Chapter 3
Volatile Components of Tomato Fruit and Plant Parts Relationship and Biogenesis
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Ron G. Buttery and Louisa C. Ling Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, CA 94710
A comparison is made of the volatile component concentrations in the macerated (blended) forms of tomato fruit and leaf and to a lesser extent in macerated flower, calyx and stem. These studies show that some processes such as the formation of C6 lipid derived volatiles are similar between fruit and leaf. Formation of higher carbon number lipid derived volatiles (e.g. 4,5-epoxy-(E)-2decenal), however, only occurs in the fruit. Other processes such as the formation of carotenoid related (e.g. 6-methyl-5-hepten-2one) and amino acid related (e.g. nitro, nitrile and thiazole) volatiles seem to be largely confined to the fruit. Terpenoid hydrocarbons occur in the leaf but not the fruit, except for (-)-alpha-copaene in the mature green fruit. Lipid oxidation processes occur in the first few minutes after maceration but glycoside hydrolysis and amino acid derived volatile biogenesis seems to occur during the ripening process in the intact tomato. The authors have been carrying out a continuing study of the volatile aroma and flavor components of tomatoes. The control of tomato flavor, in both the agricultural production of tomatoes and their processing, could benefit from basic knowledge of the biogenesis or chemogenesis of the flavor components. This information is also important to any genetic approaches in flavor control. The leaves and other plant parts have aromas which bear a resemblance to the aroma of the fruit. Using specialtissueculture techniques it has been found that some planttissuecan be transformed into ripe fruit liketissue(J). It seemed then that knowledge of the volatiles of different plant parts may give us some clues to biogenesis in the fruit. The authors have therefore made a study of the volatiles of tomato leaves and other plant parts and compared the volatiles to those of the fruit.
This chapter not subject to U.S. copyright Published 1993 American Chemical Society
In Bioactive Volatile Compounds from Plants; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
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BIOACTTVE VOLATILE COMPOUNDS FROM PLANTS
Division of Flavor Components into Groups. To simplify the study it is useful to divide the tomato (fruit and plant) volatiles into several groups. These are listed in Table I. We will discuss each group separately. In general, unless otherwise mentioned, the method of isolation of volatiles and their capillary GLC- MS analysis is similar to that described previously by the authors. This involved first blending of the fruit or plant material with a small amount of water, holding of the blended material for 3 minutes for enzyme generation of volatiles, then addition of excess saturated CaCl solution to halt further enzyme action. After addition of internal standards the volatiles were swept from the vigorously stirred mixture to a large (10g) Tenax trap with a flow (3L/min.) of purified air for 1 hour. Extraction of the trap with diethyl ether and distillation removal of most solvent gave the concentrate for GLC-MS.
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Lipid Derived Volatiles. Volatiles thought to be derived from lipids, principally unsaturated fatty acids, are listed in Table Π. Also listed in Table II is a comparison of the concentrations found for these compounds in the blended fruit and leaf. Most of these compounds had been identified in previous studies of tomato volatiles (2). Two compounds, however, were only recently identified in tomatoes for the first time by the authors. These are 4,5-epoxy-(E)-2-heptenal (2 isomers) and 4,5-epoxy-(E)-2-decenal (2 isomers). Their mass spectra and GLC retentiontimesare consistent with those of authentic samples (C7 epoxide major MS ion at 68,39,29,55,81,97,110 and GLC K.I. DB-1 1036: CIO epoxide major MS ions at 68,39,29,55,81,95,139 and K.I. 1340). An unidentified compound (apparently QHgOz), occurring at ca. 1 ppm concentration in the leaves and in a lower level in the fruit, had a mass spectrum similar to that reported for 2-hexen-4-olide which had been identified previously in raspberry (J), asparagus (4) and bread volatiles (5), however, the GLC retention index of the tomato unknown was somewhat different from that reported (5). Epoxides of the type identified in tomatoes were first discovered by Swoboda and Peers (6) in copper catalyzed vegetable oil oxidation and more recently found by Grosch and coworkers (cf. 7) in soybean oil and related products. They are fairly unstable compounds. The inertness of fused silica capillary columns has made their analysis more feasible. The 4,5-epoxy-(E)-2-decenal occurs in the blended tomato fruit up to 100 ppb but we have been unable to find it or theC.,compound in the blended leaves. The 2 main isomers (E,Z)- and (E,E)- of 2,4-decadienal occur at less than 1/3 the concentration of the C epoxide so that it seems that this compound probably results from some oxidized lipid precursor rather than be formed by oxidation of the dienal. The epoxides are difficult to isolate in their pure forms to determine their odor thresholds in water solution. However, Grosch and coworkers (7) have used a method (called AEDA) of threshold determination in the carrier gas effluent of the fused silica capillary columns and found the C epoxide aldehyde to be a moderately potent odorant. 10
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In Bioactive Volatile Compounds from Plants; Teranishi, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
3.
BUTTERY & LING
Volatile Components of Tomato Fruit and Plant 25
Table I. Miyor groups of volatiles in fresh tomatoes and leaves
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I. Π. ΙΠ. IV. V.
Lipid derived. Carotenoid related. Amino acid related. Terpenoids (C and C ). Lignin related and other miscellaneous. 10
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Table Π. Lipid derived volatiles identified in fresh tomato fruit and fresh plant leaves blended and held 3 min. before enzyme deactivation Cone, in pppb 3
Compound
Fruit
Leaves
l-Penten-3-one l-Penten-3-ol Pentanal (Z)-and (E)-Pentenal Pentanol (Z)-2-Pentenol (Z)-3-Hexenal Hexanal (E)-2-Hexenal (Z)-3-Hexenol Hexanol (E,Z)-and (E,E)-2,4-Hexadienal Unknown Ο Η , 0 (E)-2-Heptenal l-Octen-3-one (E,Z)- and (E,E)-2,4-Heptadienal 4,5-epoxy-(E)-2-Heptenal (2 isomers) (E)-2-Octenal (E,Z)-and (E,E)-2,4-Decadienal 4,5-epoxy-(E)-2-Decenal (2 isomers)
450 100 5 100 30 40 15000 2000 470 120 4 10 74 40
