Cos(mos) Lettuce: What's the Difference Between Salad Grown in Space and on Earth?

Red cos, or romaine, lettuce grown on the International Space Station has been compared to that grown on the ground so that astronauts in the future can grow and eat fresh leafy vegetables aboard the ISS.

Red Romaine lettuce being grown in VEGGIE plant growth pods on board the International Space Station. Credit: NASA

Researchers have been looking into growing vegetables on the ISS for years in order to try to provide astronauts with nutrients that they can't currently get from pre-packaged space food. Plants have been successfully grown from seed in the appropriately-named Veggie plant growth units since 2014, but research so far has mostly focused on how to increase growth, with some work also looking at the macronutritional value (calories, protein, fats, and carbohydrates) of different crops. Little research, however, has been done looking at the micronutrients like vitamins, or the microbes that live on the leaves of these space greens.

Investigating the microbial ecology of the lettuces is very important in assessing whether or not they are safe for the astronauts to eat. The current set-up of the Veggie pods doesn't involve any filtration, so the plants are exposed to all microbes that might be in the cabin air of the ISS. The number of bacteria and fungi on the Veggie-grown lettuce leaves was relatively low compared to the typical numbers found on Earth-farmed lettuce, and all tests for specific human pathogens were negative, meaning that microbiologically at least, the lettuce is safe for astronauts to eat.

Researchers also wanted to test the micronutrients in the vegetables to see what might change under space conditions, because of the focus on supplementing specific vitamins lacking in astronauts' diets. There was no significant difference in levels of anthocyanins (flavonoid antioxidants that can have anti-inflammatory properties), but there were some changes to certain elements. The differences though, were not according to whether they were grown in space or on the ground but instead corresponded to different harvesting methods. When the lettuce was harvested repeatedly both in space and on the ground, iron and potassium levels were significantly lower than when it was just harvested once.

While it is promising that the red lettuce grown on the ISS was safe to eat, the researchers want to do further work looking at how it should be grown and harvested in order to best supplement the astronauts' diets.

https://doi.org/10.3389/fpls.2020.00199

Khodadad, C.L.M., Hummerick, M.E., Spencer, L.E., et al. Microbiological and Nutritional Analysis of Lettuce Crops Grown on the International Space Station. Frontiers in Plant Science 11, 199 (2020)