FLAVOR CHEMISTRY OF ETHNIC FOODS Edited by FERHDOON SHAH|D| and CHI-TANG HQ Flavor Chemistry of Ethnic Foods Flavor Flavor Chemistry Chemistry of of Ethnic Ethnic Foods Foods Edited Edited by by Fereidoon Fereidoon Shahidi Shahidi Department Department of of Biochemistry Biochemistry Memorial Universiry Memorial University of of Newfoundland Newfoundland St St lOM John S ‘s, Newfoundland Newfoundland AlB AIB 3X9 3X9 Canada Canada Chi-Tang Chi—Tang Ho Ho Deparrmenr of Food Science Department of Fond Science Cook C00k College C0 lleg e Rutgers The State Universiry University of New lersey Jersey P.O Box 231 PO New Brunswick Brunswick, Nl08903-023/ NJ 08903-0231 Springer Science+Business Science+Business Media, Media, LLC LLC Springer Llbrary Data Library of of Congress Congress Cataloglng-In-Publlcatlon Cataloging—in—Pub1ication Data Flavor ehe.lstry cheulstry of of ethnle ethnic faods Foods // [edlted [edited byl by] Fereldoon Feraidoon Shahldl Shahidi, Chl Chi Flavor -Tang —Tang Ho Ho p ecu • "Proeeedlngs Che.lcal Congress Cangress "Proceedings of a meetlng meeting held durlng during the Flfth Fifth Chemical of of Narth North A.erlea America, held held NoveMber November 11-15 11-15, 1997 1997 In in Caneun Cancun, Mexlea"Mexico'-T.p -T.p versa verso Ineludes Includes blbllagraphieal bibliographical referenees reFerences and and Index index ISBN 978-1-4613-7166-3 ISBN 978-1-4615-4783-9 (eBook) DOI 10.1007/978-1-4615-4783-9 1 Flavor Flavor 2 Foad Odar Food——0dor 3 Coakery Cookery, International International I Shahldl Shahldl, Fereldaan Fereldoon, 19511951 II II Ha Ho Chl-Tang Chl—Tang, 19441944— III Caneun III Chemleal Chemical Cangress Congress of of North North AMerica America (5th (5th ,= 1997 1997 :, Cancfin, Mexleal Mexico) TP372.5.F54 TP372.5.F54 1999 1999 664' 884' de21 5——dc21 99-28547 CIP CIP Proceedings in Proceedings of of aa meeting meeting held held during during the the Fifth Fifth Chemical Chemical Congress Congress ofNorth of North America, America, held held November November 11-15,1997, ll-15, 1997 in Cancun, Mexico ISBN ISBN 978-1-4613-7166-3 978-1-4613-7166-3 ©1999 Springer Science+Business Media New York I Plenum Publishers in 1999 Origina1ly Originally published by Kluwer Academic Academic/Plenum Softcover reprint of the hardcover 11 st edition 1999 10 I l098765432l A C.I.P C.l.P record for this book is available from the Library of Congress AII All rights reserved No part any form by any No part of of this this book book may may be be reproduced, reproduced, stored stored in in aa retrieval retrieval system, system, or or transmitted transmitted in in any form or or by any means, means, electronic, from the electronic, mechanical, mechanical, photocopying, photocopying, microfilming, microfilming, recording, recording, or or otherwise, otherwise, without without written written permission permission from the Publisher PREFACE Flavor is an important quality characteristic of all foods Both odorod0r- and taste-active flavor is a chemically-derived phenomecomponents are involved Although perception of flavor non, a flavor's flavor’s acceptability and desirability is highly affected by the cultural background and ethnic diversity of the consumers On this basis, there are distinct differences and particularities in the ingredients as well as the methods of preparation of foods in different respecific environment, culture, and gions of the world, and these are also affected by the specific flavors of foods, induced by processing, are also ethnicity of the people Changes in the flavors important factors affecting their diversity and characteristics The use of different types of fish sauce, as well as condiments and spices, sauce, such as soy sauce, tomato sauce, and fish defining the cultural and international nature of prepared is of particular importance in defining foods The source of raw material, particularly when they are available only in certain parts of the world, can also have a profound effect on the availability and popularity of such products The availability of better and faster modes of transportation and the migration of individuals, each resulting in the intermingling of different cultures, have allowed production of a new generation of prepared foods such as American-Chinese, among others The present monograph assembles a collection of scientific scientific contributions on flavor flavor and chemistry of international foods presented during the 5'“ 5th Chemical Congress of North America, 1997, in America, held held in in November November 1997, in Cancun, Cancun, Mexico, Mexico, or or subsequently subsequently solicited solicited by by the the editors We are grateful to the authors for their outstanding cooperation and contributions that made the production of this state-of-the-art monograph possible Fereidoon Shahidi Shahidi Fereidoon Chi-Tang Ho Ho Chi-Tang v V CONTENTS CONTENTS Flavor and Chemistry of Ethnic Foods: An Overview C.- T Ho F Shahidi and C.-T Flavor Components of Shoyu and Miso Japanese Fermented Soybean Seasonings Akio Kobayashi and Etsuko Sugawara l ofIndonesian Flavor Characteristics of Indonesian Soy Sauce (Kecap Manis) A Apriyantono, H Husain, L Lie, M Jodoamidjojo, and N L Puspitasari-Nienaber 15 Volatile Compounds Isolated from Sa Cha Sauce Chao-Yin Tai and Chi-Tang Ho 33 ofFish Formation Fomiation of Volatile Acids during Fermentation Fennentation of Fish Sauce Sauce Norlita G Sanceda, Emiko Suzuki, and Tadao Kurata 41 Flavor Chemistry of Selected Condiments and Spices Used in Chinese Foods Chi-Tang Ho, Jiangang Li, and May-Chien Kuo 55 Character-Impact Aroma Components of Coriander (Coriandrum sativum L.) Herb Herb K R Cadwallader, R Surakamkul, S.-P Yang, and T E Webb Wasabi, Japanese Horseradish, and Horseradish: Relationship between Stability and Antimicrobial Properties of Their Isothiocyanates Hideki Masuda, Yasuhiro Harada, Toshio Inoue, Noriaki Kishimoto, and Tatsuo Tano Flavor Characteristics and Stereochemistry of the Volatile Constituents of Greater Galangal (Alpinia galanga Willd.) Kikue Kubota, Yuki Someya, Yoshiko Kurobayashi, and Akio Kobayashi 10 Pandan Leaves (Pandanus amarjyllifolius) amaryllifolius) l0 Volatile Composition of Pandan J Jiang 77 85 97 105 vii VII viii Vlll 11 11 Emission of Blanched Broccoli Volatiles in Headspace during Cooking Piiivi Raimoaho, and Tuomas Virtalaine Heikki Kallio, Paivi Contents 111 111 12 12 Flavor of Kweni (Mangifera odorata Griff), an Exotic Tropical Fruit Fmit C H Wijaya, A Apriyantono, T May, H Raharja, and T T A Ngakan 119 119 13 13 Use of Electronic Nose Technology to Examine Apple Quality Arthur M Spanier, John C Beaulieu, Karen L Bett, and Ken Gross 127 127 14 14 Flavor and Chemistry of Uncured and Cured Meat of Harp Seal (Phoca groenlendica) Fereidoon Shahidi and Ming-Xia Lin 141 141 Pyrazinesin 15 in Pan-Fried Zousoon 15 Characterization of Volatile Aldehydes and Pyrazines Tzou-Chi Huang, Yea-Chyi Chiou, and Chi-Tang Ho 151 151 16 16 Changes in Flavor-Related Compounds in Meat Treated with Organic Acids Hector Escalona, Sharon K Ogden, Isabel Guerrero, and Andrew J Taylor 159 159 17 17 Flavor Differences Due to Processing in Dry-Cured and Other Ham Products Using Conducting Polymers (Electronic Nose) Toldni Arthur M Spanier, Monica Flores, and Fidel Toldra 169 169 18 Thermally Generated Volatiles in Roselle Tea 18 Thennally Pi-Jen Tsai, Tzou-Chi Huang, Shyh-Hung Chen, and Chi-Tang Ho 185 185 19 19 Phenolic Compounds as Astringent Factors in Black Tea Liquors E Ponce and A J Taylor 197 197 20 Tequila Aroma 20 Mercedes G Lopez 211 211 21 21 The Formation and Release of Odor Active Compounds during Oxidation of Vegetable Oils Oils Vegetable J P Roozen, P A Luning, and M A Posthumus 219 219 22 Influence of Seed Roasting Process on the Changes in Volatile Compounds of 22 Influence the Sesame (Sesamum indicum L.) Oil Oil Su Noh Ryu, Seong Min Kim, Junwu Xi, and Chi-Tang Ho 229 Ix) l\) \O 23 Volatile Components Formed from Various Sugars with B-Alanine I)-Alanine in Actual 23 Cookies Sukie Nishibori, Toshihiko Osawa, and Shunro Kawakishi 239 24 Aroma Formation in Dried Mullet Roe as Affected by Lipoxygenase Bonnie Sun Pan and and Chia-Ming Chia-Ming Lin Bonnie Sun Pan Lin 251 251 Identified in Preserved Duck Eggs 25 Volatile Compounds Identified Jianhong Chen and Chi-Tang Ho 263 Index 269 269 1 FLAVOR CHEMISTRY CHEMISTRY OF OF ETHNIC FLAVOR ETHNIC FOODS FOODS An Overview An Overview F Shahidi‘ Shahidi I and and C.-T c.-T H02 H02 F IDepartment of Biochemistry, Memorial University of Newfoundland 'Depa11ment John's, Newfoundland, AlB St John’s, AIB 3X9, Canada 2Department of Food Science, Cook College, Rutgers The State University of New Jersey, New Brunswick, New Jersey 08903 Ethnic and international foods have gradually been integrated into our daily diets in North America However, the existing literature on flavor flavor characteristics and chemistry of such foods remains fragmentary and diverse An attempt has been made to present a summary of the current status of knowledge in this area INTRODUCTION INTRODUCTION Flavor is an important sensory aspect of the overall acceptability of foods The flaflaof food food is both its odor-active volatiles and taste-active taste-active non-volatiles non-volatiles vor vor of is influenced influenced by by both its odor-active volatiles and However, methods of preparation and heat processing as well as presence of other ingredients and seasonings might exert a profound effect on the characteristics and "ethnic" “ethnic” flaflavor of certain foods Proximity of cultures and ethnic groups has also caused modification modification in certain food food formulations formulations in in order order to to offer offer an an "international" to them them As As an exin certain “international” flavor flavor to an example, while Chinese food food has has preserved preserved its overall authenticity, authenticity, it it has certain ample, while Chinese its overall has undergone undergone certain modification and and transformation transformation which which has has led led to availability of of the the so-called so-called AmeriAmerimodification to the the availability can-Chinese or North American-Chinese cuisines FLAVOR GENERATION GENERATION IN IN FOODS FOODS — - ROLE OF INGREDIENTS INGREDIENTS FLAVOR ROLE OF AND METHODS AND PROCESSING PROCESSING METHODS Flavor of foods is generated by the action of enzymes, fermentation or heat-processing operations Ingredients or combination of specific ingredients present in different food formulations formulations of of ethnic ethnic origin origin may may influence influence the the formation formation of of Maillard Maillard reaction reaction products products as as Flavor ChemiSl1y of Ethnic Ethnic Foods, Foods, edited edited by by Shahidi Shahidi and and Ho Ho Flavor Chemistry of Kluwer Academic /I Plenum Publishers, New York, 1999 I999 I 22 I-lo F Shahidi and C -T Ho well as effects on lipids via oxidation or participation in Maillard reactions as well as reaction of amino acids and proteins with carbohydrates Other food components such as specific amino acids may modify spices and condiments as well as certain vitamins and specific flavor of foods and thus lead to generation of specific specific "ethnic", “ethnic”, such as Chinese, Japathe flavor nese, Indian, Thai, etc., aromas in selected foods flavor has been the subject of a number of reThe Maillard reaction in relation to flavor er al., 1993) An views (Bailey, 1998; Hurrell, 1982; Mottram, 1994; Nursten, 1986; Tressl et important reaction associated with the Maillard reaction is Strecker degradation which inot-amino acids in the presence of a volves oxidative deamination and decarboxylation of a-amino dicarbonyl compound This leads to the formation of an aldehyde containing one less on-aminoketone Strecker aldehydes, mercapcarbon than the original amino acid and an a-aminoketone or-aminoketones as well as hydrogen sulfide, sulfide, ammonia and acetaldehyde toaldehydes and a-aminoketones are formed from degradation of cysteine Lipid degradation may also afford aldehydes that could participate in the Maillard reaction These compounds serve as important intermediates for the formation of many odoriferous compounds Breakdown of methionine as well as thiamine may also provide a number of intermediates as well as heterocyclic and sulfurous compounds (Shahidi, 1989) The Maillard products formed may further react with one another Thus, interaction of furfural, furanones and dicarbonyl compounds with other reactive compounds such as amino compounds, hydrogen sulfide, sulfide, thiols, ammonia and aldehydes may produce an array of flavor-active compounds, including heterocyclics, among others flavor-active Lipid components of food may also undergo different reactions via autoxidation, thermal oxidation, photooxidation and lipoxygenase-assisted lipoxygenase-assisted oxidation to produce a wide range flavor-active compounds While the primary products of lipid oxidation, hydroperoxides, of flavor-active are odorless, their breakdown leads to the production of aldehydes, ketones, alcohols and hydrocarbons, among others Free fatty acids may also be formed via thermal hydrolysis of lipids Substituted fatty acids may further cyclize to produce lactones and other flavor-acflavor-active compounds The The role aroma generation literature tive compounds role of of lipids lipids in in aroma generation has has been been reviewed reviewed in in the the literature (Chen and Ho, 1998; Mottram, 1998; Shahidi and Cadwallader, 1997; Skibsted et al., 1998) Different sauces produced via brine fermentation processes are used in many ethnic foods Shoyu is a popular Japanese sauce from soybean that is used widely in Japan and other South East Asian countries, but Miso is not internationally internationally as popular because of its paste consistency (Chapter 2) Meanwhile, black soybeans are brine fermented to produce moromi which is subsequently cooked with coconut sugar and spices to afford Indonian soy sauce known as Kecap manis (Chapter 3) Meanwhile, a complex ingredient which includes dried shrimp, fish, fish, sugar and roasted sesame, among others affords Sa Cha sauce (Chapter 4) which is important in Chinese cuisine Meanwhile, brine fermentation of fish fish affords fish fish sauce which is again very popular in Vietnam and other South East Asian countries (Chapter 5) Furthermore, soy sauce, garlic, scallion and shallot as well as ginger, star anise and black or Shiitake mushroom are among the condiments and ingredients used in Chinese foods and are responsible for many volatile and non-volatile components responsible for the rich and delicate delicate flavor flavor of Chinese dishes that are popular worldwide (Chapter 6) In addition, coriander fruit is used as a spice spice while its fresh leaves serve as important important culinary culinary herbs, more commonly known as Chinese parsley parsley (Potter and PagerFager1990; Chapter 7) Meanwhile, the importance of Wasaki and Japanese horseradish in son, 1990; food flavors flavors has been been documented (Chapter 8) 8) The rhizomes of greater galangal galangal are also widely used throughout throughout the South South East Asian countries (Chapter 9) and pandan pandan leaves widely have a strong strong characteristic characteristic aroma which is desirable desirable in various various bakery bakery products, sweets sweets and home cooking 10) cooking (Chapter 10) Flavor Chemistry of Ethnic Foods Cooking of broccoli, an important vegetable, affords a range of volatiles, including glucosinolate degradation products with sulfur or nitrogen heteroatoms (Chapter 11) Meanwhile, flavor extracts extracts from from fruits fruits such such as as kweni, an exotic exotic tropical fruit may may find find apapMeanwhile, flavor kweni, an tropical fruit of foods, foods, including including plication in the the food food and and flavor flavor industries (Chapter 12) Flavor quality quality of plication in industries (Chapter 12) Flavor fruits may be assessed and compared using an electronic nose apparatus (Chapter 13) Meat products from different sources such as those from harp seal (Chapter 14) and as affected by nitrite curing (Chapter 14) or use of organic acids (Chapter 15) or pan-frying (Chapter (Chapter 16) and fermentation fermentation (Chapter (Chapter 17) of interest interest Role of lipids in these these meatmeating 16) and 17) is is of Role of lipids in based foods foods is is also also quite quite important important based Tea is is one one of of the the most most popular popular drinks drinks in the world world The The flavor and astringency astringency of of tea tea Tea in the flavor and is affected by by the the method of preparation as well well as as the the type and content content of of phenolics is affected method of preparation as type and phenolics prepresent (Chapters (Chapters 18 and 19) An alcoholic alcoholic beverage, (Chapter 20) is found sent 18 and 19) An beverage, tequila tequila (Chapter 20) is found to to have have aa typical flavor, but are similar similar to those found found in and sake sake typical flavor, but compounds compounds involved involved are to those in wines wines and Many of the foods are prepared using oil as a frying medium The release of odoractive compounds compounds during during oxidation oxidation of of vegetable oils (Chapter (Chapter 21) 21) as as well well as as those arising active vegetable oils those arising from roasting of of seeds, seeds, such such as as sesame, sesame, prior prior to oil removal removal may may play an important important role role in in from roasting to oil play an the aroma aroma of of final products (Chapter (Chapter 22) 22) In addition various sugars in in foods foods may interact the final products In addition various sugars may interact to produce which is responsible, at at with specific amino amino acids acids such such as as B-alanine j3-alanine to with specific produce maltol maltol which is responsible, least in in part, part, for the flavor flavor of of cookies cookies (Chapter (Chapter 23) 23) least for the Finally, flavor of of certain certain exotic exotic food food products products such such as as dried dried roe which is is conconFinally, flavor roe mullet, mullet, which sidered aa delicacy delicacy in in Japan Japan and and Taiwan, Taiwan, similar similar to sturgeon caviar caviar in in Europe, Europe, is is especially especially sidered to sturgeon affected by by its its high high content content of of unsaturated unsaturated fatty fatty acids acids and and free free amino amino acids acids (Chapter (Chapter 24) 24) affected Preservation of of duck duck egg egg or or pidan by covering covering them them in in aa paste paste of of lime, lime, charcoal, charcoal, caustic caustic Preservation pidan by soda and and salt salt affords affords aa product product which has aa transparent transparent and and brown brown egg egg while while and and aa semisemisoda which has solid and and hard hard egg egg yolk yolk which which possesses possesses aa fresh fresh sulfur sulfur odor odor with some alkaline alkaline sense sense solid with some (Chapter 25) In all international food preparations, specific specific aromas and flavor flavor volatiles are generated via interaction of ingredients or are formed as a result of chemical changes induced during processing and preparation as well as use of spices and condiments Therefore, study of flavor flavor attributes of international foods opens a new area of research which could shed light, light, not not only only on on the the basic and interactions in their their generation, generation, shed basic reactions reactions and interactions involved involved in but would also also improve our appreciation appreciation of of existing existing complexities complexities of of cumulative cumulative role role of of but would improve our chemicals involved flavor perception perception chemicals involved in in flavor REFERENCES REFERENCES flavor development In Flavor of Meat Meat Products and Sea/oods, SeClfoods, ed Bailey, M.E Maillard reactions and meat flavor ofMeat, F Shahidi, Blackie Academic and Professional, London, 1998 pp 267—289 267-289 Chen, JJ and Ho, C.-T., C.-T., The The flavor of pork pork In In Flavor Flavor ofMeat, ofMeat Meat Meat Products Products and and Seafoods, Seafoods, ed ed F Shahidi, Blackie Blackie Chen, and Ho, flavor of F Shahidi, Academic and Professional, London, 1998 I998 pp 61-83 Hurrell, R.F Maillard reaction in flavor flavor [n AJ MacLeod, Elsevier, Amsterln Food Flavors, eds I.D Morton and A.J 399-432 dam, 1982.pp I982 pp 399—432 In Thermally Generated Flavors: Maillard, Maillard Mottram, D.S Flavor compounds formed during the Maillard reaction ln eds T.H T.H Parliament, Parliament, M.l Morrello and and RJ McGorrin, American American Microwave and and Extrusion Extrusion Processes, Processes, eds Microwave M.J Morrcllo R.J McGorrin, Chemical Society, Society, Washington, DC, 1994 Chemical Washington, DC, 1994 pp pp 104-126 l04~l26 Nursten, H.E Aroma compounds from the Maillard reaction In Developments in Food Flavors, eds G.G Birch and M.G Lindley, Elsevier, London, 1986 pp 173-190 In Flavor Chemistry: Trends and Developments, eds R Teranishi, R.G ButShahidi, F Flavor of cooked meats ln tery and F Shahidi, ACS Symposium Series 388, American Chemical Society, Washington, DC, 1985 pp 188-201 Aroma Formation in Dried Mullet Roe 257 Table 2 (Continued) Table RI' RI‘ Compounds' Compoundsl 2241 2254 2284 2377 2398 2414 2441 2450 2467 2482 2495 2514 2531 2552 2562 Unknown Unknown Peak no 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 Unknown I-hexadecanol acetate l—hexadecanol Unknown 3-hexadecene 3-hexadecene Unknown 9-octadecen-I-ol 9-octadecen-1-ol Unknown Unknown Unknown Unknown Unknown Unknown Unknown Unknown Percentage (%) Odor; 2.21 2.21 0.55 0.55 0.44 13.05 30.79 30.79 6.34 8.12 1.78 6.10 1.62 3.12 3.93 3.36 1.70 1.88 burnt rubber ·Possessed odor but too dilute to be detected by GC-FID GC-FlD *Possessed 'Retention index on Carbowax-20M ‘Retention identified based on standard MS library data (Hewlett-Packard Co 1988) 2Compounds were tentatively identified 33"_,, odorless odorless I-pentan-3-01, and 3-penten-2-01 (fish-like) were also present in both volaEthanol, 1-pentan-3-ol, 3-penten-2-ol (fish-like) tile concentrates Meanwhile 2-pentanol (sautéing), (sauteing), 3-hexanol (odorless), 2-methyl-2buten-l-ol (organic solvent-like), 2-methyl-2-butan-1-ol buten-l-01 2-methyl-2-butan-l-01 (beany, slightly metallic) and (fish, trimethylnonanol (slovent-like) were found only in the headspace, and I-penten-3-01 1-penten-3-ol (fish, fish-like), 1-heptanol I-heptanol (fried, sautéing), sauteing), 1-tetradecanol I-tetradecanol (seaweedy), l-pentadeI-pentadeor cooked fish-like), 9-octadecen-I-ol (both odorless) only in the steam distillate canol and 9-octadecen-1-ol Aldehydes Aldehydes Only aldehydes were identified in the headspace adsorbed by Tenax TA 33 Methylbutanal yielded an odor character of banana essence (Table 1) This compound was found crayfish tail meat and gave a green-plant like aroma (Vejaphan et al., aI., 1988) It was also in crayfish present in processed shrimp, clam and squid (Pan and Kuo, 1994) In explosion-puffed dehydrated potato, it gave a burnt and aldehyde-like off_odor(15 flavor off-odor"5’.1• The differences in flavor Rexanal was detected without giving notes detected were probably due to concentration Hexanal and odor at the concentrations present (Table 1) l) This compound was also found in other shellfish (Pan and Kuo, 1994; Spares, 1970) No short-chain aldehydes were found in the shellfish steam distillate (Table 2) Ketones Ketones 2-Decanone, 3-penten-2-one and nonadecane-2,4-dione were the 33 ketone comidentified in the headspace (Table 1) 2-Decanone was also present in cooked craypounds identified fish, fish, shrimp, krill and corbicular (Pan and Kuo, 1994) Other isomeric forms of pentenone were found in oyster (Josephson et al., 1985) and roasted shrimp (Kubota et al., 1986), but CS-C 10 ketones generally found in not the 3-penten-2-one detected in dried mullet roe The C8-C10 seafoods were not identified identified in dried mullet roe 258 258 B Sun Sun Pan Pan and and C.-M C.-M Lin Lin B Esters Ethylacetate ester was was detected detected in concentrates with with odor character of of Ethylacetate ester in both both volatile volatile concentrates odor character dried mullet mullet roe roe (Table (Table l) I) or or roasted roasted mullet mullet roe roe (Table 2) The The odor odor may may come come from from aa difdried (Table 2) different compound that has had a RI closely associated with acetic acid ethyl ester Since this the keynote compound of of mullet mullet roe confirmation of of the the structure structure is is this may may be be the keynote compound roe products, products, confirmation being done Cyclic Compounds Compounds Cyclic 2-Pentylfuran was found in the steam steam distillate distillate (Table (Table 2) 2) This This compound, compound, or com2-Pentylfuran was found in the or aa comof caramel caramel and and preserved dates that that differed differed pound similar RI, RI, contributed contributed to to the the odor odor of pound with with similar preserved dates from being being an an off-odor off-odor contributor contributor to to several several fats fats and and oils oils (Krishnamurthy at 1967), or from (Krishnamurthy et al I967), or not contributing contributing to to the the flavor flavor quality quality of of crayfish crayfish (Vejaphan (Vejaphan et al., aI., 1988) 5-Methyl-2-furnot 1988) 5-Methyl-2-furancarboxaldehyde was detected in the steam distillate and contributed to an almond aroma to the dried mullet roe (Table 2) Unidentified Odorous Odorous Components Components Unidentified unidentified (TaIn spite of the fact that half of the volatile compounds remained unidentified bles 1l and and 2), 2), desirable desirable flavor flavor notes, notes, including fruity, beany, beany, herbal, herbal, celery-like, celery-like, squashbles including fruity, squashlike, green and grassy, an odor similar to banana essence, dried bamboo leaves and sauted-food flavor flavor were were found found in dried mullet mullet roe roe volatile volatile sautéd-food in dried Undesirable odors resembling organic solvent, paint, bleach, bleach, and and metallic were also also Undesirable odors resembling organic solvent, paint, metallic were detected The volatiles collected by Tenax TA consisted of more fruity components (6) detected The volatiles collected by Tenax TA consisted of more fruity components (6) than the steam distillate (2), while the latter had more fish-like, tuna-like, seaweedy and than the steam distillate (2), while the latter had more fish-like, tuna-like, seaweedy and roasted mullet mullet roe aroma components components indicative indicative of of heating heating in in distillation distillation accelerated accelerated the the roasted roe aroma of dried dried mullet mullet seafood flavor formation particularly producing the keynote keynote compounds compounds of seafood flavor formation particularly producing the roe Role of of Mullet Role of Lipoxygenase Lipoxygenase in Formation Formation of Mullet Roe Roe Aroma Aroma Among the the odorous odorous compounds compounds identified identified in the volatiles of dried dried mullet mullet roe, roe, alcoalcoAmong in the volatiles of hols, aldehydes, and ketones were likely derivatives of lipid oxidation Lipids contributed of the the roe Polyunsaturated fatty fatty acids acids contributed contributed 33.54%, 33.54%, to 17.6% wet weight to 17.6% wet weight of roe Polyunsaturated (98.19+ 129.53) / 678.98 to the total and that of unsaturated fatty acids was 75.54% of total (98.l9+l29.53) amount (Table 3) Fatty acids containing a 1,4-pentadiene moiety can serve as substrates at., 1986) of LOX and result in seafood aroma formation (Kuo and Pan, 1991; Kubota et al., C I8 :2' Cm, C 183 , C2024 C20 :4 ,' respectively, and produced LOX reacted with unsaturated fatty acids Cm, aI., 1997b) In addition, 5-, fish aromas (Pan et al., volatile compounds with green, and fresh fish 12-, and 15-LOX activities were in mullet mullet roe roe at at levels much lower than correcorre12-, and I5-LOX activities were found found in levels much lower than sponding activities activities in in mullet mullet gill”) gill(7) Therefore, Therefore, model systems were were developed developed using gill sponding model systems using gill LOX to test the effect of endogenous LOX activities in mullet roe on its lipids in aroma formation The gill gill LOX LOX was purified using 0.2M phosphate buffer (pH (pH 7.0) 7.0) in in order The was partially partially purified using 0.2M phosphate buffer order to wash wash the the HPT-adsorbed HPT-adsorbed LOX for 22 times times (Table (Table 4) 4) The washings were combined and and to LOX for The 22 washings were combined used to treat the lipids extracted from from mullet mullet roe lipids alone alone smelled fishy used to treat the lipids extracted roe Roe Roe lipids smelled slightly slightly fishy (Table V) of the the LOX LOX added added to roe lipids lipids yielded with odor odor comcom(Table V) Inhibition Inhibition of to the the roe yielded aa mixture mixture with parable to the roe roe lipids lipids Increases Increases of of LOX LOX in the reaction mixture increased increased odor odor parable to that that of of the in the reaction mixture 259 Aroma Formation Formation in in Dried Dried Mullet Mullet Roe Roe Aroma Table 3 Changes Changes in in fatty fatty acid acid composition composition of of lipid lipid extracted extracted from from fresh fresh grey Table grey roe(1) after reaction with hydro- xyapatite (HPT) partially-purified mullet roe“) partially-purified oxygenase gill lip lipoxygenase LOX reacted 43 LOX Fatty acids 22 Control Saturated FA C14:0 C1410 C15:0 Cl5:0 C16:0 Cl6:0 (166.05) 6.72 2.55 99.95 5.68 21.88 9.27 20.00 (285.21 ) (285.21) 2.88 74.69 194.58 3.64 9.42 (98.19) 95.10 3.09 (129.53) 16.28 5.54 13.24 14.32 80.15 678.98 C17:0 C 7:0 C18:0 C1810 C19:0 Cl9:0 C24:0 Monoenoic acid C14:1 C 14:1 C16:1 C 16:1 C18:1 C1821 C20:1 C22:1 Denoic acid C18:2 C20:2 HUFA 4" C18:3 C1813 C20:3 C2013 C20:4 C20:5 C2015 C22:6 C2216 Total 25ml mg/g-lipid 3’ 25rnl rnglg-lipid (166.19) 6.51 2.66 100.65 5.60 21.99 9.08 19.70 (281.75) 2.80 73.57 192.13 3.74 9.51 (96.00) 93.13 2.87 (127.31) 15.75 5.27 12.72 14.47 79.10 671.25 (%) ’ (%) (- 1.2%) (- 2.2%) (- 1.7%) 50rnl 50ml (169.43) 6.95 2.50 101.55 5.72 21.85 9.91 20.95 (282.44) 2.81 74.51 192.18 3.53 9.40 (95.83) (95.33) 93.17 2.66 (122.87) 15.33 5.11 11.28 13.61 77.54 670.57 (%) ’ (%) (- 1.0%) (- 2.4%) (-5.1%) (5.1%) Roe was was dissected dissected from from mullet mullet sampled sampled in in Dec the GSI GSI was was 12%; lipid content content was Roe Dec the 12%; lipid was 17.6% 17.6% Quantification Quantification based on intemal internal standard standard C13:0 C13:0 based on Highly Highly unsaturated unsaturated fatty fatty acid acid (no (no of of double double bond bond = 3) 3) Lipoxygenase Lipoxygenase (LOX) (LOX) extract extract of ofO.55mg protein/ml with specific activity activity of of73 02 nmole/min-mg nmole/min-mg O.55mg protein/ml with aa specific 73 O2 protein ml and and 50 respectively was was reacted reacted with with roe roe lipid at 25° for 2h In control, control, the the volvolprotein in in 25 25 ml 50 ml ml respectively lipid at 25° for 2h In ume of of LOX LOX extract extract was was replaced by phosphate phosphate buffer buffer ume replaced by % reduction from the control intensity with additional flavor flavor notes of green and fresh fish-like fish-like It is thus assumed that the LOX's LOX’s present in gill extracts were similar to those endogenous in mullet roe catasite-specific oxidation of the polyunsaturated fatty acids in roe lipids forming odorlyzed site-specific fish-like aroma Similar findings findings showed ous compounds contributing to green and fresh fish-like that fatty acids reacted with LOX produced I-octen-3-ol l-octen-3-o1 possessing grassy and mushflavor notes in mushroom, yeast, ayu and shrimp (Josephson et al., aI., 1984, room-like flavor I984, 1985; I985; Kuo and Pan, 1992; Hirano et al., aI., 1992) I-Octen-3-ol 1-Octen-3-ol and total volatiles increased with increases in LOX activity, and decreased with the addition of LOX inhibitor (Kuo and Pan, 1991) Changes in Unsaturated Fatty Acids in Lipoxygenase Catalyzed Aroma Formation It was thought that LOX-catalyzed aroma generation was at the expense of depletion of polyunsaturated fatty acids Therefore, composition of fatty acids was compared before 260 260 B Sun Pan and C.-M Lin Table Table 4 Protein Protein content content and and lipoxygenase lipoxygenase activity activity in in mullet mullet gill gill extract extract treated treated with with hydroxyapatite hydroxyapatite (HPT) (HPT) LOX Times of washing Treatment Crude extract' HPT treated supematantz supematant2 washing3 Phosphate buffer washing} 0.08M 1st l st 2nd 1st lst 2nd 0.2M Protein (mg/ml) Specific Specific activity (Oznmole/min-mg (02nmole/min-mg protein) 3.80 0.90 30 14 l l,699 11,699 2,409 0.63 0.21 0.2] 0.23 0.08 l05 105 79 667 134 l34 6,760 1,414 Total activity (O2 (02 nmole/min) 'In 0.05M phosphate buffer, pH and lmM I mM glutathione ‘In extract=95: I 00 (v/v), mixed and stirred for 20 min, then centrifuged at 3000xg for 2HPT:crude extract=95:l00 3Washed with 250 ml phosphate buffer (pH 7) 1-2 l~2 times, then centrifuged at 3000xg for and after LOX reaction with the roe lipid (Table 3) In this, saturated fatty acids did not I %, while dienoic acids were show any decrease Monoenoic acids were reduced by about 1%, reduced by about 2%, regardless of the LOX activities that differed by times The reduction in highly unsaturated fatty acids (HUFA) increased to 5.1% from 1.7% as the LOX activities doubled, indicative of that HUFA's HUFA’s are the prefered substrates for LOX catalysis CONCLUSIONS The endogenous LOX activities in mullet roe are likely involved in generation of the fresh-fish like aroma The catalysis of LOX on HUFA, possibly followed by mild non-enfresh-fish of the the dried dried mullet mullet zymatic reactions, reactions, ie ie Maillard-type Maillard-type browning, browning, leads to the production of zymatic leads to the production flavor as proposed in Figure roe flavor l Mullet harvested at different stages of roe development characterized by different physiological and biochemical conditions including different flavor quality However, LOX activities may produce roe products of not quite the same flavor the HUFA contents of the products may not differ as much, because the keynote compounds are LOX-catalyzed HUFA derivatives of extremely low threshold values Table 5 Aroma Aroma generated generated from from lipid lipid extracted extracted from from fresh grey mullet roe and and Table fresh grey mullet roe reacted with HPT-partially-purified reacted with HPT-partially-purified gilllipoxygenase gill lipoxygenase Lipoxygenase extract (ml) (ml) ', extract () 10 10’2 10 20 20 40 40 Slightly-fishy Slightly-fishy + + + + +++ + Odor 33 Odor Green Fresh-fish-like Fresh-fish-like Overall odor intensity intensity33 + + + + + + + + + + + + +++ +++ ++++ ++++ ++++ ++++ specific activity of 88 nmole O2 0, consumed /min»mg Imin-mg protein I, 0.28 mg protein/ml, with a specific LOX was inhibited by addition of 6N HCI lI mt ml 33 Odor description and intensity was evaluated by panelists and ranked from no odor, to odor "+" to “++++" "++++" after LOX was reacted with the roe lipid at 25 25°C with increasing intensity being “+” °C for 2h Aroma Formation Formation in in Dried Dried Mullet Mullet Roe Roe Aroma 261 261 ACKNOWLEDGMENT ACKNOWQEDGMENT This research research was was supported supported by by the the National National Science Science Council Council of of the the Republic Republic of of This China under under aa grant grant (NSC (NSC 85-2321-B-019-012 85-2321-B-019-012) The taxonomy taxonomy of of the the sea sea algae algae was was done done China ) The by Dr Dr Jane Jane Lewis Lewis of of the the Institute Institute of of Marine Marine Biology, Biology, National National Taiwan Taiwan Ocean Ocean University, University, by Keelung, Taiwan Taiwan Keelung, REFERENCES REFERENCES A.O.A.C Official Official methods methods ofanalysis, of analysis, l4th 14th eds eds Assoc Assoc Oj]'icial/lnalytical Official Analytical Chem Chem Washington, Washington, D.C., D.C., USA USA 1984, A.O.A.C I984, 28,053 28, 053 Chang, C-F.; C-F.; Lan, Lan, S.C.; S.C.; Pan, Pan, B.S B.S Feed Feed administration administration of of 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Huang, Huang, W.L.; W.L.; Tsai, Tsai, C.H.; C.H.; Chang Chang K.L.B K.L.B Effects Effects of of protease protease inhibitors inhibitors from from rice rice bran bran and and sweet sweet potato potato on on browning browning of of dried dried mullet mullet roe roe Food Food Sci Sci (Taipei) (Taipei) 1997, I997, 24, 24, 7~77 75—77 Sapers, Sapers, G.M G.M Flavor Flavor quality quality in in explosion explosion puffed puffed dehydrated dehydrated potato potato 2 Flavor Flavor contribution contribution of2-methylpropanal, of 2-methylpropanal, 22.S methylbutanal methylbutanal and and 3-methylbutanal 3-methylbutanal J J Food Food Sci Sci 1970,35,731-734 1970, 35, 73 IY734 Schomburg, Schomburg, G.; G.; Dielman, Dielman, G G Identification Identification by by mass mass of of retention retention parameters parameters J J Chromatogr Chromatogn Sci Sci 1973, I973, 11, 11, 151-154 l5l—l 54 Vejaphan, Vejaphan, W; W.; Hsieh, Hsieh, T.C-Y; T.C-Y; Williams, Williams, S.S S.S Volatile Volatile flavor flavor compounds compounds form form boiled boiled crayfish crayfish (Procambarus (Procambarus c/arkii) clarkii) tail tail meat meat J J Food Food Sci Sci 1988,53,1666-1670 I988, 53, l666—l670 25 25 VOLATILE COMPOUNDS IDENTIFIED IN IN VOLATILE COMPOUNDS IDENTIFIED PRESERVED DUCK DUCK EGGS EGGS PRESERVED Jianhong Chen Chen and and Chi-Tang Chi-Tang Ho Jianhong Ho Department of Food Science Cook College, Rutgers The State University of New Jersey New Brunswick, New Jersey 08903 Volatile compounds of preserved duck eggs and cooked duck eggs were isolated by a simultaprofiles in neous steam distillation/extraction method and analyzed by GC and GC/MS Flavor profiles both egg products were compared The preserved duck eggs have a fresh sulfur, weak roasty, and alkaline alkaline odor odor Pyrazines, Pyrazines, hydrogen hydrogen sulfide, sulfide, and and ploysulfur ploysulfur compounds compounds were were exclusively exclusively and identified in in the the preserved preserved duck duck eggs, eggs, while while more more long chain aldehydes aldehydes existed existed in in the the cooked cooked identified long chain duck eggs INTRODUCTION INTRODUCTION flaAlthough egg is one of the most popular foods in the world, few studies on the flavor of eggs eggs have have been been reported and no no specific specific compounds compounds have have been to be be rerevor of reported and been determined determined to sponsible for characteristic egg flavor flavor MacLeod and Cave are the pioneers to investigate the egg flavor flavor (MacLeod and Cave, 1975, 1976) Using a simultaneous distillation and exidentified over 100 volatile flavor flavor compounds in cooked hen's traction method, they have identified hen’s eggs Those Those classes classes of of compounds compounds are are hydrocarbons, eggs hydrocarbons, furans, furans, pyrazines, pyrazines, pyrroles, pyrroles, carboncarbonflavor was later published by Maga yls, alcohols, indans, and benzenes A review of egg flavor (Maga, 1982), where he discussed the previous studies on the flavor flavor of whole egg, egg yolk, fermented egg, and dehydrated egg products, etc Two papers on scrambled egg flaflavor were recently published (Matiella and Hsieh, 1991, Warren et al., 1995), I995), and some sulfide, thirane, dimethyl disulfide, disulfide, and sulfur-containing compounds such as dimethyl sulfide, 200°C, sulfides, tetrahydrothiophene were identified identified When the eggs were heated at 200 °C, some sulfides, nitriles, thiazoles, thiophenes, pyridines and more pyrazines were produced from eggs aI., 1990) (Umano et al., I990) Eggs are mostly consumed as cooked eggs, scrambled eggs, or as an important food ingredient in other food products Salted eggs and preserved eggs are two traditional egg products in China ChemistlY ofEthnic of Ethnic Foods, edited edited by by Shahidi Shahidi and and Ho Flavor Chemistry I-lo Kluwer Academic Academic // Plenum Plenum Publishers, York, 1999 Kluwer Publishers, New New York, 1999 263 264 J Chen and C.-T Ho C.-T."o Preserved duck egg, which is also called pidan, alkalised egg, alkaline-gelled egg, one-thousand-year egg, or century egg, is a traditional and very popular food product in China Preserved duck eggs have transparent and brown egg white, and semisolid or hard egg yolk This kind of food has its characteristic aroma, which can be described as fresh sulfur odor with some alkaline sense There are several methods to prepare this egg product Two common processes to prepare preserved duck eggs were described as following (Hou, 1981, Steinkraus, 1995): I995): "Make a paste of 1500 g lime, 960 g charcoal, 300 g caustic soda, and 240 g salt “Make Stir to make a paste and used it to cover the shells of about 100 I00 duck eggs Then cover the eggs with rice hulls to prevent their sticking together and store in an earthware jar sealed with mud After weeks, the eggs are ready for consumption In another procedure, strong tea is mixed with yellow mud to form a thin paste in which the eggs are dipped and covered with the paste Lime, table salt, and caustic soda are mixed and boiled The coated eggs are placed in the bubbling mixture and then removed and placed placed in in an an earthware earthware jar jar sealed sealed with with mud mud The The eggs eggs are are ready ready for consumpmoved and for consumption after I month" tion after month” Preserved duck eggs eggs can can be be also also prepared by immersing in aa water solution containcontainPreserved duck prepared by immersing in water solution ing sodium chloride, chloride, sodium sodium hydroxide, hydroxide, or or sodium sodium carbonate carbonate with with other other ingredients ingredients for ing sodium for around half month (Su and Lin, 1993) I993) During the preparation process of duck eggs, alkaline chemicals will migrate from the solution or paste through egg shell to egg white and egg yolk The results of the migrathe pH value of egg white and egg yolk, detion of alkaline chemicals are increasing of the'pH naturation and gellation of egg protein, and other chemical reactions The volatiles volatiles of of preserved duck eggs eggs were were studied studied before before (Zhang (Zhang et al., ai., 1989) The The preserved duck 1989) The present study study used used the cooked duck duck eggs eggs as as aa control control to to elucidate elucidate the the flavor flavor difference difference bebepresent the cooked tween cooked preserved preserved duck duck eggs eggs and and cooked cooked fresh fresh duck duck eggs eggs tween cooked EXPERIMENTAL SECTION SECTION EXPERIMENTAL Material Preserved duck eggs and and fresh fresh cooked cooked duck duck eggs eggs were purchased in in aa local Asian Preserved duck eggs were purchased local Asian food supermarket The The ingredients of the the preserved duck eggs eggs were were stated as "duck food supermarket ingredients of preserved duck stated as “duck egg, egg, salt water, water, tea tea leave, sodium carbonate” carbonate" Organic Organic solvents solvents were from Fisher Fisher Scisalt leave, sodium were purchase purchase from Scientific (Springfield, (Springfield, NJ) Antifoam A solution (30 (30 % % of of concentrate) concentrate) was was aa product product of of entific NJ) Antifoam A solution Sigma Chemical Company (St Louis, MO) Isolation of of Volatiles Volatiles Isolation After removing the the shells, shells, the the preserved preserved duck duck eggs or cooked cooked duck duck eggs eggs were were After removing eggs or smashed in in aa food food processor Three hundred hundred grams grams of of egg egg paste paste were were put put in in aa round round flask flask smashed processor Three After spiking spiking with with tridecane tridecane as as an an internal internal standard, and adding adding two two drops drops of of antiofoam antiofoam After standard, and solution to avoid foam foam generation, generation, the the volatile compounds were simultaneously distilled distilled solution to avoid volatile compounds were simultaneously and extracted extracted using modified Linkens-Nickerson apparatus for for 90 90 minutes minutes Methylene and using aa modified Linkens-Nickerson apparatus Methylene chloride was as the extraction solvent solvent After extraction, organic organic solvent containing chloride was used used as the extraction After extraction, solvent containing volatiles was was then then concentrated concentrated to to 0.2 0.2 mL mL under under aa gentle gentle stream of nitrogen nitrogen gas gas before before GC GC volatiles stream of and GC/MS analysis Volatile Compounds Compounds Identified Identified in in Preserved Preserved Duck Duck Eggs Eggs Volatile 265 265 Gas Gas Chromatography (GC) (GC) and and Gas Chromatography/Mass Chromatography/Mass Spectrometry (GC/MS) Analysis The gas chromatography was performed on a Varian Varian Model 3400 3400 equipped equipped with aa flame ionization detector (FID) and a nonpolar fused silica silica capillary column (DB-I, 60 60 m flame 1.0 f.1m pm film film thickness, J&W Scientific) Scientific) The column temperature was x 0.32 mm (i.d.), 1.0 programmed from 40°C to 260°C at the rate of 3°C 3°C Imin /min The injector and and detector temtein300°C, respectively The flow flow rate of the helium perature were maintained at 270°C and 300°C, mL/min The volume of the injected sample was I f.1L, pL, and the spilt ratio carrier gas was I1 mLimin 25:1 was 25: I GC/MS analysis was performed using an HP Model 5790 GC coupled with a HP 5970A mass-selective detector The capillary column and temperature program were the same for as GC analysis Mass spectra were obtained by electron ionization at 70 ev and quantification was based on the GC/FID data, and mass scan from 33 to 300 Compound quantification identification was based on mass spectra obtained from the GC/MS compound identification RESULTS AND DISCUSSION The odor of the preserved duck eggs paste was like fresh sulfur, weak roasty, and alflavor kaline; while smell of the paste of the cooked duck eggs was dominated by a fatty flavor The compositions of identified identified volatile compounds in preserved duck eggs and cooked duck eggs are listed in Table The compounds are listed according to their elution order Different aroma profiles profiles were observed, and a total of 26 volatile compounds were identified in the two egg products identified In preserved duck eggs, the largest identified compounds were 5,6-dihydro-2,4,6trimethyl-4H-l,3,5-dithiazine, trimethyl-4H-I,3,5-dithiazine, 2-butanone, ethanol, hydrogen sulfide, acetaldehyde, 3-hydroxy-2-butanone (acetoin), and 2-butenal in decreasing order In ln the cooked duck eggs, the largest identified identified compounds were hexanal, ethanol, pentanal, and heptanal in decreasing order In terms of classification classification of volatile compounds, sulfur containing compounds and pyrazine more pyrazine compounds compounds are are exclusively exclusively identified identified in in preserved preserved duck duck eggs, eggs, while while many many more aldehydes exist in cooked duck eggs Sulfur compounds usually have aa meaty aroma and possess a very low odor threshold value Hydrogen sulfide sulfide can be a degradation product of sulfur containing amino acids such as cysteine, or peptides such as glutathione or some proteins (Zhang et al., 1988) aI., 1988) Hydrogen sulfide sulfide was detected in heated eggs, and its generation was increased with heating temperature and pH value (Germ, 1973) The alkaline pH of preserved duck eggs can facilitate hydrogen sulfide sulfide Hydrogen Hydrogen sulfide sulfide and acetaldehyde, which were formed in in preserved duck eggs, are very very active and important precursors of sulfur-containing comcompounds Figure lI shows the formation mechanisms of 3,5-dimethyl-1,2,4-trithiolane 3,5-dimethyl-I,2,4-trithiolane and 5,6-dihydro-2,4,6-trimethyl-4H-I,3,5-dithiazine et al., at., 1974) 1974) Both Both compounds compounds 5,6-dihydro-2,4,6-trimethyl-4H-I ,3,5-dithiazine (Boelens (Boelens et have have aa cooked cooked meaty meaty flavor, flavor, and and were were identified identified in in preserved preserved duck eggs The The compound compound of of 3,5-dimethyl-1,2,4-trithiolane 3,5-dimethyl-1,2,4-trithiolane was was reported reported in in volatiles volatiles of of cooked cooked potato, potato, beef, beef, chicken chicken and and mutton mutton (Brinkman, (Brinkman, I972, 1972, Horvat, Horvat, I976, 1976, Nixom, Nixom, 1979), 1979), while while 5,6-dihydro-2,4,65,6-dihydro-2,4,6tri1nethyl-4H-1,3,5-dithiazine trimethyl-4H-l,3,5-dithiazine was was identified identified in in volatiles volatiles of of cooked cooked beef, beef, mutton, mutton, shrimp shrimp and and roasted roasted chicken chicken (Ohloff (Ohloff and and Flament, Flament, I978, 1978, Brinkman, Brinkman, 1972, 1972, Wilson, Wilson, 1972, 1972, Tang, Tang, et et al., at., I983) 1983) Pyrazine Pyrazine compounds compounds have have typical typical roasty roasty and and nutty nutty aroma aroma Conditions Conditions that that favor pyrazine pyrazine formation formation are are high high temperature, temperature, low low moisture, moisture, and and alkaline alkaline condition condition Pyrazine Pyrazine 266 266 C.-T J Chen and C T Ho Table Volatile compounds identified identified in preserved duck eggs (PRE) and cooked (COE) I duck eggs (CDE) Cone (ppm) Conc Compounds' Compounds” Hydrogen sulfide sulfide Acetaldehyde Ethanol Acetone 2,3-Butanedione 2-Butanone 2-Butanol 2-Butenal 3-Methylbutanal Pentanal 3-Hydroxy-2-butanone Pyrazine Hexanal Methylpyrazine 2-Heptanone Heptanal 2,5-Dimethylpyrazine Ethylpyrazine 2-Ethyl-6-methylpyrazine 2-Pentylfuran Octanal 3-Ethyl-2,5-dimethylpyrazine 2-Nonanone Nonanal 3,5-Dimethyl-I,2,4-trithiolane 3,5-Dimethyl-1,2,4-trithiolane 3,5-Dimethyl-I,2,4-trithiolane 3,5-Dimethyl-1,2,4-trithiolane 5,6-Dihydro-2,4,6-trimethyl-4H-I,3,5-dithiazine 5,6-Dihydro-2,4,6-trimethyl-4H-1,3,5-dithiazine 5,6-Dihydro-2,4,6-trimethyl-4H-I ,3,5-dithiazine 5,6-Dihydro-2,4,6-trimethyl-4H-1,3,5-dithiazine Rib RI” PRE