Identification of Impact Aroma Compounds in Tomato: Implications to New Hybrids with Improved Acceptance through Sensory, Chemical, Breeding and Agrotechnical Techniques
Authors: Naim Michael , Takeoka Gary R. , Rabinowitch Haim D. , Buttery Ron G. 
Published: December 2021

The tomato, a profitable vegetable crop in both the USA and Israel, has benefited significantly from intensive breeding efforts in both countries, and elsewhere (esp. Holland). : Modem hybrids are highly prolific and resistant to a variety of major pests. They produce attractive, firm fruit for both processing and fresh-marketing. In all cases, however, reduction in flavor and aroma have occurred concomitantly with the increase in yield. Sugars-acids ratio dominate fruit taste, whereas aroma volatiles (potent at minute ppb and ppt levels) contribute to the total characteristic tomato flavor. An increase in sugars (1-2%) contributes significantly to tomato fruit taste. However, because of energy reasons, an increase in fruit sugars is immediately compensated for by a decrease in yield. Our main objectives were to: (a) pinpoint and identify the major impact aroma components of fresh tomato; (b) study the genetic and environmental effects on fruit aroma; (c) determine precursors of appealing (flavors) and repelling (off-flavors) aroma compounds in tomato. Addition of saturated salts blocked all enzymatic activities prior to isolation of volatiles by dynamic and static headspace, using solvent assisted flavor evaporation (SAFE) and solid phase micro-extraction (SPME) from highly favored (FA-612 and FA-624) and less preferred (R 144 and R 175) tomato genotypes. Impact aroma components were determined by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC- MS) and aroma extract dilution analysis (AEDA). The potent odorant (Z)-1,5-octadien-3-one, was identified for the first time in fresh tomato. From the ca. 400 volatile compounds in the headspace of fresh tomato, the following compounds are proposed to be impact aroma compounds: (Z)-3-hexenal, hexanal, 1-penten-3-one, 2-phenylethanol, (E)-2-hexenal, phenyl acetaldehyde, b-ionone, b-damascenone, 4-hydroxy-2,5-dimethyl-3-(2H)-furanone (FuraneolR), (Z)-l,5-octadien-3-one, methional, 1-octen-3-one, guaiacol, (E,E)- and (E,Z)- 2,4-decadienal and trans- and cis-4,5-EPOXY -(E)-2-decenal. This confirms the initial hypothesis that only a small number of volatiles actually contribute to the sensation of fruit aroma. Tomato matrix significantly affected the volatility of certain impact aroma components and thus led to the conclusion that direct analysis of molecules in the headspace . may best represent access of tomato volatiles to the olfactory receptors. Significant differences in certain odorants were found between preferred and less-preferred cultivars. Higher consumer preference was correlated with higher concentrations of the following odorants: l-penten-3-one, (Z)-3-hexenal, (E,E)- and (E,Z)-2,4-decadienal and especially Furaneol, whereas lower consumer preference was associated with higher concentrations of methional, 3-methylbutyric acid, phenylacetaldehyde, 2-phenylethanol, and 2-isobutylthiazole. Among environmental factors (salinity, N source, growth temperature), temperature had significant effects on the content of selected aroma compounds (e.g., 3-methylbutanal, 1- penten-3-one, hexanal, (Z)-3-hexenal, (E)-2-hexenal, 2-isobutylthiazole, 6-methyl-5-hepten- 2-one, 1-octen-3-one, methional, 2-phenylethanal, phenyl acetaldehyde, and eugenol) in fresh tomatoes. Salt stress (20 mM NaCl) increased the content of odorants such as (Z)-3-hexenal, 2-phenylethanol and 3-methylbutanal in the R-144 cultivar whereas salinity had minor effects on 1-pentene-3-one, 2-isobutylthiazole and b-ionone. This fundamental knowledge obtained by comprehensive investigation, using modem chemical, sensory and agrotechnical methodology will assist future attempts to genetically modify the concentrations of key odorants in fresh tomatoes, and thus keep the tomato production of Israel and the USA competitive on the world market.