Lipid-Derived Flavor Compounds in Fresh and Dehydrated Tomato

Chapter 9

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Lipid-Derived Flavor Compounds in Fresh and Dehydrated Tomato Products Karl Karmas, Thomas G. Hartman, Juan P. Salinas, Joseph Lech, and Robert T. Rosen Center for Advanced Food Technology, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903

Lipid derivedflavorsare produced in tomatoes duringripeningvia the action of endogenous enzymes such as lipoxygenase. They may be further influenced by nonenzymatic oxidative decomposition reactions which occur during processing and storage. This investigation focused on the determination of lipid oxidation derivedflavorsin the fresh and dehydrated tomato products using dynamic headspace concentration (purge and trap - thermal desorption) gas chromatography-mass spectroscopy (GC-MS) procedures. The effects of ripening and the lipoxygenase activity upon the generation of lipid oxidation compounds in fresh tomatoes were studied. Comparisons were made to dehydrated sun-dried tomatoes. The lipid oxidation profiles detected in these systems and their role in flavor development are discussed.

Tomato is the world's third most popular fruit. The world wide production is approximately 49,202,000 metric tons (7). The knowledge of the volatile and semivolatile compounds present is important in understanding which ones contribute most to its flavor, overall quality and biochemical changes. These changes result from ripening and processing such as heating, drying, canning and storage. Many investigations have been carried out to determine the volatile and semivolatile composition of tomatoes and tomato products and over 400 compounds have been previously identified (2). Many of these are products of lipid oxidation and Maillard browning reactions. Lycopene and β-carotene breakdown products are common oxidative decomposition products as are the appearance of Strecker aldehydes from thermal processing. Other typical compounds are the C6 aldehydes and alcohols as a result of lipoxygenase activity. Of the over 400 compounds that have been found in tomatoes none have the character impact of tomato (2). However, the major contributors to fresh tomato

0097-6156/94/0558-0130$08.00/0 © 1994 American Chemical Society In Lipids in Food Flavors; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


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KARMAS ET AL.

Lipid-Derived Flavor Compounds in Tomato Products

aroma have been determined to be c/i-3-hexenal, β-ionone, hexanal, βdamascenone, 1 -penten-3 -one, 3 -methy lbutanal,taaw.y-2-hexenal,2-isobuty lthiazole, 1-nitrophenylethane and /raws-2-heptenal (3). Some of the methods used for tomato analysis are simultaneous steam distillation and solvent extraction, headspace analysis and dynamic headspace concentration (4,5). Of these methods the headspace concentration (purge and trap) methods are most similar to the methods used in this paper. In some investigations tomato flavor volatiles were purged and trapped on to Tenax adsorbent and then eluted with diethyl ether (6,7,8,9). In our experiments the organics are desorbed off of Tenax and Carbotrap or Carbosieve S-IEt with heat (short path thermal desorption) (10,11). It was the objective of this study to develop a rapid analytical method (combined purge and trap and short path thermal desorption) for assessing the volatiles of fresh and dehydrated tomato products. The differences between sun dried and fresh tomatoes were profiled. This investigation is the first report on the volatile flavor profile of sun-dried tomatoes. It is hoped that this work can eventually lead to better understanding of the quality of tomatoes as the result of changes in ripening and processing. Materials Samples of sun-dried tomatoes were purchased from a local food store. Samples of fresh tomatoes of the variety "Mountain Pride" was purchased from a local farmer. D-8 toluene (internal standard) was obtained from Aldrich Chemical Company (Milwaukee, WI). Tenax TA was obtained from Alltech Associates (Deerfield, IL). Silanized glass wool, Carbotrap 20/40 mesh, and Carbosieve S-ΙΠ 60/80 mesh was from Supelco Inc. (Belefonte, PA). The short path thermal desorption supplies and accessories were from Scientific Instrument Services (SIS) Inc. (Ringoes, NJ). Experimental Sun dried tomatoes were cooled with liquid nitrogen and then ground to a powder with a Bell Art Micromill which was cooled with dry ice. The powdered sundried tomatoes (5 g) were placed into a 1/2 inch χ 14 inch glass tube. Both ends of the glass tube were plugged with silanized glass wool. An internal standard was matrix spiked (200 ppb based on the total weight of the powdered sun-dried tomatoes) into the sample. The glass sample tube was attached to the SIS Purge and Trap System. In two separated experiments, the tube was purged and trapped for 30 min at 80°C and 50°C with nitrogen at a flow rate of 40 ml/min onto a Tenax-Carbotrap trap. Each trap was dried 45 min using 40 ml/min flow of dry nitrogen to remove water. The Tenax/Carbotrap trap was then thermally desorbed into the GC-MS at 220°C for 5 minutes. Fresh tomatoes, unblanched and blanched, (10 min in boiling water) were

In Lipids in Food Flavors; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

131


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LIPIDS IN FOOD FLAVORS

blended to a slurry with a Cuisinart model DL8 food processor. The slurried tomatoes (100 g) were added into a 100 ml Wheaton Purge & Trap Apparatus. An internal standard of d-8 toluene was matrix spiked at the 165.3 ppb level (dry basis) (72) into the slurried tomatoes. The sample was purged and trapped for 30 min at 53°C with nitrogen at a flow rate of 40 ml/min onto a Tenax-Carbotrap trap. The trap was dried 45 min using 40 ml/min flow of dry nitrogen at room temperature to remove water. The trap was then thermally desorbed into the GCMS. The traps from the purge and trap step were thermally desorbed into the GC-MS using an SIS model TD-1 short path thermal desorption system. The desorption conditions were 220°C for five minutes. The gas chromatograph was a Varian 3400 installed with a 60 m χ 0.32 mm DB-1 capillary column (J&W Scientific Co.) with a 0.25 pm film thickness. The injector temperature was 250°C; the split ratio was 10:1. The column was temperature programmed from 20°C (hold time of 5 min during the thermal desorption step to achieve cryofocusing) to 40°C (0 min hold) at a rate of 10°C/min; then to 150°C (0 min hold) at a rate of 2°C/min; and finally to 280°C at a rate of 4°C/min with a 20 min hold at the upper limit. The GC column was inserted directly into the ion source of the mass spectrometer via a heated transfer line maintained at 280°C. The mass spectrometer was a Finnigan Mat 8230 high resolution double focusing magnetic sector instrument. The mass spectrometer was operated in electron ionization mode (70 eV) scanning masses 35-350 once each second with a interscan time of 0.8 seconds. The mass spectrometer data was acquired and processed using a Finnigan MAT SS300 Data system. All mass spectra obtained were background subtracted and library searched against the National Institute of Standards and Technology mass spectral reference collection (10). The Wiley/NBS Registry of Mass Spectra and DB-1 Kovats retention time indices were used to help identify compounds (9,13,14). Results & Discussion Figures 1 and 2 show the chromatograms obtained for sun-dried and fresh tomatoes using purge and trap - short path thermal desorption GC-MS. The major compounds are also listed in the chromatograms. Table I show all the compounds identified and their relative concentrations (based on comparisons to the internal standard d-8 toluene). Most of the compounds detected have already been reported in the literature as tomato volatiles. Additionally, Figure 3 shows some of the compounds trapped by Carbosieve S-III and Tenax which were not retained by Carbotrap and Tenax. Four additional low molecular weight compounds could be detected with this method. Since no internal standard was injected with these four compounds, the level could not be ascertained. In this analysis the major volatile compounds in both sun-dried and fresh tomatoes are lipid derived. In sun-dried tomatoes the lycopene and other carotenoid breakdown products (15-19) are the major compounds present. These


KARMAS ET AL.

Lipid-Derived Flavor Compounds in Tomato Products 133


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3-METHYLBUTANAL 2-METHYLBUTANAL PENTANAL DIMETHYLDISULFIDE D-8 TOLUENE (I.S., 165.3 PPB) HEXANAL TRANS-2-HEXENAL aS-3-HEXEN-l-OL (LEAF ALCOHOL) HEXANOL 4 5-OIMETHYL-1 -HEXENE HEPTANAL BENZALDEHYDE DAŒTHYLTPJSULFtDE 6-METHYL-5-HEPTENÉ-2-ONE OCTANAL PHENYLACETALDEHYDE 2-I90BUTYLTHIAZOLE NONANAL METHYL SALICYLATE DECANAL BETA-CYCLCOTRAL OTRAL QERANYLACETCNE ΒΕΤΑΊΟΝΟΝΕ


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KARMAS ET AL.



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135

136


Table L Volatile Compounds Identified in Sun-dried and Fresh Tomatoes Compound

Estimated concentration (ppb)


Sun-dried 2-Methylpropanal 3 -Methy 1-2-butanone 2-Methylfuran 2-Methyl-3-buten-2-ol 3-Methylbutanal 2-Methylbutanal l-Penten-3-one 3 -Methy 1-2-butanone Pentanal Acetic acid Heptane 2-Ethylfuran 2,5-Dihydro-3,4-dimethylfuran 3-Penten-2-one Dimethyldisulfide 2-Ethoxypropane 1 -Methy lthiopropane 2-Pentenal 2-Methyl-2-butenal 3 -Methyl-1 -butanol 2,3-Dihydro-4-methylfuran 3 -Methy 1-1 -butanol 2-Methyl-l -penten-3-ol 3-Hepten-2-one Hexanal Octane 2-Furfural m»w-2-Hexenal cw-3-Hexen-l-ol 2-Methy 1-3 -penten-1 -ol Xylene Pentyl acetate 1-Hexanol Methional 2-Heptanone Heptanal

15.9 57.2 10.3 78.7 674.4 396.2 17.0 5.9 37.6 168.1 11.4

-

2.4 72.2 145.4 158.8 117.5 17.9 58.0 59.4 40.1 7.6

-

195.8 6.7 826.7 2.0

-

3.6 71.8

-

Fresh

-

68.3 4.0

75.5 13.4

71.0

-

1.5

-

25.2

-

3.5 -

-

7.7 4442.2

-

1718.5 291.7 -

-

34.7 40.0

20.8 157.5 8.9 11.3 Continued on next page


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KARMAS ET AL.


137

Table I. Continued Compound



Sun-dried

2-Acetylfuran 2,6-Dimethylpyrazine Pentanoic acid Heptanal 5-Ethyl-2(5H)-furanone Dimethylphenol Benzaldehyde 2-Heptenal 5-Methyl-2-furfural Dimethyltrisulfide Butanoic acid 6-Methyl-5-hepten-2-one 2-Pentylfuran 6-Methyl-5-hepten-2-ol Octanal γ-Hydroxyhexanoic acid Phenylacetaldehyde 2-Isobutylthiazole β-Thujene β-Terpinene D-Limonene 2,6-Dimethyl-5-heptenal (Melonal) 4-Methylbenzaldehyde 3,4-Dimethylstyrene 6-Methyl-3,5-heptadien-2-one Nonanal 3- (4-Methyl-3-pentenyl) furan (Perillen) 1-Isocyano-2-methylbenzene Fenchol 2-Nonenal 2,4-Dimethylbenzaldehyde Methylacetophenone Methyl salicylate Decanal 4,6,6-trimethyl-bicyclo-[3.1.1 .]-hept-3-en-2-one (Berbenone)

Fresh

58.6 73.9 130.2 128.1 177.9 47.0 222.0 47.8 1988.9 119.6 158.1 3.2 908.8 7.8 5.8 46.5 335.9 42.1 2.2 216.3 92.9 249.4 14.1 7.7 82.1 98.1 34.4 36.7 4.8 215.8

17.5 129.3 8.8 101.4 54.6 18.1 370.5 138.2 59.2 64.4 7.1 216.9 36.3 17.1 8.7

66.5 32.9

24.3 139.9 49.4

Continued on next page



138 Table I. Continued Compound



Sun-dried

2-Vinylbenzofuran β-Cyclocitral Dodecane β-Citral (Neral) 3 -Methyl -1 -naphthalenol 2-Decenal α-Ethylidiene benzeneacetaldehyde α-Citral (Geranial) Decahydro-1,6-dimethylnaphthalene 2,4-Decadienal 2-Undecenal Tridecane Eugenol acetate l,2-Dihydro-4,6,8-trimethylnaphthalene a-Ionene l,4,4a,5,6,8,8a-Octahydro-2,5,5,8a-tetramethyl1 -naphthalenemethanol β-Damascenone a-Copaene Tetradecane a-Ionone 4-(2,2,3,3-Tetrabutyl) phenol 6,10-Dimethyl-5,9-undecadien-2-one Epoxy-β-ionone β-Ionone Butylated hydroxytoluene (BHT) 2,6-Di-tert-butylphenol Faresene Pseudo-Ionone isomer Farnesal Nerolidol Pseudo-Ionone isomer 2-Methylpropanoic acid Famesylacetone 8

8

8

11.3 82.0 17.0 205.5 2.9

-

139.6 274.9 1.9 28.6

-

Fresh

-

17.1

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18.5

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11.0

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37.8

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11.6 5.0

25.4 0.7 1.7 2.3

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26.2 36.5 10.7 23.9 9.9 10.6 712.3 17.4 37.6 107.7 126.5 17.2 42.7 33.5 6.5 155.6 2.2 28.7

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KARMAS ET AL.


compounds are 6-methyl-5-hepten-2-one, 6-methyl-3,5-hepten-2-one, 6-methyl-5hepten-2-ol, melonal, famesylacetone, geranylacetone (6,10-dimethyl-5,9undecadien-2-one), famesal, famesene, β-cyclocitral, a-citral, β-citral, βdamascenone, a-ionone, β-ionone, pseudo-ionone, epoxy-β-ionone, a-ionene and xylene. Strecker aldehydes (16) are also present in sun-dried tomatoes. Some of these compounds are 3-methylbutanal, 2-methylbutanal, acetaldehyde, methional, 2-methylpropanal, and phenylacetaldehyde. This indicates that free amino acids and reducing sugars are key precursors to browning flavor in tomatoes. Other Maillard browning products such as furfural were also found. In the literature 3-methylbutanal and furfural have been used as processing indicators (20-21). The sun-dried tomatoes were noticeably "browned" so the appearance of Maillard reaction compounds including Strecker aldehydes should definitely be expected. In fresh unblanched tomatoes the linoleic and linolenic fatty acid breakdown (via the lipoxygenase enzyme) lead to the C6 aldehydes and C6 alcohols formation (2,5,22). Thus the major compounds are hexanal, hexanol, cis3-hexenol and imws-2-hexenal. The major portion of /raws-2-hexenal was a GC artifact caused by isomerization of the czs-3-hexenal (Chapter 19, this volume). At high concentrations hexanal can give rancid flavor while at lower concentrations it contributes to the green flavor note of tomato (2). Some of the breakdown products of lycopene, β-carotene as well as Strecker aldehydes, and other Maillard browning products were present in the fresh unblanched tomatoes but at lower levels in comparison to sun-dried tomatoes. Figure 4 shows the concentration of hexanal versus tomato type and processing technique. In all blanched samples, hexanal levels were relatively low. In fresh unblanched tomatoes the concentration of hexanal is the greatest. Hexanal levels increase as a function of ripening; this can be explained by the enzymic breakdown of linoleic acid by lipoxygenase (2,5,23). During the sample preparation steps used in our work, the tomatoes were blended to a slurry leading to cellular breakdown and the elevated activity of lipoxygenase. Blanching tomatoes decreased the amount of hexanal produced due to the denaturation of lipoxygenase enzyme. In sun-dried tomatoes the level of hexanal is lower than in fresh unblanched tomatoes. This is due to deactivation of the enzyme due to the low water activity in the dehydrated product. Figure 5 shows the concentration of /raws-2-hexenal for various tomato samples. The cw-3-hexenal has a stronger green note than the frnws-2-hexenal. Both compounds contribute to tomato aroma (2) and low concentrations of cis-3hexenal and rraws-2-hexenal contribute to desirable flavor notes. Little or no trans2-hexenal was detected in the sun-dried tomatoes. Figure 6 shows the concentration of c/s-3-hexenol for various tomato samples. The c/s-3-hexenol concentration levels can be explained similarly to the hexanal description previously given. The cis-3-hexanol has a green note flavor which contributes to tomato aroma (2). No c/s-3-hexenol was detected in the sun dried or blanched tomatoes. Figure 7 shows the concentration of 6-methyl-5-hepten-2-one versus tomato type and processing technique. As pointed out earlier, this is the major compound identified in sun-dried tomatoes. This compound is reported to have fruity flavor


139

140


PROCESSING TECHNIQUE •

SUN DRIED

Β

UNBLANCHED

•

BLANCHED

*

CONCENTRATION IS


GREATER DUE TO OVERLOAD ON COLUMN

I Figure 4.

IV

III

Concentration of hexanal versus tomato type and processing technique. I: sun-dried tomatoes, P&T at 80°C; II: sun-dried tomatoes, P&T at 50°C; III: red tomatoes, P&T at 53°C; IV: medium ripe tomatoes, P&T at 53°C; V: green tomatoes, P&T at 53°C.

PROCESSING TECHNIQUE •

SUN DRIED

Η

UNBLANCHED

* • *

BLANCHED COMPOUND NOT OBSERVED

Figura 5.

I II III IV V Concentration of /raws^-hexenal versus tomato type and processing technique. I: sun-dried tomatoes, P&T at 80°C; II: sun-dried tomatoes, P&T at 50°C; III: red tomatoes, P&T at 53°C; IV: medium ripe tomatoes, P&T at 53°C; V: green tomatoes, P&T at 53°C.


9.

KARMAS ET AL.

Lipid-Derived Flavor Compounds in Tomato Products 400 η

PROCESSING TECHNIQUE 360-

* g


„ ' 320 -

Β

SUN DRIED UNBLANCHED

I Figure 6.

III

IV

V

Concentration of m-3-hexen-l-ol versus tomato type and processing technique. I: sun-dried tomatoes, P&T at 80°C; Π: sundried tomatoes, P&T at 50°C; III: red tomatoes, P&T at 53°C; IV: medium ripe tomatoes, P&T at 53°C; V: green tomatoes, P&T at 53°C.

I Figure 7.

II

II

III

IV

V

Concentration of 6-methyl-5-hepten-2-one versus tomato type and processing technique. I: sun-dried tomatoes, P&T at 80°C; II: sundried tomatoes, P&T at 50°C; III: red tomatoes, P&T at 53°C; IV: medium ripe tomatoes, P&T at 53°C; V: green tomatoes, P&T at 53°C.


141



142

quality at low concentration while at higher concentrations it may impart off-flavor (15). In sun-dried tomatoes the concentration of 6-methyl-5-hepten-2-one is greater than in fresh products. During sun drying, conditions are optimal for the photooxidation and or nonenzymatic oxidation degradation of lycopene. In the fresh tomatoes it appears that the level of 6-methyl-5-hepten-2-one increases as a function of ripeness. In the blanched tomatoes the level of 6-methyl-5-hepten-2one is less than in the unblanched, and this may indicate that there is a combination of both thermal and enzymic breakdown occurring. Thus chemical changes in tomatoes can be used to reflect different levels of processing and ripening. The relevant pathways include lipid breakdown as well as Maillard browning. Indicator compounds can be selected specifically to represent age and degree of processing. Acknowledgements We acknowledge the Center for Advanced Food Technology (CAFT) mass spectrometry facility for providing instrumentation support. This is New Jersey Agricultural Experiment Station (NJAES) publication #F-10569-3-93. Literature Cited 1. 2. 3.

4. 5. 6. 7. 8. 9. 10.

Davies, J. N.; Hobson, G. E. CRC Crit. Rev. Food Sci. Nutr. 1981, 20, 205-279. Petro-Turza, M. Food Rev. Internat. 1987, 2, 309-351. Buttery, R. G.; Teranishi, R.; Flath, R. Α.; Ling, L. C. In Flavor Chemistry: Trends and Developments; Teranshi, R.; Buttery, R. G.; Shahidi, F. Eds.; ACS Symp. Ser. 388; American Chemical Society: Washington D.C., 1989; pp 213-222. Hayase, F.; Chung,T.-Y.; Kato, H. Food Chem. 1984, 14, 113-124. Maarse, H. Volatile Compounds in Foods and Beverages, Marcel Dekker, Inc.: New York, 1991; pp 247-281. Buttery, R. G.; Teranishi, R.; Ling, L. C. J. Agric. Food Chem. 1987, 35, 540-544. Buttery, R. G.; Teranishi, R.; Ling, L. C.; Flath, R. Α.; Stern, D. J. J. Agric. Food Chem. 1988, 36, 1247-1250. Buttery, R. G.; Teranishi, R.; Flath, R. Α.; Ling, L. C. J. Agric. Food Chem. 1990, 38, 729-795. Buttery, R. G.; Teranishi, R.; Ling, L. C.; Turnbaugh, J. G. J. Agric. Food Chem. 1990, 38, 336-340. Hartman, T. G.; Karmas, Κ.; Chen, J.; Shevade, Α.; Deagro, M.; Hwang, H.-I. In Phenolic Compounds in Food and Their Effects on Health I: Analysis, Occurrence, and Chemistry; Ho, C.-T.; Lee, C. Y.; Huang, M . T. Eds.; ACS Symp. Ser. 506; American Chemical Society: Washington, D.C., 1992; pp 60-76.


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11. 12. 13.


14. 15. 16. 17. 18. 19. 20. 21. 22. 23.


Hartman, T. G.; Lech, J.; Karmas, Κ.; Salinas, J.; Rosen, R. T.; Ho, C.-T. 1993. In Flavor Measurment; Ho, C.-T.; Manley, C. H. Eds.; Marcel Dekker, Inc.: New York, 1993, pp 37-60. Haytowitz, D. B.; Matthews R. H. Composition of Foods: Vegetables and Vegetable Products, Agriculture Handbook # 8-11, 1984; pp 449-458. The Restek Advantage, Industrial Solvent Analysis Simplified, January 1992, Vol.3, No.l. McLafferty, F. W.; Stauffer, D. B. The Wiley/NBS Registry of Mass SpectralData;John Wiley & Sons: New York, 1989. Cole, E. R.; Kapur, N. S. J. Sci. Food Agric. 1957, 8, 360-365. Berlitz, H.-D. Food Chemistry; Spinger-Verlag: Berlin-Heidelberg, 1987; pp 189-20, 267. Kanaseawud, P.; Crouzet, J. C. J. Agric. Food Chem. 1990, 38, 237-243. Onyewu, P. N.; Daun, H.; Ho, C.-T. In Thermal Generation of Aromas, Parilment, T. H.; McGorrin, R. J.; Ho, C.-T. Eds.; ACS Symp. Ser. 409, American Chemical Society: Washington, D.C., 1989, pp 247-256. Schrier, P.; Drawert, F.; Bhiwapurkar S. Chem. Mikrobiol. Technol. Lebensm. 1979, 6, 90-91. Eichner, K.; Ciner-Doruk, M. Prog. Food. Nutr. Sci. 1981, 5, 115-135. Kanner, J.; Harel, S.; Fishbein, Y.; Shalom, P. J. Agric. Food Chem. 1981, 29, 948-949. Frankel, E.N. Prog. Lipid Res. 1982, 1-33. Kazeniac, S. J.; Hall, R. M. J. Food Sci. 1970, 35, 519-530.

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Lipid-Derived Flavor Compounds in Fresh and Dehydrated Tomato

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