SEA-PHAGES | PYCa media turning dark

Link to this post \| posted 22 Jan, 2021 20:44
cheryl.brown@mnstate.edu	We have had some issues with our PYCa agar getting dark while being held at 45-50 C. I am trying to figure out if it could be one of the ingredients, as we did buy new yeast extract and peptone, or if this is normal and harmless.

Link to this post \| posted 22 Jan, 2021 21:03
viknesh	cheryl.brown@mnstate.edu We have had some issues with our PYCa agar getting dark while being held at 45-50 C. I am trying to figure out if it could be one of the ingredients, as we did buy new yeast extract and peptone, or if this is normal and harmless. Hi Cheryl, At high temperatures, dextrose and amino acids can undergo the Maillard reaction, which results in a darkening of the media. The products of the Maillard reaction impacts the growth of some bacteria more than others. It may be fine for you to use the darkened media, but it may impact reproducibility of bacterial growth on your plates. The way to reduce the Maillard reaction is to keep dextrose and amino acids in as cool a solution as possible. This means waiting for freshly autoclaved/molten PYCa agar to cool to ~ 60C before adding dextrose, minimizing the number of time you reheat (e.g. in the microwave) PYCa agar once dextrose has been added, and not keeping molten dextrose in the warm bath for extended periods of time. In our lab, we add dextrose to molten PYCa agar at ~ 60C, then allow the media to solidify for storage. When we want to pour plates, we melt the solidified agar in the microwave, allow it to cool to 60C before adding supplements like cycloheximide, then pour the plates. We don't keep PYCa agar in the molten state for long. I hope this is helpful.

Link to this post | posted 22 Jan, 2021 21:03

viknesh

cheryl.brown@mnstate.edu
We have had some issues with our PYCa agar getting dark while being held at 45-50 C. I am trying to figure out if it could be one of the ingredients, as we did buy new yeast extract and peptone, or if this is normal and harmless.

Hi Cheryl,

At high temperatures, dextrose and amino acids can undergo the Maillard reaction, which results in a darkening of the media. The products of the Maillard reaction impacts the growth of some bacteria more than others. It may be fine for you to use the darkened media, but it may impact reproducibility of bacterial growth on your plates.

The way to reduce the Maillard reaction is to keep dextrose and amino acids in as cool a solution as possible. This means waiting for freshly autoclaved/molten PYCa agar to cool to ~ 60C before adding dextrose, minimizing the number of time you reheat (e.g. in the microwave) PYCa agar once dextrose has been added, and not keeping molten dextrose in the warm bath for extended periods of time.

In our lab, we add dextrose to molten PYCa agar at ~ 60C, then allow the media to solidify for storage. When we want to pour plates, we melt the solidified agar in the microwave, allow it to cool to 60C before adding supplements like cycloheximide, then pour the plates. We don't keep PYCa agar in the molten state for long.

I hope this is helpful.

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PYCa media turning dark