question about media color - (Dec/30/2009 )

hello everyone,

i just want to ask about the possible reasons for different changes of culture media. I prepared RPMI with different serum (FBS) and added antibiotic, glutamine, and 2-mercaptoethanol. I am expecting that the color of the media will be the same for all bottles even with different manufacturer of serum, but I just want to know reasons why some are pinkish, light pink, and others are so red. does the change in color also mean change in pH and contamination?

thank you....

I'm not sure this is the reason, but it could potentially be photobleaching.

After sometime after open the bottle/ prepared the media, the media wil change its colour. It is not contamination. Maybe some oxidization, i guess.

The color of the media is due to the presence of phenol red. Phenol red is included in media as a pH indicator. Each bottle may have been exposed to air for different amounts of time as you prepared your media or the FBS may have a different pH (I have never heard this before but maybe it is possible).

soymilk14 on Dec 30 2009, 07:57 AM said:

Most cell culture media are buffered using a carbonate/bicarbonate buffer system (the bicarbonate in the media also supplies a metabolic requirement). When the media is exposed to air it slowly loses C02 and becomes more alkaline (and the phenol red pH indicator becomes more red). This is why cultures need to be incubated in 5% CO2 to maintain pH.
The variations in the colors of your media are due to the different times the individual bottles were open during the addition of supplements (hence diff losses in the amount of CO2). Also some bottles may not be sealed as well as others.
If you place the different media into a 5% CO2 atmosphere for a few hours they will all take on the same color.

To minimize pH changes during cell handling people often include 10-20 mM HEPES buffer (pH 7.2) in their medium.

Hope this helps.