I am working on cell culture. I realized the cells haven't good growth... and the flask isn't clear. there isn't any evidence of contamination. finally, I understood that my FBS isn't clear and after adding to RPMI...make it cloudy.
Hello Nasrin Soltani
The cloudiness of serum could be because of the presence of fibrin, calcium phosphate or fatty ester of cholesterol or some protein precipitate. This cloudiness of serum could have appeared due to improper way of heat inactivation of serum such as improper thawing, inactivating serum that has not been thoroughly mixed homogeneously, inactivating serum above the recommended temperature or inactivating serum for a longer period of time than recommended 30 minutes.
Also, repeated freeze-thaw and long-term storage at 2-8° C could lead to cloudiness of FBS. Another reason could be contamination, which as you mentioned is not likely.
Best.