rooney, & Earp, 1986). The endosperm texture of the milletkernels consists of largely floury portion and crumbles tofine grits when the seed coat is partially or fully peeled off.In view of these textural peculiarities, efforts to decorticatethe millet by known cereal milling methodologies includingabrasion or friction mills or following such other dehullingmethods have not been successful till date. Because of this,the millet is invariably pulverized to flour and the wholemeal is used to prepare the conventional foods, namely,unleavened pancakes (roti), stiff porridge or dumpling(mudde) and thin porridge (ambali) (Malleshi & Hadimani,1991). The seed coat normally imparts dark colour, chewytexture and characteristic musty odour to the food productsand these factors largely hinder their acceptability by thenon-traditional millet consumers. Some of health benefitsassociated with regular intake of millet foods, such as thehypocholesterolemic, hypoglycemic and antiulcerative

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530 S. Shobana, N.G. Malleshi / Journal of Food Engineering 79 (2007) 529–538

characteristics indicate the scope for its utilization by thenon-traditional millet consumer also. Hence, providingthe millet similar to rice, wheat or in the form of ready-to-cook convenience cereal would improve its acceptabilityand making available the decorticated millet paves way forthis. Since, the anti-nutritional factors of the millet,namely, polyphenols and phytates are mainly concentratedin the seed coat and aleurone layers (McDonough et al.,1986; Ravindran, 1991), decortication lowers their contentsand as a result improves the bio-availability of the nutri-ents. The recent work in the Department of Grain Scienceand Technology, Central Food Technological ResearchInstitute, Mysore, India, on the modification of the milletendosperm texture by hydrothermal treatment has lead todevelopment of a process for decortication of finger millet(Malleshi, 2002; Malleshi, 2003). In line with that, detailedinvestigations were undertaken to optimize the processparameters for decortication of the millet and also to deter-mine some of the functional properties of the product.

2. Materials and methods

A popular variety of finger millet (Indaf 5), procuredfrom National Seeds Corporation, Mysore, India, wascleaned to free from extraneous matter, shriveled and dam-aged grains and was used for the studies.

2.1. Hydrothermal treatment

2.1.1. HydrationThe millet was steeped in excess water maintained at dif-

ferent temperatures ranging from ambient (30 �C) to closeto the gelatinization temperature of its starch (70 �C), with10 �C increment. The steeped grains were withdrawn atregular intervals, the water layer adhering to the surfaceof the kernel was blotted off and the moisture contentwas estimated by air drying method (AACC, 2000). Guidedby the kinetics of hydration, about 50 kg material wassteeped for 8 h at 30 ± 1 �C (33 ± 2% moisture content)and was used for the steaming studies.

2.1.2. Steaming

The steeped millet (2 kg batch) was spread in steel traysof dimension 40 · 80 · 3 cm (w · l · t), covered by anothertray to prevent the grains from wetting by the condensedsteam, and steamed in an autoclave (Krauss Maffee Mun-chen, Germany) at ambient, 1, 2, 3, 4 and 5 kg/cm2 pres-sures separately for varying duration ranging from 2 to20 min. The optimum duration for steaming at each ofthe pressures was determined by withdrawing the materialat different time intervals and ensuring complete gelatiniza-tion of the starch content of the kernel. It was judged bythe absence of white belly observed by cut opening the ker-nel and also by the formation of homogenous translucentspread on pressing the kernel between two glass slides.Guided by the experiments on steaming, about 50 kg ofmillet steeped to 33 ± 2% moisture content at 30 ± 1 �C

and steamed at atmospheric pressure for 20 min was usedfor the drying studies.

2.1.3. Drying

The steamed material was mixed uniformly and dried to12 ± 2% moisture content in a mechanical cross flow driermaintained at 40 ± 2 �C. Followed by that, about 50 kg ofthe millet steeped to 33 ± 2% moisture at 30 ± 1 �C tem-perature and steamed at atmospheric pressure for 20 minwas dried to 12 ± 2% moisture content and used for decor-tication trials. The material thus processed referred toas hydrothermally treated millet (HTM) in the foregoingtext.

2.2. Decortication

The HTM was size graded using a cereal sifter-cum-gra-der fitted with screens of 1405 lm (12 mesh BSS) and1003 lm (16 mesh BSS) openings, into ‘+1405 lm’,‘�1405 lm’, ‘+1003 lm’ and ‘�1003 lm’ and used fordecortication. The decortication trials were conducted indifferent abrasive and friction type cereal milling machin-ery, namely, Engleburg huller (Sri Ganesha EngineeringWorks, Chennai, India), McGill miller (H.T. McGill,Houston, Texas, USA), horizontal cone polisher (DahanuIndustrial Works, Thane, India), horizontal carborundumdisc mill (Muhlenbau Agencies, Bangalore, India) and bar-ley pearler (Satake Engineering, Co, Ltd, Hiroshima,Japan). The influence of incipient moist conditioning theHTM on its decortication characteristics were also exam-ined. Decortication in the horizontal twin carborundumdisc mill alone, and that too after moistening the kernelswas promising with respect to detaching the seed coat with-out pulverizing the endosperm matter. Accordingly, todetermine the optimum moisture level and tempering timeprior to decortication, the millet in 2 kg batches wassprayed with 2–10% additional water, mixed well and tem-pered for 5–30 min and then decorticated. Guided by thequalities of the decorticated millet under each of the mois-ture levels, the material was sprayed with 6.0% additionalwater, tempered in rotary bins for about 10 min and decor-ticated in horizontal carborundum disc mill. The clearancebetween the discs was maintained at 1.35 ± 0.05 mm(slightly lesser than the diameter of the grain) by suitablyadjusting the lever of the mill. The milling fractions,namely, the head grains, grits (brokens) and the seed coatmatter were collected separately, equilibrated and weighed.The millet, decorticated to 15 ± 1% degree of decorticationusing the protocol developed (Fig. 1) was used for determi-nation of some of its functional properties including cook-ing characteristics.

2.3. Microscopic examination

Native, HTM and the decorticated millet kernels werecut open to expose the endosperm and mounted on metallicstubs with the aid of double side scotch tape and were gold

Cleaning (manual/mechanical)

Steeping in water (30 ˚C, 8 h)

Drying in a mechanical drier at 40 ˚C

Steaming (atmospheric pressure, 20 min)

Grading

Moist conditioning (6% moisture, 5–10 min)

Decortication (carborundum coated horizontal disc mill)

FINGER MILLET

Hydrothermally treated millet

Aspiration

DECORTICATED MILLET SEED COAT BROKENS

Fig. 1. Flow chart for the preparation of decorticated finger millet.

S. Shobana, N.G. Malleshi / Journal of Food Engineering 79 (2007) 529–538 531

coated (about 100 A) in a KSE 2 AM evaporation Seevacgold sputter. The samples were scanned in LEO 435 scan-ning electron microscope and the selective portions of theendosperm including granular organization of the starch,and cell walls and also the topography of the seed coatof the native and the HTM were photographed.

2.4. Functional properties

The native (control), HTM and the decorticated milletwere examined for some of the physical characteristics(1000 kernel weight, volume, hardness, colour, solubilityand swelling power, dough characteristics), and nutrientcomposition. A brief account of the methodology followedfor these are as follows.

2.4.1. Physical characteristics

One thousand kernels were counted in a Numegral graincounter (Tecator Co. Hoganas, Sweden) and their weightwas recorded whereas, the volume of 1000 kernels wasdetermined by toluene displacement method. Based on themass and volume, the apparent grain density was calcu-

lated. The kernel size was measured using digital Verniercalipers and the force required to crush individual grainsto their breaking point was determined using a Kiya hard-ness tester (Kiya Seisakusho Ltd., Tokyo, Japan), and anaverage value of 20 kernels were recorded as hardness.The apparent colour was measured in a double beam UV–visible spectrophotometer with integrating sphere model(UV 2100/3100, Shimadzu Town, Japan) against bariumsulfate (100% reflectance) standard and, the difference inreflectance values between the standard and the sample(DE) was recorded. The material was pulverized in Udycyclone mill (UD Corporation, Boulder, USA) fitted with0.5 mm screen and the whole meals were used for determi-nation of the nutrient composition and also swelling powerand solubility index (Leach, McCowenan, & Schoch, 1959).

2.4.2. Nutrient composition

The whole meals from the native, HTM, and the decor-ticated millet were analyzed for protein, fat, and total aswell as acid-insoluble ash following AACC (2000) proce-dures. The calcium and phosphorus contents were deter-mined according to AOAC (1999) and Fiske and SubbaRow (1983), respectively. The samples were also analyzedfor the dietary fibre (Asp, Johansson, Hallmer, & Silje-strom, 1983), starch (Holm, Bjorck, Drews, & Asp,1986), phytate phosphorus (Thomson & Erdman, 1982)and total polyphenol (Swain & Hillis, 1959) contents.

2.5. Pasting characteristics

The native and the decorticated millet flour samples(2 g) were mixed with 18 ml water to obtain 10% (w/v)slurry and, the same was subjected to a controlled heating(8 min), cooking (6 min) and cooling (9 min) cycle underconstant shear in a rapid visco-analyser (Newport Scien-tific, Warriewood, Australia) to determine the pastingcharacteristics (AACC, 2000).

2.6. Dough characteristics

The decorticated millet flour (50 g on 14% moisturebasis) was mixed with 35 ml of cold water (30 �C) andthe dough characteristics in terms of water absorption,mixing profiles, dough development time, water uptakeand stability were recorded in a Brabender farinograph(AACC, 2000). But, in the case of native millet, the farino-grams were recorded after mixing the flour with cold water(30 �C) and also hot water (90 �C) separately.

2.7. Cooking time

About 10 g of decorticated kernels was dropped in100 ml boiling water in a beaker and heating was contin-ued, a few grains were withdrawn from the beaker at every30 s and pressed between two glass slides. The spreadabilityas well as the translucency of the spread was observed bypassing a light beam from the bottom, and time taken


for attaining constant diameter of the spread and totaltranslucency was considered as cooking time.

3. Results and discussion

The equilibrium moisture content (EMC) of the nativemillet was 33 ± 2%, 37 ± 1% and 41 ± 1% at 30, 50 and70 �C respectively and the time taken to attain 34 ± 2%moisture content at 30, 50 and 70 �C was about 7, 1 and0.5 h respectively (Fig. 2). This shows that, the rate of imbi-bition of water was higher for the samples steeped at ele-vated temperatures. The rate of hydration was rapid inthe initial period of soaking that too till the kernelsattained about 50% of the EMC and slowed down thereaf-ter irrespective of the temperature of steep water. Similarobservations have been reported by Kaddus Miah, Haque,Paul Douglass, and Clarke (2002), for paddy. The smallsize of the millet kernel (1.5 ± 0.3 mm diameter) (Fig. 3a)provides large surface area for rapid hydration comparedto rice or other bolder grains. The millet endosperm con-tains loosely packed starch granules, non-starchy polysac-charides, cell walls, matrix proteins as well as proteinbodies, and also a small proportion of lipid globules.Hence, the moisture content of the steeped kernels will bethe additive of the water absorbed by starch, protein andnon-starchy polysaccharides and also the water moleculesentrapped in the inter-granular space besides the waterabsorbed by the seed coat. Hydration of the grains nearto the EMC is a pre-requisite for parboiling of cerealsunder normal conditions and the rate of hydration alsodepends on the characteristics of cereals and this is truewith respect to finger millet also. However, maximum

Fig. 2. Hydration characteristics of native finger millet steeped at differenttemperatures.

temperature of steep water could be 70 �C or just belowthe gelatinization temperature of the particular cereal.Since, the gelatinization temperature of the millet starchranges between 65 and 85 �C (Paramahans, Wankhede, &Tharanathan, 1980), a few of the starch granules wouldbe gelatinized during steeping at about 70 �C, there byincreasing its EMC compared to the millet steeped at 30or 50 �C. Visible fissuring or burst opening of the kernelswere not noticed in the material steeped at 70 �C indicatingthe feasibility of hot water soaking method of parboilingfor finger millet. In the case of parboiling of rice, hot watersoaking is advocated mainly to save time, to minimise themicrobial load as well as development of odour (Desika-char, Majumder, Pingale, Swaminathan, & Subrahma-nyan, 1955). This holds good with finger millet also.

The influence of steaming on the characteristics of themillet indicated that, steam pressure and the duration ofsteaming profoundly influenced the degree of starch gelati-nization and the endosperm texture of the millet. It wasobserved that, steaming for 20 min at atmospheric pres-sure, 15 min at 1 kg/cm2, 10 min at 2 kg/cm2, 5 min at3 kg/cm2, 3 min at 4 kg/cm2 and just 2 min at 5 kg/cm2

pressure gelatinized the starch content of the millet. Therewere no visible cracks or fissuring of the kernels on steam-ing but it intensified the dark colour of millet. The watercontent of the kernels may facilitate gelatinization andswelling of starch granules during steaming and causesdenaturation of the proteins. In the process the starch–lipidinteraction occurs and also the protein bodies loose theirintegrity. This in vivo biotransformation may lead to thetextural modification of the millet endosperm similar tothe observations made in rice on parboiling by Bhattach-arya and Ali (1985).

Drying the steamed millet exhibited considerable influ-ence on the physical properties of the product. It not onlyincreased the intensity of the dark colour (Fig. 3b) but alsocaused slight undulations, peripheral deformation and a lit-tle shrinkage in the size of the kernel (Fig. 3c). While, dark-ening or the browning could be due to polymerization ofphenolics and pigments such as anthocyanins (Hrazdina,1971), the undulations on the surface could be due to thedesorption of water and also due to the cementing of theendosperm components during drying the kernels. It wasobserved that the material dried to 12 ± 2% moisture con-tent at about 40 �C was slightly mellowable and less friableand could withstand the impact during milling whereas, thematerial dried at temperatures higher than 50 �C washighly brittle and cracked into grits during decortication.Accordingly, the steamed millet dried in a cross flow driermaintained at 40 �C was more suitable for decortication. Inthe case of rice also, it has been reported that, drying thesteamed rice at temperatures higher than 60 �C inducesthe cracks and causes large-scale breakage during milling(Henderson, 1954). About 5 kg batch of the steamed milletwas also sun dried and it was noted that the morphology ofthe sun-dried material was comparable to the mechanicallydried (40 �C) sample.

Fig. 3. Effect of processing on morphological features of the millet: (a) native, (b) hydrothermally treated millet (HTM), (c) HTM, as seen in scanningelectron microscope (magnification 50·), (d) decorticated millet, and (e) cooked millet.


The preliminary investigations on decortication of thehydrothermally treated millet dried at different tempera-tures to varying moisture levels, indicated that, both drying

conditions as well as the moisture content of the driedmaterial influence decortication characteristics. Rapid dry-ing of steamed kernels by exposing them to temperatures


higher than 50 �C causes steep moisture gradient betweenthe interior and surface portions in the kernel till majorquantum of moisture is removed and as a result, slightperipheral expansion and contraction at the interior ofthe grain occur. This manifests in compressive stress atthe surface and tensile stress at the centre leading to devel-opment of cracks in the grains (Kunze, 2001). On the otherhand, drying at about 40 �C or lower than that, causes slowmovement of moisture within the kernel and it does notcause extensive fissuring.

Dehusking and debranning experiments of the HTM inEngleburg huller, McGill miller, horizontal cone polisher,barley pearler and similar cereal milling machinery work-ing on the principles of abrasion or friction were not fruit-ful. On the otherhand, decortication in horizontal disc millwherein both the discs are embedded with carborundum(about 20 grade) was found effective. This could be dueto the peeling of the seed coat while, the grains spinbetween two emery coated discs. Further, it was noticedthat, moistening the surface of the HTM by spraying with6 ± 0.5% additional water and tempering for a short time(5–10 min) was highly advantageous with respect to decor-tication of the millet. Incipient moistening not only softensthe seed coat but also renders it leathery and soft and getsscrapped between the twin carborundum discs of the mill.While, less than 4% additional water was insufficient tomoisten the seed coat effectively, addition of more than8% moisture not only caused stickiness and lump forma-tion among the grains, but also caused elongation of thekernels to some extent during milling. Size grading the mil-let to near uniformity improved the decortication charac-teristics considerably and reduced the breakage of thekernels. The milling fractions consisted of the decorticatedhead grains, grits and the seed coat. The degree of decorti-cation (% of the kernel removed mainly in the form of seedcoat during milling) was 15 ± 3% and the yield of headgrains and grits or the brokens were 82 ± 5% and 3 ± 2%respectively (Table 1). The millet was decorticated to15 ± 3% degree of decortication because, lesser degree ofdecortication yielded grains with some portion of testalayer remaining with the millet kernels and affected theappearance, cooking as well as its eating qualities. Millingthe millet to higher than 15 ± 3% degree of decortication

Table 1Yield of decorticated millet with and without incipient moist conditioning

Parameter Decortication withoutmoist conditioning

Decortication aftermoist conditioning

Steaming time (min) 20 ± 0.5 20 ± 0.5Steaming temperature (�C) 98 ± 1 98 ± 1Drying temperature (�C) 40 ± 2 40 ± 2Additional moisture (%) – 6.0Yield (g%)

Decorticated head grains 45 ± 5 82 ± 5Brokens (grits) 35 ± 3 3 ± 2

Seed coat 20 ± 2 15 ± 3

Yield values are average ± standard deviation of three independent mill-ing experiments.

resulted in removal of endosperm portion also. Since, thegerm portion of the millet is located in a slightly depressedportion of the kernel surrounded by characteristic ridges(McDonough et al., 1986), it remained intact with the dec-orticated grains even at 15% degree of decortication. Thedecorticated material was of near spherical shape andcream coloured with glassy and translucent look (Fig. 3d)and could be cooked similar to rice (Fig. 3e). Normally,soaking the cereals or legumes in water and drying as suchand also after steaming reduces the intactness between theseed coat and the endosperm due to leaching of the watersolubles and the chemical binders such as ‘gums’ and pec-tinacious material between the seed coat and the endo-sperm. In addition, due to the differential expansion andcontraction of the seed coat and the endosperm duringhydration and dehydration, the intactness between thesetwo botanical components gets loosened and that facili-tates decortication. But in the case of finger millet, eventhough a slight swelling on hydration and a slight contrac-tion on drying occur, it did not result in loosening of seedcoat from the endosperm on the other hand the seed coatappeared fused with the endosperm. This was evident fromthe fact that, milling the millet in conventional cereal millsworking on the principle of friction or abrasion did nothelp in detaching the seed coat from the endosperm. Hence,this phenomenon observed in finger millet has been uniqueamong cereals. Steaming causes gelatinization and retro-gradation of starch leading to the formation of a compactmass by the starch granules. In the process, the air spacesand the minute voids in the endosperm disappear andreduce the amount of light scattering at the interstitialspaces thereby giving glassy and translucent look for thedecorticated millet. Similar results have been observed inrice and sorghum (Bhattacharya & Ali, 1985; Young,Haridara, Rooney, & Waniska, 1990).

3.1. Microscopic examination

The scanning electron photomicrographs of endospermportions of the native (Fig. 4a) and decorticated millet(Fig. 4b) clearly show that, the starch granules are large,lenticular and small spherical type and are rather looselypacked in native millet which is in confirmatory with theobservations made by McDonough et al. (1986). But inthe case of decorticated finger millet, the endospermappears to be a homogenous mass with starch granulesdevoid of their distinct shape, size and the cell walls. Theseobservations clearly reveal that, the orderly polyhedralstructure of starch granules has been changed into coherentmass, namely, the transformation of crystalline form ofstarch granules into an amorphous one. This could be thepossible reason for acquiring a greater strength or hardnessto resist breakage during milling (Sridhar & Manohar,2003). Hydrothermal treatment also caused slight changesin the seed coat morphology with special reference to col-lapse of minute protrusions or mounds present on the outerlayer of the testa of native kernel (Fig. 4c and d). The

Fig. 4. Endosperm textures of native (a), decorticated millet (b) (magnification 1.00 K·) and the topography of native (c) and hydrothermally treated anddried kernels (d) (magnification 500·), as seen in scanning electron microscope.


hydrothermally treated millet exhibited shrunken andirregular shape (Fig. 3c) in contrast to the globose structureof the native millet, which may be due to the differentialexpansion and contraction of the grain during hydration,steaming and drying processes.

3.2. Physicochemical characteristics

The hydrothermal treatment increased the hardness ofthe millet from 1.1 to 7.1 kg/cm2, measured in terms ofbreaking or crushing strength of the kernels. The bulk den-sity of the decorticated millet was slightly higher thannative millet (Table 2), probably due to removal of the seedcoat, and also due to the reduced porosity in the kernel. Inthe case of rice also, similar observations have beenreported (Pillaiyar & Mohandoss, 1981).

Protein, fat, calcium and phosphorus contents of thedecorticated millet were 6.3%, 0.9%, 0.18% and 0.10%and were lower by 22%, 40%, 43% and 48% respectivelythan the native millet. The reduction in some of the nutri-ents could be mainly due to separation of the seed coat, asit has been reported that, the seed coat contains about 28%

of protein, 49% calcium and 14% phosphorus (Kurien,Joseph, Swaminathan, Subrahmanyan, & Daniel, 1959).Similar observations have been made by Subrahmanyan,Sreenivasan, and Dasgupta (1938), on parboiling of riceand by Serna-Saldivar, Clegg, and Rooney (1994) on sor-ghum. Decortication reduced the dietary fibre content ofthe millet by about 33.2% but at the same time, the propor-tion of soluble fibre content increased considerably. Theincrease in the soluble fibre content of the product has spe-cial nutritional significance because of its physiologicaladvantages in terms of hypoglycemic and hypocholestero-lemic characteristics. Formation of the resistant starch alsocontributes towards dietary fibre content and complementsthe health benefits of the millet. The loss of nutrientsincluding the dietary fibre could be regulated by judiciousmilling. The reduction in polyphenols and phytate phos-phorus contents on decortication of millet was 74.7% and39.8% respectively and this may provide nutritional advan-tages with respect to increased bio-availability of mineralsand protein (Erdman, 1981). McDonough et al. (1986)reported that testa layer of the millet is highly pigmentedand contributes for the bulk of polyphenols and tannin

Table 2Physicochemical characteristics of the native, hydrothermally treated and decorticated millet (dry weight basis)a

Parameter Native Hydrothermally treated Decorticated

Appearance Spherical Spherical and shrunken Spherical and opaqueColour (% whiteness, DE) Brown (3.2 ± 1, 78.6) Dark brown (2.3 ± 0.9, 85.0) Light cream (10.8 ± 1.2, 59.3)Hardness (kg/cm2) 1.1 ± 0.5 7.2 ± 0.4 7.1 ± 0.61000 kernel wt (g) 2.9 ± 0.4 2.8 ± 0.5 2.6 ± 0.51000 kernel volume (ml) 2.1 ± 0.3 2.0 ± 0.5 1.7 ± 0.4Density 1.379 ± 0.019 1.40 ± 0.028 1.501 ± 0.032Protein (g%) 8.1 ± 0.7 8.0 ± 0.5 6.3 ± 0.6Fat (g%) 1.5 ± 0.2 1.4 ± 0.3 0.9 ± 0.2Starch (g%) 68.1 ± 2.0 65 ± 3.2 74.0 ± 3.4Total dietary fiber (g%) 22.0 ± 1.2 21.1 ± 1.6 14.7 ± 1.8Soluble dietary fibre (g%) 2.5 ± 0.6 2.0 ± 0.6 2.4 ± 0.5Insoluble dietary fibre (g%) 19.7 ± 1.0 19.1 ± 1.2 12.3 ± 1.0Minerals (g%) 1.9 ± 0.1 1.5 ± 0.1 1.0 ± 0.2Acid insoluble ash (g%) 0.12 ± 0.02 0.08 ± 0.01 0.07 ± 0.01Calcium (mg%) 317 ± 17 309 ± 12 180 ± 15Phosphorous (mg%) 211 ± 8 157 ± 6 109 ± 10Phytate (mg%) 236 ± 7 222 ± 8 142 ± 8Polyphenols (mg%) (catechin equivalent) 265 ± 7 228 ± 7 67 ± 9Equilibrium moisture content (%), at 30 �C 33 ± 0.5 46 ± 1.0 55 ± 0.5Solubility (%), at 30 �C 3.9 ± 0.5 7.4 ± 0.3 8.5 ± 0.4Swelling (%), at 30 �C 70 ± 4 165 ± 8 190 ± 7Swelling (%), at 80 �C 260 ± 8 263 ± 5 270 ± 11Cooking time (min) 17 ± 1 18 ± 1 5 ± 1

DE—colour deviation from standard barium sulfate.a Average ± standard deviation of three independent determinations.

0

50

100

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2 4 6 8 10 1 14 16 18 20 22 24

Time (min)

Vis

cosi

ty (

RV

U)

0 8 14 23Heating Cooling Holding

Native

Decorticated

50 95 5095

Temperature ( C)

Fig. 5. Pasting characteristics of native and decorticated finger milletdetermined in rapid visco-analyser at 10% (w/v) concentration.


content of the millet, and hence, significant reduction in thepolyphenol contents occurs on decorticating the millet.Similarly, phytate phosphorus is located largely in the scu-tellum and to a smaller extent in the aleurone cells (Pore &Magar, 1979; Wada & Maeda, 1980) and in view of that,reduction in phytate phosphorus occurs on decorticationof millet (McDonough et al., 1986). Reduction in someof these constituents has nutritional advantages since, theseare considered as antinutritional factors and their reduc-tions improves the bioavailability of minerals (Erdman,1981).

3.3. Pasting characteristics

The pasting characteristics of the native and decorti-cated finger millet flours recorded in the rapid visco-ana-lyzer are presented in Fig. 5. The decorticated milletexhibited noticeable (7.5 RVU) cold paste viscosity, whichremained more or less constant during heating, cookingand cooling phases. From the viscograms it may be notedthat gelatinization temperature (76 �C), and the peak vis-cosity (180 RVU) of the millet are typical to cereals whereas the pasting characteristics of the decorticated finger mil-let were similar to precooked starchy foods (RaghavendraRao, Sreedharamurthy, & Desikachar, 1982).

3.4. Dough characteristics

The dough prepared by mixing the native millet flourwith cold water was of very poor strength and consistency(Fig. 6a), whereas, that prepared with hot water (Fig. 6b),

exhibited moderate consistency and dough strength(500 BU in 1.5 min), but collapsed after 9 min of mixing.In contrast to that, the flour from the decorticated milletabsorbed 64% cold water and reached to near 500 BU con-sistency within 1 min and dropped gradually to 300 BUafter mixing for 9 min (Fig. 6c). The high water holding

Minutes9 6 3 0

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a

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BU

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Minutes

BU

Minutes

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9 6 3 0 c

9 6 3 0

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100

b

Fig. 6. Farinograms of native and decorticated finger millet: (a) native(cold water), (b) native (hot water) and (c) decorticated (cold water).


capacity of the decorticated millet may be due to the pres-ence of the gelatinized starch and its, stability could be dueto intermolecular adhesiveness of the starch. The poordough characteristics of the native millet prepared by mix-ing with cold water is due to very low hydration character-istics of raw starch but, addition of hot water to the milletflour and mixing immediately, partially gelatinizes thestarch and as a result the adhesiveness of the flour particlesincreases, and this is reflected by the dough consistencyduring initial stages of mixing. However, the dough charac-teristics of decorticated finger millet exhibits characteristicsof pre-gelatinized flour and also indicates its suitability forchapathi (unleavened pan cake) and bakery products.

3.5. Cooking characteristics

The decorticated millet cooks to soft textured discretegrains within 5 min when dropped into boiling water.

The cooked millet retained the discreteness and sphericalshape of the kernels (Fig. 3e). This enables its consumptionalong with sambar (traditional pulse based spicy gruel) sim-ilar to rice or after seasonings with spices and can also beused to prepare snacks, savoury/sweet dishes. Processingof the decorticated millet for preparation of the expandedmillet similar to expanded rice (Malleshi & Ushakumari,2003) and utilization of expanded millet as adjunct in con-fectionery have been highly promising. The decorticatedmillet could be size graded to semolina or flour for utiliza-tion similar to wheat and can also be used for the prepara-tion of traditional millet products such as mudde (stiffporridge) roti (unleavened pancake) and ambali (gruel).Exploratory experiments on utilization of the millet flourin bakery products, as a thickener in soups and beverages,and also in the form of flaked and puffed product has beenencouraging. Hence, the product has potential as a newfood material for the non-traditional millet consumersworld wide.

4. Conclusion

The floury texture of finger millet endosperm could betransformed to corneous texture by hydrothermal treat-ment followed by low temperature drying. This in vivobio-transformation of the endosperm texture enablesdecortication of the millet in horizontal carborundumcoated twin disc mill. The decorticated millet could becooked as discrete grains similar to rice, which was not pos-sible hitherto. Thus, it holds high promise for diversifiedfood uses similar to rice and wheat and also for prepara-tion of value added products.

Acknowledgements

The financial support received from the All India Co-coordinated Small Millet Improvement Project of ICAR,New Delhi, to carryout this research work is gratefullyacknowledged.

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Preparation and functional properties of decorticated finger millet ( Eleusine coracana

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