|Baldwin, Elizabeth - Liz|
Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/10/2011
Publication Date: 3/1/2011
Citation: Bai, J., Baldwin, E.A., Imahori, Y., Kostenyuk, I., Burns, J., Brecht, J.K. 2011. Chilling and heating may regulate C6 volatile aroma production by different mechanisms in tomato (Solanum lycopersicum) fruit. Postharvest Biology and Technology. 60:111-120. Interpretive Summary: Tomatoes have flavor problems that have consumers complaining. One problem is that they are stored or shipped at too low a temperature, and they are sometimes heated to control decay. Temperature abuse can cause flavor problems through the reduction of aroma compounds. The mechanism for this is not understood and studied in this paper by measuring the aroma compounds as well as the enzymes and genes that synthesize them.
Technical Abstract: Hexanal, Z-3-hexenal, E-2-hexenal, hexanol, and Z-3-hexenol are major tomato (Solanum lycopersicum L.) volatile aromas derived from oxygenation of unsaturated fatty acids. Chilling and heating may suppress production of these C6 volatiles. The objective of this research was to determine the responses of lipoxygenase (LOX), hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH), enzymes, which are involved in the oxylipin pathway, to chilling and heating in terms of gene expression and enzyme activity. ‘Tasti-Lee’ and ‘Sanibel’ tomatoes, harvested at different stages of fruit development, were ripened to full (red) ripe stage at 20 °C. Fruit were then treated by either chilling (5 °C for 5 days) or heating (52 °C hot water for 15 min), then cooled with 23 °C tap water to 25 °C and placed at 20 °C for 4 days, or held continuously at 20 °C as the control. Both chilling and heating remarkably reduced C6 aldehyde and alcohol aroma volatiles immediately after treatment, and the levels of aldehydes did not fully recover after 4 days at 20 °C. Chilling down-regulated TomloxA, B, C, but not D expression, but increased overall LOX activity. Chilling also down-regulated HPL and ADH expression immediately after treatment, however, after 4 days at 20 °C, both genes were up-regulated compared to the control. HPL activity in chilled tomatoes was reduced, but recovered to control levels after 4 days at 20 °C. ADH activity in chilled fruit decreased after 4 days at 20 °C. On the other hand, heating greatly up-regulated TomloxB and C expression, even after 4 days at 20 °C, and slightly down-regulated TomloxA and D, while increasing overall LOX activity. Heating up-regulated both HPL and ADH, and that effect persisted for 4 days at 20 °C. However, heating reduced the activities of HPL for 4 days at 20 °C and ADH immediately after treatment. The results indicate that heating and chilling regulate C6 volatile production by different mechanisms. Chilling-inhibited C6 volatile production may be due to down-regulation of gene expression, except for TomloxD, and subsequent reduction of HPL and ADH enzyme activities in the oxylipin pathway. Heating-inhibition of C6 volatile production, however, does not appear to be due to down-regulation of gene expression, but HPL and ADH activities were briefly suppressed.