| Almost any imaginable experiment aimed at detecting the metabolism of astrobiological microbial life forms will require measurements to be performed on two sample systems -- one that contains viable life forms, and a second, which has been sterilized to serve as a control. Successfully creating the control is essential in discerning if any signal from the non-sterile system is biogenic in nature. Accordingly, it is valuable to study how to best achieve the control condition. One of the most likely methods of creating a control is through application of heat sterilization. To effectively create a control through heat sterilization, the process must meet two requirements. First, it must inactivate viable organisms within the original sample. Second, the chemical composition of the sample after sterilization must be as similar as possible to that of the initial pre-sterilized sample. In practice, achieving these two requirements simultaneously is difficult. If a sample is heated longer and to warmer temperatures than necessary, it is likely that unwanted chemical changes will occur. On the other hand, preserving the sample's chemical properties by lowering the temperature or total process time will threaten sterilization quality.;A method of assessing the balance between sterilization quality and sample degradation was postulated consisting of generating curves called sterilization quality distributions (SQDs) for different sterilization processes. The SQD method was applied to a prototype of an astriobiology life-detection instrument that employs autoclave heat sterilization, called the Microbial Detection Array (MiDA). The final results show that a target sterilization quality can be reached up to 2.5 times faster for a dry sample than for a sample that has been mixed with water. On the other hand, stirring a sample/water mixture allows for full sterilization to be reached at a temperature that is up to 50°C lower than for a dry sample. |
