Some foods just aren’t meant to go in the fridge – like tomatoes. As some consumers have long known, refrigerating them permanently impairs their flavour, but the reasons were elusive. New insights into why this happens may some day help us develop varieties that retain their flavour during cold storage.
A team led by Harry Klee of the University of Florida in Gainesville got their teeth into the problem by studying the expression of more than 25,000 genes in two tomato varieties. They looked at these genes before and during chilling, and after returning the tomatoes to room temperature.
Chilling, a major stress for a tropical plant such as the tomato, reduced the activity of hundreds of genes. Some of these produce enzymes responsible for synthesising the volatile chemicals that make tomatoes taste sweeter and give them a more complex, appealing aroma.
Many of the enzymes never recovered, even after the tomatoes were back at room temperature. Taste tests confirmed that chilling did, indeed, give rise to less flavourful tomatoes.
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Further analysis showed that chilling led to changes in DNA methylation, affecting many genes. Since methylation is a common mechanism for turning genes on and off for long periods, this may account for the long-lasting effect of chilling on flavour, says Klee.
With this knowledge, breeders may be able to modify the temperature-sensitive enzymes to be more robust, or else select tomato varieties with gene variants that are naturally less inhibited by cold, he says.
Elizabeth Baldwin, a plant physiologist with the US Department of Agriculture’s research lab in Fort Pierce, Florida, agrees. “With this knowledge, we could definitely do breeding or genetic manipulation,” she says.
The other message of Klee’s work, of course, is a simple one: “Don’t put your tomatoes in the fridge,” says Baldwin. “They lose their aroma.”