Is the significant difference in flocculent precipitation of fetal bovine serum from different batches a quality issue

When the schedule is tight, do not directly return or exchange based on the amount of precipitate alone; first use cell data to make a judgment. It is recommended to prepare two serum batches at 10% and 15% concentrations, inoculate 293T cells and mesenchymal stem cells, and set up an old batch or a batch with less precipitate as a control. For 293T cells, transfection efficiency and growth curve can be examined; for MSCs, focus on observing adherence, refractility, nuclear morphology, and doubling time. If a batch with more flocculent material shows little difference in cell performance after centrifugation/filtration compared with the other bottle, it can continue to be used; for key MSC experiments, try to use the serum batch with more stable performance to avoid affecting the results.

When communicating with the supplier, do not just say there is a lot of precipitate. Attach the batch numbers of the two bottles, the thawing method, photos of the precipitate, and preliminary cell results, and ask them to explain or provide another bottle from the same batch or a small trial sample. If the 10-day lead time would slow down the experiment, ask the supplier to send a new batch or aliquoted small samples first, and at the same time aliquot the existing serum into 50 mL portions and freeze them to reduce repeated freeze-thaw cycles. Less precipitate in domestic serum does not mean it is better. Some processes remove fibrin, which may affect the retention of certain cytokines, so it is not recommended to judge quality based only on the amount of precipitate.

Two bottles from different batches show significant precipitate differences; first check the appearance and supernatant clarity. If there are white flocculent precipitates and the supernatant is not turbid, consider fibrinogen precipitation; if the precipitate is grayish, the supernatant is turbid, or the color is yellowish, be alert to protein denaturation or operational contamination. Check the COA of both bottles for endotoxin, total protein, hemoglobin, pH, etc. Endotoxin levels generally do not directly manifest as flocculent precipitates but mainly affect cell status. You can centrifuge the batch with more flocculent precipitates at low speed, collect the supernatant, and prepare complete medium simultaneously with the other bottle for a cell control.