Science& tech
Cool start for some varieties takes important flavours from one of the most beneficial ‘ fruits’ in the garden
ardeners traditionally mark this weekend as the best time of the year to safely plant out tomato seedlings. Although many of us refer to them as vegetables, tomatoes are actually a fruit, being the seed bearing part of the plant.
The flavour of a ripe tomato varies greatly depending on the variety; however one thing is consistent — home grown tomatoes tend to be much more flavourful than tomatoes bought from the supermarket.
There have been many studies showing the health benefits of tomatoes, mostly thanks to the compound lycopene, a bright red phytochemical responsible for the red colour of a tomato.
The consumption of lycopene- rich tomatoes and tomato products has been associated with a reduced incidence of a number of different types of cancers including prostate, lung, and stomach.
An increased plasma lycopene level has also been associated with reductions in cardiovascular disease and there are a few studies showing that 10 weeks of eating lycopene- rich foods, including tomato paste, can protect the skin against sunburn.
Supermarket tomatoes are bred for high yields and durability and tend to be consistent in their size, shape and underwhelming flavour.
To ensure they arrive in store looking perfectly round and ripe, most commercial tomatoes are picked when they are green, as they are less likely to bruise or break.
During shipping they are kept refrigerated, which slows down the ripening process during transit. Once at their destination, they are warmed up to room temperature allowing them to fully ripen while sitting on a supermarket shelf.
In contrast, homegrown tomatoes are typically picked when already red and mature after ripening on the vine and don’t go through a refrigeration process. Many people would agree that freshly picked home grown tomatoes taste better and it seems like refrigeration is partly responsible for this.
This week research published in the journal Proceedings of the National Academy of Sciences reopened the debate around whether or not you should store your tomatoes in the fridge and showed that the way that we handle our supermarket tomatoes is having a detrimental effect on their flavour.
The study involved mimicking commercial tomato handling by refrigerating green tomatoes at 5C for up to a week, then kick- starting the ripening process by storing them at room temperature for up to three days.
With RNA sequencing they found refrigeration reduced the activity of the tomatoes’ cold signalling, metabolism, ripening and volatile synthesis genes by affecting DNA methylation — the mechanism that cells use to control which genes get turned on and off.
The tomatoes stored in the fridge for seven days showed a 65 per cent reduction in the volatile compounds associated with flavour and did not return to a normal level even after being left to recover for three days at room temperature.
The flavour of a tomato is determined by the interactions of
also known as Nanogirl, is an Auckland University nanotechnologist who is passionate about getting Kiwis hooked on science. Tweet her your science questions sugars, acids and around 20 volatile compounds. The study found that though cold storage did not significantly affect the tomatoes’ sugars or acids, it did reduce the effectiveness of enzymes involved in producing the flavour- inducing volatile compounds. These compounds cannot be stored long- term as they are released as a gas, so they take the tomato flavour and aroma with them leaving a cold, flavourless refrigerated fruit. The research concluded that current commercial tomato handling is partly responsible for the relative lack of flavour in supermarket tomatoes. Ideally the best way to find flavour- packed tomatoes is to grow your own, just make sure you don’t store them in the fridge.