Sulfur Compounds in Foods - American Chemical Society

Chapter 1

Sulfur Compounds in Foods An Overview 1

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Cynthia J. Mussinan and Mary E. Keelan

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International Flavors and Fragrances, Research and Development, 1515 Highway 36, Union Beach, NJ 07735 International Flavors and Fragrances, 800 Rose Lane, Union Beach, NJ 07735

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The importance of sulfur compounds to theflavorand off-flavor characteristics of foods is well known and continues to be studied. Mechanistic studies have led to a greater understanding of the formation and mode of action of these compounds. Recently, however, more attention has been given to some of their non-sensory characteristics, particularly to their antimicrobial and anticarcinogenic effects.

For years researchers have investigated the sulfur compounds present in various foods. Cooked foods typically contain numerous sulfur compounds, especially heterocyclic compounds like thiazoles, thiophenes, thiazolines, etc. In 1986, Shahidi et al. (7) reported that 144 sulfur compounds had been identified in beef. Other heated food systems like bread, potato products, nuts, popcorn, and coffee also contain many sulfur compounds. Aliphatic thiols have been found in fruits, vegetables, dairy products etc., as well as in heated foods. No discussion of the occurrence of sulfur compounds in foods would be complete without mention of their major role in the various allium species. Indeed, more than half of the volatile compounds reported in garlic, onion, leek, and chive contain sulfur (2). Comprehensive reviews of the literature concerning the role of thiazoles, thiophenes, and thiols in food flavor through 1975 can be found in Maga's series of review articles (3-5). Sensory Properties While the occurrence of sulfur compounds is of interest, their sensory properties can be critical to theflavorof a food. According to Boelens and van Gemert (2) "most of the volatile sulfur compounds are essential constituents of the material. That means they are necessary for the sensory quality, but that they are not characteristic. A small number of the sulfur compounds, however, are characteristic compounds..." These compounds, by themselves, can be recognized as having the same

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Mussinan and Keelan; Sulfur Compounds in Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

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SULFUR COMPOUNDS IN FOODS

basic organoleptic character as the material. They are the so-called characterimpact compounds. Examples are shown in Table I. Since some of these compounds have extremely low threshold values, they can be important to the flavor of a food at the ppb level. For example, one of the compounds reported in onion, propyl propane thiosulfonate, has a powerful and distinct odor of freshly cut onion (14). Since the threshold of this compound (1.5ppb) is several hundred times lower than its concentration (0.5ppm), it undoubtedly makes a significant contribution to the overall onion flavor (75).


Table I. Character-Impact Sulfur Compounds

Food Bread

Comoound 2-acetyl thiazoline

Reference 6

Cabbage Coffee Grapefruit Passionfruit

dimethyl sulfide furfuryl mercaptan 1 -p-menthene-8-thiol 2-methyl-4-propyl-1,3-oxathiane

7 8 9 10

Potato Tomato Truffle

methional 2-isobutyl thiazole bis(methylthio)methane

11 12 13

Although sulfur compounds are important contributors to the flavor of many foods, they have also been implicated in off-flavor development (Chin and Lindsay, Chapter 8, Nairn et al., Chapter 7). Because they have such low thresholds, only small quantities can have a deleterious effect on the organoleptic character of a food. Even in meat where sulfur compounds are very important to the organoleptic character, high levels of volatile sulfides can form undesirable flavors (76). Although hydrogen sulfide may be important to the aroma of various fresh citrus juices, dimethyl sulfide has been implicated in off-flavors in canned orange and grapefruit juices. The latter compound probably comes from heat degradation during processing (77). Hydrogen sulfide, dimethyl sulfide, and dimethyl disulfide have been associated with the cooked, cabbage-like, sulfurous odor and flavor that occurs when milk is heated. This undesirable character develops during ultra-hightemperature (UHT) sterilization, but typically disappears after several days of storage (18). Analysis The minute quantities of sulfur compounds found in many foods makes their analysis and quantitation a challenging problem. Extraction without further fractionation, will, in many cases, not result in a high enough concentration of these trace sulfur constituents to permit their identification by gas chromatogra-



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MUSSINAN AND KEELAN

Sulfur Compounds in Foods: An Overview

phy/mass spectrometry (GC/MS). Element-selective detectors are useful tools for quickly locating sulfur compounds in complex mixtures and for monitoring their presence through subsequent isolation and fractionation steps (79, Mistry et al., Chapter 2). The most commonly used sulfur detector is the flame photometric detector (FPD) (20). More recently, a new chemiluminescence detector (SCD) was developed for GC (27, Steely, Chapter 3). The SCD is reported to be sensitive, selective and linear. In a 1988 applications note (22), dimethyl sulfide was determined in beer by headspace analysis without any preconcentration. Levels of this compound in beer are typically l-1000ppb. Atomic emission detection (AED) has recently been commercially developed for gas chromatography. The AED can be tuned to selectively detect any element in any compound that can be eluted from a GC (23). Using these detectors as guides, the analyst can target thosefractionsor areas of a chromatogram containing sulfur for careful analysis by GC/MS or other hyphenated techniques like supercritical fluid chromatography/mass spectrometry (SFC/MS). Artifacts When attempting to analyze for sulfur constituents, the possibility of artifact formation must be carefully considered (Block and Calvey, Chapter 6; Spanier et al., Chapter 5). Many sulfur compounds are thermally unstable. Therefore, it's not surprising that the high temperatures typically encountered in the inlet of a gas chromatograph can lead to artifact formation. As Block (24) pointed out, many of the thiosulfinates and related sulfoxides found in garlic and onion are thermally unstable, in some cases even at room temperature. He suggests that "many of the socalled 'new compounds' being reported are simple artifacts resulting from decomposition of the fragile primary flavorants in the injection port, column, and heated transfer line connecting the GC to the MS." In order to guard against this misinterpretation, researchers need to test their analytical methods using standard compounds and conditions identical to those under which the analysis is run to verify their stability. In cases where instability is evident, alternative, low-temperature methods such as liquid chromatography or NMR need to be used. Formation The mechanism of formation of sulfur compounds has also been studied in depth, either directly, or using model systems (Tressl et al. Chapter 18). Nonvolatile precursors to volatile sulfur compounds in foods are the sulfur containing amino acids (cysteine/cystine, and methionine), reducing sugars, and thiamin (vitamin Bl). The amino acids and reducing sugars react in the so-called Maillard reaction first described by L.C. Maillard in 1912 (25) and since extensively studied (26). The dicarbonyls which form during this reaction catalyze the Strecker degradation of cysteine to mercaptoacetaldehyde, acetaldehyde, hydrogen sulfide and other compounds (27). Similarly, the Strecker degradation of methionine produces methional which further hydrolyzes to methyl mercaptan and hydroxypropionaldehyde. The volatile sulfur compounds, hydrogen sulfide and methyl mercaptan, are highly odored and quite reactive. Both will readily react with carbonyl compounds and carbon-carbon double bonds to yield many potent flavor compounds (28). In addition to the Maillard reaction which involves a thermal degradation, methionine


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may degrade by enzymatic means to form dimethyl sulfide, another very powerful flavor compound (28). These small, reactive molecules may serve as precursors for other sulfur containing flavor compounds. For example, hydrogen sulfide may re act with furanones leading to the formation of sulfur containing heterocycles (29). Methanethiol may also further react forming mono-, di- and trisulfides (29). The thermal degradation of thiamin (vitamin Bl) provides another source of sulfur con taining flavor compounds, many of them heterocyclic (30', Guntert et al., Chapter Π).


Functional Properties While the sensory properties of sulfur compounds have been of interest for many years, recent attention has focused more heavily on some of the other functional properties of these compounds. Certain sulfur compounds have been found to have antioxidative, antimicrobial, and human medicinal properties. Antioxidative Properties. When cooked meat is refrigerated, a rancid or stale fla vor usually develops within 48 hrs. This character has been termed "warmed-over flavor"(WOF) and is generally attributed to the oxidation of lipids. Various syn thetic and natural antioxidants have been used to reduce the development of WOF. Among the natural antioxidants used are the sulfur containing amino acid cysteine, and various Maillard reaction products. Eiserich and Shibamoto (Chapter 20) found that certain volatile sulfur heterocycles derived from Maillard reaction sys tems can function as antioxidants. Natural phenols of white grapes undergo browning reactions during oxida tion resulting in the formation of an undesirable brown color. Using caffeic acid as a model for fruit juice phenols, Cilliers and Singleton (37) studied the effect of thiols on browning. The presence of cysteine or glutathione was found to reduce the oxidation of caffeic acid, thus protecting itfrombrowning. Medicinal Properties. According to Lawson (32), garlic is one of the most re searched medicinal plants with about 940 research papers published between 1960 and 1992. The biological studies have been primarily concerned with its cardiovas cular, antimicrobial and anticancer effects as well as its hypoglycemic, heavy-metal poisoning antidote, and liver-protective effects (32). Most of the studies on garlic have focused on its organosulfur compounds because studies have shown that re moval of the thiosulfinates eliminates many of these effects. Almost all human studies on the lipid-lowering effects of garlic and garlic products showed signifi cant decreases in serum cholesterol and serum triglyceride. Reports that onion and garlic contain hypoglycemic (blood sugar reducing) agents go back about 50 years. In fact, the ancient literature reveals their use in treating diabetes (33). Garlic, and to a lesser extent onion, have been found to possess antimicro bial properties. They are extensively used in the Oriental diet and have been used to treat various ailments, especially those associated with bacterial infections (34). The antibacterial effect of garlic has been attributed to allicin, S-2-propenyl 2propenethiosulfinate. Garlic extract has been found effective against various strains of influenza virus in mice (33). Kubota and Kobayashi (Chapter 19) iso lated two sulfur compounds from the fruit of Scorodocarpus borneensis Becc.("wood garlic") which were found to possess antibacterial and/or antifungal


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MUSSINAN AND KEELAN

Sulfur Compounds in Foods: An Overview 5

properties. Neither of these compounds had been previously found in the allium genus. Various organic sulfides present in Allium have been found to have anticarcinogenic activity. For example, allyl sulfide, a constituent of garlic oil, inhibited colon cancer in mice exposed to 1,2-dimethylhydrazine, and allyl methyl disulfide, allyl methyl disulfide, allyl disulfide, and allyl sulfide all inhibited benzo[a]pyreneinduced neoplasma of the forestomach and lung in female mice (35). Lam et al. (Chapter 22) investigated the ability of 2-n-butyl thiophene, a constituent of roast beef aroma, to inhibit chemically induced carcinogenesis in three different tumor systems. This compound was found to be effective in the forestomach, lung, and colon models. Downloaded by 192.64.121.225 on March 25, 2016 | http://pubs.acs.org Publication Date: July 29, 1994 | doi: 10.1021/bk-1994-0564.ch001

Conclusion The chemistry of sulfur compounds in foods is very complex and continues to be extensively studied. Both cooked and uncooked foods contain organoleptically im portant sulfur-containing compounds. Conversely, the off-odors of numerous foods have been attributed to sulfur compounds. In addition to their sensory properties, recent work has been increasingly geared towards other functional properties of these compounds, especially antioxidant, antimicrobial, and anticarcinogenic ef fects. These areas will, no doubt, continue to be the subject of research for years to come. Literature Cited 1. Shahidi, F.; Rubin, L.J.; D'Souza, L.A. CRC Crit. Rev. Food Sci. Nutr. 1986, 24, 141. 2. Boelens, M.H.; van Gemert, L.J. Perf. & Flav. 1993, 18, 29. 3. Maga. J.Α.; CRC Crit. Rev. Food Sci. Nutr. 1975, 6(2), 153. 4. Maga. J.A.; CRC Crit. Rev. Food Sci. Nutr. 1975, 6(3), 241. 5. Maga. J.Α.; CRC Crit. Rev. Food Sci. Nutr. 1976, 7(2), 147. 6. Teranishi, R.; Buttery, R.G.; Guadagni, D.G. In Geruch-und Geschmackstoffe; Drawert, F., Ed.; Nurnberg: Verlag Hans Carl, 1975; 177-186. 7. Buttery, R.G. In Flavor Science: Sensible Principles and Techniques; Acree, T.E.; Teranishi, R., Eds.; ACS Professional Reference Book; American Chemi cal Society: Washington, DC, 1993; 259-286. 8. Tressl, R.; Silwar, R. J.Agric.Food Chem. 1981, 29, 1078. 9. Demole, E.; Enggist, P.; Ohloff, G. Helv. Chim Acta 1982, 65, 1785. 10. Winter, M.; Furrer, Α.; Willhalm, B.; Thommen, W. Helv. Chim Acta 1976, 59(5), 1613. 11. Buttery, R.G.; Seifert, R.M.; Guadagni, D.G.; Ling, L.C. J. Agric. Food Chem. 1971, 19, 969. 12. Buttery, R.G.; Teranishi, R.; Ling, L.C.; J. Agric. Food Chem. 1987, 35, 540544. 13. Sloot, D.; Harkes, P. J. Agric. Food Chem. 1975, 23, 356. 14. Boelens, M.; de Valois, P.J.; Wobben, H.J.; van der Gen, A. J. Agric. Food Chem. 1971, 19, 984.




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15. Mussinan, C.J. Chemtech 1980, 10(10), 618. 16. Bailey M.E.; Rourke, T.J.; Gutheil, R.A.; Wang, C.Y-J. In Off-Flavors in Foods and Beverages; Charalambous, G., Ed.; Elsevier: New York, 1992; 127169. 17. Shaw, P.E.; Wilson IIΙ, C.W.; J. Agric. Food Chem. 1982, 30(4), 685. 18. Azzara, C.D.; Campbell, L.B. In Off-Flavors in Foods and Beverages; Chara lambous, G., Ed.; Elsevier: New York, 1992; 329-373. 19. Mussinan, C.J. In Flavor Science: Sensible Principles and Techniques; Acree, T.E.; Teranishi, R., Eds.; ACS Professional Reference Book; American Chemi cal Society: Washington, DC, 1993; 169-224. 20. Brody, S.S.; Chaney, J.E. J. Gas Chromatogr. 1966, 4, 42. 21. Shearer, R.L.; O'Neal, D.L.; Rios, R.; Baker, M.D. J. Chromatogr. Sci. 1990, 28(1), 24. 22. Jones, L.; Application Note No. 003; Sievers Research, Inc.: Boulder, CO, 1988. 23. Buffington, R. GC-Atomic Emission Spectroscopy Using Microwave Plasmas; Hewlett-Packard Company: Avondale, PA, 1988. 24. Block, E.J. J. Agric. Food Chem. 1993, 41, 692. 25. Maillard, L.C. Compt. Rend. Acad. Sci. Paris 1912, 66, 154. 26. Waller, G.R.; Feather, M.S., Eds.; The Maillard Reaction in Foods and Nutri tion; ACS Symposium Series 215; American Chemical Society: Washington, DC, 1983. 27. de Roos, K.B. In Flavor Precursors: Thermal and Enzymatic Conversions; Teranishi, R.; Takeoka, G.R.; Guntert, M., Eds.; ACS Symposium Series 490; American Chemical Society: Washington, DC, 1992; 203-216. 28. Scarpellino, R.; Soukup, R.J. In Flavor Science: Sensible Principles and Tech niques; Acree, T.E.; Teranishi, R., Eds.; ACS Professional Reference Book; American Chemical Society: Washington, DC, 1993; 309-335. 29. Schutte, L. In Phenolic, Sulfur, and Nitrogen Compounds in Food Flavors; Charalambous, G.; Katz, I., Eds: ACS Symposium Series 26; American Chemi cal Society: Washington, DC, 1976; 96-113. 30. Guntert, M.; Bruning, J.; Emberger, R.; Hopp, R.; Kopsel, M.; Surbury, H.; Werkhoff, P. In Flavor Precursors: Thermal and Enzymatic Conversions; Teranishi, R.; Takeoka, G.R.; Guntert, M., Eds.; ACS Symposium Series 490; American Chemical Society: Washington, DC, 1992; 140-163. 31. Cilliers, J.J.L.; Singleton, V.L. J. Agric. Food Chem. 1990, 38, 1789. 32. Lawson, L.D. In Human Medicinal Agents from Plants; Kinghorn, A.D.; Balandrin, M.F., Eds.; ACS Symposium Series 534; American Chemical Society: Washington, DC, 1993; 306-330. 33. Fenwick, G.R.; Hanley, A.B. CRC Crit. Rev. Food Sci. Nutr. 1985, 23(1), 1. 34. Elnima, E.I.; Ahmed, S.A.; Mekkawi, A.G.; Mossa, J.S. Pharmazie 1983, 38(11), 747. 35. Weinberg, D.S.; Manier, M.L.; Richardson, M.D.; Haibach, F.G.; Rogers, T.S. J. High Res. Chromatogr. 1992, 15(10), 641. RECEIVED April 5,

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Sulfur Compounds in Foods - American Chemical Society

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