Volatile Profile Changes and Visual Appearance of Tomatoes after Low Temperature Storage

Chilling injury (CI) is a physiological disorder that occurs at temperatures lower than the chilling threshold. Although low temperatures slow ripening and thus seemingly prolong storage, tomato fruit may never achieve the normal color and aroma that develops when they are stored exclusively at non-chilling temperatures. The irreversible damage that may occur at chilling temperatures potentially renders the fruit unmarketable. Changes in volatiles are an important indicator of CI with the effects occurring before the appearance of external CI symptoms. Some volatile compounds contribute to desirable fresh tomato aroma while others have negative attributes that produce unwanted off-flavors. In this study, ‘Tasti Lee’ tomatoes harvested at the pink ripeness stage were stored at 5, 12.5 or 20 °C, the latter being considered the control (non-chilling) temperature and 12.5 °C the putative chilling threshold temperature. Color (a* value) was measured and appearance was subjectively evaluated daily. Fruit from 5 and 12.5 °C storage were transferred to 20°C after 5 and 10 days to examine the color and volatile recovery. Fruit were considered fully ripe when the average a* value for a treatment measured at the distal end of the fruit reached a plateau and homogenized tissue samples were then frozen for volatile measurements. Aroma volatiles were analyzed by GC-MS using the SPME headspace method. Tomato fruit stored at 20 °C reached full ripeness in 4 days, fruit stored continuously at 12.5 °C required 14 days, whereas the 5°C-stored fruit never achieved color values equivalent to fruit from the other two temperatures even after 20 days. On the other hand fruit stored for 5 days at 5 or 12.5 °C all recovered upon transfer to 20 °C and reached similar color values, whereas for fruit transferred after 10 days the 5°C-stored fruit showed irreversible damage and failed to achieve full red color. Volatile profiles were negatively affected and did not recover after storage for 10 days at either 5 or 12.5 °C. This study contributes to further the understanding of the nature of CI in tomato fruit harvested at a more advanced ripeness stage than is usual for commercial operations as well as quantifying the extent of the CI effect on volatiles that precedes visible injury. The pattern of changes in the aroma volatile profile that occurs in tomato fruit during low temperature storage can be an indicator of the true chilling threshold temperature.