Understanding Color Changes in Cell Culture Media
News 24 4 月, 2025
During cell culture, changes in media color often reflect the condition of the cells. Typically, media appears red due to its pH (~7.4) and the presence of phenol red. However, the exact color can vary depending on the media type. For instance, DMEM tends to appear darker than RPMI-1640 because it contains more phenol red. Some media are colorless or pale yellow if phenol red is not included.
But what does it mean when your media turns purple or yellow instead of red?
Let’s break down the causes of these color shifts and what they signal about your cells.
Media Turns Redder or Purple
When media sits open for a while, it may turn darker than usual. This is usually due to the NaHCO₃ buffering system. After opening, NaHCO₃ breaks down and CO₂ escapes, making the media more alkaline.
To restore the normal color: → Slightly loosen the cap and place the bottle in a CO₂ incubator for a while. The color should return to normal.
Can this darker media still be used?
Some cells tolerate slight pH shifts and grow fine.
However, sensitive cell lines (e.g., BV2 cells) may suffer, showing increased floating or detachment.
Tip: After preparing complete media, aliquot into 50 mL tubes and use within 1 week. For small volumes, store in 15 mL tubes.
Media Turns Yellow
Phenol red turns yellow in acidic conditions—but it may also signal contamination. Common reasons include:
- Normal metabolism – Cells produce acid, turning red media to orange/yellow.
→ Orange media often indicates healthy cell growth, no concern needed. - High density or overgrowth – If media turns yellow quickly after media change, your culture might be too dense or consuming nutrients fast.
→ Time to split or passage the cells. - Poor cell condition or contamination – If the media turns yellow and cloudy, and you observe granules under the microscope, suspect:
- Bacterial contamination
- Mycoplasma contamination
Mild contamination can be managed with antibiotics or mycoplasma treatment kits.
Severe contamination? Best to discard the culture after proper disinfection.