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CornStarchCorn
Starch
1
Corn Refiners Association1701 Pennsylvania Avenue, N.W.
Washington, D.C. 20006-5805202-331-1634 Fax: 202-331-2054
www.corn.org
CONTENTS
CONTENTS
11th EditionCopyright 2006
Member Companies ............................................................. 2Foreword ............................................................................. 3Introduction ......................................................................... 4Starch and the Starch Granule .............................................. 5The Corn Wet Milling Process ............................................ 7Physicochemical Properties of Starch ................................. 10Commercial Corn Starches ................................................. 13
Unmodified, regular or common corn starch .................... 13Genetic variations of corn starch ....................................... 13Modified starch ................................................................... 15
Acid-modified corn starch ........................................... 15Oxidized corn starch ................................................... 16Dextrins ...................................................................... 17
Cyclodextrins ..................................................................... 19Starch derivatives ............................................................... 20Pregelatinized starches ....................................................... 23Bleached starches ................................................................. 23
Status of Starches Under Federal Regulations ..................... 24Shipping and Handling Dry Starches ................................... 25Cooking Procedures for Starches ........................................ 26Handling Cooked Starches .................................................. 29Enzyme Conversion of Starch ............................................. 31Analytical Examination of Starch ........................................ 33Glossary .............................................................................. 37
FIGURES1. Layers of starch formed around the hilum ........................ 52. Shape of six common starch granules ................................ 63. Corn starch photographed under polarized light .............. 64. A kernel of corn ................................................................ 75. The corn wet milling process ........................................... 86. Amylose and amylopectin molecules .............................. 117. Micelle formation in amylose molecules ......................... 128. Effect of temperature on gelatinization ............................ 269. Effect of agitation on gelatinization ................................. 2710. Effect of pH on gelatinization ........................................ 28
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Archer Daniels Midland CompanyP.O. Box 1470Decatur, Illinois 62525
Cargill, IncorporatedP.O. Box 5662/MS62Minneapolis, Minnesota 55440-5662
Corn Products International, Inc.5 Westbrook Corporate CenterWestchester, Illinois 60154
National Starch and Chemical Company10 Finderne AvenueBridgewater, New Jersey 08807-0500
Penford Products Co.(A company of Penford Corporation)P.O. Box 428Cedar Rapids, Iowa 52406-0428
Roquette America, Inc.1417 Exchange StreetKeokuk, Iowa 52632-6647
Tate & Lyle Ingredients Americas, Inc.(A subsidiary of Tate & Lyle, PLC )P.O. Box 151Decatur, Illinois 62521
MEMBER COMPANIES
Plants:Cedar Rapids, Iowa 52404Clinton, Iowa 52732Columbus, Nebraska 68601Decatur, Illinois 62525Marshall, Minnesota 56258-2744
Plants:Blair, Nebraska 68008-2649Cedar Rapids, Iowa 52406-2638Dayton, Ohio 45413-8001Decatur, Alabama 35601Eddyville, Iowa 52553-5000Hammond, Indiana 46320-1094Memphis, Tennessee 38113-0368Wahpeton, North Dakota 58075
Plants:Bedford Park, Illinois 60501-1933Stockton, California 95206-0129Winton-Salem, North Carolina 27107
Plants:Indianapolis, Indiana 46221North Kansas City, Missouri 64116
Plant:Cedar Rapids, Iowa 52404-2175
Plant:Keokuk, Iowa 52632-6647
Plants:Decatur, Illinois 62521Lafayette, Indiana 47902Lafayette, Indiana 47905Loudon, Tennessee 37774
PLANT LOCATIONS
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Each day of the year, in some manner or another, everyAmerican's life is touched by one of our most abundant re-newable resources, corn starch. From the clothing we wearto the food on our table, corn starch is a component of tensof thousands of manufactured products that define our mod-ern lifestyle.
The use of starch is chronicled in records of the early Egyp-tians, who manufactured papyrus using a starch coating.Roman records indicate that those early innovators founduses for starch in foods, medicine, cosmetics and fabrics. Itwas not until the middle of the nineteenth century, however,that the process for large-scale efficient extraction of starchfrom corn was developed. The development and continualimprovement of this process has enabled the corn refiningindustry to offer American consumers abundant supplies ofstarch tailored to meet the most exacting needs of individualcustomers.
Our tenth edition of Corn Starch reviews the chemistry of thestarch granule, describes how corn refiners extract starchfrom the corn kernel, how it is treated to produce specialproducts and reviews handling and analytical procedures forstarches. We hope that you will find this guide useful andwill not hesitate to contact the Corn Refiners Association, ifwe can provide you with further information on starch andits products.
Audrae EricksonPresidentCorn Refiners Association
Readers are advised that the information and suggestions containedherein are general in nature and that specific technical questionsshould be referred to the Association or member companies. Ques-tions as to the price and/or availability of the products describedshould be directed to individual Association members.
FOREWORD
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INTRODUCTION
The corn plant (Zea mays) isa high-capacity, factory forefficiently converting largeamounts of radiant energyfrom the sun into stablechemical energy. This en-ergy is stored as cellulose,oil and starch in the cornplant and in the corn kernel.
The corn plant is also one ofnature's greatest multipliers.Approximately four monthsafter planting, a single kernelof corn weighing about oneone-hundredth of an ouncewill yield 800 kernels weigh-ing eight ounces. In compari-son to this 800-fold seed mul-tiplication in corn, wheatwill produce a 50-fold yieldper seed planted.
By careful genetic control,corn has been developedwhich can grow in the tem-perate and semi-tropicalareas throughout the world.With annual production ofcorn topping 10 billion bush-els, the United States ranksas the world's largest growerof corn. Since the corn grainaverages about 70-72% starch(dry basis) this enormousquantity of corn provides analmost unlimited raw mate-
rial supply from whichstarch may be produced.
In 1844, Colgate & Co. builtsmall corn starch factories atJersey City, New Jersey, andColumbus, Ohio. In 1848,the much larger KingsfordCornstarch Plant was builtin Oswego, New York. Sincethat time, starch technologyhas steadily improved andproduction has increasedmany-fold. Today, cornstarch dominates the world'sindustrial and food starchmarkets.
This booklet presents abrief, simplified descriptionof the manufacture of starchby the corn refining (wetmilling) process, a summaryof the physicochemical prop-erties of starch that make itof such great value to man-kind and general informa-tion about how starch isused in food and industrialapplications. We hope youfind this information useful.If you wish further informa-tion on starch, corn or cornrefining, please contact theCorn Refiners Associationor its member companies.
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STARCH AND THESTARCH GRANULE
Starch exists as a major car-bohydrate storage product inall plants containing chloro-phyll. In the process knownas photosynthesis, greenplants extract energy fromsunlight to form glucosefrom carbon dioxide andwater. Glucose fuels plantgrowth processes and is theprimary building materialfor plant support structuressuch as cellulose and hemi-cellulose. When the plantreaches maturity, the repro-duction cycle begins, culmi-nating in pollination andformation of the starch- andoil-rich seed embryo. Starchand oil exist in the corn ker-nel to supply energy to thegerminating seed. Starch is acarbohydrate polymer madeby the linking of glucoseunits end-to-end into verylong chains, similar tothe stringing together ofpearls in the making of apearl necklace.
Newly-synthesized starch islayered around a hilumnucleus within the plant cell,in structures called granules(Figure 1). Starch granulesvary in size and shape, char-acteristic of specific plantsources. Figure 2 shows thecomparative sizes andshapes of granules from sixcommon starches. Starchmolecules are orientedwithin granules in specificcrystalline patterns. This is
illustrated in Figure 3,showing the Maltese crosspattern characteristic ofthese crystal structures,viewed in aqueous suspen-sion under polarized light.
The highly structured natureof the starch granule is dem-onstrated by its greatstrength. After all the pulver-izing, pumping, centrifugalcirculation and physicalattrition in the wet phases ofthe corn wet milling opera-tion, followed by drying,grinding and mechanical orair transportation of the drystarch, practically all of thegranules remain intact.Granule integrity also per-sists in both modified andderivatized starches.
Isolated starch is typically adry, soft, white powder. It isinsoluble in cold water, alco-hol, ether and most organicsolvents. Starch, if kept dry,is stable in storage for indefi-nite periods. Though starchgranules are physically du-rable, they can be disruptedquite easily. If granules inwater suspension are gradu-ally heated, they begin toabsorb water. The granuleshydrate, increase in size andfinally lose their structuralintegrity. This results in lossof characteristic birefrin-gence and opacity, an in-crease in viscosity, and theeventual formation of a paste
Figure 1Layers of starch formedaround the hilum
á -d-glucopyranose unit
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or gel. This process is re-ferred to as starch pasting orgelatinization. The tempera-ture at the which gelatiniza-tion of a starch occurs — thegelatinization temperature — is dependent upon suchfactors as starch concentra-tion, pH of the suspension,rate of heating, the presenceof certain salts, and the spe-cific procedure being fol-lowed. Under well-definedconditions, starches can beclassified using gelatiniza-tion temperature as a meansfor differentiation.
The properties of the starchgranule are dependent uponthe arrangement of thebonds which link glucoseunits to one-another withinthe starch molecule itself.The starch molecule is ahomopolymer of repeating
anhydroglucose units joinedby an alpha-glucosidic link-age, the aldehyde group ofone unit being chemicallybound to a hydroxyl groupon the next unit throughhemiacetal linkages. In moststarches the alpha-1,4-linkagepredominates, with onlyoccasional 1,6-linkages. The1,4-linkages yield straightchain starch moleculescalled amylose, while the1,6-linkages serve as thebranching point in branched-chain starch moleculescalled amylopectin (Figure6). The proportions ofthese two types of starchmolecules are establishedgenetically and are relativelyconstant for each species ofstarch. For example, cornstarch contains 27% of thelinear amylose polymer,potato starch 20%, and tapi-
Figure 2Shape of six commonstarch granules
Figure 3Corn starch photographedunder polarized light. Notetypical “Maltese cross”pattern
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oca starch 17%.
Plant geneticists havelearned to manipulate ge-netic controls in corn andhave developed commercialvarieties of corn that containall branched-chain starchamylopectin molecules arecalled waxy maize. At theother extreme, a variety con-taining as high as 70%straight chain amylose mol-ecules is grown commer-cially, and is called high amy-lose corn. 82% and higheramylose hybrids have re-cently been announced. Thegranules of waxy maize gela-tinize much like normalcorn starch. High amylosecorn, on the other hand, willnot gelatinize even in boilingwater, but must be pressurecooked or hydrated by treat-ment with dilute sodiumhydroxide. More detaileddiscussion of the effect ofthese variations in molecularstructure is presented later.
The inherent properties ofthe starch granule can bealtered by mild chemicaltreatment and/orderivatization. Oxidationwith sodium hypochlorite,for example, decreases thegelatinization point in di-rect proportion to the quan-tity of chemical used. Simi-lar effects are observedwhen starch is derivatizedwith ethylene oxide or
THE CORN WETMILLING PROCESS
other reagents. In contrast,starch derivatives can bemade in which the granulewill not gelatinize at allwhen exposed to the severeconditions of moist heatand pressure.
The granular structure ofstarch, one of nature's fasci-nating architectural forms, isa vital element in the flex-ibility of commercialstarches to fill specific prod-uct needs.
Endo
sper
m
Germ
Starchand
Gluten
Hull andFiber
Starch
Corn kernels have threemain parts: the seed coat orpericarp, the starchy en-dosperm, and the embryo,commonly called the germ(Figure 4). The pericarp isthe outer skin or hull of thekernel which serves to pro-tect the seed. The en-dosperm, the main energyreserve, makes up about 80%of the total weight of thekernel. It is about 90% starchand 7% gluten protein, withthe remainder consisting ofsmall amounts of oil, miner-als and trace constituents.The embryonic germ con-tains a miniature plant madeup of a root-like portion andfive or six embryonic leaves.In addition, large quantitiesof high energy oil arepresent to feed the tiny plantwhen it starts to grow, as
Figure 4A kernel of corn
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along with many substancesrequired during germinationand early development.
The corn wet milling pro-cess is illustrated in Figure 5,in which the kernel is sepa-rated into its componentparts, and those parts arethen further subdivided andrefined.
Corn wet millers buyshelled corn that is deliveredto the plant by truck, bargeor rail car. Normally #2grade corn is purchased,based on USDA standards.
Incoming corn is cleaned toremove extraneous materialsuch as pieces of cob, foreignseeds, stray metal, and finegrit. It then is conveyed tostorage silos, holding up to350,000 bushels, until readyto go to the refinery.
Cleaned corn is transportedto large tanks called steeps.Warm water (125o-130oF)containing small quantitiesof dissolved sulfur dioxide iscirculated through the steepsfor approximately 24-48hours to soften the kernel.Sulfur dioxide and water
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Shelled Corn
CornOil
NutritiveSweeteners
StarchProducts
FeedProducts
Corn Cleaners
Steep Tanks
Steepwater
GermSeparators
Germ
Grinding Mills Screens CentrifugalSeparators
Fiber Gluten Starch Slurry
Starch Driers
DextrinRoasters
UNMODIFIEDSTARCH
MODIFIEDSTARCHDEXTRINS
HydrocloneStarch Washing
Refinery
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Fermentationand Other Chemicals
SteepwaterEvaporators
Starch Driers
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ModificationTanks
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Figure 5The corn wet millingprocess
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react during steeping to formsulfurous acid, which con-trols undesirable fermenta-tion and assists in separationof starch and protein. Duringsteeping, the soluble compo-nents are extracted from theintact kernel. At the conclu-sion of steeping, water isdrained from the kernels andconcentrated in multipleeffect evaporators to yieldconcentrated steepwater.This protein-rich extractmay be used as a nutrient formicroorganisms in the pro-duction of enzymes, antibi-otics and other fermentationproducts. Most steepwater,however, is combined withfiber and gluten in the pro-duction of animal feed ingre-dients. Further informationon feed products producedby corn wet millers may befound in the booklet CornWet Milled Feed Products,available on the Corn Refin-ers Association website,www.corn.org.
Softened corn kernels nextpass through mild attritionmills to loosen the hull andfree the germ from thestarch-rich endosperm. Wa-ter is added to the attritionmills and a thick slurry ofmacerated kernels andwhole germ results. Becausethe germ at this stage con-tains 40-50% oil, it is lighterthan the endosperm andhull. Centrifugal force is
used to isolate the germ.
Clean, separated germ isdried and the crude oil isremoved by mechanicalpresses and/or solvent ex-traction. The crude oil maybe refined to yield a finequality salad and cooking oilor a raw material for thepreparation of corn oil mar-garines. Extracted germ mealis used in animal feed. Fur-ther information on produc-tion and use of corn oil maybe found in the booklet CornOil, available on the CornRefiners Associationwebsite, www.corn.org.
The remaining mixture ofhull and endosperm thenpasses through a series ofgrinding and screening op-erations. Large hull particlesare retained on screens andremoved, while finer proteinand starch particles passthrough. The hull is added toanimal feed or washed andmilled in the production ofrefined corn fiber (bran).
The water slurry of starchand gluten protein is nextseparated by centrifugation.Because starch and glutendiffer widely in buoyantdensity, nearly completeseparation is obtained. Typi-cal operations yield a glutenstream containing over 60%protein, while the starchstream is over 99% starch.
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The gluten is dried and soldas gluten meal (60% protein).
The white, nearly-purestarch slurry is furtherwashed to remove smallquantities of solubles. Atthis stage the starch slurrymay be further processed tomake any common (unmodi-fied) corn starch or con-verted to make sweetenersor fermentation products.Various modified orderivatized starches may beproduced by treating theslurry of washed starch withchemicals or enzymes. Aftertreatment, the products arerecovered by filtration orcentrifugation and the starchis dried.
PHYSICOCHEMICALPROPERTIES OF
STARCHWhat is starch? Starch is ahighly functional carbohy-drate in its unmodified state.It is also a highly reactivecarbohydrate, which may bemodified physically, chemi-cally or enzymatically tomeet specific needs.
Starches have four majorphysicochemical propertiesthat make them useful infood and industrial applica-tions. Both types of starchmolecules—amylose andamylopectin (Figure 6)—arepolyhydroxy compoundsand hydrate when heated inwater, combining with indi-
vidual water molecules.As the molecules hydrate,they increase in size, immo-bilize much of the waterpresent, thicken the aqueoussystem and form a paste.The first useful physico-chemical property, thicken-ing, gives many food prod-ucts such as puddings,gravies, sauces and pie fill-ings their desired physicalcharacteristics. This prop-erty is also useful in manyindustrial starch applica-tions.
The second useful physico-chemical property is theability of the starch paste todisperse and suspend otheringredients or particulatematter. In many foods, fatsand proteins are suspendedand/or emulsified in starchpastes. In coatings for paperand in some adhesives, clayparticles are suspended inthick starch pastes.
When starch pastes are al-lowed to cool, they thickenand can congeal into a semi-solid gel. The third usefulphysicochemical property,gel formation, provides thebody typical of starch-basedpuddings, salad dressingsand some types of adhesives.
The fourth useful physico-chemical property of starchpaste is its ability to producestrong adhesive films when
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spread on smooth surfaces anddried. The major industrialuses of starch, such as papercoating and sizing, textile siz-ing, corrugated board manu-facture and all adhesive appli-cations utilize this property.
These four important proper-ties vary in degree from onestarch source to another.When the structures of linearand branched starches wereelucidated and methods were
Figure 6Amylose (top) andAmylopectin (bottom)molecules
developed for detectingand quantifying the twotypes of molecules, theirfunctional properties werefinally explained.
Straight chain amylosemolecules tend to line upparallel to each other insolution. As the solutioncools, there is less energyavailable to keep the mol-ecules apart. The hydroxylgroups on parallel amylose
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molecules exert attractiveforces and the molecules arepulled together. This phe-nomenon, illustrated in Fig-ure 7, is often referred to asretrogradation. The overallresult is a gelled paste. Theoriented areas are calledmicelles. Starches with ahigh percentage of amyloseare difficult to gelatinizebecause of the extra energyneeded to hydrate and disin-tegrate the firmly- bonded,crystalline aggregates ofamylose. After gelatiniza-tion such starches form firmgels and when properly pre-pared, yield strong, toughfilms.
A t the opposite end of thefunctional spectrum are the
waxy starches, which arenearly 100% amylopectin.They gelatinize easily andyield nearly-transparent,viscous pastes that retro-grade slowly to weak gels.Between these extremes isfound a wide range of natu-ral starches as well as manystarch modifications andderivatives. Based on thebehavioral diversities ofnative starches, the starchchemist, by selection of theproper raw material, fol-lowed by application of se-lected modification orderivatization techniques,can devise products with abroad range of functionalcharacteristics.
Figure 7Micelle formation inamylose molecules
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UNMODIFIED, REGULAR,NATIVE OR COMMON
CORN STARCHIf the starch produced by thecorn wet milling process issimply dried, it is called acommon, regular or unmodi-fied corn starch. It is avail-able in various physicalforms: corn starches may besold as fine or coarse pow-ders, as flakes, as pearls orbe agglomerated to largerparticles.
Slight variations can be in-troduced into unmodifiedstarch by adjusting pH, bymild heat treatment, or byadding small quantities ofchemicals or adjuvants be-fore or after drying. Suchstarches will then performmore effectively in specificapplications. For example,common starch intended forenzyme conversion may beadjusted to a specific pH andsmall amounts of inorganicsalts that facilitate enzymeaction may be added.Starches for food use are alsooften pH adjusted.
More unmodified cornstarch is sold than any othertype. It is used in the manu-facture of corrugated board,coated and sized paper, pa-perboard, adhesives, saladdressings, beer, cannedfoods, dry food mixes (suchas puddings, cakes, baking
COMMERCIALCORN
STARCHES
powder, etc.), moldingstarch, laundry starch, etc.
Unmodified corn starch,when cooked, has such greatthickening power that pastescontaining more than 4-5%solids are too thick tohandle. Further, such pastesgel very rapidly whencooled. For many useshigher solids-containingpastes with reduced ten-dency to thicken or with theability to form softer gels arerequired.
The chemical compositionof starch — highly oxygen-ated carbon compounds —make starch an excellentproduct for use as a chemicalfeedstock. Many industrialproducts, which today arederived from petrochemicalfeedstocks, are increasinglybeing synthesized fromstarch or cellulosic feed-stocks. Examples of currentcommercial products of thistype include the use of cornstarch in the productionof biodegradable plastics.
GENETIC VARIATIONS OF
CORN STARCHMany applications requirestarches in which propertiesother than viscosity havebeen modified. For manyyears, tapioca starch was thechoice for puddings, fruitfillings and certain types of
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hard biscuits. When the sup-ply of tapioca became shortduring the late 1930's, andlater became unavailable,intensive research was be-gun to develop a geneticvariety of corn that con-tained starch with proper-ties similar to tapiocastarch. A type of corn firstfound in China in 1908 andmaintained as a genetic curi-osity was called waxy cornbecause of its waxy appear-ance. The starch in this cornhad properties similar tostarch from tapioca.
An active breeding programwas begun in 1956-57 to de-velop a commercial varietyof corn that retained thewaxy maize characteristics.By 1944, sufficient waxymaize was grown to demon-strate that it could be pro-cessed by the wet millingmethod to yield a starch thatwas a satisfactory replace-ment for tapioca.
Waxy maize starch, which isessentially 100% amylopec-tin, yields pastes that arealmost clear when cool, non-congealing, and when driedin thin films, yields a trans-lucent, water-soluble coat-ing. Waxy starches are usedfor thickening a wide varietyof prepared foods. Mostcommercial waxy starchesare modified by crosslinkingand/or derivatization to
further enhance their advan-tageous properties.
The development of waxymaize encouraged geneti-cists to look for a mutantthat might yield a starchwith a much higher amylosecontent than regular corn.Such a starch, it was postu-lated, should be an excellentfilm former and might bespinnable into a fiber. Ge-netic research ultimatelyresulted in the commercialdevelopment of two cornhybrids, one containingabout 55%, the other about70% amylose. Recent re-search has resulted in devel-oping starches with greaterthan 80% amylose. The ulti-mate goal is to have nativehybrid corn starch with100% amylose.
High-amylose granules aresmaller than those fromregular or waxy maize cornand they often have unusualshapes. Some granules donot gelatinize or lose theirbirefringence even whenboiled for a long time. How-ever, they will gelatinize indilute alkali or alkalinesalts, or when heated inwater under pressure atelevated temperatures. Thesolutions must be kept hotor the amylose quickly gelsand retrogrades. High amy-lose starches are used toproduce sizes for textiles
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and to produce quick-settingconfectionery gums. Highamylose starches appear tobe resistant to human diges-tion (hence, "resistantstarches") and may findapplication in reduced-calo-rie food products.
Active research programsare now being conductedinto new methods to alterthe genetic makeup of cornto produce starches whichhave the characteristics andfunctionality of the starchderivatives discussed below.Several are now commer-cially available. The geneti-cally engineered starchesallow processors to usefewer chemicals in theirproduction, and to claim"native" labeling in additionto their unique functionalityand their contribution to thedevelopment of new foods.
MODIFIED STARCHNative starches have certaininherent features for use inthe development of foods,pharmaceuticals and indus-trial products. Among otheradvantages, they are readilyavailable, generally low inprice, and yield a simple,consumer-friendly labelwhen listed in an ingredientpanel.
However, the advent ofmore sophisticated process-
ing systems made it apparentthat the natural properties ofraw starches could not meetthe demanding processingrequirements of increasinglysophisticated product formu-lations.
In order to meet such manu-facturing requirements,starch chemists developedmodified starches. The tech-niques and chemicals usedto manufacture food andindustrial modified starcheshave been thoroughly re-searched and tested to ensuresafety and functionality.Modified food starches arestrictly defined and regu-lated by the United StatesFood and Drug Administra-tion (FDA) in 21 CFR Chap-ter 1, paragraph 172.892, andindustrial modified starchesare covered by 21 CFRChapter 1, paragraph178.3520.
Acid-modified corn starchThe first method used com-mercially to reduce the vis-cosity of starch pastes wasthe acid-modification pro-cess patented by Duryea in1899. In this method, astarch-watersuspension isagitated while being sub-jected to mild treatmentwith dilute mineral acid attemperatures elevated butbelow the starch gelatiniza-tion temperature, for varying
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periods of time. When testsshow the desired viscosityhas been reached, the acid isneutralized with sodiumcarbonate and the starch isfiltered, washed and dried.In this manner a series ofstarches yielding pastes ofdecreasing viscosity areproduced.
The primary reaction takingplace during acid-modifica-tion is hydrolysis of gluco-sidic bonds in starch mol-ecules. This limited andcontrolled hydrolysis pro-duces two important conse-quences. First, since thestarch molecule is so large,only a small amount ofcleavage is needed to mark-edly reduce viscosity. Sec-ond, disruption of bondswithin the granule weakensthe granule structure. Likethe parent starch, all acid-modified starch pastes havereduced viscosities whenwarm, yet have a strong ten-dency to gel when cooled.This suggests that acid-modi-fication reduces chain lengthbut does not substantiallychange the molecular con-figuration. When starch frag-ments reorient, the cooledpastes can and will set tofirm gels. These so-calledacid-modified or thin boilingstarches are used in largequantities in textile warpsizes, especially for cottonsand cotton polyester blends.
The starch pastes, applied towarp yarns and dried, serveas an adhesive to bind thefibers in the warp givingincreased strength and resis-tance to abrasion needed inthe loom during weaving.The lower viscosity acid-modified starches are alsoused in calendar and sizepress applications in thepaper industry to enhanceprintability and abrasionresistance of the paper sur-face. This ability to formfirm gels is utilized by theconfectioner in the manufac-ture of starch-based gumcandies.
Oxidized corn starchA second method for reduc-ing the viscosity and alteringthe properties of starch isoxidation. Although oxidiz-ing agents such as chlorine,hydrogen peroxide and po-tassium permanganate canbe used, oxidized starchesproduced by the corn wetmilling industry are almostexclusively made using so-dium hypochlorite as theoxidizing agent.
As in the case of acid-modifi-cation, aqueous starch sus-pensions under continuousagitation are treated withdilute sodium hypochloritecontaining a small excess ofcaustic soda (NaOH). Thereagent solution is addedslowly to the starch suspen-
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sion in a reactor which ismaintained at about 120oF.Cooling water in the reactorjacket or external heat ex-changers remove heat gener-ated during the oxidation reac-tion. When the correct amountof reagent has been added andsufficient time for reaction haselapsed, the viscosity of thestarch is determined. Whenthe desired degree of oxidationis reached, the starch slurry istreated with a reducing agentsuch as sodium bisulfite toremove excess hypochlorite,adjusted to the desired pH,filtered, washed and dried.Products with a wide range ofmodification can be produced.
Oxidized starch retains itsoriginal granule structure andis still insoluble in cold water.It is extremely white due to thebleaching action of the sodiumhypochlorite. In addition tohaving decreased viscosity,oxidized starch pastes are rela-tively clear and show a re-duced tendency to thicken orset back when cooled. Whendried, oxidized starch films areclear and tough. Because thehighly oxidized starches giverelatively clear pastes at highsolids, they are sometimesreferred to as gums.
Treatment of starch with so-dium hypochlorite bringsabout a random oxidation of alimited number of hydroxylgroups to carboxyl or carbonyl
groups, with the resultingrupture of the adjacentglucosidic bond. Since theoxidation occurs in thepresence of excess sodiumhydroxide, the carboxylgroups are neutralized,resulting in a sodium salt.Since the sodium salt ofthe carboxyl group isbulkier than the parenthydroxyl group, it is postu-lated that the tendency ofthe amylose molecules toassociate and retrogradeinto gels is reduced. Themajor uses for oxidizedstarches are in the paperindustry as tub, size pressand calendar sizes; in thetextile industry as warpsizes and as componentsin adhesives. They areused in food applicationswhere high solids, lowviscosity and a creamybody are desired, suchas in bakery fillings. Oxi-dized starches performwell in batters and bread-ing due to good adhesionto meat products.
DextrinsDextrins are producedfrom starch by dry heatingor roasting unmodifiedstarch with or without anacid or alkaline catalyst.In this process, unmodi-fied starch, dried to about5-7% moisture, is usuallyacidified with very smallamounts of mineral acid
18
and placed in heated, agi-tated vessels called reactorsor roasters. The temperatureis increased at a controlledrate and then maintained at amaximum temperature forvarying lengths of time. Theresulting product is cooled,blended and sometimesaged. Another dextrinizationmethod utilizes a fluid bed,in which unmodified starchis placed in a reactor andsuspended or "fluidized" ina stream of heated air. Thestarch is then acidified and,as in the conventional or"roaster" process, heatedunder controlled conditionsof time and temperatureuntil the desired end productis attained. With severaldegrees of freedom possiblein such processes, a range ofdextrins with widely varyingproperties is produced.
During dextrinization, thegranule is not destroyed butgranule integrity is dis-rupted. When dextrins aresuspended in water andheated, the granules swelland then undergo a "peel-ing" action, separating intolayers that eventually breakfree and disperse. The extentof occurrence of this behav-ior varies with the degree ofconversion of the dextrin.
Dextrins differ from othermodified starches in that,
not only are they reduced inviscosity, but they also haveappreciable cold water solu-bility, reduced tendency togel and increased reducingpower. High solids solutionsof some of the more highlyconverted dextrins producetacky, quick-setting adhe-sives used in making alltypes of paper products(bags, laminates, paperboxes, paper tubes andenvelopes).
There are several theoriesregarding what takes placeduring the dextrinizationprocess. The process reducesthe strength of the chemicalbonds, which give the starchgranule its integrity andbrings about generalizedmolecular scissions thatboth reduce molecular sizeand alter molecular arrange-ment. In those cases whereacids are present, simplehydrolytic cleavage is be-lieved to occur. A combina-tion of hydrolysis, recombi-nation and formation of newglucosidic linkages likelyaccounts for altered pasteviscosities and congealingcharacteristics.
There are three major typesof dextrins: white, yellowand British gums. Dependingon the processing conditionsinvolved, there may be manysubtypes.
19
White DextrinsThe first type, white dex-trins, have a white colorsimilar to original cornstarch, but have reducedviscosities, and cold watersolubilities ranging from 5 toover 90%. White dextrinsproduce light colored pastesthat set to soft but definitegels. The lower solubilityproducts yield pastes similarto the most highly acid-modified thin-boilingstarches. The higher solubil-ity white dextrins (40-90%)can be used at much higherconcentrations to yield verysoft gels.
Yellow DextrinsYellow or canary dextrins arethe second type. By using lessacid, higher temperatures andmore time, dextrins with highwater solubility and a dis-tinct yellow color can beproduced. The yellow dex-trins are used to produce highsolids pastes (40-60%) that arevery tacky and, when appliedin thin films, dry rapidly.They make excellent adhe-sives, especially for paperproducts.
British GumsBritish gums, the third type,are produced by adding littleor no acid to very dry starchand then roasting a long timewith slowly increasing tem-perature. They are tan to
light brown in color andhave a distinct caramelizedodor. A range of productsresults, varying from low tohigh solubility. The pastesprepared from these dextrinsvary from nearly solid gelsthrough very soft gels toviscous liquids.
CyclodextrinsAlthough similar in name todextrins, cyclodextrins areproduced through quite dif-ferent processes and havedifferent uses. Cyclodextrinsare produced through treat-ment of starch with aglucosyltransferase enzyme.The resulting water-solubleproduct takes the physicalshape of a hollow cone, withan interior cavity of differentsizes depending on the pro-duction method. A uniqueproperty of the interior ofthe cone is its hydrophobicnature, enablingcyclodextrins to be used toencapsulate a wide variety ofcompounds.
Uses for cyclodextrins in-clude encapsulation for con-trolled flavor release, mask-ing odors and tastes,stabilizing emulsions, in-creasing foaming power, andcontrolling or maskingcolor. These properties arefinding increasing applica-tions in chemical, pharma-ceutical and food markets.
20
Starch derivativesSince the starch moleculecontains many primary andsecondary hydroxyl groups,it can be modified by chemi-cal derivatization.
Unlike the modificationsthus far discussed,derivatization may or maynot reduce the viscosityof the parent starch.Derivatization is used toimpart different propertiesto the derivative than thoseof the parent starch. Thisallows the derivative to meetmore effectively the require-ments of specific end uses.Countless starch derivativeshave been described in tech-nical literature and in pat-ents, but only a limited num-ber are manufactured andused commercially.
The derivatization of starchdiffers from most chemicalmodifications of polymersin that the changes in proper-ties are attained with veryslight changes in the mol-ecule itself. In fact, all com-mercial derivatives are pre-pared under such mildconditions (usually in aque-ous suspensions) that thestarch granules retain theirintegrity. This allows theproducts to be handled inprocessing and applicationin much the same manner asthe common starches previ-ously discussed.
Starch derivatives are usu-ally prepared by adding thedesired reagent to an agi-tated suspension of cornstarch in water. By adjustingthe pH of the slurry with analkali, and sometimes with acatalyst, the mild reactionsproceed on the ungelatinizedstarch at only slightly el-evated temperatures. Aftersufficient reaction time, thederivatives are recovered byfiltration or centrifugation,washed with water, driedand packaged.
Two basic types of deriva-tives are prepared commer-cially:
Crosslinked/inhibitedCrosslinked starches, some-times referred to as inhibitedstarches, are made to over-come the sensitivity ofstarch sols to shear and pro-cessing conditions. This isaccomplished by treatingstarch in the granule statewith trace amounts of bi-functional agents capable ofreacting with hydroxylgroups on two different mol-ecules within the granule.
Reagents such as phosphorusoxychloride or sodiumtrimetaphosphate may beused as crosslinking agents.Very small amounts of theseagents can exert a markedeffect on the behavior ofthe cooked starch. The de-
21
gree of crosslinking controlsthe rate and extent to whichstarch swells on cooking.Crosslinking decreases thesensitivity of starch sols totemperature, agitation andacids, improving resistanceto loss in viscosity.
StabilizationStarch is stabilized againstgelling by using monofunc-tional reagents. These re-agents react with hydroxylgroups on the starch to in-troduce substituent groupsthat interfere with intermo-lecular association betweenstarch molecules. Certainreagents may also introducespecific functionality intostarches, e.g., increasingtheir water combining capac-ity or viscosity, or impartinga positive charge to thestarch molecule.
Hydroxyethyl starches—Toproduce hydroxyethylstarch, a starch slurry is ad-justed to an alkaline pH anda salt is added to suppressthe tendency of the starch togelatinize. Ethylene oxide invarying quantities is addedslowly to the agitated slurryand allowed to react for theproper time. Mosthydroxyethyl starchesare also acid-modified toreduce their viscosity. Thehydroxyethylated starch isrecovered by filtration,washed and dried. The intro-
duction of the hydroxyethylgroup reduces the gelatiniza-tion temperature of thestarch and results in clear,stable pastes. Hydroxyethylstarches are widely used insurface sizing and coatingpaper.
Cationic starches—Reactionof corn starch with tertiaryor quaternary amines yieldsquaternary ammonium oramino alkyl starches. Whendispersed, these starchesexhibit positively chargedparticles that are stronglyadsorbed by negativelycharged cellulose fibers inthe manufacture of paper.Less starch is used; but,more importantly, nearly allof the cationic starch in solu-tion is adsorbed by the pa-per, leaving very little in theeffluent going to the wastedisposal system. This greatlyreduces the biological oxy-gen demand (BOD) load. Inaddition, cationic starchpromotes the retention offilters and pigments in thesheet while reducing the lossof very fine paper fibers. Theadditional retained fiber andthe ability of the starch tobond the cellulose fiberstogether give greatly in-creased internal strengthto the sheet. This substantivecharacteristic of cationicstarches makes them usefulalso as surface sizes and asan adhesive in pigmented
22
coatings. With the growinguse of recycled paper stockin the manufacture of paper,more highly treated cationicstarches are necessary togive strength and fiber reten-tion properties. Computerprinter paper requires highercation treated starches toyield properties needed tofunction properly.
Starch acetates—Corn starchcan be acetylated with aceticanhydride or vinyl acetateunder carefully controlledconditions of pH, tempera-ture and time. After reac-tion, the starch is isolated byfiltration, washed and dried.Sufficient acetyl groups areintroduced to prevent retro-gradation of the starch paste.Acetylated starches are usedto size textile warps, yieldingtough, yet flexible yarns.The reduced tendency tocongeal makes starch ac-etates easy to pump and toapply at the slasher.
Starch acetates are also usedas food starches. For ex-ample, waxy maize starchcan be crosslinked withphosphorus oxychloride andthen acetylated with aceticanhydride or vinyl acetate toproduce an excellent thick-ener, texturizer or stabilizerused in preparing a widevariety of products.
Starch succinates—The use of
succinic anhydride insteadof acetic anhydride yieldsstarch succinates, which arealso used as thickeningagents for foods. The 1-octenyl succinic ester is alsoprepared and has affinity forfats and oils superior to thatof other derivatives. Thesestarches act as emulsifiers insuch products as salad dress-ing, flavors and beverages.
Starch phosphates—Starch canbe esterified with monoso-dium orthophosphate orsodium tripolyphosphate toyield starch phosphateswhich produce gels that aremore stable than those pro-duced from the parentstarch. The phosphatedstarches are used mainly inpreparing food products.
Hydroxypropyl starches—Propylene oxide added to analkaline starch suspensionreacts with the starch toyield hydroxypropyl deriva-tives. When made in accor-dance with 21 CFR 172.892,hydroxypropyl starches areused in food products wherelow temperature or frozenstability is needed.Hydroxyethyl starch canonly be used in food packag-ing and industrial applica-tions.
Other starch derivatives—Starch can be etherified bytreatment with acrolein.
23
Such ethers may then beesterified with either aceticor succinic anhydride.Starches are also esterifiedwith phosphorus oxychlo-ride and then etherified withpropylene oxide.
Pregelatinized starchesSuspensions of most starchesand starch derivatives can begelatinized and dried toyield a broad variety ofpregelatinized starches. Thisis normally done on a singledrum dryer with applicatorrolls. The starch slurry isheated to gelatinize it, in-stantaneously dried andground to desired granula-tion requirement. Theseproducts can be dispersed incold water with agitation toyield pastes comparable tothose obtained by cookingthe raw starch. Thepregelatinized starches makepossible the production ofmany unique food and in-dustrial products that do notrequire heat for preparation."Instant" adhesives and "In-stant" starch-based puddingsare examples of these typesof products. New types ofcold-water soluble (CWS)starches are made usingaqueous/alcohol reaction,which causes the granule toswell and retain its structurewithout being ruptured.Such starches yield easier touse, smoother bodied prod-ucts. Newer mechanical
processes being used arespray drying and extrusion.Often these procedures in-volve the application of sev-eral treatments.
Bleached starchesEven though starches arequite white, certain usesrequire starches that arestark white. Such productsare manufactured fromstarches by treating themwith small amounts of suchagents as hydrogen peroxide,peracetic acid, ammoniumpersulfate, potassium per-manganate, sodium chloriteor sodium hypochlorite. Theconditions of application aredesigned to whiten withoutproducing any detectablechemical change in thestarch. The bleached starchis recovered on continuousfilters or centrifuges, washedwith copious amounts ofwater to remove traces ofinorganic salts formed fromthe bleachingagent, dried andpackaged.Bleachedstarches performfunctionally inthe same man-ner as the parentstarch but arelower in micro-biological population due tothe bleaching agents used.They areused in the manufacture ofpills and body powders.
Corn starch photo-graphed at 3000x.
24
STATUS OFSTARCHES
UNDERFEDERAL
REGULATIONS
The Food and Drug Admin-istration has proposed toaffirm the "generally recog-nized as safe" (GRAS) statusof food grade unmodified orcommon starches as well aspregelatinized starches. Inaddition, the same regula-tions proposed affirming theGRAS status of unmodifiedstarches with differing amy-lose/amylopectin contents,such as high amylose andwaxy corn starches. Theseproposals are found in 50 FR12821-12825. Corn starcheshave been affirmed as GRASfor use in food contact sur-faces in 21 CFR 182.70 and182.90. Dextrins have alsobeen affirmed as GRAS bythe Food and Drug Adminis-tration. Regulations coveringdextrins may be found in 21CFR 184.1277.
Two specific regulationspromulgated by FDA coverthe bleached, the modifiedand the derivatized starchesapproved for use in foodsand in food packaging.These regulations specifythe treatment approved, setlimits for either the quantityof modifying agent used inpreparing the product and/or the amount introducedinto the starch. They alsospecify the names to be usedfor modified starch in ingre-dients lists. In the ingredi-
ents list on the label of afinished food, the name is,"food starch- modified." Thetwo regulations are: Foodstarch-modified — 21 CFR172.892; and Industrialstarch-modified — 21 CFR178.3520.
For food starch-modified,these regulations cover acid-modified, bleached, oxi-dized, esterified and etheri-fied starches, and starchestreated with various combi-nations of these treatments.
For industrial starch-modi-fied, the regulations coverstarches treated by similarmethods, as well as irradi-ated starches and starchestreated with specific surface-active agents. Industrialstarch-modified regulationsspecify the use of these prod-ucts as a component of ar-ticles for food packaging,processing and storage.
In addition to regulatoryactions by the Food andDrug Administration, vari-ous groups such as the FoodChemicals Codex, U.S. Phar-macopeia and the NationalFormulary have issued guide-lines and specifications forstarches, modified starchesand dextrins intended forspecific uses.
25
SHIPPING ANDHANDLING DRY
STARCHES
Dry starches are available inmultiwall paper bags and inrail car or bulk truck ship-ments. Other containerssuch as paper drums, metaland rubber containers ofvarious sizes, and corrugatedboxes can be used but re-quire special arrangementsbetween user and supplier.Bulk bags up to 2000 poundsmay be useful for industrialusers, while smaller bags (25and 50 lb.) are available forretail customers. Bulk instal-lations vary in size fromthose with capacity for a fewthousand pounds to thosewith capacity to handle sev-eral bulk rail hopper cars ofstarch at one time.
Because starch is a finelydivided organic material,handling conditions thatcreate dust may increase therisk of explosion. Explosionprevention measures includethe use of non-sparking met-als, explosion proof electri-cal motors and eliminatingsparks, flames and hot sur-faces in starch handling ar-eas. Compliance withOSHA, EPA and local safetyand health regulations isrequired.
Starch from a dry bulk han-dling station can be trans-ported to points of usethroughout a plant by prop-erly designed air, vacuumand mechanical systems.Dry starches can also beslurried in water andpumped to the point of use.Because starch settles rap-idly from water, continuousagitation or recirculation isnecessary to maintain a sus-pension. Proper design ofboth dry and wet starch han-dling systems is necessary.Starch manufacturers willsupply engineering assis-tance in designing such sys-tems.
Starch is very stable and canbe stored for long periods ifkept dry. Like many otherorganic materials, however,it will degrade and decom-pose if allowed to becomedamp. Because starches aresomewhat hygroscopic, theywill vary in moisture contentdepending upon the humid-ity of the atmosphere inwhich they have been stored.Storage should avoid areaswhere aromatic products arestored, as starches canreadily pick up flavors.
26
COOKINGPROCEDURES
FOR STARCHES
Most applications forstarches require that they besuspended in water and thenheated above the gelatiniza-tion temperature. The viscos-ity of the resulting paste isdependent on many vari-ables, such as starch type,solids concentration, pH,amount of agitation duringcooking, rate of heating,maximum temperaturereached, time held at thattemperature and the pres-ence of other ingredients inthe suspension.
As pointed out earlier, gela-tinization temperature willvary with the type of starchselected for use. Further, theobserved gelatinization tem-perature of a specific starchmay vary with the physicalconditions imposed uponthe system. As shown inFigure 8, if starch undercertain specific conditionsof concentration, pH andagitation is heated in a water
bath maintained at 90oC, theobserved gelatinization tem-perature and the resultingviscosities are not the sameas with the bath maintainedat 95oC. The 90oC cookreaches its maximum viscos-ity in about 18 minutes andthen remains relatively con-stant. The 95oC cook, on theother hand, reaches its maxi-mum in just over 9 minutes,but then gradually decreasesin viscosity. The granulessubjected to the more rapidtemperature rise reach theirmaximum expansion andthen begin to rupture with aresulting loss of viscosity.Adverse starch breakdowncan be reduced or preventedby using a low level ofcrosslinking.
The effect of agitation on thegelatinization and break-down of corn starch isshown in Figure 9. In thisexperiment a 5% starch sus-pension at room tempera-
Figure 8Effect of temperature ongelatinization
Cooked to 95oC
Cooked to 90oC
Corn starch cooked in water to 90oCWater-Starch Ratio: 20
Time (minutes)3 6 9 12 15 18 21 24
180
150
120
90
60
30
0
Visc
osity
(sec
onds
)
27
ture was placed in a waterbath maintained at 90oC andagitated at two differentspeeds. The solid line showsthat the paste agitated at 100rpm required approximately18 minutes to reach its maxi-mum viscosity and then re-mained constant for the lastthree minutes. In contrast,the suspension agitated at200 rpm reached a maximumviscosity after 6 minutes,followed by a rapid viscositydecrease and then a contin-ued, but much slower, vis-cosity decrease. In the 200rpm cook, improved heattransfer caused the tempera-ture to rise at a faster rateand the granules to gelati-nize more rapidly. The me-chanical action of the 200rpm agitator, however, rup-tured the swollen granulesresulting in a sharp drop inviscosity. Continued agita-tion brought about onlyslight viscosity decreaseafter the granules were me-
chanically ruptured.Crosslinking reducesviscosity loss due to shearingof the granule by use of agi-tators, pumps and homog-enizers.
The effect of pH on cornstarch gelatinization andbreakdown is demonstratedin Figure 10. The referencesample at pH 4.0 yields atypical cooking curve fornormal corn starch. Increas-ing the pH to 7.0 causedmore rapid gelatinization,but yielded a comparableviscosity in the cookedpaste. Increasing the pHfrom 4.0 to 7.0 increased theability of the starch granuleto hydrate and gelatinize,but did not provide suffi-cient alkalinity to produceappreciable viscosity break-down after gelatinization.However, when the pH wasincreased to 10.0 with alkali,gelatinization occurred in amuch shorter time due to an
Figure 9Effect of agitaion ongelatinization
200 r.p.m.
100 r.p.m.Corn starch cooked in water to 90oC
Water-Starch Ratio: 20
Time (minutes)3 6 9 12 15 18 21
180
150
120
90
60
30
0
Visc
osity
(sec
onds
)
Agitator speeds given in r.p.m.
28
increased rate of hydrationof the starch molecules. Thehigher alkalinity also rup-tured some of the swollengranules with a resulting lossof viscosity. Although notshown in Figure 10, if thestarch had been dispersed in2% sodium hydroxide solu-tion, it would have gelati-nized without any addedheat to a relatively stable,but less viscous paste thanthat produced by heating atpH 10.0.
The final curve on Figure 10shows the viscosity behaviorof a starch suspension ad-justed to pH 2.5. Gelatiniza-tion began much like thesuspension at pH 7.0, but thepaste attained a lower maxi-mum viscosity and then un-derwent a rapid and continu-ing loss of viscosity. At pH2.5 and at temperatures ap-proaching 80oC the starchmolecules probably undergo
glucosidic cleavage, weaken-ing the entire granular struc-ture, which ultimately disin-tegrates yieldingwater-dispersible fragmentsof lower molecular weight.The effects of other materi-als in the solution on the rateof gelatinization of starchand the characteristics of theresulting pastes also can beobserved. For example,when cooked in 10% sucrosesolutions, starches gelatinizeless rapidly and form lessviscous pastes, since sucrosebinds water so that less isavailable for granule gelati-nization. When the diastaticenzyme alpha-amylase ispresent, marked decreases inviscosity occur. If beta-amy-lase is present, the viscositydrops and up to 60% of thestarch may be converted tomaltose. If glucoamylase ispresent, the starch may beconverted to over 95%glucose.
4.0 pH
7.0 pH
Corn starch cooked in water to 90oCWater-Starch Ratio: 20
Time (minutes)0 3 6 9 12 15
210
180
150
120
90
60
30
0
Visc
osity
(sec
onds
)
10.0 pH
2.5 pH
Figure 10Effect of pH ongelatinization
29
Another method for prepar-ing starch pastes involvescontinuous pressure cook-ing, often referred to as jetcooking. In this process thestarch suspension is mixedwith steam and then injectedinto a pressure vessel, whereit is held for a very shortperiod of time at tempera-tures over 100oC and at pres-sures higher than atmo-spheric. The paste is thenflashed down to atmosphericpressure, with resultantevaporative cooling and con-centration. If desired, somemodification of the starchmay be obtained by addingsmall quantities of specificchemicals to the starchslurry before injection intothe cooker. This allows theuser to alter the properties ofthe starch paste in a continu-ous process to meet the re-quirements of his specificuse, but it does mean that theuser must assume responsi-bility for controlling thedegree of modification ac-complished.
Since starch properties canalso be altered byderivatization and modifica-tion, almost unlimited varia-tions can be obtained. Thisversatility has made pos-sible the development ofmany specialty starch prod-ucts designed for specificfields of application. It isimpossible to discuss the
many products commer-cially available in this briefdiscussion. Typical applica-tions for food and industrialstarches, and dextrins areincluded at the end of thisbooklet. Any reader wish-ing assistance with theseproducts is encouraged tocontact individual membercompanies of the Corn Re-finers Association. Theywould be pleased to offerassistance in selecting thecorrect product and in rec-ommending proper methodsof application.
HANDLINGCOOKED
STARCHES
Cooked starches may beused hot, at room tempera-ture or chilled. The properconditions for altering thetemperature must be appliedto the hot paste if the desiredresults are to be obtained.Conditions are often de-signed for a specific applica-tion, but some general guide-lines follow:
1. Hot starch pastes continueto lose viscosity if main-tained near boiling tempera-tures. They should be cooledto the temperature at whichthey are to be used immedi-ately after cooking.
2. Starch pastes lose viscosityin direct proportion to theforce of agitation. If viscosityis to be maintained, gentle
30
but thorough agitationshould be used after cooking.
3. Starch pastes increase inviscosity as they are cooled.The amount of agitationapplied during cooling af-fects the physical character-istics of the cooled paste.Continuous agitation duringcooling yields pastessmoother in texture and withfewer tendencies to gel thanthose not stirred. Con-versely, maximum gellingdemands that no agitation beapplied during cooling.
4. Undercooked starchpastes yield gels that releasewater upon standing.Though often referred to as"weeping," as the more cor-rect term is syneresis. Selec-tion of the proper starchproduct, thorough cookingand proper cooling elimi-nates syneresis.
5. Dilute starch pastes, par-ticularly those of unmodi-fied and acid-modifiedstarches, may develop a dis-tinct cloudiness. This cloudis the result of retrogradation
of the amylose polymer inthe starch. Retrogradation isthe process of molecularalignment and dehydrationthat produces large, looselybound molecular aggregates.Given sufficient time and noagitation, these aggregatesmay precipitate (settle).Clouding and precipitationcan be prevented by keepingstarch pastes at a tempera-ture of about 170oF withgentle, continuous agitation.Oxidized, certainderivatized and mostdextrinized starches havereduced tendency to retro-grade. Waxy starches do notexhibit this retrogradationphenomenon to any markeddegree.
6. Due to the ready accessi-bility of sugars, starchpastes are excellent mediafor the growth of many air-borne microorganisms. Ifstored at or near room tem-perature for more than 24hours, preservatives must beadded to prevent fermenta-tion, loss of viscosity andeventual spoilage.
31
ENZYMECONVERSION
OF STARCH
Starch pastes of all types aresusceptible to hydrolysis byamylolytic enzymes result-ing in shorter polymer chainlengths and sharply reducedviscosities. Enzyme hydroly-sis is widely used, particu-larly in the textile and paperindustry and in the prepara-tion of corn syrups and dex-trose.
Cotton warp yarns are com-monly sized with starches togive them the neededstrength for proper weaving.However, the starch must beremoved from the wovencloth before it is dyed. Adiastatic enzyme (alpha-amylase) that rapidly hydro-lyzes starch to short, watersoluble fragments is usedfor this purpose. The en-zyme is applied to wet cloth,allowed to stand for the cor-rect period of time to permitthe enzyme to act on thestarch, and the solubilizedhydrolysates are thenwashed from the cloth withwarm water.
Paper manufacturers uselarge quantities of starch thatis enzyme converted in thepaper mill. The enzymeconversion process allowsthe papermaker to replacethe modified or derivatizedstarches with unmodifiedstarch for some applications.It also allows the paper-maker to custom convert
starch to the viscosity re-quired for specific applica-tions. In a typical paper ortextile mill, bulk starch isautomatically scaled intoconverting equipment,where it is slurried in waterat the correct concentration(35-40% starch suspensionsfor high solids conversions).The starch slurry is adjustedto the desired pH, alpha-amylase is added and a pro-grammed heat cycle is set inoperation. In a typical con-version cycle, steam is ap-plied to a closed, jacketed,agitated vessel heating thestarch suspension to 80oC in15 minutes. This swells thestarch and initiates rapidenzyme conversion. Theconversion is held at 80oCfor 45 minutes and thenheated to about 105oC in 15minutes. The elevated tem-perature is maintained for 30minutes to inactivate theenzyme and thoroughly dis-perse the starch.
At the conclusion of the105oC holding period, thestarch is cooled to the tem-perature at which it is to beused by one of severalmeans. If it is intended foruse as a tub size or for appli-cation at the size press on apaper machine, it will quitelikely be cooled by dilutionwith cold water. Pigments orother chemical aids may beadded simultaneously with
32
the dilution water.
If the conversion is intendedfor use in preparation of apigmented coating for paper,it is cooled by adding it to a"clay slip" which is a highsolids mixture of clay orother pigments with dispers-ing agents, dyes and otherchemical aids. Since papercoating is accomplished atvery high speeds, the rheo-logical properties of thestarch-clay-chemical mix(coating color) must be care-fully controlled.
Primary control of the finalviscosity of enzyme-con-verted starch is achieved byvarying the quantity of en-zyme utilized, but variationof the physical conditionsimposed upon the systemalso affects the characteristicsof the converted starch. Batchsystems are often employed,but continuous systems arealso in use commercially.
Generally, starches used forenzyme conversion are un-modified and are specially
prepared for this use. Theyare usually pH adjusted andbuffered; small quantities ofvarious adjuvants are incor-porated in the slurry beforedrying and special dryingtechniques may be used.
The major use for enzyme-converted starch occurs rightin the wet milling plant,where each year billions ofpounds of starch are con-verted to nutritive carbohy-drate sweeteners. These pro-cesses utilize alpha-amylase,beta-amylase, glucoamylase,debranching enzymes andisomerases. They are dis-cussed in a booklet entitledNutritive Sweeteners fromCorn, available on the CornRefiners Associationwebsite, www.corn.org.
Enzyme treatment today isfrequently used to preparestarch for subsequentderivatization and process-ing steps, which result in thecreation of products withunique physical and func-tional properties.
33
ANALYTICALEXAMINATION
OF STARCH
The chemical literature con-tains descriptions of count-less methods for determin-ing the chemical andphysical properties of starch.
The Corn Refiners Associa-tion, through its TechnicalAffairs Committee, hasspent many years developingand standardizing analyticalprocedures for starch andstarch derived productswhich are practical and ef-fective. The committee ac-tively continues its work onstandardization of analyticalprocedures today.
As a result of this extensivework, the Corn RefinersAssociation publishes theseanalytical procedures and
makes them available to thepublic. These methods arepublished in Analytical Meth-ods of the Member Companies,available from theAssociation’s website,www.corn.org.
By cooperation with theAssociation of Official Ana-lytical Chemists many ofthese methods are availablethrough that organization'sreference publications aswell.
The Corn Refiners Associa-tion has published manyanalytical procedures appli-cable to unmodified andmodified starches and dex-trins, sweeteners and cornbyproducts.
34
CORN REFINING INDUSTRY PRODUCT USE
ALCOHOLIC BEVERAGES, BREWINGBeer, liquor
BEVERAGES, NON-ALCOHOLICCarbonatedProtein drinksFruit drinks & juicesPowdered mixes
BAKING, SNACK FOODSBaking powderBars, energy & snackBiscuitsBreads & rollsCakesCookiesCrackersDoughnutsExtracts and flavorsFood coloringFrosting, icing, glazesPiesPotato chipsPowdered sugarPretzelsSpicesYeast
CANNED FRUITS & VEGETABLESFruits & berriesFruit fillingsSoupsTomato saucesVegetables
CEREALSCerealsCereal bars
CONDIMENTSCatsupGraviesMayonnaiseMustardOriental saucesPickles, pickle productsRelishesSalad dressingsSauce mixes
Unmo
dified
star
chMo
dified
star
chDe
xtrins
VinegarWorcestershire sauce
CONFECTIONERY & GUMChewing gumChocolatesConfectioneryLicoriceMarshmallowsNougats
FATS AND OILSMargarinePan coatings
FORMULATED DAIRY PRODUCTSCheese spreads & foodsCoffee whitenerCondensed milkFrozen creamYogurt
ICE CREAM & FROZEN DESSERTSFrozen puddings/custardsIce cream or milkPowdered mixesSherberts, water ices
JAMS, JELLIES, PRESERVESFruit buttersJamsJelliesMarmaladePreserves
MEAT PRODUCTSBolognaBreakfast meatsChicken productsDried meatsFish, seafoodHotdogsMincemeatSausagesSurimi
MIXES, PREPAREDCake mixesCookie, brownie mixesDessert mixesDried foods
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Eggs, frozen or driedFrosting, icing mixesGelatin mixesGravy mixesInstant breakfast foodsInstant teaPancake, waffle mixesQuickbread mixesSeasoning mixesSoups, dried
SYRUPS & SWEETENERSChocolate, cocoaDessert toppingsFruit and tableLow calorie sweetenersSoda fountain
MISC. FOODSBaby FoodDesserts (puddings/custards)Dietetic preparationsInvalid feedingsPeanut butterPrecooked frozen meatsRice & coffee polish
HOUSEHOLD NEEDSAir freshenerBatteriesBriquettesCleanersCrayons & chalkDiapersLaundry careMatchesMetal cleanerTrash bagsTwine, cord, string
PERSONAL CARECosmeticsDeodrantHair styling productsSurgical dressings
PHARMACEUTICALSAntibioticsAsprin
Coatings (food & drug)Cough dropsDrugsMedicinal syrupsPharmaceuticals
TOBACCOTobacco
ANIMAL FEEDCatCattleDogFishSwine
CHEMICALSAcetic AcidAgrochemicalsDispersing agentsEnzymesFermentation processesFood acidsIndustrial alcoholInsecticidesOrganic solventsPharmaceuticals
PAPER, PAPER RELATED PRODUCTSAbrasive paper & clothBookbindingEnvelopesGlassineLabelsPaperParchmentPrinting inksStrawsWallpaper
PASTE,ADHESIVESAdhesivesBinders, binding agentsGluesGumsMucilagesPastes
TEXTILECord polishing
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TEXTILES cont.Dyes & dyeingOilclothPrintingSizing materialsTextileWindowshades, shade cloth
BUILDING MATERIALSCardboardCeramicsCoatings (wood, metal)Cork productsFiberglassFirberboard, plywoodGlass or rock woolLaminatedLinoleumPaints and varnishesTile, ceilingWall treatment compoundWallboard
MINING/METALLURGYElectroplatingGalvanizingMetal platingOre refining, separation
MISC. INDUSTRIALBoiler compoundsExplosivesFiltersFireworksLeather tanningLubricating agentsOil-well drillingPlastics, incl. degradableProtective colloidsRefractoriesRubber (cold process)ShoesTires (rubber)Water recovery (industrial)
CORN REFINING INDUSTRY PRODUCT USE
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GLOSSARY
To aid in the understanding of industry-specific informationin this booklet, technical terms are explained in the text atthe points where they are first used. For reader convenience,definitions of some of the more difficult terms and of termshaving special meanings in the corn refining industry arelisted here.
Amylose – A starch molecule made up of glucose unitschemically arranged in long straight chains.
Amylopectin – A starch molecule made up of glucose unitschemically arranged into branched chains.
Anhydroglucose units – The basic C6H10O5 unit that occursrepeatedly in all starch molecules.
Aqueous – Containing water.
BOD – Biological oxygen demand, the measure of theamount of oxygen in a body of water used over a period oftime through bacteria and plankton activity to stabilize de-composable organic waste.
Brabender – Amylo-viscograph unit used to measure viscos-ity.
Carbohydrate – A chemical compound composed of carbon,hydrogen and oxygen (starch, sugar and cellulose are three ofthe most common examples).
Congeal – To change from a liquid to a semi- solid, non-fluidmass.
Convert – To change to a lower molecular weight form, asby dextrinization, hydrolysis, etc.
Corn – The seed from commercially grown maize (Zeamays) used primarily for animal feed and corn-derived foodand industrial products; not sweet corn.
Derivative – A product obtained by reacting starch with achemical compound, resulting in unique physical and func-tional properties.
Enzyme – Any of a class of protein molecules that catalyzespecific biochemical transformations, as in the conversion ofstarch to glucose.
Fluidity – Reciprocal of viscosity.
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Fractions – The two types of molecules found in starches---linear and branched; amylose and amylopectin.
Gel – A firm, semi-rigid, cooled starch paste resembling ajelly; to form a gel.
Gelatinize – To cook starch in aqueous suspension to thepoint at which swelling of the granules take place, forming aviscous sol.
Genetics – A branch of biology dealing with hereditaryvariations in plants and animals. As an applied science, it isused to improve corn by breeding desired characteristicsinto new varieties.
Glucosidic cleavage – The hydrolysis of a glucose polymerwhereby water is the agent, which, under acid or enzymecatalysis, acts to split apart the glucosidic bond holding adja-cent glucose units together and regenerates an hydroxylgroup on each glucose component.
Granule – The small, grain-like storage particle produced inplants, consisting of starch molecules arranged in character-istic patterns.
High amylose starch – A starch containing over 50% amy-lose (usually 55-70% ).
Hydrate – A molecular-water association.
Hydrolysis – Process of splitting a molecule into smallerparts by chemical reaction with water.
Hydroxyl (OH) group – A chemical radical consisting of oneoxygen and one hydrogen atom.
Hygroscopic – Readily absorbing and retaining moisture.
Kernel – A whole grain or seed of a cereal, especially corn.
Linkage – The specific bonding arrangement by which mol-ecules are joined to form larger molecules.
Micelles – The tight bundles into which linear starch mol-ecules and the linear segments of the branched molecules aredrawn together.
Molecule – A unit of matter; the smallest portion of a com-pound that retains chemical identity with the substance inmass.
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Mutant – An offspring different from its parent in some well-marked characteristic.
Oxidation – The act of oxidizing which is brought about byincreasing the number of positive charges on an atom or theloss of negative charges.
pH – A measure of the acidity or alkalinity of a solution, pH7 being neutral, lower values acid and higher values beingalkaline.
Polymer – A very large, complex molecule formed bychemically joining a large number of identical smaller units(or monomers) in a repeating pattern.
Retrogradation – Dehydration and reversion of cookedstarch from a paste to a condition of insolubility.
Slurry – Suspension of starch in water, with or without othercomponents of corn.
Stable – Term indicates that the starch paste does not changeappreciably in viscosity, clarity or texture with age.
Starch paste – The thick, viscous, smooth suspension formedby cooking starch in a water suspension to a point above itsgelatinization temperature.
Steepwater – Water containing dissolved protein, mineralsand other substances in which corn has been soaked or"steeped" during the initial stages of the corn refining pro-cess.
Suspension – A heterogeneous mixture of an insoluble granu-lar or powdered material with a fluid.
Synthesize – To build up a compound by the union of sim-pler compounds or of its elements.
Viscosity – Term used to indicate the resistance of liquids toflow; often used to describe the thickness of a starch paste.
Waxy maize – A variety of corn, the starch content of whichconsists solely of branched molecules.
Wet milling – A process for separating corn into its compo-nent parts using a water-sulfur dioxide system.
Corn Refiners Association1701 Pennsylvania Avenue, N.W. • Washington, D.C. 20006-5805
202-331-1634 Fax: 202-331-2054 • www.corn.org
