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Job Title: Research scientist
The reason 1X liquid media from a manufacturer is often better then medium made in your lab from a DPM is the difference in the quality of water. The better commercial media companies monitor endotoxin and heavy metal contaminents in their water and have processes in place to control them. Water grows bacteria rapidly and unless you control growth you will have endotoxin produced by the gram negative organisms. Many systems have a bacterial filter at the end of the line and the pressure of the water passing through will rupture the gram-negative bacteria and release endotoxin. It is a good practice to change this filter once a month. It is also true that the use of ceramic grinding stones produces a lot of heat. This is why the most heat-labile components are added last during a DPM run, so that they are exposed to the heat the least amount of time. Like with a liquid medium, the timing of addition of the media components is a science in itself. If made correctly and you have high quality water, the DPM should be fine as the components in a standard formulation are usually there in excess. There are ways to make a DPM which allows for the a fine powder to be sprayed through an orifice so rapidly as to result in the components seeing minimal heat (jet milling). Some manufacturers have switched to this method while others still use ball milling or use one or the other dependent on the size of the run. A good manufacturer also protects the liquid medium from light degradation during both manufacturing and storage.