To prevent tomatoes from becoming too ripe before they reach the grocery, they typically have been picked while still green. While being packed, an ethylene gas is used to trigger the fruit ripening before they are stored and then shipped at low temperatures. But chilling the tomatoes degrades their flavor so the slightly different method was developed.
Ideally, tomatoes should be picked ripe and then sold immediately, as they are at farm stands, says Jinhe Bai, Ph.D. But this isn't always possible for commercially sold tomatoes, which are often stored and then shipped over long distances. To produce a better tasting tomato, we added a hot water pre-treatment step to the usual protocol that growers follow. We found that this pre-treatment step prevents flavor loss due to chilling.
The process involves dipping the green tomatoes in hot water 125 degrees Fahrenheit for about five minutes and then cooling them at room temperature. The tomatoes are then chilled between 41 and 55 degrees and after fully ripened are tested for aroma and flavor.
What the researchers discovered with this altered process is that:
Tomatoes heated before chilling had higher levels of flavor compounds (6-methyl-5-hepten-2-one, 2-methylbutanal and 2-phenylethanol) than non-heated fruit, and they tasted better.
Chilling suppresses production of oxygen, nitrogen and sulfur-containing heterocyclic compounds, ketones, alcohols and aldehydes, including 13 important aroma components of tomato flavor. But hot water-treated fruit actually produced higher concentrations of these important aroma contributors even with subsequent chilling.
The researchers are monitoring flavor compounds at other time points as well such as when the tomatoes are green, soon after the process is performed, and when they are partially ripened. They will combine this information with data on fully ripened tomatoes in an effort to develop a better commercial process, which can easily be implemented in the current commercial system without risking fruit decay.
The researchers also experimented with alternative methods to using hot water such as incubating the green tomatoes with methyl salicylate or wintergreen oil which is an antifungal fumigant generally recognized as safe by the U.S. Food and Drug Administration.
They also successfully preserved the flavor of the tomatoes by picking them at a later stage than growers do such as when they are half-green and half-pink. Next they treated them with a gas approved by the U.S. Environmental Protection Agency to make the tomatoes more tolerant to cell death and deterioration at higher storage temperatures. By doing so they avoided the chilling step to help maintain the flavor.
The researchers plan to closely compare the flavor-saving qualities of all techniques, Bai said. Once the researchers determine if one of the methods is better, they will approach food processing firms to determine if they are interested in adopting the technique.
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