Pick-and-Eat Salad-Crop Productivity, Nutritional Value, and Acceptability to Supplement the ISS Food System

Pick-and-eat Salad-crop Productivity, Nutritional Value, and Acceptability to Supplement the ISS Food
System (VEG-04A, VEG-04B, and VEG-05) is a set of translational experiments with plant research
combined with human sensory and behavioral research. Considerable ground research was conducted to
develop and support protocols that were tested in flight. The VEG-04 flight experiments conducted in 2019
consisted of growing Mizuna mustard under different lighting spectra, with the first experiment harvesting
plants at a single time point and the second using a cut-and-come-again repetitive harvest approach. VEG-05
was conducted on ISS Dec. 2022 through March 2023, growing ‘Red Robin’ dwarf tomatoes under the same
lighting spectra. In addition to understanding plant growth, development, and produce yields under different
lighting conditions, goals for VEG-04/05 were to understand microbial food safety and develop safe handling
practices for crops grown in Veggie. The human-specific foci of this project included collecting data on
behavioral health and performance aspects of crops and crop care and assessing sensory acceptability of the
consumed crops. Crew were able to consume produce and conduct sensory evaluations for the produce of the
VEG-04 studies, although due to challenges maintaining adequate moisture for plants during growth of the
VEG-05 tomatoes, insufficient fruit were formed for crew consumption. For VEG-05, plant samples were
taken to conduct microbiome and transcriptomic evaluation, as well as the planned food safety assessment
and elemental analysis. Key takeaways from the VEG-04/05 experiments, coupled with other data collected
from earlier Veggie crop testing, indicate that crop yield is similar between ground and flight when plants are
not stressed. Maintaining plants in a manually watered system such as Veggie is challenging, especially over
long durations, and it is hard to avoid water-related stresses. Some differences between ground and flight plant
nutrient content have been shown, but these are not consistent between species or experiments and are
influenced by experiment timing, crop type, harvest scenario, and other environmental conditions. Microbial
counts and compositions vary between flight and ground plants, and microbes typical of the space station
environment are often associated with ISS-grown plants. Human pathogens are rarely identified on spacegrown plants and have only been found below levels of concern to human health. The only human pathogens
identified in Veggie-grown crops were S. aureus in one plant in the VEG-04B experiment at very low levels.
The safe handling practice approach seems effective at keeping space plant products safe for human
consumption. Microbial communities vary between shoot/fruit, and root/adventitious root tissues in tomato,
and between shoot and root tissues in other experiments. Generally, there is greater microbial diversity and
higher culturable counts in aerial microbiomes of ISS-grown plants, compared with those grown on the ground.
Transcriptomic data for tomato leaves and adventitious roots indicate differences in response to light, with the
blue-rich-lit plants showing higher percentages of differentially expressed genes (DEGs) than do red-richgrown plants. DEGs separate based on tissue type but overlap based on the plant growth environment (flight
and ground). Biological processes related to differential gene expression are being characterized, and there are
some differences between light treatments and environment in those, but stress processes are strongly
indicated, especially in adventitious roots, which were much more pronounced in flight-grown plants. VEG04/05 data indicate that astronauts enjoy growing and eating plants in spaceflight in general. Overall, plants
adapt well to the space environment, and this project demonstrates the potential for space-grown crops. In
order to increase the integration of crops in spaceflight, further work is needed on crop selection, hardware,
and translation of ground safety and cleaning practices to the resource restrictions of spaceflight. This research
was co-funded by the Human Research Program and Space Biology (MTL#1075) in the ILSRA 2015 NRA
call.