This project focused on two main research areas: 1) The development of a space-ready yogurt starter culture, and an associated engineering demonstration, and 2) The development of a preliminary disposable packet system and concept of operations that is capable of storing the media and microbes and also allows yogurt production. The results attained in these two areas are discussed below.
Space-ready yogurt culture development - The yogurt starting culture must be able to withstand storage in space for extended periods, especially if used on multi-year missions such as Mars habitation scenarios. Genetic engineering of the starter culture can potentially allow expression of desiccation and or radiation tolerance genes to extend the shelf-life of the yogurt starter strain. In addition, engineering could also enable the production of targeted vitamins, nutraceuticals, useful enzymes, and medicines. As a demonstration of this potential, we engineered green fluorescence protein (GFP) into one of the yogurt starter strains, Streptococcus thermophilus to facilitate detection. The engineered strain was used to make yogurt containing GFP which was analyzed by fluorescence microscopy. The engineered strain retained the GFP gene in a plasmid vector during the yogurt incubation period even in the absence of the selective antibiotic, chloramphenicol, which ensured that genetic engineering of the starter strain is compatible with production of antibiotic-free yogurt for safe consumption. This demonstration indicates that other, more complex, engineering efforts for stasis and targeted products may be warranted. The other approach involved using other relevant Generally Regarded As Safe (GRAS) microbes for yogurt production. Bacillus coagulans and B. subtilis (Fig. 2) were chosen because they are probiotic, form very stable spores which tolerate long-term storage and naturally produce vitamin K which is found deficient in the current astronauts’ diet. We made yogurt by using Bacillus strains alone or with conventional yogurt starter strains. Yogurt made from Bacillus species alone was not as acidic as that with yogurt starters and had cheesy flavor.
Prototype flight yogurt production system - We designed and successfully tested a packet system using a food-compatible plastic bag and associated fittings to store the dry milk powder and starter culture separately. This allowed initial scalding of the milk with hot water to inactivate potential contaminating microbes. The separation was removed to allow mixing of the milk and culture after the milk had cooled down. The temperature was monitored by a contact liquid crystal thermometer on the packet surface. In addition, we designed a powered, dedicated yogurt incubation system to maintain the mixture at 44oC for 8 hrs. and cool it down to 4oC until serving. The system utilizes a switchable thermoelectric heating/cooling process to maintain reliability and simplicity. A variant of this system could be utilized for actual operations.
This project started at a Technology Readiness Level (TRL) of 1. The work completed during this project brought it to approximately a TRL of 3 as we conducted laboratory research and analyses that validated the overall concept. Future work would need to focus on increasing organism longevity, validating the concept in spaceflight, and the development of food safety monitoring and control systems.More »
|Organizations Performing Work||Role||Type||Location|
|Ames Research Center (ARC)||Lead Organization||NASA Center||Moffett Field, CA|
|Johnson Space Center (JSC)||Supporting Organization||NASA Center||Houston, TX|