Evaluation of the Impact of Hot Water Treatment On Flavor Compounds of Fresh Tomatoes

In June of 2008, two varieties of tomato fruit, Florida 47 (F47) and Tasti-Lee (TL), were harvested mature green and submerged in water at 25º C (control) or 52º C for 5 minutes or 54º C for 2.5 minutes.  The fruit were then gassed with ethylene at 100 ppm for 48 hours and ripened at 20º C.  Ripeness was evaluated by measuring color (CIE a*) on the blossom end of the fruit until a* reached an acceptable value. When selected as fully ripe, fruit firmness, sugars, organic acids, and volatile compounds were measured on half the fruit while a trained panel evaluated sensory quality on the other half.  The remaining fruit was homogenized for 30 s and 40 mL of homogenate was removed and frozen at -20º C for subsequent sugar and acid analysis by HPLC.  After 3 min, 10 mL saturated CaCl₂ was added to 25 mL of homogenate that was flash frozen and stored at -80º C for aroma volatile analysis using GC-FID on polar and non-polar columns.  There were significant differences for glucose, fructose, citric and malic acids.  Sugar differences were due to variety where TL had higher levels of sugars than did F47, especially when heated.  F47, however, exhibited lower levels of citric and malic acids when heated at 52 ºC for 5 min compared to controls.  There were significant differences for three aldehydes (hexanal, trans-2-hexenal, trans-2-heptenal), two alcohols (ethanol, 2+3-methyl butanol), three ketones (acetone, 1-penten-3-one and furanone) as well as 1-nitro-2-phenylethane and methysalicylate of the 28 aroma volatiles measured that are important to tomato flavor.  These differences were sometimes due to treatment and sometimes more related to variety, but often heating F47 resulted in an increase in volatile levels, which was evident in multivariate analysis.  The experiment was repeated in December, 2008.  There were no differences in glucose, fructose or malic acid, but citric acid was reduced in fruit heated at 52 º C for 5 min for F47 and for both treatments for TL compared to controls.  There were significant differences for 8 aldehydes (trans-2-penenal, cis-3-hexenal, 2+3-methylbutanal, trans-2-hexenal, trans-2-heptenal, phenyacetaldehyde, methianal and benzaldehyde), 3 alcohols (2+3-methylbutanol, linalool and 2-phenylethanol), two ketones (β-ionone and furanone) as well as 1-nitro-2-pheylethane for F47.  Again, sometimes the 52º C treatment increased volatile levels. In conclusion, there were differences between varieties, but heating sometimes increased aroma for F47 and reduced acids in both varieties.