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Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionCereal Grains Structure & CompositionVijay SinghAssociate ProfessorDepartment of Agricultural & Biological EngineeringUniversity of Illinois at Urbana-Champaign, Urbana, IL1st Brazil-U.S. Biofuels Short CourseSão Paulo, BrazilJuly 27 - August 7, 2009Topics of Discussion Structure of Corn Kernel– Hand dissection exercise StarchProteinOilFiberOther ConstituentsCorn CompositionUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStructure of Cereal Grains Cereals are members of grass familyProduce dry,dry oneone-seededseeded fruit,fruit called caryopsisCaryopsis is also called kernel or grainCaryopsis consists of– Fruit coat or pericarp, which surrounds seed and is tightly adheredto seed coat– Seed, which consists of germ or embryo and endosperm enclosedb a nucellarbyll epidermisidi andd a seedd coat All cereal grains have these same parts in approx. samerelationship to each otherStructure of Corn KernelPericarpEndospermGermTip CapUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionScanning Electron Micrograph (SEM) ofDissected Steeped Corn KernelPericarpEndospermPericarp 5 to 6% of kernel dry weightCuticleEpidermisMesocarpCross cellsTube cellsSeed coat Cells in pericarp: hollow tubes,channels for water absorption viatip cap Seed coat: semipermeable Walls of pericarp contain celluloseand pentosans, no lignin.University of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionAleurone layer Aleurone layer beneath seed coat Aleurone layer cells contain protein bodies (good amino acidprofile), oil bodies, and no starch. It is rich in minerals (phytin) Removed with pericarp in wet millingGerm 10 to 12% of kernel dry weightStores nutrients and mineralsContains 81 to 85% of total kernel oil (mostly triglycerides)Composed of embryo and scutellumScutellum contains oil bodiesUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionCorn Germ: Phytic Acid (Phytate) Phytate is principal storage form of phosphorus in many planttissues– Yellow Dent Corn Whole Corn (0.89%)Endosperm (0.04%)Germ (6.25%)Pericarp (0.07%)(Inositol hexakisphosphate, IP6)Endosperm 82 to 84% of kernel dry weight, 86 to 89% starch byweightg In corn both translucent and opaque endosperm are foundwith a single kernelUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionEndosperm Translucent endosperm (Hardendosperm)– Tightly packed with few or no air spaces– Polygonal shaped starch granules– Starch granules are held together by amatrix protein– Protein bodies are zein Opaque Endosperm (Soft endosperm)– Starch granules are spherical– Starch granules covered with proteinmatrix that does not contain proteinbodiesSoftEndosperm True density is measure of endospermhardnessSEMs of Corn EndospermUniversity of Illinois at Urbana-ChampaignHardEndosperm

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionSEMs of Corn EndospermCells in corn endosperm containing tightly bound starch granulesSource: USDA/ARS/ERRCSEM of Cells in Soft EndospermAir space, loosely packed starch granules, thin protein matrix andexposed starch granulesSource: USDA/ARS/ERRCUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionSEM of Cells in Hard EndospermTightly packed starch granules with adhering protein matrix andfew exposed starch granulesSource: USDA/ARS/ERRCCorn Hand Dissection ExerciseUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionCorn Kernel Hand DissectionStarch, Protein, Oil, Fiber and Other MinorConstituentsUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStarch Primary source of stored energy in cereal grains 60-75%60 75% weight of grain Used in several food and industrial applicationsStarch Physical Structure Found in form of granule in cereal grains Granules are formed inside plastidsp In wheat, rye, barley, sorghum inside a plastid there is a singlestarch granule In rice and oats there are several or compounds starchgranules Starch granules grow in layersUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionGrowth of Starch GranuleStarch Chemical Composition Starch is a polymer of a six-carbon sugar D-glucose The structure of D-glucose can be shown in ring form or openchainUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStarch Chemical Composition Starch consists primarily of D-glucopyranose polymerslinked together by alpha 1,4 and alpha 1,6 glycosidic bonds Polymer are of two kinds– Amylose, smaller linear polymer, alpha 1,4 bondsStarch Chemical Composition Polymer are of two kinds– Amylose,Amylose smaller linear polymerpolymer, alpha 11,44 bonds– Amylopectin, larger branched polymer, branching at alpha 1,6 bondsUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStarch Chemical Composition The molecular size of polymer (degree of polymerization, DP)for– Amylose is 1,500-6,000– Amylopectin is 300,000-3,000,000 Dent corn typically has 23-25% Amylose and 75-77%Amylopectin Waxy corn has less than 1% Amylose and more than 99%A lAmylopectinti High-amylose corn has 55-70% Amylose and 30-45%AmylopectinStarch Chemical Composition Amylose molecules due to their long and linear nature formcomplexes with chemical compounds– For example with iodine amylose molecules give blue color– Test for determination of waxy corn hybridsUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionCrystallinity Emerges From AmylopectinStructureAmylopectin superhelicalstructure.Oostergetel and vanBruggen,gg1993Jenkins et al., 1994100% amylopectin: 40%crystallineHigh-amylose: 15% crystallineHairy Billiard Ball ModelRobertson et al 2006University of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionChannels from Surface to HilumAmylopectin StructureAlpha A attackNon reducing endsGluco A attackA-ChainsC-ChainReducing endB-ChainsGranule SurfaceUniversity of Illinois at Urbana-ChampaignGranule Center

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionAmylopectin StructureNon reducing endsReducing terAmylose Structure: HelixSix anhydrous glucose units per helix turnReducing endUniversity of Illinois at Urbana-ChampaignNon Reducing end

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionProperties of Starch Crystallinity– Packing of amylose and amylopectin within starch granule is notrandom but is very organized– A, B and C X-ray patters– Most cereal starches give the A pattern Birefringence– Under polarized light, starch granules show birefringence in formof a “maltesemaltese crosscross”Starch X-ray Diffraction PatternCorn and most cerealsexhibit A-pattern, butamylomaize are closerto B-pattern(exhibited by mosttubers like potato)Robyt, 1998University of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionBirefringenceCharacteristics of Starch in Cereal Grain The size, shape and structure of starch granules varies amongbotanical sources Size of granules range from less 1 μm to 100 μm Shapes can be spherical, ovoid or angularUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionCharacteristics of Starch in Cereal GrainCerealGrainGelantinizationTemperature( 62-72Round/Polyhedral 15Rice*68-78Polygonal3-8S hSorghum68 und/Lenticular 28*Individual not compound granulesStarch Granular Changes in Relationship toViscosityFully SwollenIntact Granules,Granulespolymer begins to leachSwelling inGranulesStarch GranulesUniversity of Illinois at Urbana-ChampaignGranules Begin toBreak, polymer continue of solubilize(drop in viscosity)Solubilized polymers beginTo reassociate (rise inViscosity)

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionProteinsStructure of Protein Proteins are built from a repertoire of 20 amino acidsAmino AcidsAmino GroupNH2HCAcid GroupCOOHRGeneral Structure of Amino Acid.The R group is the side chain. Amino Acidsare commonly grouped by their type of RgroupsUniversity of Illinois at Urbana-ChampaignAlanineArginineAsparagine AsnAspartic AcidAsparagine orAspartic AcidCysteineGlutamine GlnGlutamic acidGlutamine orGlutamic rosineValineThree LysMetPheProSerThrTrpTyrVal

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStructure of Protein A protein is a polypeptide with a specific sequence of amino acids and tridimensional structure The acid and amino group of each amino acid are involved in the peptidebonds and form the backbone of proteinStructure of Protein Primary Structure– Sequence of amino acids SecondarySd SStructure– R goup on amino acid can react with other R groups (one of thefactors)– Hydrogen bondsSulfhydrylGroupUniversity of Illinois at Urbana-ChampaignDisulfideBond

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionStructure of Protein Tertiary Structure QQuaternaryy structureStructure of Protein Three dimensional structure of protein determines its properties– e.g.g whether proteinpis soluble in water or not Heat or alteration of pH can denature proteinsUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionClassification of Protein Generally classified into four types according to their solubility (work by T. B.Osborne)– Albumins: soluble in water e.g. egg white– Globulins: soluble in dilute salt solutions– Prolamins: soluble in 70% alcohol– Glutelins: soluble in dilute acid or base This classification is widely used but the fractions obtained are not clear cut– e.g. prolamins have limited solubility in water at low ionic strength– better classification can be done by several analytical techniques such aselectrophoresis, isoelectric focussing, gel filtration etc.Albumins & Globulins Most of the physiologically active proteins (enzymes) are presentin albumins and globulins These proteins in cereal grains are mainly in aleurone layer, bran& germ fractions– Very low in endosperm Good amino acid balance High in Lysine, Tryptophan and MethionineUniversity of Illinois at Urbana-Champaign

Ist US-Brazil Fulbright Course on Biofuels, SaoPaulo, BrazilSingh – Corn Structure and CompositionProlamins & Glutelins These are storage proteins In cereal grains mainly founds in endosperm Low in nutritionally important amino acids– Lysine, Tryptophan and MethionineGrrams of ProteinVariation in Protein ContentGlutelinsProlaminsAlbumins and GlobulinsProtein ContentUniversity of Illinois at Urbana-Champaign