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Chapter 1

New Trends and Developmentsin Flavor Chemistry

An Overview

Roy TeranishiWestern Regional Research Center, Agricultural Research Service,

U.S. Department of Agriculture, Albany, CA 94710This chapter gives an overview of new trends anddevelopments in flavor chemistry. One importantdevelopment was made possible by advances inanalytical methodology, that is, the identificationof numerous compounds with known flavor characteristics. As more and more compounds are correlatedwith characteristic flavors, there is a trend tostudy flavor precursors and to explain how flavoris developed and released. Many of the newestdevelopments in flavor chemistry are in the area offlavor production from plant and animal sources;this trend has come about because of the public'sfear of the words "chemical" and "synthetic". Inthis chapter, words such as these are discussedin terms of the public's perception of them versusa chemist's viewpoint. Another new trend is tounderstand the chemical reactions involved in theprocessing and storage of foods in order to bringfoods to consumers at optimum acceptability.

Prior to the 1950s only about 500 flavor compounds were known (1).Since then, with the advent of modern instrumention, thousands ofcompounds have been characteri zed in hundreds of different foods(2). There have been many books published on flavor research workshops and symposia, some of which are held on a periodic basis andsome on special occasions and topics, covering various aspects offlavor (3-20). A l s o , there are many excellent reviews which everyserious flavor chemist should consult (21-43).Advances i n analytical methodology introduced i n the I960 1s wereapplied from the early 1970s (3 5, 12, 131 14). Previous to gaschromatography, fra cti onal di s t i l l a t i ons and column chromatographyo f colored derivatives were the primary means of separations. Sizeo f sample required for d i s t i l l a t i on i s , of course, enormous comparedto what i s required for gas chromatography. The resolut ion of separation by gas chromatography i s far superior to that attained by

This chapter not subject to U.S. copyrightPublished 1989 American Chemical Society

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In Flavor Chemistry; Teranishi, R., et al.;ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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2 FLAVOR CHEMISTRY: TRENDSAND DEVELOPMENTSf r a c t i o n a l d i s t i l l a t i o n . A l s o , th e advent of i n f r a r e d , n u c l e a r mag-n e t i c r e s o n a n c e , and mass s p e c t r o m e t r y has made i t p o s s i b l e to makes t r u c t u r a l d e t e r m i n a t i o n s w i t h mi c r o amounts. T h u s , w i t h t h e use ofmodern a n a l y t i c a l me t h o d s , t h e number of compounds w i t h known f l a v o rc h a r a c t e r i s t i c s i n c r e a s e d i n the 1970's and 1980's. T h e s e advan ceshave s e t the s t a g e f o r t h e p r e s e n t t r e n d s and d e v e l o p m e n t s i n f l a v o rc h e m i s t r y .Many of t h e n e w e s t d e v e l o p m e n t s i n f l a v o r c h e mi s t r y a r e i n the a r e ao f f l a v o r p r o d u c t i o n f r o m p l a n t and a n i m a l s o u r c e s ; h e n c e , s i g n i f y i n g t h e p o p u l a r i t y of t h e t e r m " b i o t e c h n o l o g y " . T h i s t r e n d hascome a b o u t b e c a u s e of t h e f e a r of t he p u b l i c of t h e w o r d s " c h e m i c a l "and " s y n t h e t i c " .The w o rd " n a t u r a l " i s u s e d i n o p p o s i t i o n to t h e w o r d " s y n t h e t i c "w i t h t h e c o n n o t a t i o n t h a t " n a t u r a l " p r o d u c t s a r e s a f e r t h a n " s y n t h e t i c s " , but t h e r e a re many t o x i n s made by p l a n t s and animal s w h i c ha r e v e r y d e t r i me n t a l to man ( 4 4 - 4 7 ) . M o r e o v e r , w h e t h e r c h e m i c a l sa r e made i n f l a s k s by man or made by p l a n t s and a n i m a l s , nocompounds ar e made on e a r t h o t h e r t h an t h o s e p e r m i t t e d by t h e l a w so f n a t u r e . T h e r e f o r e , a l l m o l e c u l e s on t h i s e a r t h ar e " n a t u r a l " .T h i s d e f i n i t i o n i s f r o m a c h e m i s t s v i e w p o i nt , and i s i n a g r e em en tw i t h a d i c t i o n a r y d e f i n i t i o n of " c h a r a c t e r i s t i c of or e x p l a i n a b l e byt h e o p e r a t i o n s of t h e p h y s i c a l w o r l d " .How ev e r , The Food and Drug A d m i n i s t r a t i o n d e f i n i t i o n s ( 4 8 ) a r e :"The term ' a r t i f i c i a l f l a v o r ' or ' a r t i f i c i a l f l a v o r i n g ' means anys u b s t a n c e , the f u n c t i o n of w h i c h i s to im par t f l a v o r , w h i c h i s notd e r i v e d f r o m a s p i c e , f r u i t or f r u i t j u i c e , v e g e t a b l e or v e g e t a b l ej u i c e , ... , or f e r m e nt a t i o n p r o d u c t s t h e r e o f . ... The t e rm' n a t u r a l f l a v o r ' or ' n a t u r a l f l a v o r i n g ' means t h e e s s e n t i a l o i l ,o l e o r e s i n , e s s e n c e or e x t r a c t i v e , p r o t e i n h y dr o l y s a t e , d i s t i l l a t e orany p r od u c t of r o a s t i n g , h e at i n g or e n z y m o l y s i s , w h i c h c o n t a i n s thef l a v o r i n g c o n s t i t u e n t s d e r i v e d f r o m a s p i c e , f r u i t or f r u i t j u i c e ,v e g e t a b l e or v e g e t a b l e j u i c e , e d i b l e y e a s t , h e r b , b a r k, b ud, r o o t ,l e a f or s i m i l a r p l a n t ma t e r i a l , meat, s e af o od , p o u l t r y , e g g s , d a i r yp r o d u c t s , or f e r me n t a t i o n p r o d uc t s t h e r e o f . " I t i s t h i s s e t ofw o r d s , "or f e r m e nt a t i o n p r o d u c t s t h e r e o f " , w h i c h has s e t o f f af l u r r y of a c t i v i t y i n b i o t e c h n o l o g y i n o r d e r to use t h e w o r d s" n a t u r a l f l a v o r i n g " on the l a b e l of f o o d p r o d u c t s .The p u b l i c has an u n b a s e d f e a r o f c h e m i c a l s " and " s y n t h e t i c s " and anu n b a s e d c o n f i d e n c e i n " n a t u r a l " compounds and p r o d u c t s . The p u b l i cs h o u l d be e d u ca t ed t h a t t h e r e ar e no d i f f e r e n c e s i n t h e mo l e c ul e su s e d i n f l a v o r i n g s w h i c h ar e made by man i n f l a s k s or by p l a n t s anda n i m a l s . How ev e r , b e c a u s e of t h i s f e a r , t h e re i s a t r e n d i n t h e useo f " n a t u r a l s " , ma t e r i a l s f r o m p l a n t s and animal s ( i n c l u d i n g m i c r o o r g a n i s m s ) o b t a i n e d by b i o t e c h n o l o g y , o v er " s y n t h e t i c s " , m a t e r i a l sf r o m c h e m i c a l l a b o r a t o r i e s .P l a n t s and animal s h a v e b e e n s e l e c t e d by c l a s s i c a l g e n e t i c methodsf o r o p t imum y i e l d , c o l o r , t e x t u r e , d i s e a s e r e s i s t a n c e , e t c . I t i st i me f o r p l a n t s and animal s to be s e l e c t e d f o r o p t imum f l a v o r . In

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1. TERANSHI N ew Trends and Developments in FlavorChemistry 3t h i s l o n g r a n g e p l a n , f l a v o r c h e m i s t r y w i l l h e l p i n t h e s e l e c t i o n o fp l a n t s and animals fo r a c c e p t a b i l i t y w h e t h e r i t i s by t he c l a s s i c a lo r modern g e n e t i c e n g i n e e r i n g me t h o d s .I n t h e s h o r t r a n g e p l a n , r aw m a t e r i a l s c an b e h a r v e s t e d , p r o c e s s e d ,s t o r e d and s h i p p e d t o b r i n g more f l a v o r f u l f o o d p r o d u c t s t o c o n s u me r s . V e r y f ew f o o d p r o d u c t s a r e u s e d d i r e c t l y as g r o w n on thef a rm. G r a i n s must be m i l l e d , made i n t o f l o u r , and then baked t omake breads and other c e r e a l p r o d u c t s . F r u i t s and v e g e t a b l e s mustb e p i c k e d a t a t i me t o g i v e o p t imum f l a v o r and t e x t u r e . Most mea t s ,r e d o r w h i t e f l e s h , a r e a lmo s t f l a v o r l e s s u n t i l h e a t e d. C h emi c a lr e a c t i o n s i n v o l v e d i n t he above s i t u a t i o n s must b e u n d e r s t o o d i no r d e r t o b r i n g f o o ds t o c o n s um e r s a t o p t imum a c c e p t a b i l i t y .The d ev elopmen t o f modern a n a l y t i c a l methods h as p e r m i t t e d t h e e x amina t i o n o f v o l a t i l e s f r om f r e s h f r u i t t o d e t e rmin e w h en t o p i c kt h e f r u i t . I t i s t h e u s u a l c o nc e pt t h a t f r u i t s a r e a t t h e i r b e s tw h e n p i c k e d " t r e e - r i p e " . However, i n e x t r em e c a s e s , a s w i t h bananasand p e a r s , t h e s e f r u i t s must b e p i c k e d w h en har d and gre en and bep e r m i t t e d t o s o f t e n and r i p e n o f f t h e t r e e . I f t he s e f r u i t s a r ep e r m i t t e d t o r i p e n on t h e t r e e , t h e y become mea ly a n d u n a c c e p t a b l e .Some f r u i t , l i k e s t r a w b e r r i e s and p e a c h e s , a r e o f b e s t q u a l i t y w h enl e f t t o r i p e n o n t h e p l a n t s . A p p l e s h a v e b e e n shown t o have t h eb e s t aroma i f p i c ke d a l mo s t r i p e and develop the mos t aroma a b o u t aw e ek or two a f t e r p i c k i n g .Man has u s e d b i o t e c h n o l o g y f o r c o n v e r t i n g raw m a t e r i a l s t o f o o d p r o d u c t s f o r many c e n t u r i e s . P r o d u c t i o n o f b e e r i s t h o ug h t t o d at eb a ck t o a b o u t 6000 BC i n a n c i e n t B a b y l o n i a . Th e p r e d e c e s s o r s o f s o ys a u c e and mi s o seem t o have o r i g i n a t e d i n C h i n a some 2500 y e a r sag o. Man ha s b e e n u s i n g p r o du c t s a l t e r e d by micro or gani sms, and hasl e a r n e d by t r i a l and e r r o r w h i c h o f t h e p r o d u c t s a r e s a f e t o e a t a ndw h i c h a r e n o t . Modern s c i e n t i f i c methods a r e now b e i n g a p p l i e d t oe x p l a i n w ha t chemical and p h y s i c a l a l t e r a t i o n s a r e a c c omp l i s h e d b ym i c r o o r g a n i s m s . A l s o , f u r t h e r advan cemen ts i n b i o t e c h no l o g y w i l lp r o b a b l y b e made t o make s u c h s y s t e m s e v e n more e f f i c i e n t , p e r h a p se v e n b y p a s s l i v i n g o r g a n i sm s b y u s i n g o n l y enzymes. As more andmore compounds a r e c o r r e l a t e d w i t h c h a r a c t e r i s t i c f l a v o r s , t h e r e i sa t r e n d t o s t u d y f l a v o r p r e c u r s o r s and t o e x p l a i n how f l a v o r i sd e ve l o p e d and r e l e a s e d , e s p e c i a l l y s i n c e now i t c an b e d e t e rmine de x a c t l y w h i c h e nant i ome r i s making t h e c o n t r i b u t i o n t o a c h a r a c t e r i s t i c aroma.The e r a o f p u b l i s h i n g a l a r g e number o f compounds i d e n t i f i e d a s t oc h e m i c a l s t r u c t u r e s i s s l o w l y c h an g in g t o an e r a i n w h i c h c o n s t i t u e n t s a r e i d e n t i f i e d a s t o w h i c h a r e t h e i m p o r t a nt c o n t r i b u t o r s t ot h e c h a r a c t e r i s t i c o d o r s . More and more s e n s o r y a n a l y s e s a r e s t a t i n g o d o r t h r e s h o l d v a l u e s a s w e l l as o d o r q u a l i t y .I n t h e e v a l u a t i o n o f c o n t r i b u t i o n t o t a s t e , amino a c i d s and p e p t i d e sa r e b e i n g s t u d i e d as t o s w e e t , s a l t y , b i t t e r , sour and umami [ b r o t h ymo u t h - f e e l , s e e ( 1 9) ] s e n s a t i o n s . I n t h e p r o d u c t i o n o f g r a v i e s ands o u p s , p r o t e i n s a r e h y d r o l y z e d t o s m a l l e r mo l e c u l e s w h i ch ev oke

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4 FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTSmore t a s t e s e n s a t i o n s t h a n do t h e l a r g e p r o t e i n m o l e c u l e s . S y s t e m a t i c s t u d i e s of amino a c i d s and p e p t i d e s a r e p r o v i d i n g i n t e r e s t i n g d a t a w h i c h w i l l be u s e f u l i n o p t i m i z i n g c o n d i t i o n s to y i e l dt h e g r e a t e s t amount of a c c e p t a b l e t a s t e s and m i n i m i z i n g u n d e s i r a b l et a s t e s .

A s a n a l y t i c a l m e t h o d o l o g y i s i m p r o v e d , t h e known number of comp o u n d s c o n t r i b u t i n g to f l a v o r w i l l be i n c r e a s e d , and f l a v o r c h e m i s t r y w i l l become more a p p l i e d . I n d u s t r i a l o r g a n i z a t i o n s w i l l bea b l e to u t i l i z e t h e i n f o r m a t i o n g a i n e d i n f u n d am e n t a l r e s e a r c h toi m p r o v e t h e q u a l i t y of t h e i r p r o d u c t s . At t h e same t i m e , t h e r e w i l lb e more of a d a t a b a s e on w h i c h to b u i l d a b e t t e r u n d e r s t a n d i n g oft h e mechanisms of p e r c e p t i o n of t a s t e and o l f a c t i o n .

A s t h e demand f o r n a t u r a l f l a v o r s i n c r e a s e s , and as c o n s t i t u e n t sc o n t r i b u t i n g to s u c h f l a v o r s a r e i d e n t i f i e d , f l a v o r c h e m i s t r y w i l lb e a p p l i e d i n t h e b i o t e c h n o l o g i c a l p r o d u c t i o n of s u c h f l a v o r s .A l s o , p r o c e s s i n g met h od s w i l l be f o l l o w e d to r e t a i n most of thef r e s h f l a v o r s of raw m a t e r i a l s . C a s e s i n w h i c h f l a v o r i s d e v e l o p e d d u r i n g p r o c e s s i n g , modern a n a l y t i c a l methods w i l l be a p p l i e d toa d j u s t p r o c e s s i n g c o n d i t i o n s to p r o d u c e t h e o p t imum d e s i r a b l ef l a v o r s . T h u s , f l a v o r c h e m i s t r y has r e a c h e d a s t a g e w h e r e i t i s nowb e i n g a p p l i e d to i m p r o v e t h e f l a v o r of f o o d s , f r e s h and p r o c e s s e d ,r e a c h i n g many c o n s u m e r s .

Literature Cited1. Weurman, C. Lists of Volat i le Compounds in Foods, 1st Edit ion;Division of Nutrition and Food Research TNO: Zeist, TheNetherlands, 1963.2 . Volat i le Compounds in Food; S. van Straten and H. Maarse, Ed.;Division of Nutrition and Food Research TNO: Zeist, TheNetherlands, 1983. Supplement 1, 1984; 2, 1985; 3, 1986; 4,1987.3. Symposium on Foods: The Chemistry and Physiology of Flavors; H.

W . Schultz, E. A. Day, and L. M. Libbey, Ed.; A V I : Westport,Connecticut, 1967; 552 pp.4. Gustation and Olfaction; G. Ohloff and A. F. Thomas, Ed.;Academic Press: London, 1971; 274 pp.5. Teranishi, R., I. Hornstein, P. Issenberg, and E. L. Wick.Flavor Research: Principles and Techniques; Marcel Dekker, Inc.:New York, 1971; 315 pp.6. Aroma Research; H. Maarse and P. J. Groenen, Ed.; Pudoc:Wageningen, 1975; 245 pp.7. Geruch- and Geschmackstoffe; F. Drawert, Ed.; H. Car l : Nurnberg,1975; 299 pp.8. Phenolic, Sulfur, and Nitrogen Compounds in Food Flavors; G.Charalambous and I. Katz, Ed.;ACS Symposium Series 26. AmericanChemical Society: Washington, DC, 1976; 215 pp.9. Progress in Flavour Research; D. G. Land and H. E. Nursten, Ed.;Applied Science Publishers, Ltd.: London, 1979; 371 pp.

1 0 . Food Taste Chemistry; J. C. Boudreau, Ed.; ACS Symposium Series115, AC S : Washington, DC, 1979; 262 pp.1 1 . Flavour '81; P. Schreier, Ed.; de Gruyter: Ber l in , 1981; 780 pp.

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1. TERANISHI NewTrendsandDevelopments inFlavorChemistry12. Flavor Research: Recent Advances; R. Teranishi, R. A. Flath, andH. Sugisawa, Ed.; Marcel Dekker, Inc.: New York, 1981; 381 pp.13. Analysis of Volatiles; P. Schreier, Ed.; de Gruyter: Berl in ,

1984; 469 pp.14. Analysis of Foods and Beverages: Modern Techniques; G.Charalambous,Ed.; Academic Press: New York, 1984; 652 pp.15. Progress in Flavour Research 1984; J . Adda, Ed.; Elsevier:Amsterdam, 1985.16. Topics in Flavour Research; R. G. Berger, S. Nitz , and P.Schreier, Ed.; H. Eichorn: D-8051 Marzling-Hangenham, 1985; 476pp.17. Chemical Changes in Food during Processing; T. Richardson and J.W. Finley, Ed.; AVI: Westport, Connecticut, 1985; 514 pp.18. Chemistry of Heterocyclic Compounds in Flavours and Aromas; G.Vernin, Ed.; E l l i s Horwood, Ltd.: Chichester, 1982; 375 pp.19. Umami: A Basic Taste; Y. Kawamura and M. R. Kare, Ed.; MarcelDekker, Inc.: New York, 1987; 649 pp.20. Flavour Science and Technology; M. Martens, G. A. Dalen and H.Russwurm, Jr., Ed.; Wiley: London, 1987; 566 pp.21. Ohloff, G. Importance of minor components in flavors andfragrances. Perfumer and Flavorist 1978, 3, 11.22. Ohloff, G., Recent developments in the f ie ld of naturally--occurringaroma components. In Progress in the Chemistry ofOrganic Natural Products, 1978, Vol. 35, p. 431, (founded by L.Zechmeister) W. Herz, H. Griseback, G. W. Kirby, Ed.;Springer-Verlag: Wien - New York.23. Ohloff, G., and I. Flament. Some recent aspects of thechemistry of naturally occuring pyrazines. In The Quality ofFoods and Beverages. Chemistry and Technology. Vol. 1, G.Charalambous and G. Inglett, Ed.; Academic Press: New York,1981; p. 35.24. Ohloff, G., I. Flament,, and W. Pickenhagen. Flavor chemistry,Food Reviews International, 1985, 1(1): 99.25. Maga, J. ., and C. E. Sizer. Pyrazines in foods, Handbook ofFlavor Ingredients, 2nd Edition, vol. 1; CRC Press: Cleveland,1975, p. 47.

26. Maga. J. A. Thiazoles in foods, i b i d . , p. 228.27. Maga, J. A. Bread flavor, i b i d . , p. 669.28. Maga, J. A. The role of sulfur compounds in food flavor. PartI. Thiazoles, CRC C r i t . Rev. Food Sci. Nutr., 1975, 6(2): 153.29. Maga, J. ., Part II. Thiophenes, i b i d . , 241.30. Maga, J. ., Part III. Thiols, i b i d . , 1976,7(2): 147.31. Maga, J. ., Lactones in food, i b i d . , 8(1): 1.32. Maga, J. ., Phenolics in food, i b i d . , 1978, 10(4): 323.33. Maga, J. ., Amines in food, i b i d . , 10(4): 373.34. Maga, J. ., Furans in food, i b i d . , 1979, 11(4): 355.35. Maga, J. ., The chemistry of oxazoles and oxazolines in food,i b i d . , 1981, 14(3): 285.36. Maga, J. ., Pyrazines in foods: an update, i b i d . , 1982, 16: 1.37. Maga, J. ., Flavor potentiators, i b i d . , 1984, 18: 231.38. Maga, J. ., The flavor chemistry of wood smoke, Food ReviewsInternational, 1987, 3(1 & 2): 139.39. Bel i t z , H. -D . , and H. Wieser. Bitter compounds: occurrence andstructure-activity, i b i d . , 1985, 1(2): 271.

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6 FLAVOR CHEMISTRY: TRENDS ANDD EVELOPMENTS40. Petro-Turza, M. Flavor of tomato and tomato products, i b i d . ,1986-1987, 2(3): 309.41. Carson, J. F. Chemistry and biological properties of onions and

garlic, i b i d . , 1987, 3(1 & 2): 71.42. Fukushima, D. Fermented vegetable protein and related foods ofJapan and China, i b i d . , 1985, 1(1): 149.43. Bioflavour '87; edited by P. Schreier, in press.44. Toxic Constituents of Plant Foodstuffs; I. E. Liener, Ed.;Academic Press: NewYork, 1969; 500 pp.45. Hirono, I. Natural carcinogenic products of plant origin, CRCCr i t . Rev. Toxicol. 1981, 8(3), 235-277.46. Nutritional and Toxicological Aspects of Food Safety; M.Friedman, Ed.; Plenum Press: NewYork, 1984; 584 pp.47. Plant Toxicology; M. P. Hegarty, L. F. James, R. F. Keeler, Ed.;Dominion Press: Melbourne, 1985; 623 pp.48. Code of Federal Regulations, Food and Drugs, Vol. 21, Part101.22, Office of the Federal Register, National Archives andRecords Administration, U. S. Government Printing Office:Washington, D. C., Apr i l , 1988.

RECEIVED August 30, 1988

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