By Maymona Al Hinai, University of Michigan Dietetics Intern

During my dietetic internship rotation in The Farm at St. Joe’s, I learned a lot of amazing things about farming, how to deal with plants, preparing health recipes, and CSA (community supported agriculture). I also try new things for first time such as kale, collard greens, basil and farmer market! One of the interesting things that I come across while I am here was to keep harvested tomatoes outside and not in the cooler. Coming from a very hot county like Oman, I always stored tomatoes in the refrigerator to extend their life and keep the molds away, I only keep them outside if it is green or unripe.

To fill my research curiosity, I decided to make a very simple experiment to test whether the tomatoes left outside the refrigerator has any differences than the tomatoes in the refrigerator. I pick up some red and ripe cherry tomatoes from the farm and divided them to two groups (group A and group B, 7 cherry tomatoes in each). I stored group A on the counter at room temperature around 77 F and stored group B in the refrigerator at 41 F for 5 days. After I take off the tomatoes from the fridge and let their temperature down to room temperature, I blinded the groups and let my friends in the farm taste the tomatoes and notice any differences. The result was unclear as some found tomatoes in the fridge sweeter, softer, and riper where others found that these are the features of tomatoes left in the counter. Because the results were mixed, I try the experiment in different verity of tomatoes, the slicing tomatoes. For the slicing tomatoes, the difference was more clear and obvious as the tomatoes stored on the counter was more flavored and softer compare to tomatoes stored at lower temperature. This means that low temperature can affect the tomatoes and induce certain changes.

Well, unlike me maybe you already know that you should not store tomatoes in the refrigerator and keep it on the counter, but do you know why? Or what is the scientific evidence of this practice? Here are some of the research conducted to study this issue.

A study in New Zealand investigated the nutritional implication of storing harvested tomatoes in three different temperature at 45 F in a refrigerator, and at 59 and 77 F in temperature controlled incubators for 10 days (1). The results showed that tomatoes stored at 59 and 77 become redder than tomatoes stored at 45. This is because lycopene accumulation – a compound responsible for the red color of tomatoes and good for heart health too- was 2-fold more in tomatoes stored at higher temperature compare to tomatoes stored in the refrigerator. Moreover, the tomatoes acidity was higher in tomatoes stored at 59 and 77 F than at 45 F which may be due the decrease in acid production at low temperature.

Another study published in the Journal of Food Science found that the tomatoes ripe smell, flavor, and sweetness was significantly lowered at temperature below 55 F compare to 68 F, an effect caused by decline in the production of specific compounds at low temperature (2). In a more recent investigation, researchers found that storing tomatoes at low temperature induce a chilling injury that decrease their smells (3). Chilling injury is  physiological changes caused by improper storage temperatures of postharvest fruit and vegetables (4). Chilling injury makes tomatoes welt, change their texture, fail to fully ripe, loss flavor and smell, and decay (4).

So given what was discussed, what is the ideal temperature to store tomatoes? Well, according to the FAO, ripe tomatoes should be stored at 55-60 F (13-15 °C) whereas mature-green tomatoes can be stored at 65-72 F (18-22 °C). Storing tomatoes at proper temperature is important to preserve the nutrients, flavor, and quality of the tomatoes.

Now you know why they always say keep the tomatoes out of the fridge!

PS:

The Farm at St. Joe’s has a farmer market in the main entrance of St. Joe’s hospital every Wednesday. Stop by on Wednesday, to pick up a super delicious cherry tomatoes with other good veggies:)

Also, Check this link for other proper fruit and vegetable storage temperature: http://www.fao.org/WAIRdocs/x5403e/x5403e09.htm.

References:

1. Toor RK, Savage GP. Changes in major antioxidant components of tomatoes during post-harvest storage. Food Chem. 2006;99:724–7.
2. Maul F, Sargent S.A., Sims C.A., Baldwin E.A., Balaban M.O. HDJ. Tomato Flavor and Aroma Quality as Affected by Storage Temperature. J Food Sci. 2000;65:1228–37.
3. Farneti B, Alarcón AA, Cristescu SM, Costa G, Harren FJM, Woltering EJ. Chilling-Induced Changes in Aroma Volatile Profiles in Tomato. Food Bioprocess Technol. 2015;8:1442–54.
4. Misael O. Vega-Garcı´a, Greici L´opez-Espinoza JCO, Jos´e J. Caro-Corrales, Francisco Delgado Vargas and JAL-V. Changes in Protein Expression Associated with Chilling Injury in Tomato Fruit. J Am Soc Hortic Sci. 2010;135:83–9.