Spring 2000

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The

Monell

Connection

The Monell Connection. . .

from the Monell Chemical

Senses Center, a nonprofit

scientific institute devoted to

research on taste, smell,

and chemosensory irritation.

What Tastes Good to You?

While all of the above factors certainlycontribute to food choice, many expertsregard palatability as the most importantdeterminant of food selection in industrializedcounties. We eat what we like. If it tastesbad, we don’t eat it. Yet, what is palatability?Can it be measured?

“Palatable” is defined circularly by thedictionary as “pleasing to the palate or taste.”While most people commonly use variationsof the words “like” and “dislike” to describetheir reactions to food, palatability and likingare sometimes used interchangeably. Thiscan hinder attempts to measure either variable,unless the terms are defined very carefully.Most scientists consider palatability to be anattribute of food, while liking is consideredto be an affective, or psychological, responseof a person.

Another common source of confusion isthe distinction between liking/palatability andpreference. Preference refers to the selectionof one food over another. It is sometimesinferred that if a food or drink is preferred, thatmeans it is palatable. However, because a preference is always expressed within a certain context, a preferred food isn’t necessarilymore palatable or better-liked. For example,a woman trying to lower her cholesterolmay like ice cream more than frozen yogurt;but when given the choice, she will prefer theyogurt for her mid-afternoon snack. In general,foods that are more palatable and give morepleasure are preferred over less palatable foods.

The earliest occurrences of food choiceinvolved animals needing information while

Excess consumption of salty, sweet,and fatty foods has been linked tovarious disease states, and scientists at Monell and elsewhere are trying to understand what accountsfor individual differences in food preferences.

Considering all the choices that we are confronted with, howdo we ever decide what to eat? It seems

like such an overwhelming decision, but it’sone that most of us make many times every day.And, it’s a decision that researchers –– fromthe basic scientists at Monell to marketinganalysts at food and beverage companies ––want to understand.

Over much of human history, the limitedfood choices were governed primarily byavailability and economic concerns, and boththese factors remain important considerationsin the 21st century. Today, the food selectionprocess is also strongly influenced by variedlearned cultural, social and contextual factors.For example, while bread is a major sourceof starch in the United States, it is infre-quently eaten in much of Asia, where rice isthe standard starchy staple. Considerationsrelated to nutrition and health also enter thepicture, whether someone is trying to loseweight, train for the Iron Man triathlon, lowertheir blood pressure, or just “eat healthy.”

Sea urchins, ice cream, sour pickles, caviar, kasha, milk, sausage, fermented beanghee, pizza, habenero peppers, cabbage, emu, coconut, espresso, soy protein, fetacod, kim chee, salsa dip, hot dogs, mango, escargots...

A Perspective...

Substances and practices that are particularlypleasurable also seem to connote potentialdanger. Whether this belief is a peculiarityof our society is unclear. I think it probablyis not, although fears focused on these relatively harmless taste substances may beparticularly well-developed in the United States,for many historical and cultural reasons.

But it is not just in taste that what we senseas good may be designated bad. We are seeing more stories about how environmentalodors and perfumes are harmful. Odor-freeoffices, buildings and even communitiesnow exist or are being planned. A colleaguerecently showed me a card from his dentistthat proclaimed the office to be perfume-free(from my memory of the pain associatedwith dental office odor, I would appreciateanything but those “natural” dental odors,including perfume).

Some people do seem to be very sensitiveto many odorous chemicals and much moreresearch, some of it now underway at theCenter, is needed to understand the nature of this phenomenon. But if one considersour evolutionary history with odorous chemicals, it is hard to justify a prohibitionof perfume for the general public. Indeed,the best perfumes are often made up largelyof so-called “natural” substances.

For odors, there is considerable and vigorous debate over whether what we like(or dislike) is innately determined, due toour individual experiences, or both. My owninclination is to believe that liking for someodors is predisposed as a consequence ofnatural selection to be positive or negative.But, this innate bias can be strongly, evenoverwhelmingly, influenced by individualexperience. This is a topic of active researchat Monell. Whatever the outcome of thisdebate, it is indisputable that odors are potentemotional stimuli, evocative and mood-altering.Perhaps this deeply affective characteristiccontributes to the identification of certainodors as dangers.

So, in the next ad for the medical center,will we see the wife restraining the husbandfrom approaching the perfume counter in thedepartment store? I certainly hope not. Goodtastes and good smells are not necessarily orinherently bad. Indeed, the opposite is morelikely to be true. Here as elsewhere, moderation,not prohibition, is probably the wisest course.

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Clearly, eating too many sweet, fattydoughnuts or too much salty, processedmeat can be unhealthy –– as can be toomuch of just about anything. But the moregeneral idea seems to be that foods we enjoyeating, particularly those that taste good, aredangerous and must be avoided. This viewis exemplified by the titles of 3 books Iown: “Killer Salt,” “Sugar Blues,” and “InBad Taste, The MSG Syndrome.”

Why do people fear foods that havesweet, salty and savory tastes? One strikingcharacteristic of these three prototypicaltaste substances is that their pleasantness is in large degree a part of our biology. Theevidence for an innate liking for sweet tasteis incontrovertible. Sweets are highly preferred by most omnivores and herbivores.Newborn or even premature infants stronglyprefer sweets on their very first presentation.Sweet taste has even been shown to releaseendogenous opioids, thereby reducing pain.There is evidence, though certainly lessextensive, that liking for salty and umami(savory, MSG) tastes is also innate. By 4-6months of age, infants begin to prefer saltytasting liquids and this preference does notseem to be a consequence of early feedingwith salt. The liking for umami taste substances,when placed in certain foods, is also evidentin newborn and very young children, anindication that the preference for umamisubstances requires little or no environmentalinput.

Could it be that because these substancesare inherently attractive is why they are feared?

There is a clever ad on TVfor a local medical center. It goes somethinglike this: A man is shopping with a woman,presumably his wife, at a grocery store. Asthey walk down the aisle, a guilty look crosseshis face as he throws a bag of doughnutsinto the shopping cart. When he glances inthe other direction, the wife quickly scoopsup the doughnuts and returns them to theshelf. Clearly, the doughnuts are “bad.”After hearing some specific details about the medical center, we see him again, thistime looking longingly at the processedmeat counter; the wife lovingly pulls himaway. The message is unmistakable. She andthe medical center staff know what is good forhim and, more importantly, what is bad for him.

What interests me about this ad is theunderlying assumption that the foods thepoor fellow liked are “bad.” And, the wisewife and medical staff are the good guys,recognizing this and trying to protect himfrom his injurious desires.

Is Good Bad?

Gary K. BeauchampDirector

George Preti, Ph.D.

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body odors and the analysis of human secretionsand excretions. Now a specialist with aworldwide reputation, Preti jokingly refersto himself as “Dr. Body Odor.”

It was his expertise in mass spectrometrythat provided Preti the opportunity to get inon the ground floor when Monell was in itsformative years. Used for determining thestructure of organic molecules, the mass spectrometer helps chemists to identifyunknown components, particularly thosefound in complex biological mixtures. “I’ve taken mass spectrometry into places where

An organic chemist’sresearch has led to advances in the understanding of odors produced during the humanreproductive cycle, as well as to progress in dealing with a rare disease.

The Science

it’s never been used before,” Preti says, “using it to study odors associated with such areas as women’s vaginas, people’s mouths,and the human underarm.”

Implications for Ferti l i tyPreti finds research involving odors of thehuman underarm particularly fascinating.“Many organic chemists go looking forexotic plants, trees, or animals to get physiologically active compounds for medicinalpurposes,” he explains. “I look under people’sarms.” Preti has shown that compoundssecreted from both male and female under-arms can alter the length and timing of thefemale menstrual cycle. He believes furtherexamination will demonstrate that componentsof male underarm secretions can induce asubtle endocrine change in hormones associatedwith the menstrual cycle. “Ultimately wemay find that these compounds, which areactually primer pheromones, may be used to adjust the cycle so that a woman knowsexactly when she’s ovulating,” he comments.“We also may be able to use components ofunderarm odors to influence hormonal levelsso that we can correct certain types of reproductive infertilities that occur in theluteal phase of the cycle.”

Dr. George Preti approaches sciencefrom many different standpoints in his roleas an organic chemist at Monell. He is firstand foremost a researcher, but he is alsocalled upon to act as professor, clinician, andenvironmental sleuth. A member of the Center’sstaff for 29 years, Preti came to Monell in 1971 to study mammalian chemical communication. For the past two decadeshis work has focused primarily on human

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with answers,” he says. “That’s a good feeling.”About 20 to 25 percent of the patients he

sees test positive for TMAU. Although thereis no cure, Preti can recommend helpfuldietary changes and some symptomatictreatments. He presented his findings at thefirst international conference on trimethyl-aminuria at the National Institutes of Healthlast year, and remains optimistic aboutadvances in treating the condition. In addition,one of his patients has started a supportgroup for people who suffer from the condition.Henry Lawley, a senior research specialistwho has worked with Preti for the past 22years, says the chance to see these patientsadds an important dimension to theirresearch. “In many cases, we can offer helpto people whose lives have been devastatedby this disorder,” Lawley says.

The majority of patients who don’t haveTMAU suffer from halitosis that originateson the back of the tongue. “People don’trealize that bacterial plaque can build up on the tongue,” Preti says. “Their teeth andgums may look fine, but their tongues arecovered with bacterial plaque.” Brushing thetongue, which Preti explains is a commonpractice in many cultures, goes a long waytoward solving the problem.

A native of Brooklyn, Preti attendedPolytechnic Institute in Brooklyn, then didhis graduate work at MIT, earning his Ph.D.in organic chemistry in 1971. At MIT hespecialized in the mass spectrometry workthat led him to Monell. Now in the processof raising funds to update his sophisticatedequipment, Preti is looking to expand hisresearch efforts to investigate odorants produced by aging skin.

According to Preti, his personal sense of smell is no more acute than the average person’s. That’s probably lucky, given thathe spends a lot of time around unpleasantodors. “It’s just like many people in the fragrance industry,” Preti comments. “Youjust learn to pay close attention to the odorants around you.” Just for the record,his personal favorite scent is pine.

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in odor analysis, we are quite often asked to tackle certain problems. In this case wewere approached by the AgricultureDepartment to look at odor problems thatare associated with mushroom and swinefarming in eastern Pennsylvania.” Pretiexplains that as suburban housing developmentshave expanded further into rural areas, someof the new residents are complaining aboutodors emanating from nearby farms. So,Preti’s research team has spent the last yearin the lab analyzing odors from mushroomsoil and pig slurry, searching for treatmentsto ameliorate the offending odors. Usingabsorbents and cross-adapting agents, theteam has had good success in the lab. Theproject now moves into the field, where theywill put the formula to the test on a workingfarm in collaboration with the University ofPennsylvania Veterinary School. “I’ve spentall my life living in and around big cities, soI wasn’t familiar with these particular issues.We just knew there was an odor problem,”Preti says. “It demonstrates how you can useyour basic knowledge in a practical application,and come up with answers.”

Shedding Light on a Rare DisorderPreti maintains a close affiliation with theUniversity of Pennsylvania, conferring withspecialists and serving as an adjunct professorin the dermatology department. Part of Preti’sgoal in the classroom is to educate the nextgeneration of dermatologists about a raregenetic condition called trimethylaminuria(TMAU). Also known as “fish odor syndrome,”TMAU is a metabolic disorder that can sporadically cause people to emit a malodorthat in some instances may resemble rotting fish.

The chemistry of human underarmodors –– how they’re produced andcarried to the skin’s surface –– isremarkably similar to that of odorsources controlling reproductiveendocrine behavior in non-humanmammals.

Many of Monell’s corporate sponsorsinvolved with personal care and fragranceproducts follow Preti’s work closely. “They’veall synthesized the critical armpit ingredientswe have discovered, so their perfumers knowexactly what they’re trying to cover up.”

Suburban Living Versus Farm OdorsPreti is also seeing direct results of his workin a project with the Pennsylvania Departmentof Agriculture. “Because of our expertise

People with TMAU lack an enzymethat allows them to metabolizetrimethylamine, which is formedfrom choline. Choline occurs inmany foods, including fish, eggs,and several varieties of beans. Byincreasing awareness of TMAU,Preti has been able to help peoplewhose odor production has confounded the medical community.

Preti receives referrals from clinicians,dentists, and others regarding odor productionproblems that haven’t been solved by standardclinical processes. He estimates he sees about30 cases a year from across the country, andsome from as far away as Europe and CentralAmerica. Over the years, Preti and hisresearch associates have developed a half-dayclinical workup –– unfunded except fordonations from patients –– for people withodor problems. “We’ve been quite successfulwith diagnosing problems and coming up

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Mushrooms, curry, turnips, caraway seed, marmalade, lemon grass, blue cheese,anchovies, harissa, arugala, chickpeas, sauerkraut, persmmons, eggs, rhubarb,shrimp paste, cilantro, okra, liver, quinces...

Because liking is complex –– a psycho-logical attribute linked to an emotionalresponse to sensory stimuli –– it is difficult to measure. For humans, the most commonmethod of measuring liking involves self-report,which is often assessed using numerical scales.Because this involves conscious self-reflectionon the part of the person, some researchershave argued that self-report measures arenot objective.

Many studies, especially those with youngchildren, have used facial expressions knownto be associated with pleasure responses to infer liking and palatability. And somescientists have searched for physiologicalmarkers that might indicate an individual’sunconscious response to a food’s palatability,such as heart rate, salivary flow, or morerecently, brain activity. While some of thesepossibilities are promising, they still requireadditional study. However, using measure-ment devices to assess liking for a food can interfere with establishing a naturalistic eatingsituation, potentially limiting any conclusions.In general, self-reports are easy to use andprovide the most information in most conditions.

Humans are omnivores. Through evolutionwe are predisposed not only to like sweet,fatty, high-density foods, but also to avoidnew, unknown –– potentially dangerous ––foods. That we can acquire a wide variationof food likes and dislikes is a wonderfuldemonstration of our adaptability, and onethat is still only partially understood.

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trying to decide whether to ingest an unfamiliar substance. From an evolutionaryperspective, it is believed that the sensationof sweetness, indicating calories and energy,came to be associated with pleasure. Bittertaste, which signals the hazard of poison, was perceived as unpleasant. Thus, the sense of taste –– which conveys information onsubstances about to be ingested into the body ––is closely tied to the affective responses ofpleasure and displeasure.

As is evident by the wide range of differentfoods that are liked and disliked by individualstoday, factors other than our evolutionaryhistory must contribute to individual preferences.Learning is thought to play a critical role,and one of Monell’s most active researchprograms is exploring the role of early experi-ences on the acquisition of food likes anddislikes in infants and young children. Atthe other end of the age spectrum, changesof taste and olfactory sensitivities, liking,and food preferences that occur with the agingprocess are also under study. And, scientists atMonell and elsewhere are working to understandthe influence of genetic factors on sensitivityto and liking for various taste qualities.

What TastesGood to You?continuedfrom page 1

The uniquely human ability toacquire likes for innately unpalatabletastes and irritants, such as chilipeppers and caffeine, is facilitatedby repeated exposure, but the mechanisms that underlie this shiftare unknown.

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M o n e l l P u b l i c a t i o n s Here are brief summaries of selected papers

describing ongoing work of Monell scientists.

For information about these studies or other

research at Monell, call 215.898.4236.

The Monell Connection

Address correction requestedNonprofit Org.U.S. POSTAGE

PAIDPhiladelphia, PAPermit No. 1994

3500 Market StreetPhiladelphia, PA19104-3308

Leslie J. Stein, Ph.D.Editor & Writer

Karen IvoryWriter

Mary M. Chatterton, J.D.Resource Development

Sandra Gelak Design

Telephone215.898.6666

Emailinfo@monell.org

Web Sitewww.monell.org

ATP levels. In this paper, Drs. Horn, Addis,and Friedman report that the effectiveness ofthese inhibitors is increased synergistically ––more than expected –– when given in combination.In parallel experiments, combined treatmentalso enhanced neuronal activation in severalbrain regions thought to be involved in thecontrol of feeding.

Together, these experiments suggest thatthe body monitors information about differentaspects of fuel metabolism. This information isintegrated to give the brain an indication ofoverall energy status, which then is translatedinto feeding behavior.

Neural substrate for an integrated metabolic controlof feeding behavior. Charles C. Horn, AleymayehuAddis (Kansas State University), and Mark I.Friedman. American Journal of Physiology, 1999,276, R113-R119.

the secretion pattern of chemicals as they arereleased from living neural tissue.

Cells are kept alive and functional byimmersing slices of brain tissue from rodentsin a bath of oxygenated artificial cerebrospinalfluid. The slice is then placed on a transfermembrane, similar to blotting paper, which trapssignal molecules as they are released from cells.Because cells in the slice are still connectedand functional, they are able to communicate.Thus, the influence of intercellular regulationon secretion patterns can be studied with theslice blotting method, along with effects ofdrugs, modulators and other chemical stimuli.

Slice blotting: a method for detecting the release ofimmunoreactive substances from living brain tissue.Graeme Lowe. Journal of Neuroscience Methods,1999, 90, 117-127.

How LivingBrain Cells

Communicate

Who Tells theBrain When

It’s Time to Eat?

Food supplies the energy necessary to maintainlife. Molecules of carbohydrate, fat, and proteinare constantly broken down within cells tounleash chemical energy. This energy is thentransferred to an energy-carrier molecule, typically ATP, which is used by cells to powervarious processes of the body: for example,muscle contraction or synthesis of larger moleculessuch as proteins.

Because the body is constantly using andlosing energy, it needs to be able to monitorenergy status, and also to signal the brain toinitiate eating when energy stores are low.Research from Dr. Friedman’s laboratory suggeststhat some aspect of the production of ATP ismonitored in the liver.

Previous studies have demonstratedincreased feeding in rats following administrationof various metabolic inhibitors that suppressbreakdown of specific fuels or reduce liver

Information processing in the brain relies oncoordinated communication among networksof nerve and supporting cells. A multitude ofchemical messengers, including neurotrans-mitters and neuromodulators, mediate interactions among and within intricate cellularnetworks. Other signals such as growth factorsare important in guiding the early developmentof the nervous system. Some chemicals act inthe immediate vicinity of their release, whileothers can diffuse to exert long range effectson entire networks of nerve cells.

Defining and unraveling the intricate workings of these complex networks is a difficulttask. Existing methodologies using preservedbrain tissue have localized cells containingvarious chemical signals, as well as those withspecific receptors. To complement these studies,Dr. Lowe has devised a method to visualize