Food Chemistry 113 (2009) 71–77

Contents lists available at ScienceDirect

Food Chemistry

journal homepage: www.elsevier .com/locate / foodchem

Physico–chemical, thermal and pasting properties of fractions obtained duringthree successive reduction milling of different corn types

Narpinder Singh a,*, Richa Bedi a, Rhythm Garg a, Mukti Garg a, Jaghmohan Singh b

a Department of Food Science and Technology, Guru Nanak Dev University, Amritsar 143005, Indiab B.N. Flour Mills, Batala 143 505, India

a r t i c l e i n f o

Article history:Received 12 March 2008Received in revised form 12 May 2008Accepted 11 July 2008

Keywords:CornDent cornPopcornWhite cornSweet cornDry millingThermalPasting

0308-8146/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.foodchem.2008.07.023

* Corresponding author. Tel.: +91 183 2258802x32E-mail address: narpinders@yahoo.com (N. Singh)

a b s t r a c t

The physico–chemical, thermal and pasting properties of fractions obtained during three successivereduction milling of degermed grains of four corn types (popcorn, sweet corn, dent corn, and white corn)was studied. Popcorn and white corn gave higher coarser fraction (14–20 mesh) yield than dent andsweet corn. Protein content progressively decreased with increase in fineness in the particle size. Frac-tions of first reduction stage showed higher fat content and L* value; and lower b* value than the fractionsfrom second and third reduction stages. L* value increased whereas ‘a*’ and ‘b*’ values decreased withincrease in fineness of the fractions. To, Tp and DHgel, peak viscosity, breakdown, setback and final viscos-ity increased while pasting temperature decreased with increase in fineness of the fractions. The resultsshowed that the successive reduction dry milling of a single corn type could produce fractions with var-ied characteristics.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

There are five general classes of corn–dent corn, popcorn, flourcorn, flint corn, and sweet corn. ‘Floury corn’ also known as ‘soft’corn has kernels consisted of almost entirely soft starch and hasa small portion of hard starch. Floury corn usually has a roundedor flat crown, but is of less commercial value. Dent corn kernelscontain both hard and soft starch and become indented at maturitywith a depressed crown (Evers & Millar, 2002). Sweet corn (Zeamays L. subsp. mays Saccharata Group) has higher sugar contentthan other corn types and is eaten after boiling or roasting orstored in frozen or canned form. Popcorn (Zea mays L. var. tunicataLarrañaga ex A. St. Hil) is mainly used for popping. White corn is ahybrid of dent corn with whiter colour starch and contains highamounts of vitreous endosperm relative to that of flouryendosperm.

Different parts of corn have different physical and chemicalproperties. The horny endosperm has 1.5–2% more protein (Wat-son, 1987b) and has a thicker protein matrix than the floury endo-sperm (Watson, 1987a). The floury endosperm is softer and easierto break than the horny endosperm (Jamin & Flores, 1998). Yellowcorn has a horny endosperm with more carotenoids (74–86%),

ll rights reserved.

16; fax: +91 183 2258820..

which is the source of the yellow colour in corn, than the flouryendosperm (9–23%) (Watson, 1987b). Hardness and breakage sus-ceptibility have been reported to be interrelated and affect the util-isation of corn (Pomeranz, Martin, Traylor, & Lai, 1984). Pomeranz,Hall, Czuchajowska, and Lai (1986) evaluated ten different dentcorn commercial hybrids for relative hardness using several differ-ent methods of hardness evaluation. Among other physical mea-surements, test weight and density showed the highestcorrelation with hardness values. Velu, Nagender, PrabhakaraRao, and Rao (2006) studied the dry milling characteristics of corngrains, which were dried in a domestic microwave oven. Lin, Abou-bacar, Zehr, and Hamaker (2001) reported that amylopectin in thegrit portion of dry milled corn had a significantly higher proportionof long chains and a postulated lower extent of chain branchingthan its flour counterpart.

Corn with lower test weight has been reported to contain lowerpercentages of the hard endosperm, and produced lower yields ofprime grits during dry milling (Rutledge, 1978). Paulsen and Hill(1985) found that yields of large flaking grits were significantly in-creased in corn with low breakage susceptibilities and high-testweight. Kirleis and Stroshine (1990) reported that the test weight,kernel density and hardness test were positively and significantlycorrelated with the milling evaluation factors determined by ashort flow milling process. Mestres, Lousin-Alexendra, Matencio,and Lahlou (1991) found that the chemical compositions (ash

72 N. Singh et al. / Food Chemistry 113 (2009) 71–77

and protein content) and physical properties (sphericity or dentkernel percentage) could be used to predict dry milling character-istics (semolina quality and quantity) of different yellow dent cornhybrids. Dry milling of corn has been studied widely (Manoharku-mar, Gerstenkorn, Zwingelberg, & Bolling, 1978; Mestres et al.,1991; Mistry & Eckhoff, 1992; Yuan & Flores, 1996); however,there is no reported work on the effect of successive reductionmilling of various corn types on the properties of resultant frac-tions. The present study reports physico–chemical, thermal andpasting properties of fractions obtained during three step succes-sive reduction milling of different corn types.

2. Materials and methods

2.1. Materials

Popcorn, sweet corn, dent corn and white corn were procuredfrom the regular fields of Himachal Pradesh from 2006–2007 har-vests. Nine endosperm fractions, germ and pericarp were collectedduring dry milling at B.N. Flour Mills, Batala. The flow diagram ofdry milling and details of rolls gap, roll differentials, rolls corruga-tions, etc. is shown in Fig. 1.

2.2. Dry milling

Cleaned grains of each corn type were degermed to remove thegerm portion. The degermed grains were then dry milled usingthree reduction stages. Degermed grains were passed throughthe first pair of break rolls (R1). The material recovered was passedthrough a 14 mesh sieve. The fraction that passed through the14 mesh sieve was further sieved through 20 mesh and 40 meshsieves. The fraction retained on 20 mesh sieve was designated asR1F1 and that passed through 20 mesh and retained on 40 meshwas designated as R1F2; while the fraction passed through40 mesh was R1F3. The fraction retained on the 14 mesh sievewas passed through the second pair of break rolls (R2). The fractionpassed through 14 mesh was sieved through 20 and 40 meshsieves as in first reduction stage and designated as R2F1, R2F2and R2F3. The material retained on 14 mesh after second reductionstage was further passed through the third pair of break rolls (R3).The material was sieved again through 14 mesh sieve and passedthrough 20 and 40 mesh sieved and fractions were designated asR3F1, R3F2 and R3F3, respectively. The speed of the fast and slowerroller was 232 and 350 rpm. The milling capacity of the mill was1 ton per hour. The material retained on 14 mesh was collectedas the pericarp portion.

2.3. Composition

Fractions obtained during dry milling were estimated for mois-ture, ash, fat and protein (%N � 6.25) content by AOAC methods(AOAC, 1990).

2.4. Hunter parameters

The fractions were ground to pass through 60 mesh sieve beforetesting for colour parameters. Colour parameters (L*, a* and b*) ofsamples were carried out in triplicate, using a Minolta CM-3500Dspectrophotometer. A glass cell containing flour was placed abovethe light source, and L*, a* and b* values were recorded. The L* valueindicates the lightness, 0–100 representing dark to light. The a* va-lue gives the degree of the red–green colour, with a higher positivea* value indicating more red. The b* value indicates the degree ofthe yellow–blue colour, with a higher positive b* value indicatingmore yellow.

2.5. Thermal properties

Thermal characteristics of flours were analysed in triplicate byusing a differential scanning calorimeter-821e (Mettler Toledo,Switzerland) equipped with a thermal analysis data station. Sam-ple (3.5 mg, dry weight) was loaded into a 40 ll capacity alumin-ium pan (Mettler, ME-27331) and distilled water was added withthe help of a Hamilton micro-syringe to achieve a flour–water sus-pension containing 70% water. Samples were hermetically sealedand allowed to stand for 5 h at room temperature before heatingin the DSC. The DSC analyser was calibrated using indium and anempty aluminium pan was used as reference. Sample pans wereheated at a rate of 10 �C/min from 20 to 100 �C. Onset temperature(To), peak temperature (Tp), conclusion temperature (Tc) and en-thalpy of gelatinization (DHgel) were calculated automatically.

2.6. Pasting properties

Pasting properties of flours were studied by using a Rapid ViscoAnalyser (Newport Scientific Pty Ltd., Warriewood NSW 2102, Aus-tralia). Viscosity profiles of flours were recorded using flour sus-pensions (10%, w/w; 28 g total weight). The temperature–timeconditions included a heating step from 50 to 95 �C at 6 �C/min(after an equilibration time of 1 min at 50 �C), a holding phase at95 �C for 5 min, a cooling step from 95 to 50 �C at 6 �C/min and aholding phase at 50 �C for 2 min. Each sample was analysed intriplicate.

2.7. Statistical analysis

The data reported are average of triplicate observations andsubjected to analysis of variance using Minitab Software (State Col-lege, PA).

3. Results and discussions

3.1. Products yield

The dry milling of the all the corn types gave higher yield ofmedium fractions (20–40 mesh) during three successive reductionstages. Dent corn gave the highest fine flour yield (10.3%) amongthe corn types studied, followed by sweet corn (9.53%), white corn(8.56%), and popcorn (7.32%). Coarser fractions (14–20 mesh) yieldwas found to be the higher for popcorn (32.29%) and white corn(31.48%), which was followed by dent (26.29%) and sweet corn(25.31%). Medium fraction and pericarp recovery was the highestfor the sweet corn and the lowest values for these fractions was ob-served for white corn. Germ yield ranged between 16.25% and17.86%; dent corn showed the highest (17.86%), followed by whitecorn (17.21%), popcorn (16.87%), and sweet corn (16.25%). Sweetcorn showed the highest pericarp recovery (7.56%), followed bypopcorn (7.31%), dent corn (6.56%) and white corn (6.29%). Pan,Eckhoff, Paulsen, and Litchfield (1996) reported pericarp yields ofsix hybrid corn varieties between 4.3% and 7.0%. Pericarp yieldsindicated how cleanly pericarp gets separated from endosperm.The recovery of all the fractions during the second reduction stagewas higher than that during first and third reduction stage. Thesedifferences may be due to difference in hardness, which is one ofthe main characteristics that affect the yield of coarse fraction.Pan et al. (1996) reported that harder endosperm corn gave greaterprime grit yield than soft corn with lower density. The endospermproducts (%) were observed to be the highest in white corn fol-lowed by popcorn, sweet corn and dent corn. Dent corn showedthe highest 100 kernel weight of 34 g, followed by sweet corn(21.5 g), white corn (18.6 g) and popcorn (16.6 g). Pan et al.

↓

Degerming

First Reduction (R1 )Cylinder Gap: 0.99 mm, Corrugations/inch: 12, Disposition: Dull to Dull, Helication: 6 inch

Sieving 14 mesh

Fraction passes through 20-mesh sieve (R1F1)

Fraction passes through 40-meshsieve (R1F2)

Fraction collectedin Pan (R1F3)

First reduction flour < 14 mesh Reduction Grits >14 mesh

Second Reduction (R2 )Cylinder Gap: 0.508 mm, Corrugations/inch: 16, Disposition: Dull to Sharp, Helication: 5 inch

Sieving 14 mesh

Second reduction flour < 14 mesh

Reduction Grits >14 mesh

Corn Grain

Fraction passesthrough 20-mesh sieve (R2F1)

Fraction passes through 40-meshsieve (R2F2)

Fraction collected in Pan (R2F3)

Third Reduction (R2 )Cylinder Gap: 0.152 mm,

Corrugations/inch: 18, Disposition: Sharp to Dull , Helication: 4 inch

Sieving 14 mesh

Third Reductionflour < 14 mesh

Pericarp (> 14 mesh)

Fraction passes through 20-mesh sieve (R3F1)

Fraction passes through 40-meshsieve (R3F2)

Fraction collected in Pan (R3F3)

Fig. 1. Flow chart of dry milling.

N. Singh et al. / Food Chemistry 113 (2009) 71–77 73

74 N. Singh et al. / Food Chemistry 113 (2009) 71–77

(1996) reported germ yields between 17.7% and 19.5% for differenthybrid corns. Difference in endosperm products may be due to dif-ferences in the ability of starch granules to be separated from theprotein matrix, and thus the degree of adhesion between starchand protein matrix that appears to be related to corn hardness,as soft corn produces larger amount of fine particles. Differencein germ, pericarp and endosperm products yields in different corntypes may be attributed to difference in the proportions of theseconstituents.

3.2. Physico–chemical properties

The composition of different fractions obtained during dry mill-ing of different corn types varied significantly (Table 1). Sweet cornshowed the highest ash content among the corn types studied. Ashcontent of the fractions obtained from dry milling of popcorn dur-ing first reduction stage was higher than the corresponding frac-tions from other corn types during similar reduction stages. Ashcontent of fractions of first reduction stage ranged from 1.08% to1.23% for popcorn, 0.83% to 1.21% for white corn, 0.85% to 1.0%for sweet corn, and 0.73% to 0.86% for dent corn. Different fractionsobtained during second reduction had lower ash content than theircorresponding fractions from the first reduction stage. Fractions ofsize <40 mesh (R3F3) obtained during the third reduction stagefrom different corn types had higher ash content than all otherfractions.

Among the corn types studied, sweet corn showed the highestfat content. Fractions obtained during the first reduction stageshowed higher fat content than their counterpart fractions ob-tained from second and third reduction stages whereas fractionsof the second reduction stage had lower fat content than fractionsof the third reduction stage. Fine fractions of the first and secondreduction stages showed higher fat content as compared to theircounterpart coarse and medium fractions. Medium fractions fromthe second and third reduction stages showed lower fat contentthan counterpart coarse and fine fractions.

Protein content for all the corn types and different fractionsfrom the reduction stages ranged between 5.4% and 12.9%. Sweetcorn showed the highest protein content (9.3%) followed by whitecorn (8.1%), popcorn (7.5%) and dent corn (5.7%). Fractions of thefirst reduction stage had higher protein content than correspond-ing fractions obtained from the second reduction stage. Proteincontent progressively decreased with increase in fineness in theparticle size in all the reduction stages. Protein and fat content of5.2% and 2% for corn flour has been reported earlier (Alexander,1987).

Table 1Proximate analysisa of fractions obtained during milling of different corn types

Reductionstages

Size(mesh)

Popcorn White corn

Ashcontent(%)

Fatcontent(%)

Proteincontent (%)

Ashcontent(%)

Fatconten(%)

R1 R1F1(14–20) 1.1cb 3.1bc 11.1d 0.8abc 2.6bR1F2(20–40) 1.4b 3.5c 10.9d 1.2c 3.3bR1F3(<40) 1.2b 4.1d 8.9c 1.1bc 3.6b

R2 R2F1(14–20) 0.7bc 1.8a 8.6bc 0.7ab 1.9aR2F2(20–40) 0.6ab 1.7a 8.4bc 0.4a 1.6aR2F3(<40) 1.0c 2.6b 7.8ab 0.9bc 3.3b

R3 R3F1(14–20) 1.0c 2.7b 8.0ab 0.8abc 2.9bR3F2(20–40) 0.6ab 1.6a 8.2ab 0.5a 1.4aR3F3(<40) 2.7d 2.4b 8.5bc 1.2c 2.9b

Whole 0.2a 7.7 7.6a 0.2 8.3c

Values with similar superscripts in column do not differ significantly (p < 0.05).a Expressed at 14% moisture basis.

Hunter colour parameters (L*, a* and b*) of different fractionsshowed significant variation (Table 2). As expected, all the frac-tions from white corn had higher L* (lightness) value than the cor-responding fractions from other corn types. Different fractionsfrom dent corn obtained in three-reduction system showed higher‘a*’ (redness and greenness) and ‘b*’ (yellowness and blueness) va-lue than those obtained from other corn types. L* value increasedwhereas ‘a*’ and ‘b*’ values decreased with increase in fineness ofthe particle (<40 mesh) size. Fractions obtained during the firstreduction stage showed higher ‘L*’ value than corresponding frac-tions from the second and third reduction stages. L* value of differ-ent fraction ranged from 82.6 to 89.5, 79.53 to 83.55, 75.83 to85.48 and 81.61 to 84.48, for white corn, popcorn, sweet cornand dent corn, respectively. L* value represents the brightness ofthe flour. The greater the value of L*, the brighter is the fraction.Colour influences the overall acceptability of grit and resultantproduct. Amongst yellow corn types, dent corn was the most yel-lowish (b* = 26.7) whereas and popcorn was the least yellowish(b* = 22.6). Fractions obtained from first reduction stage had lowerb* value (less yellowness) than corresponding fractions from sec-ond and third reduction stage. Similar trend was observed for ‘a*’value. The higher ‘b*’ value has been reported to be an indicationof the protein content (Jamin & Flores, 1998). Hunter colour L*, a*

and b* values of 81.45, 2.86 and 23.49, respectively, for corn gritshave been reported earlier (Jamin & Flores, 1998).

3.3. Thermal properties

The transition temperatures (Onset temperature, To; peak tem-perature, Tp; end set temperature, Tc) of different fractions ob-tained during three reduction dry milling are shown in Table 3.Fractions obtained during dry milling of popcorn showed lowertransition temperature as compared to fractions obtained fromother corn types. To and Tp increased with increase in fineness ofthe particles, being the highest in fine and the lowest in coarsefractions. Popcorn coarse fraction from the first reduction stagehad To and Tp of 65.38 and 73.05 �C against 64.62 and 72.38 �C,respectively, for the third reduction stage. While Tc showed the re-verse, the highest value for the coarse and the lowest for fine frac-tion. To and Tp of fractions obtained during the first reductionstages showed lower value than the corresponding fractions ob-tained during the second reduction stage. Similarly, fractions ob-tained from the second reduction stage showed lower values thatthose obtained from the third reduction stage. Tc showed a reversetrend as observed for To and Tc. Popcorn, sweet corn, dent corn, andwhite corn showed enthalpy of gelatinization (DHgel) from 2.13 to

Sweet corn Dent Corn

tProteincontent(%)

Ashcontent(%)

Fatcontent(%)

Proteincontent(%)

Ashcontent(%)

Fatcontent(%)

Proteincontent(%)

10.9d 0.9bc 2.3a 10.9d 0.7ab 2.9b 9.4d8.5bc 1.0b 3.1b 9.9cd 0.9b 3.1b 8.2bc7.5b 0.9bc 3.2b 6.9b 0.7ab 3.7b 5.2a

8.8c 0.7a 2.0a 9.5c 0.5ab 2.0a 10.8e8.7c 0.6a 1.5a 7.7b 0.4a 1.9a 8.7cd4.3a 0.8a 2.4a 6.4b 0.6ab 3.5b 7.4b

12.3e 1.3c 3.8b 12.3e 0.6ab 3.4b 9.3d11.1d 0.5ab 1.4a 7.0b 0.4a 1.7a 7.8b

7.5b 1.8d 2.4a 4.7a 1.2c 2.3a 4.7a

8.1b 0.4a 9.3c 9.2c 0.2a 7.1c 5.7a

Table 2Hunter parameters of fractions obtained during dry milling of different corn types

Reduction stage Size (mesh) Popcorn White corn Sweet corn Dent corn

L* a* b* L* a* b* L* a* b* L* a* b*

R1 R1F1(14–20) 82.4bc 3.6b 22.2b 88.2d �0.33a 9.0b 85.0d 3.4b 23.5c 82.7a 5.1d 25.1cR1F2(20–40) 83.1d 2.6a 19.2a 89.5e �0.23b 7.7a 85.5d 2.3a 20.0b 83.5ab 3.5ab 23.4abR1F3(<40) 83.5d 2.1a 18.2a 89.7e �0.15b 7.1a 85.7d 2.2a 19.0b 84.0b 2.8a 21.4a

R2 R2F1(14–20) 82.0bc 5.1d 29.9e 86.0c �0.08b 10.7c 82.6b 4.7bc 26.1de 82.3a 6.3e 27.9dR2F2(20–40) 82.8cd 4.7cd 24.9c 87.8d �0.16b 8.9b 83.8c 4.4b 25.4d 83.0ab 6.2e 27.7dR2F3(<40) 82.9cd 4.4c 24.0c 88.4d �0.29b 8.8b 83.8c 3.6b 24.2c 84.0b 4.0bc 23.9b

R3 R3F1 (14–20) 79.5a 6.3e 27.2d 82.6a �0.25b 12.3 78.8a 5.5c 27.2e 81.6a 6.4e 28.6dR3F2(20–40) 81.7b 5.8e 26.0cd 84.7b �0.23b 9.5b 81.8b 5.4c 26.0 83.4ab 6.1e 27.8dR3F3(<40) 81.7b 4.5c 24.4c 85.4b 0.01c 9.3b 82.2b 5.3c 16.3a 83.8b 4.7cd 25.2cd

Whole meal 79.3a 4.1c 22.6b 84.4b 0.36d 11.6c 82.3b 4.4bc 25.8d 82.3a 5.1d 26.7d

Values with similar superscripts in column do not differ significantly (p < 0.05).

Table 3Thermal properties of fractions obtained during dry milling of different corn types

Reduction stage Size (mesh) Popcorn White corn Sweet corn Dent corn

To (�C) Tp (�C) Tc (�C) To (�C) Tp (�C) Tc (�C) To (�C) Tp (�C) Tc (�C) To (�C) Tp (�C) Tc (�C)

R1 R1F1(14–20) 65.3abc 73.0a 81.1c 69.3c 74.5a 81.2ab 69.0b 74.4a 81.2b 70.1c 74.7bc 81.4bR1F2(20–40) 66.0cd 73.2a 80.6c 69.4c 75.2a 81.0ab 69.5d 75.2c 80.7b 70.8cd 75.1c 80.2aR1F3(<40) 66.8d 73.7b 78.6a 70.8d 76.0b 80.3a 70.0d 75.7c 79.6a 71.0d 75.4c 80.1a

R2 R2F1(14–20) 65.1ab 73.0a 81.1c 68.9bc 75.9b 82.9c 68.7b 74.2a 80.4ab 66.8a 74.1a 81.0aR2F2(20–40) 65.4ab 72.9a 80.9c 69.2c 75.9b 82.7c 68.8bc 74.4a 80.1a 68.2b 74.2a 80.7abR2F3(<40) 65.8b 73.5b 79.8b 69.4c 75.9b 82.7c 69.4cd 74.9b 79.6a 70.3c 74.7b 79.9a

R3 R3F1 (14–20) 64.6a 72.3a 80.4bc 67.2a 74.8a 83.6c 67.3a 74.0a 81.0b 66.6a 74.1a 81.0bR3F2(20–40) 65.0ab 72.9a 80.2bc 67.6a 74.9a 82.0b 67.5a 74.6ab 80.3ab 68.4b 74.4ab 80.9abR3F3(<40) 65.8b 73.2a 79.7b 68.4b 75.0a 81.7b 67.9a 74.8bc 80.0a 68.6b 74.7b 80.3a

To = onset temperature, Tp = peak temperature; Tc = final temperature.Values with similar superscripts in column do not differ significantly (p < 0.05).

N. Singh et al. / Food Chemistry 113 (2009) 71–77 75

5.53, 4.38 to 7.44, 3.1 to 7.80 and 2.96 to 8.35 J/g. DHgel increasedwith increase in fineness of particle size in the corn types. DHgel

showed trend of coarse < medium < fine fractions. Fractions ob-tained during three reduction milling showed significant variationin DHgel. Fractions obtained from the first reduction stage hadhigher DHgel than the corresponding fractions from the secondreduction, which had higher DHgel than those of the third reduc-tion. Popcorn fractions showed lower DHgel than fractions of othercorn types. DHgel is affected by factors such as starch granule,shape and percentage of large and small granules (Stevens & Elton,1971; Yuan, Thompson, & Boyer, 1993). Rombo, Taylor, and Min-naar (2004) reported To, Tp and DHgel values of 63.5 �C, 71.8 �Cand 10.21 J/g, respectively in corn flour.

3.4. Pasting properties

Peak viscosity (PV), pasting temperature (PT), breakdown (BD),final viscosity (FV) and setback (SB) values are shown in Tables 4and 5. PT provides an indication of the minimum temperature re-quired to cook the flour. Different fractions obtained from millingof popcorn showed lower PT than the fractions obtained from othercorn types. PT decreased with increase in fineness of the particlesin the fractions during all the reduction stages. Among the corntypes studied, white corn meal showed the highest PT of 88.7 �Cfollowed by sweet corn (80.67 �C), dent corn (78.2 �C) and popcorn(76.1 �C). PT increased with each successive reduction, fractionsobtained during the first reduction stage had the lower PT whilethose from the third reduction stage had the higher PT. This effectwas more pronounced in sweet and white corn. Fractions (R1F1,R1F2 and R1F3) obtained during the first reduction stage millingof sweet corn had PT of 77.9, 76.6 and 75.8 �C, respectively, whilethe corresponding fractions R3F1, R3F2 and R3F3 from the third

reduction stage showed PT of 85.9, 81.1 and 80.1 �C, respectively.PV, BD, SB and FV of fractions increased with increased finessesin particle size. The fine fraction showed higher PV than coarsefractions. These differences may be attributed to difference in pro-tein content. Sweet corn whole meal showed the highest PV, BD, SBand FV. White corn whole meal showed the lowest PV, FV and SB.Fractions obtained during the first reduction stage showed higherPV than corresponding fractions obtained during the second andthird reduction stage. R1F1, R1F2 and R1F3 fractions from the firstreduction stage of sweet corn had PV of 1204, 1532 and 1782 cP,respectively, while the corresponding R3F1, R3F2 and R3F3 frac-tions from the third reduction stage showed PV of 432, 801 and1029 cP, respectively. A negative correlation between the PV ofcorn flour and hardness of grain has been reported earlier (Alme-dia-Dominguez, Suhendro, & Rooney, 1997; Sandhu & Singh,2007). It could be inferred that corn types with higher hardnesshad tightly packed starch granules and consequently developedlower viscosity. A significant negative correlation of protein withPV (r = �0.863, p < 0.01) of flour and a positive correlation withthe rupture force of grain (r = 0.922, p < 0.01) were also observedearlier (Sandhu & Singh, 2007). The loosely packed starch granuleswith lower protein-to-starch ratio in the fine fractions seem to hy-drate and swell more rapidly in the presence of heat. On the otherhand, coarse fractions seems to have tightly packed starch granuleswith more protein-to-starch ratio that hydrate at slower rate andswell less during heat. During the final cycle of cooling (from 95to 50 �C), the viscosity increased owing to the alignment of thechains of amylose (Flores-Farias et al., 2000). SB ranged from 333to 1778 cP, the lower being for coarser fractions and higher for fi-ner fractions between 1030 and 2720 cP. The lower SB of coarsefractions indicates their lower tendency to retrograde as comparedto medium and finer fractions.

Table 4Pasting properties of fractions obtained during dry milling of different corn types

Reduction stage Size (mesh) Popcorn White corn Sweet corn Dent corn

PT (�C) PV (cP) BV (cP) PT (�C) PV (cP) BV (cP) PT (�C) PV (cP) BV (cP) PT (�C) PV (cP) BV (cP)

R1 R1F1(14–20) 75.2a 413b 36a 78.3d 867e 155c 77.9c 1204d 408e 80.2d 1006b 259cR1F2(20–40) 75.1a 866c 204b 77.5c 1469g 443d 76.6b 1532e 595f 77.8b 1546d 575fR1F3(<40) 74.9a 1570 510c 75.9a 1609h 575e 75.8a 1782f 792g 75.9a 2048e 812g

R2 R2F1(14–20) 75.3a 408b 39a 85.1h 375b 15a 80.6e 948c 245d 80.3d 978b 190bR2F2(20–40) 75.2a 703b 210b 79.0e 665d 87b 78.3c 1208d 350e 77.8b 1300c 370dR2F3(<40) 74.8a 937d 166 76.6b 1142f 385 77.0b 1290d 369e 77.8b 1592d 784g

R3 R3F1 (14–20) 76.5b 357a 10a 85h 208a 19a 85.9f 432a 32a 83.5e 882b 170bR3F2(20–40) 75.3a 658b 76a 82.3g 476c 42a 81.1e 800b 168c 79.1c 1250c 439eR3F3(<40) 75.0a 965d 221 80.5f 708d 90b 80.0d 1030c 186c 78.3b 1550d 516fWhole meal 76.1b 420b 10a 88.7i 336b 17a 80.67e 787b 132b 78.22b 578a 69a

PT, pasting temperature (�C); PV, peak viscosity (cP); BV, breakdown viscosity (cP).Values with similar superscripts in column do not differ significantly (p < 0.05).

Table 5Pasting properties of fractions obtained during dry milling of different corn types

Reduction stages Size (mesh) Popcorn White corn Sweet corn Dent corn

FV (cP) SB (cP) FV (cP) SB (cP) FV (cP) SB (cP) FV (cP) SB (cP)

R1 R1F1(14–20) 1010b 639b 1930f 1219d 2427e 1630d 2524c 1778dR1F2(20–40) 2100e 1440c 2876g 1842e 2819ef 1880ef 3550e 2579fR1F3(<40) 3063g 2004d 3100h 2075f 2980f 1990f 3957f 2720f

R2 R2F1(14–20) 886a 513a 796b 435a 1463c 616ab 1873b 1086bR2F2(20–40) 1230d 739b 1487d 909c 1508c 650b 2300c 1423cR2F3(<40) 2194 1423c 1786e 1030c 1850d 1148c 3124d 2316

R3 R3F1 (14–20) 817a 470a 523a 333a 742a 342a 1308a 665aR3F2(20–40) 1270d 689b 1030c 595b 1106b 490a 2415c 1555cR3F3(<40) 2533f 1789 1872ef 1173d 2677e 1816e 3193d 2160eWhole 1116c 688b 710b 393a 1816d 1160c 1105a 596a

FV, final viscosity (cP); SB, setback (cP).Values with similar superscripts in column do not differ significantly (p < 0.05).

76 N. Singh et al. / Food Chemistry 113 (2009) 71–77

The increase in viscosity with temperature may be attributed tothe removal of water from the exuded amylase by the granules asthey swell (Ghiasi, Varriano-Marstson, & Hoseney, 1982). BV (mea-sure of the cooked starch to disintegration) for different corn frac-tions in all the three reductions stages ranged from 11 to 511 cP forpopcorn, 9 to 575 cP for white corn, 69 to 784 cP for dent corn, and32 to 792 cP for sweet corn. The lowest BV of R3F1 fraction of pop-corn obtained during the third reduction stage and R3F3 fraction ofwhite corn obtained during the third reduction stage indicated it’sgreatest paste stability. During cooling from 95 to 50 �C, the viscos-ity increased owing to the alignment of the chains of amylose (Flo-res-Farias et al., 2000). SB is the measure of syneresis of starchupon cooling of the cooked starch pastes, ranged between 471 cPfor fraction R3F1 of popcorn obtained during the third reductionstage to 2004 cP for R1F3 fraction of popcorn obtained during thefirst reduction stage. It ranged between 333 cP for R3F1 fractionof white corn obtained during the third reduction stage to2075 cP for R1F2 fraction of while corn obtained during the firstreduction stage. The lowest SB of R3F1 fraction of popcorn andwhite corn obtained during the third reduction stage indicatedtheir lower tendency to retrograde.

4. Conclusion

The physico–chemical, thermal and pasting properties of frac-tions obtained during three successive reductions milling of deger-med grains of four corn types (popcorn, sweet corn, dent corn, andwhite corn) differed significantly. The fractions with varied charac-

teristics can be produced by successive reduction dry milling of asingle corn type.

References

Alexander, R. J. (1987). Structure and composition. In S. A. Watson & P. E. Ramstad(Eds.), Corn chemistry and technology (p. 356). St. Paul, MN: AmericanAssociation of Cereal Chemists.

Almedia-Dominguez, H. D., Suhendro, E. L., & Rooney, L. W. (1997). Factors affectingrapid visco analyzer curves for the determination of corn kernel hardness.Journal of Cereal Science, 25, 93–102.

AOAC (1990). Official methods of analysis of the association of official analyticalchemists (15th ed.). Washington, DC: AOAC.

Evers, T., & Millar, S. (2002). Cereal grain structure and development: Someimplications for quality. Journal of Cereal Science, 36, 261–284.

Flores-Farias, R., Martinez-Bustos, F., Salinas-Moreno, Y., Chang, Y. K., Hernandez, J.S., & Rios, E. (2000). Physicochemical and rheological characteristics ofcommercial nixtamalised Mexican corn flours for tortillas. Journal of theScience of Food and Agriculture, 80, 657–664.

Ghiasi, K., Varriano-Marstson, E., & Hoseney, R. C. (1982). Gelatinization of wheatstarch and starch-surfactant interaction. Cereal Chemistry, 59, 86–88.

Jamin, F. F., & Flores, R. A. (1998). Effect of additional separation and grinding on thechemical and physical properties of selected corn dry-milled streams. CerealChemistry, 75, 166–170.

Kirleis, A. W., & Stroshine, R. L. (1990). Effects of Hardness and drying air temperatureon breakage susceptibility and dry-milling. Cereal Chemistry, 67, 523–528.

Lin, Y. P., Aboubacar, A., Zehr, B. E., & Hamaker, B. R. (2001). Corn dry-milled grit andflour fractions exhibit differences in amylopectin fine structure and gel texture.Cereal Chemistry, 79, 354–358.

Manoharkumar, B., Gerstenkorn, P., Zwingelberg, H., & Bolling, H. (1978). On somecorrelation between grain composition and physical characteristics to the drymilling performance in maize. Journal of Food Sciences Technology, 15, 1–6.

Mestres, C., Lousin-Alexendra, A., Matencio, F., & Lahlou, A. (1991). Dry millingproperties of Maize. Cereal Chemistry, 68, 51–56.

Mistry, A. H., & Eckhoff, S. R. (1992). Dry milling and physical characteristics ofalkali–debranned yellow dent corn. Cereal Chemistry, 69, 82–84.

N. Singh et al. / Food Chemistry 113 (2009) 71–77 77

Pan, Z., Eckhoff, S. R., Paulsen, M. R., & Litchfield, J. B. (1996). Physical properties anddry-milling characteristics of six selected high-oil maize hybrids. CerealChemistry, 73, 517–520.

Paulsen, M. R., & Hill, L. D. (1985). Corn quality factors affecting dry millingperformance. Journal of Agricultural Engineering Research, 31, 255–263.

Pomeranz, Y., Hall, G. E., Czuchajowska, Z., & Lai, F. S. (1986). Test weight, hardness,and breakage susceptibility of yellow dent corn hybrids. Cereal Chemistry, 63,349–351.

Pomeranz, Y., Martin, C. R., Traylor, D. D., & Lai, F. S. (1984). Corn hardnessdetermination. Cereal Chemistry, 61, 147.

Rutledge, J. H. (1978). The value of corn quality to the dry miller. Proceedings of thecorn quality conference 1977 (vol. AE-4454, pp. 158–162). Urbana, IL: Universityof Illinois.

Rombo, G. O., Taylor, J. R. N., & Minnaar, A. (2004). Irradiation of corn and beanflours: Effect on starch physicochemical properties. Journal of the Science of Foodand Agriculture, 84, 350–356.

Sandhu, K. S., & Singh, N. (2007). Some properties of corn starches II:Physicochemical, gelatinization, retrogradation, pasting and gel texturalproperties. Food Chemistry, 101, 1499–1507.

Stevens, D. J., & Elton, G. A. H. (1971). Thermal properties of starch/water system.Measurement of heat of gelatinization by differential scanning calorimeter.Starch/Starke, 23, 8–11.

Velu, V., Nagender, A., Prabhakara Rao, P. G., & Rao, D. G. (2006). Dry millingcharacteristics of microwave dried maize grains (Zea mays L.). Journal of FoodEngineering, 74, 30–36.

Watson, A. S. (1987a). Structure and composition. In S. A. Watson & P. E. Ramstad(Eds.), Corn chemistry and technology (pp. 53–82). St. Paul, MN: AmericanAssociation of Cereal Chemists.

Watson, A. S. (1987b). Measurement and maintenance of quality. In S. A. Watson &P. E. Ramstad (Eds.), Corn chemistry and technology (pp. 125–183). St. Paul, MN:American Association of Cereal Chemists.

Yuan, J., & Flores, R. (1996). Laboratory dry-milling performance of white corn:Effect of physical and chemical corn characteristics. Cereal Chemistry, 73,574–578.

Yuan, R. C., Thompson, D. B., & Boyer, C. D. (1993). Fine structure of amylopectin inrelation to gelatinization and retrogradation behavior of maize starches fromthree wax-containing genotypes in two inbred lines. Cereal Chemistry, 70,81–89.