Hi Prof. Ramarao Malla, based on my experience, I believe it may not necessarily be due to contamination. Still, there are few things you can check like salt precipitation (media composition), Ensure you have gradual co2 equilibration, pH of media, media quality and storage conditions (Media degradation or repeated freeze-thaw cycles can destabilize components- so try having aliquots and filter it before use to eliminate any precipitation), filter-sterilize FBS before adding to the media, Use high-quality tissue-culture-treated flasks. Please feel free to correct me if I'm mistaken and someone with very much expertise will help you out.

Dear Prof. Ramarao Malla,

Please note that MDA-MB-231 cells are known to be highly glycolytic, meaning they produce a lot of lactate as a byproduct of metabolism. High lactate levels can contribute to pH changes. Altering the pH of the culture media can affect the solubility of calcium and phosphate, causing them to precipitate. 

The pH of cell culture media is critical for cell viability and function. A shift away from the optimal pH (around 7.2-7.4) can lead to precipitation of various compounds.

So, ensure your culture media is at the correct pH (typically around 7.2-7.4). 

Regards,

Malcolm Nobre

white precipitate is usually indicative of contamination. Although sterility may be maintained during the culturing of cells, there is a chance that the reagents used may be contaminated. Maybe assess the sterility of reagents by leaving them at 37 degrees celsius overnight.