Aroma perception of individual volatile compounds in fresh tomatoes (Lycopersicon esculentum, Mill.) as affected by the medium of evaluation

Odor thresholds of volatile compounds in fresh tomato (Lycopersicon esculentum Mill.) were estimated and odor units calculated to determine whether the medium of evaluation affects aroma perception. The 'ascending method of limits' was used to determine odor thresholds of cis-3-hexenal, hexanal, trans-2-hexenal, hexanol, cis-3-hexenol, 2-isobutylthiazole, 6-methyl-5-hepten-2-one, geranylacetone, 2-pentenal, beta -ionone, 1-penten-3-one, 3-methylbutanol, 3-methylbutanal, acetone and 2-phenylethanol in deionized water, an ethanol (100 ppm)/methanol (500 ppm)/water mixture and a deodorized tomato homogenate. Cis-3-hexenal exhibited the highest level of odor units in all three media. Odor thresholds were lower in deionized water for all compounds than in the ethanol/methanol/water mixture (simulating levels found in homogenized tomato) and the thresholds were even higher in the deodorized tomato homogenate for most compounds. Distinct differences were noted in aroma descriptors for the compounds in different media. The results suggest that both qualitative and quantitative changes are occurring in the perception of volatile compounds in the different media and that ethanol and methanol alter perception of tomato aroma. (C) 2000 Elsevier Science B.V. All rights reserved.