In Situ Yogurt Production for Probiotic and Nutrition Delivery

摘要

Providing human nutrition and maintaining overall crew health poses major challenges in long-duration missions. Certain nutrients degrade in stored foods and supplements with time and may require in situ generation. Likewise, the crew's microbiome status is of major concern, as this is a strong determinant of overall health. This study addressed these mission needs by investigating local generation of a fresh probiotic yogurt that could potentially maintain the crew's microbiome health and generate target nutrients. We have developed a single-use packet system that stores dried milk solids and a preserved form of the yogurt starter microbes that can be hydrated using nominal food hydration systems already in use in International Space Station. The hydrated packet would be incubated at an elevated temperature for a set period to produce the yogurt, and then either refrigerated for storage or consumed immediately. The yogurt starter microbes can additionally be engineered to produce vitamins, nutraceuticals, useful enzymes, and medicines within the yogurt. As a demonstration, we expressed green fluorescent protein (GFP) in one of the yogurt starter strains, Streptococcus salivarius subsp. thermophilus. This engineered strain was used to make yogurt containing GFP, which was analyzed to confirm the stability of the GFP gene under yogurt production conditions. Expressing exogenous desiccation and/or radiation tolerance genes in the yogurt starter to elongate the shelf-life of the strain was also examined. The spore-forming and Generally Regarded as Safe (GRAS) Bacillus species was investigated as another solution for facilitating long-duration storage. The availability of genetic engineering tools and their ability to produce vitamin K, which is currently below the recommended intake in the astronauts' diet, are additional advantages. Bacillus alone and in combination with conventional yogurt starters, was also used to demonstrate the potential to use yogurt as a nutrient and probiotic storage, amplification and delivery system, which can be followed by development of living medicine delivered in the form of food for future spaceflight.