SomeMattersChemSurf

2 ChemMatters, APRIL 1999

A Light of a Different Color

www.chem-inst-can.org/ncw/96tonich2o.htmlThis site, presented by The Chemical Institute of Canada, offers a simple, at-home activity entitled Fluorescence Emission from Tonic Water. If you have ablack light, you can explore some interesting quinine chemistry.

www.users.interport.net/~kenx/You don’t need a black light to view this colorful site, created by KennethColosky, displaying pictures of fluorescent minerals. There are plenty of exam-ples and many links to other sites.

www.glogerm.com/Find out more about Glo Germ and why it is an important product to help withhandwashing and infection-control education.

Spoiled Produce—The Long and the Short of It

ethylenecontrol.com/Ethylene Control, Inc., sponsors this extensive Web site. The “About EthyleneGas” button lets you decide whether to store apples and tomatoes in the samecontainer and explains what happens to cucumbers when placed near a nec-tarine.

www.tryfridgefriend.comEverything you wanted to know about FridgeFriend is located at this site. There are links toresearch sites about ethylene gas and an added ben-efit of links to their patents on the U.S. PatentOffice site.

A Calorie-Free Fat?

www.olestra.com/This is the official site for Olean’s brand olestra. Aparticularly nice feature of this site is a well-orga-nized site map that has links to a variety of informationand data.

www.acsh.org/publications/olestra/index.html#1Read about concerns related to olestra at the American Council on Science andHealth site. It also has interesting discussions about other food safety and nutri-tion issues.

The Case of the Missing Caffeine

www.ico.org/The International Coffee Organization has a comprehensive Web site that pre-sents data about coffee, caffeine, and decaffeination processes.

www.phasex4scf.com/scf.htmYou will find an introduction to supercritical fluids at this Web site sponsored byPhasex Corporation, a company specializing in supercritical fluid processes.

Putting a High Grade on Degradables

www.pbs.org/weta/planet/exploringthemes/Planet Neighborhood, produced by WETA-TV in Washington, DC, examines theway people use down-to-earth concepts and innovative technologies to preservethe environment. There is an interesting discussion on garbage and green chem-istry at its site.

www.bedps.org/There is a Bio/Environmentally Degradable Polymer Society, and it has a Webpresence. This is a good place to find out more about BEDPs from the peopleconducting the research.

Should food be irradiated?

www.gmabrands.com/irradiation/instruct.htmThis is a great Web site if you have multimedia capability on your computer. TheGrocery Manufacturers of America has produced a short but interesting videotour of a food irradiation plant that can be viewed online.

A Round of Thanks

T his issue brings to a close another year ofChemMatters. This is our opportunity to thank

you for an exciting and informative year. We are par-ticularly pleased that so many readers have beeninvolved in the production of ChemMatters.

This year, we say goodbye to three policyboard members who have completed their terms:Carol Brown, St. Mary’s Hall, San Antonio, TX; FrankDarrow, Ithaca College, NY; and Elise Hilf-Levine,Pleasantville High School, NY. These three dedicatedprofessionals have been an important part of theChemMatters family, and we wish them luck withnew projects in their futures.

We must also thank the following teachers andstudents who have been making the effort to com-plete evaluation forms.

• Kelly Choy and students, MinnedosaCollegiate, Manitoba, Canada

• Michael Clemente, Carlson High School, Gibraltar, MI

• Susan Cooper and students, LaBelle High School, FL

• Lawrence Flick, Oregon State University, Corvallis• Regis Goode and students, Ridge View

High School, Columbia, SC• David Holder and students, Oklahoma School of

Science and Mathematics, Oklahoma City• Lisa Johnson and students, Cherry Creek

High School, Englewood, CO• Roger Knight, DeSales High School,

Louisville, KY• Steven Long and students, Rogers

High School, AR• Warren Puhl and students, Menomonie

High School, WI• Ann Marie Reardon and students, Dwight

Englewood School, NJ• Barbara Sitzman and students,Chatsworth

High School, CA• Maria Sperekakos and students, Loyola Academy,

Wilmette, IL• Debbie Warren and students, Medford Senior

High School, OR• Sue Weidkamp and students, Glencoe High

School, Hillsboro, ORWe welcome new teacher reviewers and student-teacher review teams each year.

Finally, we thank the many readers who takethe time to let us know how we are doing. Asalways, comments from you are very important. You can e-mail them with your name and schoolaffiliation to chemmatters@acs.org, or write toChemMatters, American Chemical Society, 115516th St., NW, Washington, DC 20036–4800.

CM Staff

ChemMatters, APRIL 1999 3

Vol. 17, No. 2 APRIL 1999

Production TeamMichael Shea, EditorCornithia Harris, Art DirectorLeona Kanaskie, Copy EditorBecki Weiss, Copy Editor

Administrative TeamMichael Tinnesand, Department

Head, K–12 ScienceBob Sargent, Manager,

Graphic ServicesElizabeth Wood, Manager,

Copy Editing ServicesRobin Green, Program AssistantAllegera Waters, Program Assistant

Technical Review TeamSeth Brown, University of Notre

Dame, INFrank Cardulla, Niles North High

School, Skokie, IL

Robert Van Milligan, Brunswick HighSchool, ME

Teacher’s Guide TeamPaul Groves, EditorMarlin Beitzel, ActivityDorothy Mann Lamb, Puzzle

Division of Education andInternational ActivitiesSylvia Ware, DirectorJanet Boese, Assistant Director for

Academic Programs

Policy BoardStanley Pine, Chair, California State

University, Los Angeles, CADavid Bergandine, University

Laboratory High School, Urbana, ILSusan Cooper,LaBelle High School, FL

Lawrence Flick, Oregon State University, Corvallis, OR

Tim Graham, Roosevelt High School, Wyandotte, MI

ChemMatters (ISSN 0736-4687) ispublished four times a year (Oct.,Dec., Feb., and Apr.) by theAmerican Chemical Society at 1155 Sixteenth St., NW,Washington, DC 20036–4800.Second-class postage paid atWashington, DC, and additional mailing offices.Canadian GST Reg. No. 127571347

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The American Chemical Societyassumes no responsibility for thestatements and opinions advancedby contributors. Views expressed arethose of the authors and do not nec-essarily represent the official positionof the American Chemical Society.

All rights reserved. No part of thispublication may be reproduced,stored in a retrieval system, or trans-

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© Copyright 1999,American Chemical Society

®

COVER PHOTO BY MIKE CIESIELSKI

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CM PuzzlerHave traditional methods of decaffeinationground to a halt? Find the answer in this issue of ChemMatters.

DEPARTMENTS

ChemSurf 2SomeMatters 2A Round of Thanks

ChemSumer 7Spoiled Produce—The Long and the Short of ItHunting for food in the refrigerator can sometimes be a rotten experience.Can chemistry design a method to preserve our produce longer?

MysteryMatters 12The Case of the Missing CaffeineOne student wondered how to take the caffeine out of coffee. Supercritical fluid extraction is one clue that surfaced.

As a Matter of Fact 16Should food be irradiated?Food irradiation is a hot and, many believe, safe food-handling process.Begin to formulate your own opinion with this chemical perspective. FEATURES

A Light of a Different Color 4Black light is an illuminating experience. Now you candiscover the chemistry of this phenomenon.

A Calorie-Free Fat? 9Confused about olestra and Olean? Dig into this article todigest the chemical information on this fat substitute.

Putting a High Grade on Degradables 14The development of biodegradable polymers is a perfectexample of chemistry at work, using the four Rs of “greenchemistry”—rethink, replace, reuse, and recycle.

4 ChemMatters, APRIL 1999

A piece of white cloth is placedunderneath a strange-looking pur-plish light. It glows brilliantly.

White powder placed underneath this samelight emanates a brilliant radiance. A beakerof green fluid glows with a supernaturalhue. Is this the stuff of science fiction?Hardly. The above phenomena are all aresult of a special type of light known as ablack light.

UV connectionThe black light gets its name because it

emits a type of light that you cannot see.Actually, most types of light, or electromag-netic radiation, are invisible to the naked eye(see figure opposite page). Our eyes candetect only a tiny sliver of the entire electro-magnetic spectrum, appropriately referred toas the “visible” region. A black light gives offradiation in the form of ultraviolet (UV) light.Because most sources of UV light emit violetlight along with the UV light, the luminositygiven off by a black light source appears tobe violet. However, the actual UV light that isemitted is invisible to the naked eye.

For convenience purposes, UV light isoften divided into three categories: UVA,UVB, and UVC. A black light makes use ofUVA radiation—the longest UV light wave-length and very close in frequency to visibleviolet light. Of the three types of UV light,UVA carries the least amount of energy perphoton, small packets in which light carriesits energy. UVA is thus considered the leastharmful to humans. However, care shouldbe taken never to look directly at a blacklight, because prolonged exposure can beharmful to the eyes.

Other types of UV light have shorterwavelengths and thus have higher frequen-cies. They carry more energy per photonand can cause greater harm to living things.UVB light is responsible for sunburns,which have been linked to skin cancer andeye damage. Tanning salons use primarilyUVB radiation. UVC light is used to sterilizesurfaces and medical instruments. Becausethese rays are so energetic, they can killbacteria and viruses. Some schools sterilizesafety goggles with special cabinets that useUVC radiation.

FluorescenceCertain objects, when placed under a

black light, appear different than under anordinary white light. They may appear to bebrighter or emit a completely different coloraltogether. Specialized pigments withinthese substances have the amazing ability toabsorb energy of one wavelength and thenreemit it as energy of a different wavelength.This absorption of UV light and emission asvisible light is known as fluorescence.

In the simplest case where fluores-cence occurs in atoms, a black light emitsphotons of energy that are absorbed by elec-trons of the atom. These electrons are ini-tially in the ground state, which is the lowestpossible energy level that the electrons canoccupy. However, upon absorbing a photonof UV energy, these electrons jump up to ahigher energy level. This higher energy levelis known as the excited state. However, thisexcited state is extremely unstable and onlytemporary. The electrons quickly return tothe ground state, but as they do, they “stopoff” at intermediate energy levels. With eachstop, they have a choice between dissipatingtheir excess energy as heat or emitting aphoton of light. Because the total energythey absorbed all at once is now beingemitted in more than one step—or dissi-pated as heat—each emitted photon hasonly a fraction of the energy of the initial

By Brian Rohrig

UV light that was emitted. These lowerenergy photons also have a lower fre-quency—in the visible region of the spec-trum, not the UV region.

Most fluorescent objects actually con-tain fluorescent pigments that are complexmolecular substances. Fluorescence in thesemolecules is a more complex process thatinvolves both the vibration of the moleculeand changes in the electronic configuration.

Because of fluorescence, substancesoften appear to be a different color under ablack light. The wavelengths of the emittedblack light may not correspond to the sub-stance’s color because the substanceabsorbs the light. The incident light from ablack light is invisible to us, but a fluores-cent pigment emits visible light. Thus, wesee more light coming out of a fluorescentobject than out of other nearby ordinaryobjects; hence, the glow. Because theseelectrons rapidly fall back to the groundstate, once a black light is removed from afluorescent object, the object instantlyceases to fluoresce.

A typical fluorescent lamp operates underthis same principle; therefore, its name. Thefluorescent lamp emits short-wave UV light,which is absorbed by white fluorescent pow-ders known as phosphors, lining the inside ofthe fluorescent tube. As the UV light strikesthese phosphors, it is emitted as the white,

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visible light that you see. Without this phos-phor coating, the lamp would emit harmfulshort-wave UV light.

PhosphorescenceA property closely related to fluores-

cence is that of phosphorescence, the prop-erty of “glowing in the dark”.Phosphorescent substances continue toglow after a light source is removed,whereas fluorescent substances do not.Objects that glow in the dark do so becausethey contain molecules that have the abilityto absorb energy quickly and then emit itslowly. This is because the excited electronsremain so for a period of time before gradu-ally falling back to ground state. Once all ofthe electrons fall back to ground state, thesubstance ceases to glow. That is whyobjects that glow in the dark must be fre-quently “charged up” with an outside lightsource to reexcite the electrons. Glow-in-the-dark objects appear brilliant under blacklight, because UV light is more than suffi-cient to excite these substances.

TriboluminescenceAnother closely related phenomenon is

triboluminescence. To demonstrate tribolu-minescence, go to a completely dark roomwith a Wint-O-Green Lifesaver and a pair ofpliers. If you crush the Lifesaver with the pli-ers, it will give off sparks of bluish light,which is a result of breaking the sugar crys-tals in the candies. The crystals tend to breakalong planes containing positive charges onone side and negative charges on the other.These negative charges result from excesselectrons, and the positive charges, from adeficiency of electrons. When a crystal isbroken, the negative charges try to bridgethis gap between the two planes. These elec-

trons primarily emit energy in the form of UVlight. Because Lifesavers are fluorescent,they have the ability to absorb this UV lightand emit it as visible light. Thus, the lightyou see when a Wint-O-Green Lifesaver iscrushed is primarily this absorbed UVlight—emitted as visible light.

Fluorescent usesMany household substances will fluo-

resce brilliantly when placed under a blacklight. There are fluorescent markers, paints,and crayons. Most white copy paper is fluo-rescent. Many stamps, stickers, and labelsglow beautifully under a black light. Blacklight-sensitive posters, jewelry, and clothingare available in specialty shops. You caneven buy fluorescent toothpaste, shampoo,lipstick, and fingernail polish. If you go toan amusement park, you will likely get yourhand marked with a fluorescent stamp,barely visible to the naked eye yet highlyvisible under a black light. The newlydesigned U.S. paper currency contains anti-counterfeiting strips that are only visibleunder a black light.

Fluorescence is used to make new andold clothes appear brighter. Most laundrydetergents—liquid and powder—fluorescevery brightly because of fluorescers that areadded to them, comprising up to 1% of thetotal formulation. This is how laundry deter-gent advertisements can truthfully promiseto get your clothes “whiter than white”.Although new clothing is manufactured withthe fluorescers already intact, the concentra-tion decreases with washing and wearing.Washing with detergents will restore these

The electromagnetic spectrum is composed ofelectromagnetic radiation over a wide range ofwavelengths. The visible and near-visible UVspectrums are only a small fraction of the entirespectrum.

When you crush a Wint-O-GreenLifesaver, it gives off a burst of blue light. You can see thisdemonstration of triboluminescenceonly if you first let your eyes adaptto a dark room.

6 ChemMatters, APRIL 1999

Brian Rohrig is a chemistry teacher at Aurora High School, OH. His feature article “The Demise of the‘Heavy Metal’ Artists” appeared in the December 1998 issue of ChemMatters.

REFERENCESelinger, B. Chemistry in the Marketplace, 5th ed.; Harcourt Brace: Sydney, 1998.

RELATED ARTICLESBaxter, R. Sun Alert. ChemMatters 1998, 16 (2), pp 4–6.Sweeting, L. M. Light Your Candy. ChemMatters 1990, 8 (3), pp 10–12.

How Well Do You Wash Your Hands?

A commercially available substance, known as Glo Germ, is an excel-lent example of a practical use of black light. It is available in liquidform as a bright orange, oil-based substance. A small amount is

squirted on the hands and then rubbed around thoroughly. When placed under ablack light, the hands glow a brilliant orange. After washing, the hands areagain placed under a black light, and it is evident where they were not washedproperly. The hands are then scrubbed again until all traces of the Glo Germ areno longer visible under the black light. The most commonly missed areas arearound the fingernails, the forearms, and between the fingers. Medical person-nel are often trained in proper handwashing technique using this method.

Glo Germ is also available as a white powder. Under a black light, thepowder is highly fluorescent. A small amount of powder is placed on the hands,and everything the hands touch is likewise contaminated. It is easy to see how“germs” can be so easily transmitted. Just one student with the Glo Germ pow-der on his or her hands can “infect” an entire class by shaking hands withanother student who, in turn, passes the Glo Germ onto someone else.

fluorescers. Because all clothing containsresidual detergent, some types of clothingmay appear to be especially brilliant in brightsunshine, which is more than 10% UV light.

Many liquids are also fluorescent.Antifreeze appears bright green under ablack light, and quinine, found in tonicwater, is highly fluorescent. Pouring thetonic water under a black light can create aninteresting effect. If salt is added to thetonic water, its fluorescence will decrease,because the chloride ion will react with thequinine molecule to reduce the movementof its electrons between levels. Its ability torelease energy as light, rather than heat, willbe reduced. One can say that the fluores-cence will be “quenched”.

Fluorescence in the workplace

Substances exhibiting fluorescenceunder a black light have many practicaluses. For example, a solution of fluorescein,one of the most highly fluorescent sub-stances in the world, can be used to detect ascratch on the cornea of the eye. A fewdrops of a very dilute solution are placed inthe eye, and when viewed under a blacklight, this highly fluorescent substance willadhere to a scratch on the cornea, making iteasier to see.

Forensic scientists often use blacklights at a crime scene to test for evidenceof a crime. Many types of bodily fluids arehighly fluorescent. Semen, for example, canbe detected under a black light, which mayhelp determine whether a rape has takenplace. The cleanliness of restroom facilitiescan also be checked with a black light,

because urine contains highly fluorescentcompounds (see How Well Do You WashYour Hands?).

Fluorescence is an important tool thatgeologists use in mineral identification.Many minerals that appear unimpressiveunder ordinary white light exhibit spectacu-

lar displays of color under UV light. Somecommon fluorescent minerals are fluorite,quartz, sodalite, and willemite.

Experiment with other household prod-ucts, and you will be amazed at the manysubstances all around you that display vividfluorescence under black light.

After being washed, theyare placed under a blacklight again.

It is evident where they were not washedproperly—most commonly missed areas arearound the fingernails and between the fingers.

• •• •Using plenty of soap and ascrub brush—hands arewashed.

When placed under a black light, handscovered in Glo Germ oil glow a brilliantorange.

ChemMatters, APRIL 1999 7

ChemSumer

specifically receptive organs or tissues. Human hormonesinclude insulin, estrogen, and testosterone. Ethylene, how-ever, is also found in the external environment. Bonfiresand automobiles emit ethylene, for example. When plantsare exposed to these kinds of emissions, their biochem-istry can be dramatically affected. These effects caninclude accelerated growth, altered growth, or both, aswell as more rapid ripening of fruits.

Time ripens all things?By the 1930s, the effects of ethylene on various

plants, fruits, and flowers were extensively studied, andthe use of ethylene as a commercial ripening agent hadbeen established. Today, many companies manufactureequipment that allows growers to hasten the ripening oftheir produce. These products range from “gassingrooms”, where large quantities of produce can be treated,to small containers in which produce is ripened as it isbeing transported to the point of sale.

Unfortunately for the consumer, the appearance ofthe produce typically changes much more than its taste.Taste is contingent on the manufacture of sugars or othersubstances, processes that are not sufficiently acceleratedby exposure to external ethylene. Green bananas can bemade to turn yellow quickly, but they still taste “green”.

Because fruits and vegetables produce ethylene,which, in turn, accelerates their ripening, placing fruit in asealed container will often cause it to ripen faster. This is

How can tomatoes that look so good have so littletaste? The answer may be that these winter-freshtomatoes did not naturally ripen on the vine.

Instead, they were probably picked while still green and artifi-cially “ripened” using ethylene gas. This procedure improvedtheir appearance but had little effect on their flavor.

Ripening by gasEthylene gas (C2H4) consists of two carbon atoms and

four hydrogen atoms. Each carbon is bonded to two hydrogens,and the carbon atoms are joined by a “double bond”. This is dif-ferent from a single bond because the two carbons share fourelectrons between them instead of two (see Figure 1).

Ethylene functions as a hormone in plants. Hormonesare biologically active chemicals that affect the functions of

Spoiled Produce—The Long and the Short of It

Figure 1. Molecular model representation of an ethylene (ethene)molecule. This gas is produced by many fruits and vegetables andtriggers the ripening process.

By Frank Cardulla

You arrive home from school—your stomach begging for a snack. Youopen the refrigerator, rummage around,and spy thinly sliced lunchmeat, fresh

bakery bread, honey mustard, and somejuicy red tomato slices. You build a sand-wich and take a bite expecting to savor themix of these wonderful flavors. But some-thing is wrong. Even though the tomatoes

look fine, they are tasteless!

8 ChemMatters, APRIL 1999

the idea behind placing pieces of unripe fruitin a closed paper bag. The ripening fruitproduces ethylene that is trapped in the bagand thus accelerates the ripening process.

Fruits and vegetables vary widely inboth the amount of ethylene they produceand in their sensitivity to it. Some, such asradishes, sweet corn, and cherries neitherproduce much ethylene nor are they sensi-tive to its presence. Others, like apples, apri-cots, avocados, nectarines, peaches, andpapayas are high producers of ethylene andalso highly affected by its presence. Placingthese fruits in a paper bag can have a signif-icant effect. Brussels sprouts, broccoli, cau-liflower, and cabbage—low producers ofethylene—are, however, greatly affected byits presence. Storing these in the same binwith high producers of ethylene may havean adverse effect. So, it does matter whereyou put food in your refrigerator!

The ripest fruit falls first

Although at times it may be desirableto hasten the ripening of produce, often theopposite is true. Produce must be kept frombecoming overripe or rotten while it isshipped, stored, delivered to market, sold,taken home, and then kept until it is eventu-ally consumed. Produce is often shippedand stored in a somewhat confined andsealed environment, leading to a buildup ofethylene which, in turn, can cause the pro-duce to spoil. Techniques have been devel-oped to remove much of this ethylene fromthe atmosphere surrounding the produce.

One obvious way of removing ethylene

would be to continually replace or filter theair that surrounds the produce. Large com-mercial filtering systems have beendesigned and built to do this. They canreduce the ethylene gas up to 75%.

But what can be done once the pro-duce is packed into small shipping boxes tobe sent to your local supermarket? A com-pany called Ethylene Control believes it hasthe answer. It has developed small packagescalled sachets—about the size of teabags—that contain pellets of zeolite, a porousmaterial with an appearance and texturesimilar to pumice stone or brick. The porousnature of zeolite means that a relativelysmall pellet has a large surface area. Thezeolite is saturated with potassium perman-

ganate (KMnO4)—a purple solid and anexcellent oxidizing agent, a substance thatgains electrons during an oxidation–reduc-tion reaction. KMnO4 has an affinity forcompounds, like ethylene, that contain car-bon–carbon double bonds. It can oxidizeand therefore remove ethylene.

A sachet containing KMnO4-impregnatedzeolite is placed in each box of produce. TheKMnO4 partially oxidizes much of the C2H4produced by the produce. Because the ethyl-

ene levels are decreased, the produce doesnot overripen or rot as it is shipped.

Fruits of the earthBut what can be done to keep fruits

and vegetables from rotting once you getthem home? There are a few “commonsense” rules. The old phrase “One bad applespoils the whole barrel” is not just folklore.Many rotting fruits emit large amounts of

ethylene, which, in turn, cause the remain-ing fruit to ripen and rot faster. Overripefruits or vegetables should be removed fromyour refrigerator. Do not store fruits andvegetables together; fruits tend to producelarge amounts of ethylene, and vegetablestend to be sensitive to ethylene. Make sureall your produce can “breathe”. Do not storeproduce in a sealed bag. If it is encased in asealed bag when purchased, punch a fewholes in the bag to let any ethylene escape.

There is a consumer version of thezeolite sachets called

Fridge Friend. When youplace a package ofFridge Friend in yourrefrigerator, it oxidizes

much of the ethyleneproduced by fruits or veg-

etables—keeping them fresh.The next time you go to the produce

section of your supermarket, ask yourself“Was any of this produce artificially ripenedwith ethylene?” “Has ethylene been removedfrom the produce’s environment so that itcan reach the store without being overripe?”If you do not intend to consume the producerelatively quickly, think about how you shouldstore it, and if you should also purchaseFridge Friend to help extend its useful life.

Fridge Friend or Foe?

Does Fridge Friend really work? Carefully controlled tests conducted by independent

testing agencies appear to confirm the claims of the manufacturer. In a much less

controlled test, two apricots were placed in shoeboxes, one with

Fridge Friend and one without. After nine days, the fruits supported the

Fridge Friend theory.

The same test was conducted with several other fruits and vegetables.

In some cases, little difference was noted; however, in at least one case, a

nectarine stored with Fridge Friend appeared to rot more quickly than one

stored without Fridge Friend.

If you would like to test the efficacy of Fridge Friend, there are

several variables that would need to be controlled for the

results to be valid. Think about what they are. Which

fruits or vegetables might be best to use? What is the

best way to evaluate the results?

These nectarines wereplaced in shoeboxes fornine days. In the box witha Fridge Friend sachet, thenectarine is rotten (left), andin the box without the sachet,it still looks fresh.

Frank Cardulla is a high school chemistry teacherat Niles North High School in Skokie, IL. This isFrank’s first article for ChemMatters.

RELATED ARTICLENagel, M. The Fruits of Ethylene.

ChemMatters 1989, 7 (2), pp 11–13.

These apricots were placed in shoeboxes fornine days. In the box with a Fridge Friendsachet, the apricot still looks fresh (left), and inthe box without the sachet, it is clearly rotten.

ChemMatters, APRIL 1999 9

A Calorie-Free

Potato chips—how we lovethem! After all, you can’t justeat one. This snack food

tastes so good partly because it con-tains fats. Fats often make a positivecontribution to the taste and smell offoods as well as their smooth, “slide-down-the-throat” texture. Some sci-entists believe that the reason humans getsuch pleasure from fat-filled food is thatprimitive hunter–gatherer societies hadunpredictable food sources; those with ataste for calorie-rich fat were more likely tosurvive, because fats have more caloriesper gram (9 cal/g) than carbohydrates oreven proteins. Fats, however, are associ-ated with plugged arteries, high cholesterolcounts, and early heart disease. Can weenjoy fat in our snack foods without its dis-advantages?

Snacking advantages

Before a new substance is added to aprocessed food, the manufacturer mustcomplete tests and provide extensive infor-mation about the safety of that additive. In1996, the U.S. Food and Drug Administra-tion (FDA) approved the use of a no-caloriefat called olestra. The manufacturer ofolestra satisfied the FDA, at least to theextent that the FDA approved olestra toreplace regular fats in a limited number ofsnack foods.

Chemically, olestra is a true fat: Ittastes like fat when you eat it, and it cookslike fat in the frying pan. So how can olestrabe promoted as being “calorie-free”? The

answer lies in its chemical structure. Fatsbelong to a class of compounds calledesters, which are made from large organicacid molecules linked with alcohol mole-cules. A typical fat molecule is a combina-tion of a simple three-carbon alcohol calledglycerol with three fatty acid molecules.These fat molecules are called triglycerides(see Figure 1).

Fatty acids are a class of compoundsin which a long hydrocarbon chain has acarboxyl group (–COOH) at one end. Whatmakes one fat molecule different fromanother is usually the nature of the hydro-carbon chain. Many fatty acid hydrocarbonchains contain 16–18 carbon atoms. Some-times, double bonds occur between someof the carbons. If there are no double

bonds, the fatty acid molecule isreferred to as saturated (the hydrocarbonchain contains as many hydrogen atoms aspossible); if there are double bonds, it issaid to be unsaturated or polyunsaturated(see Figure 2).

In humans, an ester (fat), made froman alcohol having three functional alcoholsand three fatty acids, is well digested and

absorbed. Chemists havediscovered, however, thatwhen an alcohol having fourfunctional alcohols and fourfatty acids is used in the for-mation of fat, the digestibil-ity and absorbability of thecompound decreases. Fivecarbon alcohols with fivefatty acids decrease the

digestibility and absorbabilityfurther still, and a six-carbonalcohol (sorbital) attached to

six fatty acids makes the compound com-pletely indigestible.

Sorbitol is expensive, so scientistslooked for a cheaper alternative. Eventually,they came up with sucrose polyesters, aclass of compounds that has as many aseight fatty acids crowded around alcoholsthat hang off a sucrose molecule ring. Thisis the basis for the no-calorie fat, olestra. It

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Glycerol Palmitic Acid Glyceryltripalmitate

+ +

CH3

CH3 3 H2O

CH3

Olean is the trade name for olestra.Proctor & Gamble has invested morethan $200 million in the development ofthe fat substitute. Consumers have beenable to enjoy chips made with olestra,and in the future, they may see icecream, peanut butter, and deep-friedfoods containing it.

Figure 1. Typical fats or triglycerides, like glyceryltripalmitate,are formed by the combination of an alcohol having three functionalalcohols (glycerol) with three fatty acid molecules (palmitic acid).

By Carolyn Ruth

10 ChemMatters, APRIL 1999

is a combination of sucrose (table sugar)and fatty acids (see Figure 3).

Properties of olestraWhy does the body digest and absorb

triglycerides but not a sucrose polyestersuch as olestra? Both types of moleculesare too large to pass unaltered through themucous membrane of thesmall intestine and into thebloodstream. With triglyc-erides, however, anintestinal enzymeknown as lipase actsas a type of molecu-lar scissors, fittinginto slotsbetween thefatty acids andsnipping them apart.But when there are toomany fatty acids clumped tooclose together, as happens with olestra andother types of sucrose polyesters, theseslots are buried, and the lipase cannot doits job (see Figure 4). Thus, olestra passes

through the humanintestines undi-gested.

According tomany people whohave triedolestra-contain-ing snacks,olestra has acreamy,tongue-

pleasingtexture.

Its effect inthe mouth is like

that of any oil, having astrong chemical affinityfor the aromatic com-pounds that give foodits taste and smell. Thecompounds extractthese substances,spread them around thetaste buds, and waftthem up to odor recep-tors in the nose.

The calorie-freeolestra has drawbacks.It triggers stomach and

intestinal discomforts in some people.There is also concern that olestra helpscarry away fat-soluble vitamins such as A,D, E, and K, as well as carotenoids—theyellow, orange, or red pigments found inmany fruits and vegetables. The FDA haslimited approval of olestra only to somesnack foods because they are often noteaten in conjunction with foods that containthese important vitamins and nutrients.Olestra-containing products must also carrya warning label indicating the possibleproblems they can cause. Such warninglabels are not unusual; artificial sweeteners

such as calcium saccharin andaspartame also carry warninglabels.

Ultimately, the public willdecide the destiny of olestra. Willit actually lower the calorie intakeof weight-conscious consumersand also reduce heart disease?Will the side-effects turn peopleagainst it? The current debateabout the value of olestra willcontinue.

Carolyn Ruth is a chemistry teacher at Harbor Creek Junior–Senior High School, PA. Her article “Sizing UpPaper” appeared as a feature article in the April 1998 issue of ChemMatters.

REFERENCESAmerican Chemical Society. ChemCom, 3rd ed.; Kendall/Hunt Publishing: Dubuque, IA, 1998. Coultate, T. P. Food: The Chemistry of Its Components; American Chemical Society:

Washington, DC, 1996.Fackelmann, K. Olestra: Too Good To Be True? Science News, January 27, 1996, p 61.Fake Fat Gets FDA’s Okay. Science News, February 3, 1996, p 68.Kirschner, E. M. Fake Fats in Real Food. Chem. Eng. News, April 21, 1997, pp 19–25.Lemonick, M. D. Are We Ready for Fat-Free Fat? Time, Jan. 8, 1996, pp 53–60.

RELATED ARTICLESBenson, K. D. Fast Fat. ChemMatters 1990, 8 (1), pp 13–15.Smith, T. Distance Running. ChemMatters 1989, 7 (1), pp 4–7.

FATT

Y AC

ID

CORE

COREDIGESTIVE ENZYME

FATT

Y ACID

CH2OHCH2OH

CH2OH

O O

H

HO

OH

OH

H

H

HO

H

H

OH

H

H H

O

Figure 3. Examine the sucrose (C12H22O11) molecule. Noticethat there are eight “–OH” groups on the molecule. Each –OHgroup can react with a fatty acid to create a sucrose polyester.

Figure 4. In the representation of a typical fat (left), a digestive enzyme breaks one of the fatty acidattachments to the core of a fat molecule. In the representation of olestra, so many fatty acids arecrowded around the core of the fat molecule that digestive enzymes cannot find a breaking point.

CH

H

H

C

H

H

C

H

H

C

H

H

C

H

Palmitic Acid

Linolenic Acid

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C C

O

OHH

H

CH

H

H

C

H

H

C

H

C

H

C

H

H

C

H

C

H

C

H

H

C

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C C

O

OHH

H

Figure 2. Palmitic acid is an example of a common saturated fatty acid.Each of the carbons is “saturated” with hydrogen atoms. Linolenic acid isan example of a common unsaturated fatty acid. It contains double bondsmaking the molecule unsaturated.

ChemMatters, APRIL 1999 11

A t least 1,000 new low-fat, reduced-fat, or fat-free products are

introduced each year, and con-sumers of all ages are seekingthem out. Consumers are willingto cut fat as long as the food stilltastes good. That’s where fat sub-stitutes come in.

Products with less fat aren’tnecessarily low in calories, how-ever. Often, there are almost asmany calories in foods that con-tain fat substitutes as there arein the full-fat products. Fat sub-stitutes fall into three categories: carbohy-drate-based, protein-based, and fat-based.

Carbohydrate-based substitutes

Carbohydrate-based substitutes were introduced in the1960s. They replace fat’s bulk and moistness but lack its cookingqualities. Food labels identify these substitutes as dextrins, mal-todextrins, modified food starches, polydextrose, cellulose, andvarious gums. Most of these carbohydrate-based substitutes arepolymers—very large molecules in which thousands of sugarunits are linked together. Fat-free cookies, for example, almostalways contain one or more of the substitutes listed above.

"Gums" are one of the most commonly used carbohydrate-based substitutes for fat. The term "gums" is usually reserved fora group of substances that are obtained as plant extracts or"flours" made from noncereals. The often-used xanthan gum,however, is secreted by a bacterium, Xanthomonas campestris.Commercially, the gum is prepared by growing the microorgan-ism in large-scale fermentation processes. Steps are taken toensure that the final product contains no viable cells of the bac-terium. The enormous molecules of this gum contain between10,000 and 250,000 sugar units. Its backbone is composed ofglucose units linked together, as they are in cellulose, except thatevery other glucose unit in the xanthan gum’s backbone carries aside chain that includes a carboxyl group.

The carboxyl groups give xanthan gum a high affinity forwater. The viscosity (resistance to flow) of a xanthan gum solu-tion in a bottle at rest can be high enough to ensure that even

large, suspended particles donot settle. As soon as the bottleis inverted, however, the sus-pension flows readily out ofthe bottle. Obvious examplesof the use of xanthan gum aresalad dressings with sus-pended particles of herbs.

Protein-based substitutesProtein-based substitutes were introduced in the 1980s.

They are made from whey (the liquid left when cheese is made),protein concentrates, or proteins from egg whites and milk. Theproteins are broken into micrometer-sized particles that slideover each other on the tongue to feel like a hydrophobic (water-fearing) fat. They can’t withstand high heat and, like the carbo-hydrates, do not behave like real fats in a frying pan. Whey isadded to fat-free cheese singles; egg whites are usually used infat-free Fig Newtons.

Fat-based substitutesFat-based substitutes have been developed more recently.

These substitutes are natural fats that have been altered to makethem harder to digest. Olestra is one of the latest and the onlyzero-calorie substitute in this category. Like the full-calorie fats,olestra can be used for frying.

Another fat-based substitute—called by the generic name,salatrim—has about 56% of the calories of traditional fats.Salatrim stands for short- and long-chain acid triglyceride mole-cules. This fat substitute is low in calories, in part because of thelower caloric value of the short-chain fatty acids, and in partbecause the long-chain fatty acids in it are not fully absorbed.

None of the fat substitutes do everything a natural fat mole-cule does, but all of them are acceptable substitutes to mostconsumers in certain foods. The market for fat substitutes issizeable: $42 million in sales of fat substitutes occurred in 1985and $495 million in sales are projected by 2000.

Fat substitutes are divided into three differentcategories. Carbohydrate-based substitutes arefound in many low-fat snack bars, and protein-basedsubstitutes are found in fat-free cheese singles andfat-free Fig Newtons. Fat-based substitutes arerepresented by products containing olestra or Oleanand products such as those made by Entemann’s,which contain salatrim.

SubstitutesFat

12 ChemMatters, APRIL 1999

MysteryMatters

By Kimberly Barstow

The ‘90s seem to represent the coffee decade—complete with now-familiar terms such as cappuc-cino, latte, espresso, and decaffeinated coffee.

Many people across the world prefer “decaf” to regularcoffee because, although the taste is the same, it lackscaffeine—a substance that gives some people the “jitters”.How is the caffeine removed from the coffee bean, whichlooks the same as a decaffeinated bean? How can the cof-fee bean still maintain its flavor?

The decaffeinating tradition

For coffee beans to be labeled “decaffeinated”, atleast 97% of the caffeine must be removed. There arethree primary methods for decaffeination: chemical extrac-tion, the Swiss water process, and supercritical fluidextraction (SFE).

Although all methods of decaffeinating coffee involvethe use of “chemicals”, one process has been traditionallyreferred to as “chemical extraction”, probably because ituses organic solvents that are not typically part of our nor-mal environment. The traditional method offers twoslightly varied options using dichloromethane (CH2Cl2) orethyl acetate (CH3CO2C2H5) as solvents. With both sol-

vents, the beans are first soaked in water to soften themand speed the decaffeinating process. The beans are thensoaked in one of the two solvents, which dissolves the caf-feine in the bean. Once the solvent has removed the caf-feine, the coffee beans are treated with steam. Thisevaporates the organic solvent along with the caffeine.

The process is identical for both solvents, but manycoffee companies prefer to use ethyl acetate to decaf-feinate their coffee. This allows them to label the beans“naturally decaffeinated”, because ethyl acetate occursnaturally in orange rinds and many other fruits. Althoughconsumers may prefer this label, it is misleading. The ethylacetate used is actually synthesized; it is not extractedfrom fruits because it would be too costly.

Both of these commercial methods have a growingnumber of detractors prompting many coffee companiesto turn toward other methods. Opposition arises becausethe solvents used can never be completely removed fromthe coffee beans. The traces left behind, however, arebelow the amounts required for the “decaffeinated” label.Because of the recognized potential hazards associatedwith the use of dichloromethane and ethyl acetate, the U.S.Food and Drug Administration and the U.S. Department ofAgriculture continue to investigate and evaluate any possi-ble dangers that might be associated with the use of thesechemicals.

The Swiss water processAnother commercial decaffeination method, the

Swiss water process, or the water decaffeination process,simply requires the coffee beans to be soaked in wateruntil the majority of the flavor and caffeine have dissolved

Beverage Amount of Caffeine(mg/serving)

Regular coffee 80–125

Decaffeinated coffee 2–4

Tea 30–75

Cola 35–60

Coffee is consumed in one form or another by about one-third ofthe world’s population. Coffee normally contains caffeine, whichhas a worldwide consumption estimated at 70mg/person/day.

The Case of the MissingCaffeine

ChemMatters, APRIL 1999 13

into it. The solution of water, coffee flavor,and caffeine is passed through an activatedcarbon filter that removes the caffeine butnot the flavor from the water. This coffee-flavored and now decaffeinated water ispoured onto the flavorless beans, and theyreabsorb the all-important flavor molecules.Coffee companies are reluctant to use thiswater-decaffeination process because itcosts four times more than the chemicalextraction decaffeination method.

Supercritical fluid extraction

SFE is a relatively new method ofdecaffeination still being developed. It issimilar to the Swiss water process becauseit avoids the use of organic solvents. How-ever, it uses the same principle as chemicalextraction to remove the caffeine. Unlikesolvent extraction, however, SFE uses car-bon dioxide (CO2) to extract the caffeine.

CO2 can exist as a solid, liquid, or gas,depending on the temperature and the pres-sure exerted on it. The line between thesestates blurs, however, when the CO2 isabove the critical temperature and criticalpressure and reaches the critical point, asseen in the phase diagram of CO2 (see Fig-ure 1). At this point, the CO2 transformsinto a “supercritical fluid”. Basically, asupercritical fluid, like a gas, takes on thesize and shape of its container, but it has adensity approaching that of a liquid. In thiscase a clear distinction between “liquid”and “gaseous” states of CO2 can no longerbe made.

The advantage of supercritical (fluid)CO2 over gaseous CO2 is its much greaterdensity, nearly equal to the density of liquidCO2 but at much lower temperatures. Like aliquid, supercritical CO2 can dissolve othersubstances, and its dissolving ability tendsto increase as the pressure of the CO2 isincreased. This ability of the supercriticalCO2 to dissolve substances is the basis forthe SFE process. It uses fluids, like CO2, toextract ingredients from food based on thesolubility of molecules in those fluids. Caf-feine can be separated from coffee becauseit is more soluble in supercritical CO2, butmost of the other compounds in coffee arenot. As a result, the consumer gets a good-tasting cup of coffee without the caffeine.

The SFE extractionprocess

Using this method, the CO2 is firstheated and pressurized to its supercriticalstate in a compression chamber. It then pro-ceeds through an extractor, where it passesthrough the coffee, dissolving the caffeine.The solution of caffeine and CO2 then movesthrough the pressure-reduction valve. There,the CO2 becomes a normal gas again as thepressure is lowered. At this lower pressure,the caffeine precipitates and is collected inthe separator. The CO2 is then recycled, andthe entire process is repeated until most ofthe caffeine has been removed. The beans inthe extractor are now decaffeinated andready to be roasted.

The ups and downsof SFE

SFE has many benefits, but it is notperfect. One major disadvantage of SFE isthat the required equipment is expensive.The traditional chemical solvents for caf-feine extraction do not require such tightly

controlled temperatures and pressures, sothe processing equipment is less costly.However, SFE is not so costly that coffeecompanies completely prohibit its use.

SFE has many advantages over otherextraction processes. The temperaturerequired for SFE is relatively low (31 °C).Because of this, heat-sensitive materials arenot affected by its use. Additionally, the SFEprocessing equipment can easily target spe-cific compounds like caffeine, dissolvingonly these unwanted substances. SFE isalso environmentally friendly. The CO2 usedto dissolve caffeine in coffee is nonflamma-ble and nontoxic. CO2 is also in abundantnatural supply throughout the atmosphere.

Coffee companies like to use the “natu-ralness” of CO2 as a selling point for theirbrand of decaffeinated coffee. Many havecreated marketing phrases that are synony-mous to CO2 for SFE-decaffeinated coffeebeans. So, the next time you see a productadvertised that features the use of “sparklingeffervescence”, you will know what that mys-terious effervescence really is.

Kimberly Barstow, of Boston, MA wrote this article last year as a high school junior at Beaver CountryDay School in Brookline, MA. Also a dancer and ballet teacher, she wrote the article at the suggestion ofher chemistry teacher, John Bean.

REFERENCESBrown, T. L.; LeMay, H. E. Jr.; Bursten, B. E. Chemistry: The Central Science, 7th ed.;

Prentice Hall: New York, 1997. Hegenbart, S. L. It’s a Gas: Gas Extraction in Food Processing. Food Product Design, May

1997, 7 (2), pp 83–86.Snow, N. H.; Dunn, M.; Patel, S. Determination of Crude Fat in Food Products by Supercritical

Fluid Extraction and Gravimetric Analysis. J. Chem. Educ., September 1997, 74 (9),pp 1108–1111.

Temperature (˚C)

Supercritical Fluid

Critical Point

Pressure (atm)

PHASE DIAGRAM OF CO2

Solid

Liquid

Gas

73

5.1

-78.2 -56.6 31.1

1

Figure 1. Phase diagrams are graphs that show the pressures and temperatures at which differentphases of a substance are at equilibrium with each other. This phase diagram represents CO2.

14 ChemMatters, APRIL 1999

S ome day, the plastic bags that holdthe garbage from our daily lives willdecompose along with their con-

tents, instead of enduring for ages in ourenvironment. They will be transformed intocompost, a rich organic mixture that helpsgardens, lawns, and crops grow. Two com-panies—Cargill, Inc., and Dow Chemical—have formed a partnership (Cargill DowPolymers LLC) and discovered a way tomake these bags using polylactic acid(PLA), a material that can be synthesizedfrom ordinary corn.

Bioenvironmentallydegradable polymer

PLA is an example of a bioenviron-mentally degradable polymer (BEDP). Likeall polymers, BEDPs consist of long molec-ular chains of repeating units, but are differ-ent than most polymers, because microbesin the soil can use them for food. Thisbreaks them down into useful materials thatcan be recycled in the environment.

Unlike BEDPs, “conventional” poly-mers, such as polystyrene, can cause dis-posal headaches, and they don’t degrade inthe environment. They take up valuablelandfill space indefinitely and can be asource of litter. Conventional polymers aretypically produced from petroleum, a non-renewable resource. PLA, however, can beproduced from corn, a renewable resource.

Garbage bags are only one example ofpossible products that could be made ofPLA. The potential list is enormous. Othersmight include razor blade handles, plastictableware, and even diapers. For BEDPs tobecome widespread, two systems are nec-essary: one that collects recyclable itemsseparately from nonrecyclable items andanother that transforms organic materialinto compost. In the United States, we havethe first in place but not the second. A com-posting system requires a shed or buildingin which the biodegradable bags—and theorganic refuse they contain—are kept at atemperature and humidity that allowmicrobes to break the polymer down into a

rich organic material. There must also be asystem that allows this compost to be dis-tributed to people who wish to use it tofetilize lawns or crops.

In European countries, which are moreenvironmentally progressive than the UnitedStates, BEDPs are becoming increasinglypopular. Some plastic bags are already onthe market in Europe that are biodegradableand can be used to collect compostablewaste. Germany and The Netherlands areactually putting regulations in place to stim-ulate the use of these materials.

What is their motivation? Space. Euro-pean countries don’t have a lot of space inwhich to bury their garbage the way we doin parts of the United States. Yet,researchers at U.S. companies and universi-ties continue to work to develop biodegrad-able polymers even though the landfillsituation in the United States is not yet asserious as it is in Europe. Cargill and Dowhave joined efforts because they believe theyhave developed an economical way to man-ufacture products made from BEDPs.

ChemMatters, APRIL 1999 15

Investigating PLA, Gary Leatham, abiochemist at Cargill Dow Polymers LLC,notes that its basis is starch. “Technically, itcan be made from any material that is fer-mentable to lactic acid,” he says. “But thecarbon source most available that is con-vertible at very fast rates is carbohydrates.A dominant one is starch. The industry hasgrown up around the ability to make sugarfrom starch. And one of the most profitablestarch crops grown is corn,” he explains.The United States is corn-wealthy.

The PLA processThe procedure begins by grinding the

corn to extract the starch. Then water andheat are used to swell it, resulting in some-thing that looks like porridge. The “por-ridge” is mixed with enzymes that convert itinto sugar, and then bacteria are added toferment the sugar. This results in lactic acid(see Figure 1). The water in the acid isremoved, producing a substance called lac-tide. Lactide, a dimer, or two-molecule frag-ment, is then polymerized—grown into longchains to make PLA. The process of conver-sion from lactide to PLA is a patentedprocess involving catalysts and controlledtemperatures. Another important aspect inthe manufacturing of PLA is something theprocess doesn’t use—organic solvents,which are typically used in the manufactureof conventional polymers. These solventscan be a source of environmental pollution.

PLA leaves the process in the form ofsmall pellets or beads. “A kernel of corngoes in, a plastic pellet comes out,” sumsup Leatham. PLA pellets are then formedinto plastic bags and other items that willeventually become compost.

Other uses of BEDPsThe uses of BEDPs don’t have to stop

with garbage bags. Justyna Teverovsky, amaterials scientist, says razor blade handlesmight be another possible use. “You canunsnap the metal head and throw the plas-tic into the compost heap,” saysTeverovsky, who works for Foster-Miller,Inc., a Waltham, MA, research and develop-ment firm. The plan for such a productreally hasn’t gone beyond the idea stage,she says.

However, another use of biodegradablepolymers, which the firm has patented, is areality. It improves on a method that takes

the sand out of sand blasting and replacesit with plastic. Essentially, this is a paintremover for airplanes. Blasting sand at anairplane to remove paint is not advisable.What has been used in the past is a plasticsubstitute for sand called media blast. Theproblem is 20,000–80,000 kg of this sub-stance is needed to strip a plane.

“Then you have all that waste. It’s clas-sified as hazardous waste because it haschromium [from the paint] in it,”

Teverovsky explains. “What we did was tomake a plastic grit based on biodegradablepolymers. You can even reprocess andreuse it,” she says. Instead of disposing ofit as hazardous waste, it gets put into abioremediation system, where the right heatand humidity encourage bacteria to“munch” on the starch-based polymer. Thebacteria give off only water and carbondioxide (CO2). What are left, saysTeverovsky, are a few pounds of hazardouswaste from the stripped-off paint instead ofthe thousands of kilograms generated usingconventional plastics.

The paint-blasting polymer is made bycombining starch with water and glycerin.This material, which the company hasn’t yet

named, starts out as corn. Because cornhas already absorbed CO2 in photosynthe-sis, there isn’t any additional CO2 added tothe atmosphere as a result of that producedby bioremediation. This biodegradable poly-mer has not yet reached the market,Teverovsky notes, because the company istrying to determine if it can be produced ata reasonable cost.

Cost is a major consideration for com-panies developing BEDPs—although corn,

for instance, isextremely abundant inthe United States andmakes a good sourcefor BEDPs. The prob-lem is that what worksin the laboratory on asmall scale needs tobe expanded to anindustrial scale toreach the market. Thiscan be an expensiveproposition. Enlargingthe process and mak-ing millions of poundsof PLAs could proba-bly get the price downto $1/kg. However,that price is still aboutfour to five times thecost of petroleum-based polymers. Forexample, polystyrene,a polymer used tomake food containersand plastic eatingutensils, among otherthings, costs approxi-

mately $0.25/kg. Leatham says his com-pany “is confident” that in the end, it canget the price of PLA down to $0.35/kg,which would make it competitive with plas-tics like polystyrene.

Still, one question remains: Will therebe enough incentives for people to buythese “green” products to create a largeenough market so manufacturers can pro-duce them economically?

Lactic acid

Polylactic acid

H

H

H

O

O

O

O

O

O

CH3

CH3

CH3

C C

C C

C

C

H

OHOH

O

H3C C C

Harvey Black is a freelance science writer living inMadison, WI. His article “Keep the Game Rolling”appeared in the February 1999 issue ofChemMatters.

RELATED ARTICLEDowney, C. Biodegradable Bags.

ChemMatters 1991, 9 (3), pp 4–6.

Figure 1. Polylactic acid (PLA) is a bioenvironmentally degradable polymer(BEDP) made from corn. It is designed to allow microbes in compost heapsto attack it and break it down into recyclable material.

1155 Sixteenth Street, NWWashington, DC 20036–4800

As a Matter of FactBy Robert Becker

Reach Us on the Web at: www.ChemCenter.org

Q. Should food be irradiated?Michael Lo

South Pasadena High School, CA

A. Food irradiation is an intriguingand controversial issue, and one inwhich fear and emotion play majorroles. Using the high-energy gammarays emitted by radioactivecobalt–60 (see Figure 1) to sterilizeour meat and poultry productssounds like a scary proposition tomany people. Yet, the idea thatthere may be dangerous bacterialevels in the next hamburger we eatis also frightening.

For many people, the wordsnuclear and radioactive conjure upimages of mushroom clouds,radioactive fallout, and radiationsickness. Needless to say, theseconcepts make it difficult for con-sumers to welcome radioactivityinto their homes and bodies. Thereality is, however, that wealready do. For example,home smoke detec-tors containradioactive americium–241, whichundergoes nuclear decay butenables the devices to detect smokeand thus save numerous lives eachyear. In addition, nuclear medicinehas become so accepted that doc-tors routinely conduct procedures inwhich their patients are injectedwith specific radioactive isotopes tohelp diagnose or treat their disor-ders. Are there risks? Certainly—but the benefits are far more signifi-cant.

Along with these perceptionsfrom the past, the public also hasmisconceptions about nuclearchemistry. It is important for con-sumers to learn, for example, thatirradiated meat does not itselfbecome radioactive. What irradia-

tion does is expose meat to high-energy gamma rays that are veryeffective at breaking covalent bonds.As a result, it kills virtually all of thebacteria in the food. However, irra-diation also breaks some of thecovalent bonds of the meat. Someresearch indicates that this can leadto the destruction of certain vita-mins in the meat—but then, sodoes cooking. Another concern isthat as new covalent bonds form,new compounds can be created,some of which may prove to be car-cinogenic (cancer-causing). Thismay indeed happen, but these com-pounds are produced at very small

concentrations. Andagain, cooking—

especiallygrilling—isnotori-

ous for producing aplethora of new andpotentially carcino-genic compounds.

What’s more,irradiation is nothingnew. In the 1920s,French scientists dis-covered that it helpedpreserve food, and in1963, the U.S. govern-ment deemed foodirradiation safe to con-trol insects in wheat.Since then, irradiationhas been approved foruse with spices, pork,fruits, vegetables,

and—more recently—poultry andbeef. Irradiation is even used byNASA to sterilize food for astro-nauts.

Although other countries haveforged ahead and taken full advan-tage of the benefits irradiationoffers, the United States continuesto drag its feet, with no major foodcompany wanting to test the waterfor fear of public retaliation. A meat-packing plant might, for example,offer consumers a choice; theycould purchase regular or irradiatedbeef. The irradiated beef would costa few cents more per kilogram,carry the required green internation-al radura symbol (see Figure 2), andbe considered a safer product tosome. However, some companiesfear becoming associated with irra-diation, and perhaps developing a

reputation for “nuking their meat”,may scare consumers away from allof their products.

Because food irradiationseems to be an issue driven moreby public fear than by scientific evi-dence, it may be a long time beforeit becomes widely accepted in theUnited States. Unless, of course, E.coli and Salmonella outbreaksbecome more common than theyalready are. In that case, it may bepublic fear that drives companies toreconsider the food-sterilizingpotential resulting from the emis-sions from a radioactive atom’snucleus.

Figure 1. Although cobalt–60 isused for food sterilization, it isalso a radioisotope used as asource of ionizing radiation in

cancer treatment.

Factoids!AS A MATTER OF

✸ Irradiation is a “cold” process thatdoes not significantly increase the tem-perature or change the physical or sen-sory characteristics of most foods.

✸ Foods can be irradiated within theirpackaging or after being frozen andremain protected against contaminationuntil opened by consumers.

✸ Irradiation can be used to destroy orinactivate organisms that causespoilage and decomposition, allowingfor extended shelf-life of foods.

✸ Foods that are sterilized by irradia-tion can be stored for years withoutrefrigeration—just like canned (heat-sterilized) foods.

✸ Irradiation offers an alternative tochemicals for use with potatoes, tropi-cal and citrus fruits, grains, spices, andseasonings to control sprouting, ripen-ing, and insect damage.

✸ Irradiation can be used to effectivelyeliminate pathogens that cause food-borne illness, such as Salmonella.However, it only complements—butdoes not replace—proper food-handling practices.

Figure 2. The U.S. Food and DrugAdministration requires allirradiated products to be labeledwith the international symbolcalled a radura and the statement,“treated with irradiation” or“treated by irradiation”.

6027Co

6028Ni

0–1

00δ

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A Light of a

DifferentColor

A Light of a

DifferentColor

A Calorie-Free Fat?Digesting the olestra and Olean controversy

As a Matter of FactShould food be irradiated?Hot topic—a chemical perspective

A Calorie-Free Fat?Digesting the olestra and Olean controversy

As a Matter of FactShould food be irradiated?Hot topic—a chemical perspective

An illuminating chemical perspective on black light

®