Few things are more disappointing than a tasteless, mealy grocery store tomato. These bland fruits are pale imitations of the vine-ripened tomatoes available from the garden at the end of summer. Tomatoes are perishable, and providing ripe, high-quality tomatoes that maintain their texture and nutritional content is a challenge for commercial growers.
A recent publication by Tsafouros et al from the Institute of Olive Tree in Greece provides a window into the intense, ongoing research aimed at understanding how and why tomatoes and other fruits ripen under various conditions. Such studies could improve the postharvest shelf-life and the quality of commercially grown tomatoes.
The authors carried out an exhaustive biochemical and molecular biological characterization of polyamine metabolism in the tomatoes. They assessed the total content of a variety of polyamines, the activity of the enzyme responsible for breaking down polyamines, the expression of all 23 genes encoding factors known to be involved in polyamine metabolism, the levels of the proteins involved in polyamine synthesis, and the levels of hydrogen peroxide, a biproduct of amine oxidases acting on polyamines. Protein levels were measured by chemiluminescent Western blots imaged using the Sapphire Biomolecular Imager from Azure Biosystems.
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Their results demonstrate that cold storage alters polyamine metabolism, and support storage of tomatoes at 10 °C after picking at commercial maturity. Lower temperatures appeared to induce a stress response, perhaps to protect against chilling injuries, while higher temperatures were associated with lower polyamine levels and lower quality fruit.
Growing the tomatoes used in this study
For this study, tomatoes were grown in a greenhouse and either picked at “commercial maturity” (when the tomato is just turning color) or left on the plant to mature for an additional week. The harvested tomatoes were stored at 5, 10, or 25 °C and after 7 days were compared to each other and to tomatoes left to ripen on the vine.
Tomatoes are typically picked before ripening and stored and transported at low temperatures in an attempt to increase the shelf-life. Tsafouros et al examined the effect on ripening of storing picked tomatoes at various temperatures for a week. The authors also characterized in detail the effect of storage temperature on the metabolism of polyamines, compounds known to play a role in fruit ripening and the content of which are known to be associated with tomato quality and shelf life.