The Microbiology of Microgreens Grown in Controlled Environment Chambers under ISS Conditions

Microgreens have been identified as a new type of pick-and-eat salad crop that can be utilized in space crop production systems. The majority of traditionally grown leafy green crops can be grown as microgreens, in addition to crops such as legumes, sunflower, buckwheat, most herbs, and corn, presenting hundreds of microgreen crop options. Notably, microgreens are nutrient dense, high in beneficial compounds like antioxidants, Vitamins C and K, and exhibit a variety of desirable flavors and textures. The short growth cycles (7-14 days), low water requirements and volume optimization potential make them a viable option for sustainable production of nutritious and flavorful crops in space. The crop production team at Kennedy Space Center is investigating the food safety aspects of microgreens grown under spaceflight relevant conditions for crew consumption. Microbiological analysis and screening for potential foodborne pathogens was performed on over 20 varieties of microgreens that have demonstrated positive horticultural attributes. Additionally, a comparison of microgreens grown hydroponically under ISS environmental conditions and similar varieties from local markets was completed to collect baseline data on the microbial load on microgreens. In an effort to improve microgreen quality, strategies to reduce the microbial load were tested, including bulk seed sanitization, harvest age, exposure to high blue light, and post-harvest chemical disinfection. The efficacy of a citric acid-based produce wash currently used for ISS grown produce and 1% H2O2 were investigated at different exposure times for reduction in bacterial and fungal counts on a variety of microgreens. Limited log reduction was achieved depending on exposure time. Our testing also demonstrated that seed sanitization impacted microbial load on microgreens and systems.