New Trends and Developments in Flavor Chemistry - ACS Symposium

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Chapter 1

New Trends and Developments in Flavor Chemistry

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An Overview Roy Teranishi Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, CA 94710

This chapter gives an overview of new trends and developments in flavor chemistry. One important development was made possible by advances in analytical methodology, that i s , the identification of numerous compounds with known flavor characteristics. As more and more compounds are correlated with characteristic flavors, there is a trend to study flavor precursors and to explain how flavor is developed and released. Many of the newest developments in flavor chemistry are in the area of flavor production from plant and animal sources; this trend has come about because of the public's fear of the words "chemical" and "synthetic". In this chapter, words such as these are discussed in terms of the public's perception of them versus a chemist's viewpoint. Another new trend is to understand the chemical reactions involved in the processing and storage of foods in order to bring foods to consumers at optimum acceptability. P r i o r to the 1950»s only about 500 flavor compounds were known (1). Since then, with the advent of modern instrumention, thousands of compounds have been characterized i n 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 and some on special occasions and t o p i c s , covering various aspects of flavor (3-20). Also, there are many excellent reviews which every serious flavor chemist should consult (21-43). 1

Advances i n a n a l y t i c a l methodology introduced i n the I960 s were applied from the early 1970»s (3 5, 12, 131 14). Previous to gas chromatography, f r a c t i o n a l d i s t i l l a t i o n s and column chromatography of colored derivatives were the primary means of separations. Size of sample required for d i s t i l l a t i o n i s , of course, enormous compared to what i s required for gas chromatography. The resolution of separ a t i o n by gas chromatography i s far superior to that attained by f

This chapter not subject to U.S. copyright Published 1989 American Chemical Society Teranishi et al.; Flavor Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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f r a c t i o n a l d i s t i l l a t i o n . Also, the advent of i n f r a r e d , nuclear magnetic resonance, and mass spectrometry has made i t possible t o make s t r u c t u r a l determinations with micro amounts. Thus, with the use o f modern a n a l y t i c a l methods, the number o f compounds with known f l a v o r c h a r a c t e r i s t i c s increased i n the 1970's and 1980's. These advances have set the stage f o r the present trends and developments i n f l a v o r chemistry.

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Many of the newest developments i n f l a v o r chemistry are i n the area of flavor production from plant and animal sources; hence, s i g n i fying the popularity of the term "biotechnology". This trend has come about because of the fear of the public of the words "chemical" and "synthetic". The word "natural" i s used i n opposition t o the word "synthetic" with the connotation that "natural" products are safer than "synt h e t i c s " , but there are many toxins made by plants and animals which are very detrimental to man (44-47). Moreover, whether chemicals are made i n f l a s k s by man or made by plants and animals, no compounds are made on earth other than those permitted by the laws of nature. Therefore, a l l molecules on t h i s earth are "natural". This d e f i n i t i o n i s from a c h e m i s t s viewpoint, and i s i n agreement with a dictionary 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 explainable by the operations of the physical world". However, The Food and Drug Administration d e f i n i t i o n s (48) are: "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 any substance, the function of which i s t o impart f l a v o r , which i s not derived from a spice, f r u i t or f r u i t j u i c e , vegetable or vegetable j u i c e , ... , or fermentation products thereof. ... The term 'natural f l a v o r ' or 'natural f l a v o r i n g ' means the e s s e n t i a l o i l , oleoresin, essence or e x t r a c t i v e , protein hydrolysate, d i s t i l l a t e or any product of r o a s t i n g , heating or enzymolysis, which contains the f l a v o r i n g constituents derived from a spice, f r u i t or f r u i t j u i c e , vegetable or vegetable j u i c e , edible yeast, herb, bark, bud, root, l e a f or s i m i l a r plant m a t e r i a l , meat, seafood, p o u l t r y , eggs, dairy products, or fermentation products thereof." I t i s t h i s set of words, "or fermentation products thereof", which has set o f f a f l u r r y of a c t i v i t y i n biotechnology i n order t o use the words "natural f l a v o r i n g " on the l a b e l of food products. The p u b l i c has an unbased fear o f c h e m i c a l s " and "synthetics" and an unbased confidence i n "natural" compounds and products. The p u b l i c should be educated that there are no differences i n the molecules used i n flavorings which are made by man i n f l a s k s or by plants and animals. However, because of t h i s fear, there i s a trend i n the use of "naturals", materials from plants and animals (including microorganisms) obtained by biotechnology, over "synthetics", materials from chemical laboratories. Plants and animals have been selected by c l a s s i c a l genetic methods for optimum y i e l d , c o l o r , texture, disease resistance, etc. I t i s time f o r plants and animals t o be selected for optimum f l a v o r . In

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

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t h i s long range plan, flavor chemistry w i l l help i n the selection of plants and animals for a c c e p t a b i l i t y whether i t i s by the c l a s s i c a l or modern genetic engineering methods.

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In the short range plan, raw materials can be harvested, processed, stored and shipped to bring more f l a v o r f u l food products to consumers. Very few food products are used d i r e c t l y as grown on the farm. Grains must be m i l l e d , made i n t o f l o u r , and then baked to make breads and other cereal products. F r u i t s and vegetables must be picked at a time to give optimum f l a v o r and texture. Most meats, red or white f l e s h , are almost f l a v o r l e s s u n t i l heated. Chemical reactions involved i n the above s i t u a t i o n s must be understood i n order to bring foods to consumers at optimum a c c e p t a b i l i t y . The development of modern a n a l y t i c a l methods has permitted the examination of v o l a t i l e s from fresh f r u i t to determine when to pick the f r u i t . I t i s the usual concept that f r u i t s are at t h e i r best when picked "tree-ripe". However, i n extreme cases, as with bananas and pears, these f r u i t s must be picked when hard and green and be permitted to soften and ripen o f f the tree. I f these f r u i t s are permitted to ripen on the t r e e , they become mealy and unacceptable. Some f r u i t , l i k e strawberries and peaches, are of best q u a l i t y when l e f t to ripen on the plants. Apples have been shown to have the best aroma i f picked almost ripe and develop the most aroma about a week or two a f t e r picking. Man has used biotechnology f o r converting raw materials to food products for many centuries. Production of beer i s thought to date back to about 6000 BC i n ancient Babylonia. The predecessors of soy sauce and miso seem to have originated i n China some 2500 years ago. Man has been using products altered by microorganisms, and has learned by t r i a l and error which of the products are safe to eat and which are not. Modern s c i e n t i f i c methods are now being applied to explain what chemical and physical a l t e r a t i o n s are accomplished by microorganisms. Also, further advancements i n biotechnology w i l l probably be made to make such systems even more e f f i c i e n t , perhaps even bypass l i v i n g organisms by using only enzymes. As more and more compounds are correlated with c h a r a c t e r i s t i c f l a v o r s , there i s a trend to study flavor precursors and to explain how flavor i s developed and released, e s p e c i a l l y since now i t can be determined exactly which enantiomer i s making the contribution to a characteri s t i c aroma. The era of publishing a large number of compounds i d e n t i f i e d as to chemical structures i s slowly changing to an era i n which c o n s t i tuents are i d e n t i f i e d as to which are the important contributors to the c h a r a c t e r i s t i c odors. More and more sensory analyses are s t a t i n g odor threshold values as well as odor q u a l i t y . In the evaluation of contribution to taste, amino acids and peptides are being studied as to sweet, s a l t y , b i t t e r , sour and umami [brothy mouth-feel, see (19)] sensations. In the production of gravies and soups, proteins are hydrolyzed to smaller molecules which evoke

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

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FLAVOR CHEMISTRY: TRENDS AND DEVELOPMENTS more taste sensations than do the large protein molecules. Systematic studies of amino acids and peptides are providing i n t e r esting data which w i l l be useful i n optimizing conditions to y i e l d the greatest amount of acceptable tastes and minimizing undesirable tastes. As a n a l y t i c a l methodology i s improved, the known number of compounds contributing t o f l a v o r w i l l be increased, and f l a v o r chemis t r y w i l l become more applied. I n d u s t r i a l organizations w i l l be able t o u t i l i z e the information gained i n fundamental research to improve the q u a l i t y of t h e i r products. At the same time, there w i l l be more of a data base on which t o b u i l d a better understanding of the mechanisms of perception of taste and o l f a c t i o n . As the demand for natural f l a v o r s increases, and as constituents contributing t o such f l a v o r s are i d e n t i f i e d , f l a v o r chemistry w i l l be applied i n the biotechnological production of such f l a v o r s . Also, processing methods w i l l be followed t o r e t a i n most of the fresh f l a v o r s of raw materials. Cases i n which f l a v o r i s developed during processing, modern a n a l y t i c a l methods w i l l be applied t o adjust processing conditions t o produce the optimum desirable f l a v o r s . Thus, f l a v o r chemistry has reached a stage where i t i s now being applied t o improve the f l a v o r of foods, fresh and processed, reaching many consumers.

Literature Cited 1. Weurman, C. Lists of Volatile Compounds in Foods, 1st Edition; Division of Nutrition and Food Research TNO: Zeist, The Netherlands, 1963. 2. Volatile Compounds in Food; S. van Straten and H. Maarse, Ed.; Division of Nutrition and Food Research TNO: Zeist, The Netherlands, 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.; AVI: 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. Carl: Nurnberg, 1975; 299 pp. 8. Phenolic, Sulfur, and Nitrogen Compounds in Food Flavors; G. Charalambous and I. Katz, Ed.;ACS Symposium Series 26. American Chemical 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. 10. Food Taste Chemistry; J. C. Boudreau, Ed.; ACS Symposium Series 115, ACS: Washington, DC, 1979; 262 pp. 11. Flavour '81; P. Schreier, Ed.; de Gruyter: Berlin, 1981; 780 pp.

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

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12. Flavor Research: Recent Advances; R. Teranishi, R. A. Flath, and H. Sugisawa, Ed.; Marcel Dekker, Inc.: New York, 1981; 381 pp. 13. Analysis of Volatiles; P. Schreier, Ed.; de Gruyter: Berlin, 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; 476 pp. 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.; Ellis Horwood, Ltd.: Chichester, 1982; 375 pp. 19. Umami: A Basic Taste; Y. Kawamura and M. R. Kare, Ed.; Marcel Dekker, 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 and fragrances. Perfumer and Flavorist 1978, 3, 11. 22. Ohloff, G., Recent developments in the field of naturally­ -occurring aroma components. In Progress in the Chemistry of Organic 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 the chemistry of naturally occuring pyrazines. In The Quality of Foods 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. Α., and C. E. Sizer. Pyrazines in foods, Handbook of Flavor Ingredients, 2nd Edition, vol. 1; CRC Press: Cleveland, 1975, p. 47. 26. Maga. J. A. Thiazoles in foods, ibid., p. 228. 27. Maga, J. A. Bread flavor, ibid., p. 669. 28. Maga, J. A. The role of sulfur compounds in food flavor. Part I. Thiazoles, CRC Crit. Rev. Food Sci. Nutr., 1975, 6(2): 153. 29. Maga, J. Α., Part II. Thiophenes, ibid., 241. 30. Maga, J. Α., Part III. Thiols, ibid., 1976,7(2): 147. 31. Maga, J. Α., Lactones in food, ibid., 8(1): 1. 32. Maga, J . Α., Phenolics in food, ibid., 1978, 10(4): 323. 33. Maga, J. Α., Amines in food, ibid., 10(4): 373. 34. Maga, J. Α., Furans in food, ibid., 1979, 11(4): 355. 35. Maga, J. Α., The chemistry of oxazoles and oxazolines in food, ibid., 1981, 14(3): 285. 36. Maga, J. Α., Pyrazines in foods: an update, ibid., 1982, 16: 1. 37. Maga, J. Α., Flavor potentiators, ibid., 1984, 18: 231. 38. Maga, J. Α., The flavor chemistry of wood smoke, Food Reviews International, 1987, 3(1 & 2): 139. 39. Belitz, H.-D., and H. Wieser. Bitter compounds: occurrence and structure-activity, ibid., 1985, 1(2): 271.

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

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40. Petro-Turza, M. Flavor of tomato and tomato products, ibid., 1986-1987, 2(3): 309. 41. Carson, J. F. Chemistry and biological properties of onions and garlic, ibid., 1987, 3(1 & 2): 71. 42. Fukushima, D. Fermented vegetable protein and related foods of Japan and China, ibid., 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: New York, 1969; 500 pp. 45. Hirono, I. Natural carcinogenic products of plant origin, CRC Crit. Rev. Toxicol. 1981, 8(3), 235-277. 46. Nutritional and Toxicological Aspects of Food Safety; M. Friedman, Ed.; Plenum Press: New York, 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, Part 101.22, Office of the Federal Register, National Archives and Records Administration, U. S. Government Printing Office: Washington, D. C., April, 1988. RECEIVED August 30, 1988

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