Hi

Iam always don it before sterilization, Due to the difficulty of controlling the pH adjustment in sterile conditions.

GOOD LUCK

Hello Juan, most media, especially of the complex kind, require prior heating, from warming to boiling, before autoclaving. I believe that this encourages as much ionization as possible so that, changes in pH by autoclaving temperatures will be insignificant. This discourages the temptation of taking the pH after sterilization. However, I always consider it wrong methodology to take the pH of some media especially basal or mineral salts media, before autoclaving. This derives from the significant effect of temperature on, first ionization, and then pH. Ionization increases with increasing temperature. As you heat up the medium, unionized components of the medium that could not ionize before autoclaving will ionize, increasing, say hydrogen ion concentration [H+], thus reducing pH (making it more acidic). Therefore, taking the pH before or after autoclaving depends on the kind of medium and the nature of substrates that constitute it.

It will depend on what stage you want to use that culture for further studies.

Hello Juan Rafael Menchú Rosal

It depend on what media you are using, for broth medium there not much difference in pH before and after sterilization

After autoclaving. When pH is a factor for bacterial growth, it is the starting pH prior to fermentation. If need be, sterile HCl or NaOH can be added to optimize the pH at use if not in the proper range.

Hello everyone

I'd recommend Mauroce's response to be elaborate and meaningfull. Pre-hear is a thoughtful practice. Goodluck

You received some good answers. It depends on the constituents of the medium you are making. If there is a reasonable amount of peptone in the medium autoclaving will not usually changed the pH. If it is a defined medium there is nothing to poise the pH of the medium from changing during autoclaving. When I made defined media for anaerobic cultivation, we would cool the medium under carbon dioxide gas after autoclaving to keep the medium anaerobic. Even though there was a considerable amount of sodium carbonate in the medium, it would drop over 2 pH units under carbon dioxide and need to be adjusted with sterile sodium hydroxide.

At point of use. This may be represented well enough by sampling after sterilization or, as Jay points out, the medium pH may change with storage. Measurement before sterilization is not very useful and can't be relied upon to represent pH in application.

Hi there,

So, you have got a nos. of good suggesstions. Besides, pH adjusting of a culture medium may depend on factors as, purpose of culturing(screening or else); pH sensitivity of your organism(s), type of culture vessels(test tube, flask or fermentor) to be used, nos. of cultures you plan in a single set of expts. and finally, the ease of adjusting medium pH. If you plan a nos. of batch cultures in a set (in test tubes or flasks), adjusting pH after sterrilisation is bothersome. but If it's in fermentors with acid/base chanenels, it is alright after autoclaving. So, it depends on purpose and available facilities. Good luck

pH of culture media should be read after autoclaving. Depending on aerobic or anaerobic growth, fastidious organisms require certain pH levels for quality growth. It is advisable you collect just a sample of the autoclaved media to avoid contaminating the whole batch

It may vary according to the media, but usually we don't observe huges changes on pH before and after autoclaving. Anyway, I agree that the media is better dissolved and most close to the conditions of use after autoclaving.

Be carefull on media that require addition of suplements after autoclaving. In this case, make the adjustments always after add the suplement.

pH should measure after autoclaving of the media. Because heating enhance the solubility of the media ingredients. So to get actual value of pH after auclaving is the best. To measure the pH of solid media you can use pH meter having flat probe as media become solidified at below 25 C. For broth media round/immersion probe is widely used.

I have a question on a similar topic than an answer. The media that I am preparing at present needs its pH to be adjusted after autoclaving while it is still hot. I would highly appreciate your suggestion on how to do this?

I would use a sterile pipet to remove a sample for pH test, then adjust the pH as needed (recap and swirl). This can be done with sterile 1N HCl or 1N NaOH. Retest to make sure pH is where it is needed. As long as it is a sterile additive and standard precautions are taken to avoid contamination. Experience with your media and charting how much is needed per volume to make a pH change will make future additions easier.

As Linda offered - the most relevant measure of pH is what the inoculum will encounter.