Chapter 9

This researcher is comparing two varieties ofcorn. Both are sources of starch, a complexcarbohydrate.

Objectives

The ComplexCarbohydrates:Starches,Cellulose, Gums,and Pectins

Key Terms

After studying this chapter,you will be able todescribe characteristics of the four categoriesof complex carbohydrates.

identify the functions of complex carbo­hydrates in food preparation.

list five physical properties of starch andliquid mixtures that affect the selection ofstarches used in food products.

compare the advantages and disadvantagesof the three main methods used to addstarches to sa uces.

analyze the role of starches in a nutritiousdiet.

196

polysaccharide

macromolecule

starch

polymer

amylose

amylopectin

granules

cellulose

carbohydrate gum

pectin

gelatinization

gelatinization point

slurry

sol

paste

gel

jlU1Ction

retrogradation

syneresis

viscosity

stability

opacity

translucency

modified starch

cross-linked starch

cold water paste

buerre manie

roux

ketosis

ketone bodies

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins 197

Breads, cereals, muffins, cakes, and cook­ies are well-liked foods in the typical U.S. diet.These foods are rich in carbohydrates. Some ofthe carbohydrates are simple carbohydrates,which you studied in Chapter 8. However,many of the carbohydrates in baked goods arecomplex carbohydrates, which are the focus ofthis chapter. See 9-1.

Complex carbohydrates are calledpolysaccharides. This is because they aremade up of many sugar units, or saccharides.Another term used to describe polysaccha­rides is macromolecules. Macl'OmoleCllles arevery large molecules that contain hundreds orthousands of atoms each.

The Types of ComplexCarbohydrates

Several types of complex carbohydratesare found in foods. These include starches, cel­lulose, gums, and pectins. These polysaccha­rides are abundant in grains, seeds, nuts,fruits, vegetables, and seaweed.

StarchesThe most abw1dant complex carbohydrate

in the diet is starch. Most starches consist ofmolecules of 100 to several thousand glucoseunits linked in chains. Because starches aremade up of many sugar units, they are poly­mers of sugar. A polymer is a large moleculethat consists of large numbers of small mole­cular units, which are linked. Starches arecomposed of glucose. Other polysaccharides

9-1 Complex carbohydrates are found in a widevariety of grains and grain-based products.

can consist of as many as six or seven types ofsugars.

A main source of starch in the diet for mostpeople in the United States is wheat flour.Wheat flour is used to make many types ofbaked goods and pasta. Starch is also found inrice, corn, potatoes, and oats. Any grain orseed is high in starch. Rye, soy, tapioca, andarrowroot are other less commonly usedstarch products in the U.S. food supply.

Starches have two basic structures. One islinear, and the other is branched. When thewuts are linked in a line (linear), they arecalled amylose. Starches that have a branchedstructure are called amylopectin. In mostfoods, starches occur as mixtures of amyloseand amylopectin.

Starch is nature's reserve carbohydratesupply. Plants produce starch in packets calledg1'al'l II les. Granules are not soluble in coldwater. The size and shape of granules varyfrom plant to plant. Of the common foodstarches, rice has the smallest granules andpotatoes have the largest. Starch granules area mixture of amylose and amylopectin mole­cules. Amylose content can range from 25% to85%. The varying amylose/amylopectin ratioswithin the granules cause each type of starcl1to perform differently in food mixtures.

Starches composed mainly of amylopectinare also called waxy starches. Tlus is because ofthe appearance of the surface of the seedsfrom which the starches come. Waxy maize isa starch from corn that has more thickeningpower that regular cornstarch.

CelluloseA second group of complex carbohydrates

are called cellulose. Cellulose is a polysaccha­ride made from large amounts of P-D-glucose.Some animals, including cows and sheep, andinsects such as termites can use cellulose as afood source. However, humans lack the diges­tive enzymes needed to break the bonds incellulose molecules. Cellulose is among thecomplex carbohydrates that are known asfiber in the diet.

Cellulose forms the rigid structure ofplants. The strings in celery and the mem­branes surrounding kernels of corn are madeup largely of cellulose.

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Carbohydrate Gums and PectinsThe last gmup of complex carbohydrates

used in food preparation are not generallyavailable to the home cook. These polysaccha­rides are called carbohydrate gums andpectins. Carbohydrate gllms are polysaccha­rides that are soluble in water and extractedfrom plants. Pectins are complex carbohy­drates that are found in plant cells and madeof chemical derivatives of sugar called sugaracids.

Gums thicken and stabilize mixtures andtrap color and flavor. The most common andwidely used is gum arabic. It surrolmds flavorparticles, protecting them from moistureabsorption, evaporation, or chemical oxida­tion. Other gums commonly used in foodsinclude karaya gum, gum tragacanth, gumagar, carageenan, and algin. Gums providestability and texture to such foods as saladdressings and gummy candies, 9-2.

=I.Z>.iIIJ'2!l1.\ ).

9-2 Gummy bears get much of their characteristictexture from carbohydrate gums.

Unit III Organic Chemistry: The Macronutrients

Pectin is a complex carbohydrate that nat­urally occurs in fruits. It can produce a stronggel that will remain stable to near 100°C(212°F). in the presence of sugar, pectin mole­cules will dehydrate. Acid will cause hydro­gen bonding to occur betvveen negativelycharged molecules, thus creating a thickenedstructure. These properties make pectin a keycomponent in jams and jellies.

Functions of ComplexCarbohydrates in FoodPreparation

Complex carbohydrates serve a number offunctions in food preparation. They providestructure, bind ingredients together, and act asabsorbing agents or thickeners. All complexcarbohydrates help stabilize food products bykeeping ingredients evenly distributedthroughout mixtures.

Provide StructureStarch is the main component of wheat

flour. Flour is the primary ingredient in mostbaked goods. Flour provides the majority ofthe bulk or structure of baked goods andmany other food products. For instance,most ready-to-eat cereals retain their shapedue to their starch content. The pieces areformed in a semiliquid state and remainshaped on drying.

Starch's ability to thicken when heatedand gel when cooled enables foods containingstarch to take and hold many shapes. Othercomplex carbohydrates also provide structurein foods. Cellulose forms the supportingframework or structure for fruits and vegeta­bles. Pectins and gums are responsible for thetexture of jams, jellies, ice cream products, andgummy-textured candies.

BindBinding agents are substances that tend to

hold two other products together. Amylosemolecules will work better than amylopectinmolecules at holding batters to vegetables andmeats during deep-frying. The binding isincreased if batter-dipped foods set for 20minutes before frying. This allows time for the

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins 199

chemical reactions needed to bind the batter tothe food during cooking. See 9-3.

Carageenan is a gum used as a bindingagent. It stabilizes the cocoa in chocolate milkso the cocoa does not settle out of the product.Carageenan is also used to stabilize ice creamand other dairy products.

ThickenStarch can thicken liquids. This function is

possible because of starch's chemical struc­ture, the size of its molecules, and the way itreacts to hea t. The molecules of starch arechemically altered as they swell and take upwater.

Starches are usually combined with liquidsin food preparation. Undamaged stardl gran­ules are not readily soluble in water nor dothey absorb water. Starch must first be heatedto break intermolecular bonds. This allowshydrogen bonds to form between the starchmolecules and water.

When starch granules are suspended inwater and then heated, gelatinization occms.Gelatil1ization is the term food scientists useto describe thickening a liquid with starch. Asthe temperature increases, so does theswelling of the granule structure. The temper­ature at which maximum swelling occurs isthe gelatil1ization point. This is the point atwhich the starch will hold the most water andhave the greatest thickening power. The starchused in instant puddings has been pre­gelatinized. This allows it to gel, or set, at tiletemperature of cold milk. The starch in regu­lar pudding mixes will not gelatinize until it ishot enough to boil. Then it will not gel until itis chilled.

Water is the main component of almostall liquids used in food prepara tion. Starchmolecules are extremely large in comparisonto water molecules. Not only are starch mole­cules large, but they have spaces betvveentheir sugar units. Imagine a tumbleweedrolling across a desert. The tumbleweed is asolid that has a ball shape. The ball is made ofmany branches wi th air spaces between them.If the tumbleweed rolls across a crumbled uppiece of paper, the paper can become stuckbetween the branches. That piece of paper willnow be carried along with the tumbleweed.

9-3 The starch in flour binds the batter to onionrings so it does not separate from the onionsduring frying.

That is similar to what happens as large starchgranules roll around in water. The very smallwater molecules will slide between sugarunits and be held in place by hydrogen bond­ing. The more water that "snuggles" into thestarch molecule, the thicker the mixture willbecome. See 9-4.

Applying heat to a starch-water mixturecauses it to thicken (gelatinization). As heat isadded, starch opens up or stretches. Thisallows water molecules to slip down betweenthe coils of the large molecule. The addition ofheat increases tile amount of water the mole­cule can trap in its coils and branches. Themore water the molecule traps, the thicker themixture will become.

Heat is needed to stretch starch moleculesand increase their thickening power.However, too much heat will cause starchmolecules to begin to hydrolyze or breakapart. This will cause the starch to lose thick­ening ability and stability. Excess heat canresult from using too high a temperature ortoo long a cooking time.

The presence of salt and sugar affectsstarch's thickening ability. Salt and sugar com­pete for water because they are also polar innature. If a large amount of salt or sugar ispresent, it will interfere with the gelling abili­ty of the starch. When sugar is combined withflour or any other starch, it will decrease thestrength and viscosity of the gel. It will alsoincrease the translucency of the paste. In most

9-4 Starch thickens because ot its ability to trap water molecules.

Starch Molecule

Each starch has different physical proper­ties. Therefore, food scientists must determinewhich starch source is best for a food product

Alginates, a group of gums, thicken dress­ings and puddings. Xanthan gum may beused to help thicken instant puddings.

Physical Properties of Starch andLiquid Mixtures

9-5 liquid and powdered pectin are available forthickening homemade jams and jellies.Commercially, pectin is used as a thickener andstabilizer in such foods as ice cream and candy.

Unit III Organic Chemistry: The Macronutrients

watermolecules

cases, low concentrations of salt have littleeffect on gelatinization or the ability to form agel. Pota to starch and some manufacturedstarches are exceptions. They are salt sensitive.Depending on the starch, salt can increase ordecrease swelling.

Pectin is used to thicken jams and jellies.Some fruits, such as crabapples and gooseber­ries, can provide enough pectin to producesuitably thick jellied products. Other fruitsrequire the addition of commercial pectin.Commercial pectin is made by extractingpectin from its fruit source. It may be driedinto a powder or sold in a liquid form forhome use. See 9-5.

The basic recipe for jams and jellies is 1%pectin and 60% to 65% sugar. The remaining34% to 39% is made up mostly of crushed fruitor fruit juice. A little hot water may be addedif needed for volume. Jams and jellies musthave a pH of 2.0 to 3.5. If the fruit is not veryacidic, lemon juice is added to achieve thedesired pH level.

Pectin will bond with other pectin mole­nIles and form a gel without sugar if calciumions are present. This is how dietetic jams andjellies are made. Pectin plus calcium also firmscanned tomatoes and pickled cucumbers.

200

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins 201

and the type of starch-liquid mixture.Scientists do this by examining how the starchworks within a food mixture. The mostimportant property to the consumer is usuallyflavor. For example, cornstarch does not tastethe same as rye flour. However, wheat flour,cornstarch, and potato starch all thickengravies and sauces without adding unpleas­ant flavors.

There are five properties that food scien­tists evaluate before selecting a starch. Theproperties they examine include: retro­gradation, viscosity, stability, opacity versustranslucency, and texture. Food manufactur­ers have to carefully evaluate all these charac­teristics of starches anytime they develop anew starch-thickened product.

Types of Starch and Liquid MixturesStarch and liquid combinations can be of

four types: slurries, sols, pastes, and gels.Sllltties are uncooked mixtures of water andstarch. They are used in the processing andchemical alteration of starches. Acids and/orbases are added to the mixtlll'e to chemicallyalter the structure of the starch molecules.

Sols are thickened liquids. They arepourable. Examples of sols include pancake,waffle, and muffin batter. Cooked sols includewhite sauce and gravy.

Pastes are thickened mixtures of starchand liquid that have very little flow. However,they are thin enough to be spread easily. Whenmaking gravy, starch can be combined withwater or milk to form a paste. The paste canthen be stirred into hot broth without lump­ing, 9-6. This method works well when thick­ening soups and stews.

Gels are starch mixtures that are rigid. In agel, molecules are bOlmd together in a three­dimensional network. This network keepsmolecules from shifting in comparison to oneanother. When two molecules of hydrogenbond together, a jUl1ctiol1 is formed. Shortstarch chains tend to form weaker jlmctions.This makes them unstable in heat. Long starchchains form firmer gels that are more stable inheat. Therefore, linear amylose starches willform more stable gels than branched amylo­pectins. By controlling the number and loca­tion of junctions, food scientists can vary thefirnu1ess and stability of gels.

9-6 Combining flour with milk or water forms astarch paste, which can be added to broth tomake a thick gravy.

Amylose molecules will set rapidly andform firm gels upon cooling. Amylopectinforms thitu1er gels or no gels at all. Amylosegels are also elastic, whereas amylopectin gelsbecome rigid. This tendency of amylopectinstarches to become rigid is a main cause ofbreads becoming stale. The rigidity is com­bit1ed with moistme loss.

RetrogradationRettogradatiol1 is the firnw1g of a gel dur­

ing cooling and standing. It occurs becausethe starch granules are trying to return to thestructure they had before cooking. Amylosewill tend to hydrogen bond to other amylosemolecules. These overlapping molecules willform crystalline structures that separate outof the gel. This is a problem with starch­thickened pie fillings or gravies that are frozenand then tl1awed.

Retrogradation is desirable when it causesa gel to thicken during cooling. It is undesir­able if it continues to the point that cracksform in the gel. Gravy left uncovered in therefrigerator will develop these cracks after acouple days.

The changes of retrogradation are accom­panied by wa ter being squeezed frombetween the molecules of the gel. Sy"etesis isthe term used for water leaking out of a gel it1storage. The liquid that separates from manymustards is an example of syneresis. Stablegels will have little or no syneresis.

An important factor related to retro­gradation is the serving temperature of a

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starch-thickened food product. A sauce willthicken as jt cools. If you are planning to servea sauce immediately, you should cook it to thedesired thickness. This is not the case withmost sweet sauces. They are often served atroom temperature. Because they will thickenas they cool, they m Llst be thiJUler than desiredat the end of the cooking time.

Acids hydrolyze starch. Because acidsbreak down starches, they will also weaken orbreak down gels. This reduces the thickeningpower of the stard1. This is why lemon pie fill­iJ1g calls for more starch than coconut creamor d10cola te cream pie filliJ1g. Lemon juice isadded after the starch has thickened lemonpie filling. The filling is then cooled rapidly tommi'TIlZe the thinning effect of the acid inlemon.

ViscosityViscosity is the resistance of a mixture to

flow. When you spill a glass of wa ter on thetable, it spreads out in a large pool. If you spilla bowl of oatmeal, it will only flow a short dis­tance before it stops. The difference betweenthe water and the oatmeal is caused by thestarch in the oatmeal.

Solids, induding dry starches, hold theirshape and stay where they are put. Liquids

Unit III Organic Chemistry: The Macronutrients

take the shape of their containers. If there is nocontainer, liquids flow to the lowest point.When you mix solids and liquids, there aresome particles trying to stay put and otherstrying to flow. The more solid that is present,the more resistance there will be to flow. Gelsare more viscous than pastes, and pastes aremore viscous than sols.

Food scientists rim viscosity tests to mea­sure how foods such as ketchup will flow. 111escientists use line-spread sheets. A foodscientist sets the cylinder in the center of theconcentric circles of the line-spread sheet. Heor she fills the cylinder with the mixturebeiJ1g measured. The scientist lifts the cylin­der, which allows the mixture to flow as faras it will. Substances will rarely flow out in aperfect circle. Therefore, the food scientisttakes readings at four equidistant points. Heor she then averages the four readings todetermine the viscosity. See 9-7.

Viscosity varies with molecular size,shape, and charge. Larger molecules are hard­er to move, and thus more viscous, than smallmolecules. Linear molecules are more viscousthan branched molecules. This is because lin­ear molecules will not roll over easily unlessthey are parallel to the direction of flow.Charged macromolecules will have more

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9-7 To measure viscosity, a sample of a sol is poured in a ring placed in the center of a line-spread sheet.After the ring is lifted and the sol is allowed to spread, readings are taken in at least four places.

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins 203

resistance to flow than uncharged molecules.This is because of the resistance of oppositecharges holding the molecules together. Themain functions of starches in food productsinclude providing viscosity, gelatinization,and structure. Therefore, linear starches, suchas amylose, are generally more useful in form­ing gels.

Viscosity could be said to be a measure ofa starch's thickening ability. Food scientistscan use viscosity tests to rank the thickeningability of different starches. The scientists candetermine the amount of each starch neededto thicken 1 cup of water to the same degree.Listing this information in a starch proportionchart creates a valuable tool for food productdevelopers. They can use the chart to easilysee how substihlting one starch for anotherwill affect a food product. For instance, chang­ing the type of starch will change the flow ofan uncooked batter. Commercial bakers havefow1d they can substitute 30% of the flour incookies with pure wheat starch. This starchhas had protein removed. Protein moleculesinteract with one anothel~ blocking the flow ofa batter. Substituting pure wheat starcl1 forflour will increase the spreading action of thebatter. This helps achieve the evenly shapedcookies available in grocery stores.

StabilityStability is the ability of a thickened mix­

ture to remain constant over time and temper­ature changes. A stable sauce can be frozenand!or reheated. It will look and taste muchthe same as when it was first prepared. Waxymaize starch is an example of a starch that isstable when frozen or heated. It is a clear, softpaste that is as thick hot as cold.

Cornstarch has more thickening powerthan flour. It is smoother in texture and moretranslucent than white flour. However, corn­starch is not as stable in prolonged heat.Cornstarch makes an appetizing mushroomgravy to serve over beef tips. However, sup­pose you had to prepare the beef tips a dayahead of time. The cornstarch gravy wouldnot thin out into a smooth sauce when reheat­ed. FloW' might be a better choice than corn­starch for thickening gravies that must be pre­pared in advance.

Opacity Versus TranslucencyOpacil:1J refers to how much an object

blocks light. Translucency is a measure of howmuch light can pass through an object. Anobject with maximum opacity allows no lightto pass through it. An object with maximumtranslucency blocks no light. Cornstarch, pota­to starch, and arrowroot produce gels that aremore translucent than gels made with wheatstarch. You can see through them to someextent. This makes these starches good choic­es for fruit sauces, fruit pie fillings, and glazes,which are translucent. Wheat flour is not usedfor most pie fillings because it becomes yel­lowish and stringy. However, wheat flour issuitable for use in chowders and white sauce,which are opaque. See 9-8.

TextureThe last property a food scientist looks at

when choosing a starch is texture. Conm1ealwill thicken a gravy, but most people wouldnot like it. The gravy would feel gritty insteadof smooth. Likewise, few people make a sauceor gravy from whole wheat flour because ofits mouth feel.

Modified StarchesFood teclmologists can alter the structw'e of

starch molecules to aclueve special physical

9-8 The opaque chicken gravy on the left is thick­ened with flour. The translucent beef gravy on theright is thickened with cornstarch. The patterns onthe plate show through the beef gravy but not thechicken.

204

properties. Starches that have been changedstructurally by chemical or mechanical meansare called lnodified starches. FDA regulations donot require that labels identify the food productfrom which a modified starch originates. 'Thiscan be a problem for those people who are sen­sitive or allergic to a specific grain product.Some of the most commonly used sources ofmodified starches are wheat, com, and soy.

Most modified starches are altered byhydrolysis. They are allowed to set in a mix­ture or slurry of water and acids or water andenzymes. Starch modification can be con­trolled to produce various levels of sweetnessand particle size. Viscosity, mouth feel, andappearance of starches can also be modified.

Cornstarch that has been modified is usedin gum candies and confections as a stabilizer.In the 1970s, it became possible to hydrolyzecornstarch to form a low-cost sweetener. Aslurry of cornstarch and acid was heatedand combined with enzymes to promote achemical reaction. The result was corn syrup.Com syrup has quickly replaced 25% of the23-billion pounds-per-year sucrose market inthe United States. Many manufacturers ofprocessed beverages, syrups, and confectionsnow rely on corn syrup and high-fructose cornsyrup. Besides low costs, these sweetenershave relatively reliable supplies.

Cross-linked starches are another type ofmodified starch. Cl'oss-linked stal'c11 ischanged chemically so cross-bonding or cross­linking takes place between starch molecules.The resulting molecular network is moreresistant to acids and separation in the freez­ing and thawing process. Potato starch willbreak down if acid is added, but modified(cross-linked) potato starch will not. Cross­linked starches will not continue to thickenduring storage and do not leak water onstanding. They are used by food scientists toproduce baby foods, salad dressings, cream­style corn, and fruit pie fillings.

Modified food starches can be made to theexact specifications needed for a food product.They have made many new food productspossible. Many frozen entrees and instant,quick-mix foods would not be possible with­out modified food starches. Modified foodstarches are used to stabilize condiments,sauces, and relishes. They increase the shelf

Unit III Organic Chemistry: The Macronutrients

life of many foods thus reducing food costs.These manufactured starches also reduceprocessor's dependence on anyone graincrop. This helps prevent shortages and keepsfood prices more constant.

Thickening Sauces with StarchStarch can be added to liquid to make a

thickened sauce in three basic ways. In eachmethod, starch granules are separated to pre­vent lumping. If starch granules combine intoa lump, the outer granules will swell. This pre­vents water from reaching the granules in thecenter of the lump. The lump remains dry inthe center, the starch loses thickening power,and the sauce becomes lumpy. The methodused to prevent lumping depends on the dish,the desired flavor, and personal preference.

Cold Water PasteOne method for preventing lumps when

thickening a sauce with starch is to form acold 'water paste. This involves quickly stir­ring the starch while adding at least an equalamount of cold water. Continue stirring untila smooth paste is formed. Once the starchgranules are evenly distributed, more liquidcan be added and the sauce can be heatedwithout lumping. This method can be used tothicken soup stock or milk gravy. It can also beused to make a gravy from broth.

Starch and FatA second method for preventing lumps in

starch-thickened sauces is to separate thestarch granules with melted fat. An equalamount of starch is added to heated fat.Once the starch is stirred into the fat, the liq­uid can be slowly added. Constant stirring isnecessary to keep the sauce smooth. Thismethod is used in making white sauce andgravy from meat drippings.

Professional chefs often thicken soups andsauces with prepared buerre manie. Buerrel1tanie is a ball of equal amounts of solid fatand starch mixed together. These balls can beadded to hot soups to thicken the broth. Theheat of the broth melts the fat. This allows thestarch granules to disperse into the broth withlittle risk of lumping. The French use this

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins

Technology TidbitModified Corn Starches

205

Instant pudding thickens withoutcooking because it contains pregela­tinized starch.

To manufacture pregelatinizedstarch, a starch slurry is heatedto above the gelatinization point.The slurry is carried in a troughbetween two heated horizontalrollers. The heated slurry driesto a thin film on the rollers. Thedried starch film is scraped offas the rollers turn. The driedstarch is then ground into apowder.

The starch in the powder hasalready been heated to its gela­tinization point. Therefore, it willthicken within minutes of beingrehydrated. This thickening with­out heating is used for instantpuddings, pie fillings, and com­mercial cake frostings.

To manufacture acid-modifiedstarch, a slurry of corn or waxymaize is mixed with HCI or sulfu­ric acid. The mixture sets for 6 to24 hours at 25°C to 55°C (77°Fto 131°F). The mixture is neutral­ized with soda ash or diluteNaOH. The mixture is then fil­tered and dried.

This type of starch is used tomake gummy candies. Thestarch forms hot concentratedpastes that gel firmly on cooling.The cooled pastes are translu­cent and have a chewy texturethat remains stable.Source: Fennema, O. FoodChemistry. 2nd Ed, Rev. & Exp. Dekker,1985 pp.'18-'19.

method to make soups and sauces. The ballscan be prepared ahead of time. They will keepin the refrigerator for several days or in thefreezer for several months. See 9-9.

Cajw1 cooks who prepare foods from ruralSouthern Louisiana commonly use a roux tothicken sauces and gravies. A raux is a gravythat has had the staTch heated in fat until itturns a rich red-brown. Toasting the flouradds a distinctive flavor to the gravy or sauce.A roux needs low heat and constant stirringduring the browning process. This preventsuneven browning and reduces the likelihoodof burning the flour. Extended heating willreduce a starch's thickening power. Therefore,a raux can have slightly more starch than fat(75 mL Pf, cup] flour to 50 mL P/, cup] fat). Itwill also take more flour per cup of liquid tothicken the mixture. Continuous stirring after

9-9 One way to thicken a stew or soup is to add abuerre manie. The ones pictured are made from2 parts flour and 1 part shortening.

thickening will l'UptLLl'e starch cells in anythickened sauce and cause the sauce tobecome thinner.

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Cooking TipIf your sauce is too thick, add more liquid.If your sauce is too thin, add one or twobuerre manie or add a cold water paste. Ifyour sauce is lumpy, try a whisk to breakup the lumps. A gravy stirrer with a spring­like end can also help eliminate lumps.

Starch and SugarThe third method for avoiding lumps in

sauces thickened with starch first requiresthoroughly combining the starch and sugar.Then gradually add the liquid. If the liquid isadded slowly with constant stirring, lumpswill have little chance to form. This is becausethe sugar helps separate the starch granulesand keep them from sticking together. Thismethod of preventing lumping is used in mostsweet sauces and puddings. The presence ofsugar also helps reduce the viscosity of theliquid. The resulting gel will be tender andsmooth rather than rigid.

Nutritional Impact of ComplexCarbohydrates

Starches can be divided into two cate­gories: digestible starches and indigestiblefiber. Like sugar, digestible starches provide4 calories of energy per gram. Starch is themost abundant and economical source of calo­ries available to people. Carbohydratesshould provide over half of your calories eachday. Carbohydrates in the form of glucose arethe only energy source the brain can use. Thebody is very efficient at changing starches andsugar to energy.

Excess carbohydrates are stored as glyco­gen. Glycogen is larger, heavier, and morebranched than most amylopectins. The morebranched the glycogen is, the more glucoseunits the body can release at a time. The bodywill usually use up glycogen stores in a littleless than two hours of vigorous exercise. Thisis why it is so important to eat carbohydratesevery 4 to 6 hours when you are awake. If youskip breakfast, your body will slow brain andorgan functions to conserve the availableglycogen. Students who skip breakfast will

Unit III Organic Chemistry: The Macronutrients

have a harder time concentrating and willremember less of what they hear.

The size of glycogen stores depends on theamount of carbohydrates consumed and howfrequently you exercise. Muscles that use upglycogen stores in exercise will increase theirfuture storing ability. The more you exercise,the more energy the muscles will store. Theless you exercise, the less glycogen will beavailable when you need it.

Glycogen is stored in two locations. Theliver stores about one-third the total glycogen.It is readily available to the brain and otherorgans when blood glucose levels drop toolow. The muscles store the other two-thirds ofthe glycogen for times of physical exertion.Suppose your body does not need carbohy­drates for immediate energy and your glyco­gen stores are full. In this case, your body willturn the excess carbohydrates into fat.

If excess starch becomes fat, why not eat ahigh-fat diet? One reason has to do with thedifferences in the way the human body usesstarches and fats. The body does not need fatto properly use starch. However, carbohy­drates must be present to combine with fatfragments for the body to use fat for energy. Ifcarbohydrates are not present, the body goesinto ketosis. Ketosis is the process of burningfat without carbohydrates. This process pro­duces ketone bodies as a by-product. Highlevels of ketones over an extended period willdamage the kidneys and interfere with thebody's normal acid-base balance. High levelsof ketones during pregnancy can cause braindamage and irreversible mental retardation inthe fetus.

Fiber t Bran, and BulkMuch has been written about how people

in the United States need to increase the fiberin their diets. Fiber, bran, and bulk are all termsused on labels and in advertising that refer toindigestible carbohydrates. As you read inChapter 8, the type of glucose determines thedigestibility of the starch. A molecule com­posed of beta-glucose is indigestible and isknown as cellulose.

Cellulose provides bulk in the diet. Ithelps you feel full and aids in digestion andelimination. Many dietary polysaccharides,

d

Chapter 9 The Complex Carbohydrates: Starches, Cellulose, Gums, and Pectins 207

mainly from the cellulose components of cellwalls, are insoluble and indigestible. Thesources of fiber in your diet are vegetables,fruits, and grains, 9-10. Cellulose gives crisp­ness and mouth feel to many foods. Somecommercial bakers add cellulose to breadproducts to improve the water-binding abilityof the flour. This slows the staling rate ofbread and has been found to improve loaf vol­ume in preparation.

Nutritional Functions of StarchesThe main function of carbohydrates is to

provide energy for bodily functions. In addi­tion to energy, carbohydrates

.:. provide bulk for the digestive processes

.:. tie up bile acids, decreasing theirreabsorption

.:. lower cholesterol levels in the blood,retarding atherosclerosis

.:. promote the utilization of fat

Carbohydrates are so important that theirmain food sources represent the largest por­tion of the USDA's MyPyramid symbol. TheDietary Guidelines recommend choosingfiber-rich fruits, vegetables, and whole grainsoften. Six ounce-equivalents of grains, twocups of fruit, and two and one half cups ofvegetables per day are recommended for a2,OOO-calorie food plan.

9-10 Fresh fruits and vegetables are excellentsources of dietary fiber.

Food FeatureThe Trouble with Beans

Dried peas and beans, whichare called legumes, are excellentsources of many nutrients.However, some people avoid eat­ing these nutritious foods due toconcerns about gas. Beans con­tain the fiber tetrasaccharidestachyose. Like other types offiber in the diet, tetrasaccharidestachyose is undigested when itreaches the large intestine. Oncein the large intestine, multiflorawork to attack and break downfiber. (Multiflora are bacteria thatnaturally live in the intestines.)By-products of this process

include acetic and lactic acids. Ifpresent in large enough quanti­ties, these acids can have a laxa­tive effect. Another by-product ofthe multiflora attack is gas.Excess gas produces flatulence,or unwelcome noise and odor.

One way to minimize problemsfrom eating beans is to take aspecial digestive enzyme. Theenzyme product is now avaiiablein many grocery stores and phar­macies. It works by breaking upthe stachyose in the stomachand small intestine. This preventsthe high levels of acids and gas

from deveioping. A drawback tothe enzyme product is that itreduces the positive effects offiber in the body. Use of thisproduct also increases thecaloric value of beans.

Another way to avoid problemsfrom eating beans is to maintaina consistent intake of high-fiberfoods. This promotes the growthof bacteria that will digest fiberwith minimal distress. Eatingyogurt also helps promote growthof beneficial bacteria.

A high carbohydrate diet is especiallyimportant for cross country runners.

.:. Finish eating 3 to 4 hoursbefore competition to keepdigestion from interfering withmuscle performance.

.:. Eat a high-carbohydrate mealwithin two hours after exer­cise to increase glycogenstorage by as much as 300%.

.:. During extended periods ofexercise, consider consum­ing a sports drink instead ofwater. Such drinks aredesigned to replace elec­trolytes and fluids whilerestoring glucose levels forenergy.

Maximum Endurance Times

57 minutes

114 minutes

167 minutes

Unit III Organic Chemistry: The Macronutrients

'.' Never restrict complexcarbohydrates.

.:. Increase exercise intensitywitholll restrictingcarbohydrates.

.:. During the week before com­petition, gradually cut backon exercise.

.:. Eat a very high carbohydratediet for several days beforecompetition.

.:. Rest the day beforecompetition.

Athletes who compete for lessthan 90 minutes at a time needonly a high-carbohydrate dietevery day.

Tips.:. Drink at least 8 glasses of

water a day..:. Choose a pregame meal that

is light and easy to digest.This meal should provide300 to 1,000 calories. Itshould provide fluids, plentyof carbohydrates, and littlefiber. Carbohydrates are eas­ily digested. Fiber absorbswater and can cause diges­tive discomfort. The best foodchoices are breads, pota­toes, pasta, and fruit juice.

Nutrition NewsCarbohydrates and theAthlete

Types of Energy Foods

55% carbohydrates, 45% fat and protein

83% carbohydrates, 17% fat and protein

94% carbohydrates, 6% fat and protein

Research indicates that dietshigh in complex carbohydrateswill improve an athlete's perform­ance. This kind of diet is knownas carbohydrate loading. A clas­sic study compared three groupsof runners eating varyingamounts of carbohydrates.Members of one group con­sumed 55% ot their calories fromcarbohydrates. A second groupate 83% of their calories fromcarbohydrates. The third grouphad 94% of thei r calories fromcarbohydrates.

First and most importantly,athletes need nutrient-densefoods. These are foods that arehigh in vitamins and minerals forthe energy provided. Athletesshould choose highly processedfoods with care because pro­cessing often removes nutrients.Reading the Nutrition Facts panelcan help athletes choose prod­ucts that are nutrient dense.

Eat for energy. The more youexercise, the higher your calorieneeds. If you compete for 90 ormore minutes at a time, heed thefollowing recommendations:.:. Eat a high carbohydrate diet

during training.

Source: Sizer, Frances and Whitney, Eleanor, Nutrition: Concepts and Controversies, 1997, pp. 383-384.

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