Aroma Chemistry of Crackers - ACS Symposium Series (ACS

Chapter 26

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Aroma Chemistry of Crackers 1

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L . F. M . Yong , T. E. Acree , Ε. H. Lavin , and R. M . Butts

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Department of Biochemistry, Faculty of Medicine, National University of Singapore, Republic of Singapore New York State Experiment Station, Cornell University, Geneva, NY 14456

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Crackers are thin low moisture biscuits consumed in many parts of the world. They are industrial products made from wheat flour, fat, water, leavening and sugar. The aroma of crackers is de rived from the chemical interaction of these ingredients during leav ening and baking. A problem with the study of cracker aroma or any fat-containing baked goods is separation of aromatic volatiles from a heterogeneous mixture of polar and lipid components. However, once the aroma volatiles have been extracted into an appropriate solvent for gas chromatography then the problem of characterizing the odor active components is fairly routine. This paper will review the present knowledge of the flavor chemistry of crackers and outline steps ap propriate for the complete characterization of cracker aroma.

Crackers are generally subdivided into three basic categories: saltines or soda crackers (also known as cream crackers in the United Kingdom), sprayed crackers, and savory crackers (Hoseney, R.C.; Wade, P. & Findley, J.W. 1988 "Soft wheat products" in press). They are a class of baked product with a unique flavor and tex ture. Crackers are usually made of wheat flower, water, fat, yeast and salt by a pro cess that combines fermentation, baking and dehydration to yield a thin low moisture product. Saltines are the simplest cracker with a typical "cracker-like" aroma. This paper reviews the basic flavor chemistry of saltine crackers and presents preliminary data on the extraction of volatile compoundsfromthese crackers. INGREDIENTS Although saltine cracker formulas have never been standardized they are very similar. Martz (1) summarized six published formulae for soda crackers showing the average range for each ingredient used. A typical formula for the production of saltine crackers is shown in Table 1 (Hoseney, filial., 1988). The uniqueness of crackers is due to the use of a two dough system one of which is called a sponge. 0097-6156/89/0409-0276$06.00/0 ο 1989 American Chemical Society In Thermal Generation of Aromas; Parliment, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Aroma Chemistry of Crackers


Table 1: Cracker formula described by Hoseney, Wade & Finley 1988. Ingredients based on weight of flour with 14 % moisture Ingredient Hour Water Yeast Shortening Salt Soda

Sponge (%) 67 27 0.02 4 :

Dough(%) 76 2 15 4 2

While several reviews on the role of ingredients are available, none of these describe the flavor chemistry of cracker sponge and dough (2, 3, 4, 5). However, some in sight into the chemistry of cracker aroma can be obtained from examination of prod ucts that have a "cracker-like aroma" such as white bread crust. MANUFACTURING PROCESS Conventionally, crackers are prepared by a sponge and dough process that takes approximately twenty-four hours. Flour, water and salt are combined with yeast and allowed to ferment to yield a sponge (also called sour dough).. More flour, water and salt are combined with the sponge to yield a dough that is leavened, formed and baked into a cracker. A prolonged sponge fermentation is thought to be required to bring about modification of flour gluten and the changes that give saltine crackers their spe cial textural and flavor properties (2, 6). Leavening can be accomplished by chemical means but the yeast fermentation produces a far better product. Though the cracker sponge fermentation is important, it is also a process that requires about eighteen hours, or approximately seventy-five percent of cracker production time. Most yeast-leavened crackers are based on the sponge-and-dough fermentation process outlined in Figure 1. Flour Water Fat & Yeast 18 h Fermentation (Lactic acid bacteria) ι Γ Sponge J Flour Water Fat & Yeast

4 h Fermentation ( Dough ) laminate, sheet, cut, salt & bake ^ Crackers

J

Figure l.Flow diagram for the typical soda cracker process.

In Thermal Generation of Aromas; Parliment, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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THERMAL GENERATION OF AROMAS

Johnson and Bailey (7), in a fundamental study of crackers involving investigation of the physical and chemical changes in dough during fermentation, had questioned the necessity of prolonged sponge fermentation in order to degrade gluten proteins and saturate the dough with carbon dioxide. As appreciable dry matter is lost during fermentation, they suggested that other, less wasteful, means might cause the same changes that lengthy fermentation accomplishes, and proposed that further research be directed toward a procedure to degrade flour proteins with suitable proteolytic enzymes. To a limited extent, proteolytic enzymes already are used to improve cracker quality and flavor. Fermentation brings about many changes responsible for the unique aroma and other eating properties that characterize commercial saltine crackers. Precise levels of flakiness, crispness, tenderness, bloom, spring, and flavor are required in a quality saltine cracker. It is generally believed that the prolonged sponge fermentation is required to produce quality crackers despite the material losses, additional equipment, space, time and labor costs. This was somewhat contradicted by Wade (8) in his work on the role of fermentation in the manufacture of saltine crackers. Although he did find that doughs with short fermentation times produced little aroma after the crackers had been cooled, packed, and stored for twenty four hours taste panels were unable to distinguish between those madefromdoughs with short fermentations and control doughs made by a process that included a long fermentation. It has long been desired to eliminate or, at least, substantially reduce such a long fermentation period without losing therichflavor and good physical properties of the final product (9,10). Micka (11) reported that efforts to shorten the fermentation time resulted in products with atypical flavor. His attempts to produce crackers using a higher percentage of yeast and shorter sponge time have not been successful. The finished product was different in texture and flavorfromthose made by the traditional procedure. MICROBIOLOGY OF CRACKER PRODUCTION Sugihara (12, 13) studied the involvement of bacterial fermentation in cracker production and concluded that bacteria play a vital role in the eighteen hour sponges used in the manufacture of soda crackers. In fact the lactobacillus population at the end of the fermentation was greater than the yeast population. This explains the observation by Faridi & Johnson (10) that the major acid present in the dough was lactic acid. However, the precise role these acids and bacteria play in the development of cracker flavor is still not clear. Pizzinatto and Hoseney (14) have demonstrated that yeast is an essential ingredient in any cracker formula. Yeasts not only adjust pH to allow enzymatic conditioning of the dough but also improve both texture and flavor of the finished crackers. CRACKER FLAVOR Literature on the cause and control of the flavor of crackers is scant. Faridi and Johnson (10) studied the chemical changes related toflavorprecursor components (organic and amino acids) during the twenty-five hour fermentation period. They measured the total soluble nitrogen, peptides, primary amines, and ammonia formed in cracker doughs as a result of the lengthy fermentation. All components increased



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significantly with a twenty hour sponge fermentation. Lactic acid was predominantly produced, followed by acetic and smaller amounts of propionic, butyric, valeric, and isovaleric acids. This is consistent with the observation that lactic acid bacteria are active in the process (12,13) Faridi and Johnson (15) have reported on a cracker flavor enhancer mixture to be used to produce a saltine cracker with a two-hour fermentation and equivalent texture, flavor, and taste to commercial saltine crackers produced by twenty four-hour fermentations. The cracker flavor enhancer mixture was formulated from a gluten hydrolysate (Promate - 200), organic acid salts, and starch as the carrier. The flavor enhancer mixture was used to replace thefreeamino acids and the seven organic acids produced during a twenty-five hour fermentation. Johnson (16) has patented a combination of gluten amino acids and a mixture of organic acids which could function as a fermentation compensator, that is, the combination could induce changes in the dough that normally require a long fermentation to achieve. Laboratory production of crackers with the same flavor quality as commercial crackers has been difficult. Micka (11) found that when crackers are produced in a laboratory and no starter sponge is kept, and equipment is kept sterile, fermentation is generally retarded and the resulting dough has a high pH and the crackers have an undesirable flavor. Dynn (17) attempted to develop a procedure for the production of experimental crackers to test flour quality. He found that the crackers made from the same batch of flour varied widely in flavor quality and concluded that commercial crackers could not be produced in a laboratory. However, Pizzinatto and Hoseney (4,14) have recently developed a procedure for the production of satisfactory experimental saltine crackers under laboratory conditions. CRACKER-LIKE AROMAS Teranishi, filal. (18) observed "cracker-like" odors in compounds such as 2acetyl-l,4,5,6-tetra hydropyridine, 2-acetylpyrazine, and 2-acetyl-2-thiazoline. From this, Folkes and Gramshaw (19, 20) speculated that heterocyclics with the following structural formula,

where the nitrogen atom and the adjacent carbon atoms form part of the ring structure, exhibit biscuit- or cracker-like odors. Based on this theory, it could therefore be expected that acetylpyrazine, 2-acetylpyridine, and 2-acetylthiazoline have a cracker-like aroma. Schieberle and Grosch (21) reported that the most intense odor, i.e. the component with the highest flavor dilution value, in white bread crust was



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or 2-acetyl-l-pyrroline. This compound was also isolated from cooked 'scented' rice and the Pandanus amaryllifolius Roxb. plant by Buttery, et at. (22, 23, 24) who described it as "popcorn-like". The similarity in aroma between the crust of white bread and crackers makes this compound an excellent candidate for cracker aroma. It is possible that 2-acetyl-l-pyrroline is formed by sugar-amino acid reactions ( 25), however, recent work implicates yeast as its source in bread (Schieberle, ibid). Wiseblatt & Zoumut (26) reacted proline and dihydroxyacetone to yield a crackerlike aroma, but the separation and identification of the component(s) responsible for the odor was not reported. However, in similar experiments, Kobayashi and Fujimaki (27) generated a cracker-like aromafroma reaction of proline and glucose in the presence of pyrrolidine and pyruvaldehyde. They identified the compound responsible for the odor as N-acetonyl pyrrole. From a reaction mixture comprising proline and glycerol Hunter et al. (28) prepared aroma concentrates which upon separation by gas liquid chromatography gaveriseto three main peaks having a cracker- or breadlike aroma. Hunter, al. (29) later reported obtaining a pentane extract from a reaction mixture of proline, dihydroxyacetone, and sodium bisulfite with a strong odor reminiscent of freshly-baked soda crackers. A compound identified in the mixture, 1,4,5,6-tetrahydro-2-acetylpyridine, was synthesized by by Buchi and Wuest (30) and described as having a cracker-like aroma. Schieberle and Grosch (31, 32, 33) were able to isolate this compound from rye and wheat bread crust and describe it as having a bread crust aroma with cracker-like notes. SEPARATION OF VOLATILES FROM CRACKERS The large amount of fat in saltine crackers causes a problem during the extraction of volatiles because of the solubility of most odor-active volatiles in fatty substances. The simplest solution is steam distillation (34) or co-distillation with solvents such as ethanol (35) followed by extraction of the distillate with non-polar solvents. Steam distillation and simultaneous extraction with the Likens-Nickerson apparatus is based on the same chemistry (37). When the distillation is done under reduced pressure (38, 39) traps cooled with liquid nitrogen are required. For example, Slott and Harkes (40) used low temperature vacuum distillation followed by solvent extraction to separate the volatile components of Gouda cheese. So called "headspace techniques", like that used by Lin (41) to separate the alkylpyrazines in processed American cheese, used nitrogen gas passed through a bed of ground cheese into tubes of Tenax and Porapak Q. The volatiles were desorbedfromthe tubes into a gas chromatograph. Generally these techniques remove only a few percent of the volatiles from the sample especially when the samples are high in fat, however, they tend to be free of any non-volatile contaminants. Selective solvent extraction of volatiles will remove volatiles with very high yields although the extracts are always contaminated with non-volatile components. For example, acetonitrile extraction followed by co-extraction with pentane was used by Vernin (38). In our experiments the direct extraction of crushed crackers with Freon 113 or ethyl acetate contained too much residual lipid. Distillation of the solvent yielded a lipid concentrate low in aroma volatiles. Attempts to use gel filtration (BioBeads S-X12fromBio-RAD) to remove the lipids but retain the odorous substances were also unsuccessful.



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Aroma Chemistry ofCrackers

Schreier et al. (42) used aqueous media to extract aroma volatiles from solid sub stances. We applied this approach to the isolation of volatiles from crackers and ob tained a lipid-free extract with a convincing cracker-like aroma. In the procedure, 1.0 kg of crackers was blended with 5.0 L of distilled water containing 250 g of sodium chloride while nitrogen gas was passed into the mixture. After standing four to five hours, it was centrifuged (Sorvall) at 2,000 rpm (4°C) for 20 minutes. The super natant was filtered through a cheese cloth and extracted with Freon™ 113 and fol lowed by ethyl acetate. Because the residual crackers still had a strong cracker-like aroma after extraction it was apparent that a more polar solvent was required. Figure 2 outlines a procedure that yielded a more complete extraction of cracker like aromas. 1 Kg Crackers crushed lLMeOH

Solids

MeOH

1L MeOH MeOH

Solids

Combine

.i—Γ C Discard j MeOH

,

Evaporate *(MeOH 22 in. Hg. 45 C Cool 4 C 24 hr. Decant)

S o l i d s

Evaporate * to 100 mL 900 mL Water 800 mL Freon™ 113

Solids ( Discard ) ( Discard

) Freon™ 113

Water Water

800 mL Ethyl Acetate Ethyl Acetate

(Discard

( I

l.GC/MS Λ 2. Odor Assay

( l.GC/MS Λ V^^Odor^ssav^^

Figure 2. Cracker extraction procedure developed by the authors to yield both polar and non-polar volatiles. The methanol at room temperature extracts both fats and volatiles. Cooling the methanolic extract desolublized most of the fat retaining most of the volatiles in solu tion. The alcoholic solution was then diluted with nine volumes of water. Back ex traction of the aqueous solution with Freon™ 113 followed by ethyl acetate yielded a non-polar and a polar fractionfreeof many contaminating non-volatiles. In this pro cedure acetonitrile, but not isopropyl alcohol, was a good replacement for methanol and pentane is a good replacement for Freon™ 113. The idea is similar to the estab-



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lished procedure used to separate essences from pomades in the production of fra grances. Both fractions obtained from crackers extracted less than one week after baking had strong cracker-like aromas. The Freon™ 113 fraction had a cracker, roasted grain, cooked rice aroma while the ethyl acetate fractions had a cracker, sweet baked good, burnt butter aroma. A preliminary analysis of the two fractions by gas chromatography-mass spectrometry on a 25 m by .22 mm methyl silicone column be tween 700 and 1800 retention indices showed the compounds listed in Table 2. Table 2: Compounds detected (by MS) in MeOH&water extracts of saltine crackers and their η-paraffin retention indices (RI) on a 0.22 mm by 25 m OV101 (0.33 mm thick) column Compound 2-acetylfuran 2-acetylpyridine 2-acetylpyrrole benzacetaldehyde benzaldehyde 2,3-dimethyl pyrizine 2,4-dimethylheptane 2,5-dimethyl pyrizine 2,6-dimethyl pyrizine ethyl pyrizine furfural furfurvl alcohol

RI 876 995 1028 1001 928 894 824 888 889 890 800 834

Compound hexadecanoic acid 1 (H)-indole-3-ethanol 2-methylpyrazine 3-methylthiopropanal maltol methyl cinnamate 2-phenylethanol phenylacetaldehyde tetradecane undecane vanillin

RI 1917 1672 811 868 1070 1096 1080 1004 1400 1100 1348

All of these compounds have been reported in similar products and are not unique ex cept for the absence of 2-acetyl-l-pyrroline. To be sure that the system could detect 2-acetyl-l-pyrroline an authentic sample was analyzed by gas chromatography-mass spectrometry on a system that could easily detect 1 pg of hexane and yielded identical spectra and retention index as a component isolated from fragrantriceaccording to the method of Buttery, et al. 1983. However, analysis of the cracker extracts using both electron impact and mass fragmentography showed no convincing evidence for the presence of 2-acetyl-l-pyrroline at greater than 1 picogram per gram of cracker. CONCLUSIONS Many aroma compounds have been identified in crackers but which ones are the most important has still not been established. Further studies of these extracts should involve the use of odor assays to sort out to aroma important compounds in crackers from the unimportant aroma compounds present. For example, the method used by Shieberle & Grosch (33) to describe the odor-active components in bread in terms of their 'flavor dilution values' and the technique called charm analysis (43, 44) both concentrate chemical investigations at retention indices with odor activity.


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ACKNOWLEDGMENTS L. F. M. Yong thanks the National University of Singapore, Republic of Singapore for granting financial assistance for his sabbatical leave, the New York Experiment Station, Cornell University, Geneva, for use of facilities, and RJR-Nabisco for providing research funds. LITERATURE CITED 1. Martz, S. A. Cookie and cracker technology: AVI Publishing Co.: Westport, CT, 1968. 2. Heppner. W. A. Bakers Dig. 1959, 33, 68-70, 85-86. 3. Al-Zubaydi, A. Ph. D. Thesis, Kansas State University, Manhattan, KS, 1959. 4. Pizzinatto, Α.; Hoseney, R. C. Cereal Chem., 1980, 57, 185-188. 5. Doescher, L. C.; Hoseney, R. C. Cereal Chem., 1985, 62, 158-162. 6. Howard, K. L. Biscuit & Cracker Baker 1956., 45, 30. 7. Johnson, A. H.; Bailev. C. H. Cereal Chem. 1924, 1, 327. 8. Wade, P. J. Sci. Food Agric. 1972, 23, 1021-1034. 9. Faridi, H. A. Master's Thesis, Kansas State University, Manhattan, KS, 1973. 10. Faridi, Η. Α.; Johnson, J. A. Cereal Chem. 1978, 55, 7-15. 11. Micka, J. Cereal Chem. 1955, 32, 125-131. 12. Sugihara, T. F. J. Food Protect. 1978, 41, 977-979. 13. Sugihara, T. F. J. Food Protect. 1978, 41, 980-982. 14. Pizzinatto, Α.; Hoseney, R. C. Cereal Chem. 1980, 57, 249-252. 15. Faridi, Η. Α.; Johnson, J. Α.; Robinson, R. J. J. Food Sci. 1979, 44, 269-270. 16. Johnson, J. A. U.S. patent 385167, 1975. 17. Dynn, J. A. Cereal Chem. 1933, 10, 628. 18. Teranishi, R.; Buttery, R. G.; Guadagni, D. G. In Geruch und Geschmackstoffer. Drawert, F. Ed.; Verlag: Nurnberg, West Germany; 1975, p. 177. 19. Folkes, D. J.; Gramshaw, J. W. J. Food Technol. 1977, 12, 1-8. 20. Folkes, D. J.; Gramshaw, J. W. Prog. Food Nutr. Sci. 1981, 5, 369-376. 21. Schieberle, P.; Grosch, W. Z. Lebensm. Unters. Forsch. 1987, 185, 111-113. 22. Buttery, R. G.; Ling, L. C.; Juliano, B. O.; Turnbaugh, J. G. J. Agric. Food Chem. 1983, 31, 823-826. 23. Buttery, R.G.; Juliano, B.O.; Ling, L.C. Chem. & Ind. 1983, 12, 478. 24. Buttery, R. G.; Ling, L. C.; Teranishi, R.; Mon. T. R. J. Agric. Food Chem. 1977,25, 1227-1229. 25. Sydow, von E.; Anjou, Κ. Lebensm. Wiss. Technol. 1969, 2, 15-18. 26. Wiseblatt, L.; Zoumut, H. F. Cereal Chem. 1963, 40, 162-169. 27. Kobayashi, N.; Fujimaki, M. Agric. Biol. Chem, 1965, 22, 1059-1060. 28. Hunter, I. R.; Walden, M. K.; McFadden, W. H.; Pence, J. W. Cereal Sci. Today 1966, 11, 493-494. 29. Hunter, I. R.; Walden, M. Y.; Scherer, J. R.; Lundin, R. E. Cereal Chem. 1969, 46, 189-195. 30. Buchi, G.; Wuest, H. J. Org. Chem. 1971, 36, 609-610. 31. Schieberle, P.; Grosch, W. Z. Lebensm. Unters. Forsch. 1983, 177, 173-180. 32. Schieberle, P.; Grosch, W. Z. Lebensm. Unters. Forsch. 1984, 178, 479-483. 33. Schieberle, P.; Grosch, W. Z. Lebensm. Unters. Forsch. 1985, 180, 474-478.




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34. Romer, G.; Renner, Ε. Z. Lebensm. Unters. Forsch. 1974, 186, 329-335. 35. Wal, Van der, B.; Kettenes, D. K.; Stoffelsma, J.; Sipma, G.; Semper, A. T. J. J. Agric. Food Chem. 1971, 19, 276-280. 37. Buttery, R. G.; Guadagni, D. G.; Ling, L. C. J. Agric. Food Chem. 1978, 26, 791793. 38. Vernin, G. The Chemistry of Heterocyclic Flavouring and Aroma Compounds Ellis Horwood Ltd.: Chichester, England; 1982, pp. 267-269. 39. Johnson, B. R.; Waller, G. R.; Burlingame, A. L. J. Agric. Food Chem. 1971, 19, 1020-1024. 40. Sloot, D.; Harkes, P. D. J. Agric. Food Chem. 1975, 23, 356-357. 41. Lin, S. S. J. Agric. Food Chem. 1976, 24, 1252-1254. 42. Schreier, P.; Drawert, F.; Heindze, I. Z. Lebensm. Unters. Forsch. 1981, 172, 257263. 43. Acree T.E., Barnard, J. & Cunningham, D.G. Food Chem. 1984, 14, 273-286. 44. Braell, P. Α., Acree, T.E., Zhou, P-G. In Biogeneration of Aromas: Parliment, T. H.; Croteau, R., Eds.; ACS Symposium Series No. 317; American Chemical Society: Washington, DC, 1986; 75-84. RECEIVED July 19, 1989


Aroma Chemistry of Crackers - ACS Symposium Series (ACS

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