Effect of Chilling and Heating Treatment on Production of Volatiles from Lipids via Oxidation in Tomatoes

Major tomato volatile aromas are formed from lipids through the lipoxygenase pathway to cis-3-hexenal, trans-2-hexenal, hexanal, cis-3-hexenol, and hexanol. The objective of this research was to determine the responses of volatile production and lipoxygenase pathway to chilling and heating treatments in tomatoes. ‘Sanibel’ tomatoes harvested at the mature-green stage were stored at 20 °C until ripe. Fruit were then treated with either chilling, hot water, or not treated as the control. Fruit samples were taken directly after treatment or after 4 days of storage at 20 °C. For each sample, pericarp from 2-4 fruit were pulverized in liquid N₂, and stored at -80 °C. For enzymatic activity assays, samples were extracted using Tris-HCl buffer, and for analysis of GC volatiles, samples were homogenized with saturated CaCl₂. Both chilling and heating treatments remarkably reduced cis-3-hexanal and trans-2-hexenal as well as other major aldehyde volatiles, and their related alcohol volatiles. The volatiles, however recovered after 4 days storage at 20 °C. Lipoxygenase activity increased due to heat treatment even after 4 days storage. The incompatible trends between the C-6 aldehyde concentrations and LOX activity indicate that the LOX isozymes measured included 9-LOX, rather than only 13-LOX, which is the isozyme that leads to tomato aroma production. Activity of hydroperoxide lyase was suppressed by both chilling and heating treatments and somewhat recovered after 4 days. The results indicate that the production of tomato aroma may be regulated by controlling HPL activity. Alcohol dehydrogenase activity was suppressed immediately after both treatments, however recovered after 4 days storage. ADH activity increased in chilled compared to control samples after 4 days storage.