The astronauts aboard the International Space Station (ISS) have managed to successfully cultivate salad crop -- red romaine lettuce -- that is free of disease-causing microbes and safe to eat, and is at least as nutritious as Earth-grown plants. This feat was achieved despite being grown under lower gravity and more intense radiation than on Earth.
Apart from a welcome change in diet, fresh produce would provide astronauts with additional potassium as well as vitamins K, B1, and C - nutrients that are less abundant in pre-packaged rations and tend to degrade during long-term storage.
Additionally, growing crops would be especially useful on long-distance space missions, like the upcoming Artemis-III missions (scheduled to land humans on the lunar South pole by 2024), the current SpaceX programme, and NASA's first crewed mission to Mars, planned for the late 2020s.
"The ability to grow food in a sustainable system that is safe for crew consumption will become critical as NASA moves toward longer missions. Salad-type, leafy greens can be grown and consumed fresh with few resources," said Dr Christina Khodadad, a researcher at the Kennedy Space Center, in a study published in the journal Frontiers in Plant Science.
Astronauts in space live on processed, pre-packaged space rations such as fruits, nuts, chocolate, shrimp cocktails, peanut butter and chicken, etc.
These have often been sterilized by heating, freeze drying, or irradiation to make them last and key a challenge for the US Space Agency NASA has been to figure out how to grow safe, fresh food onboard.
Between 2014-2016, lettuce was grown on board the ISS from surface-sterilized seeds within Vegetable Production Systems (nicknamed "Veggie"), growth chambers equipped with LED lighting and a watering system, specifically designed to grow crops in space.
The crops grew undisturbed inside the Veggie units for 33 to 56 days, until crew members ate part of the mature leaves (with no ill effects).
The remainder was deep-frozen until transport back to Earth for chemical and biological analysis.
Space-grown lettuce was similar in composition to the Earth-grown controls, except that in some (but not all) trials, space-grown plant tissue tended to be richer in elements such as potassium, sodium, phosphorus, sulphur, and zinc, as well as in phenolics, molecules with proven antiviral, anticancer, and anti-inflammatory activity.
Further tests confirmed that the leaves never carried any dangerous bacteria known to occasionally contaminate crops, such as coliform E. coli, Salmonella, and S. aureus, while the numbers of fungal and mould spores on them was also in the normal range for produce fit for human consumption.
The authors said that lettuce grown in space-borne Veggie units is safe to eat.
"The International Space Station is serving as a test bed for future long-duration missions, and these types of crop growth tests are helping to expand the suite of candidates that can be effectively grown in microgravity," said Dr Gioia Massa, project scientist at Kennedy Space Center.