Low-Endotoxin Bovine Serum Albumin Powder

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• Endotoxin Testing in Cell CultureEndotoxin testing measures bacterial lipopolysaccharide (LPS) in laboratory water, media, sera and reagents, reported in endotoxin units per millilitre (EU/mL), where 1 EU corresponds to roughly 0.1–0.2 ng of reference-standard E. coli endotoxin. The compendial methods are the LAL (limulus amebocyte lysate) assay in its gel-clot, turbidimetric and chromogenic forms under USP <85>, and the animal-free recombinant Factor C (rFC) assay under USP <86>; kinetic formats quantify down to about 0.001–0.005 EU/mL. Practical cell-culture limits are 0.25 EU/mL for water, ≤1 EU/mL for most cell-culture-grade reagents, and ≤10 EU/mL as the general industry standard for fetal bovine serum, with low-endotoxin grades at ≤1 EU/mL and ultra-low grades below 0.1 EU/mL. Endotoxin survives autoclaving and passes 0.2 µm filters, so it must be excluded at source rather than removed later.
• Bovine Serum in Cell CultureBovine serum is the liquid fraction of clotted cattle blood, added to culture medium at 5-10% to supply growth factors, hormones, transport and attachment proteins, lipids and trace elements that basal media do not contain. Fetal bovine serum (FBS) and fetal calf serum (FCS) are two names for the same product, collected from the fetus at slaughter of pregnant cows; newborn calf serum comes from calves under about 20 days old and donor bovine serum from controlled donor herds aged roughly 12-36 months, both containing more immunoglobulin and fewer growth factors than FBS. Because serum is an undefined biological material with substantial lot-to-lot variation, unresolved animal welfare questions and a volatile supply chain, defined serum-free and animal-origin-free media are increasingly preferred where the cell line will tolerate them.
• Heat Inactivation of Fetal Bovine Serum (FBS)Heat inactivation of fetal bovine serum is a controlled 30-minute incubation at 56 degrees C that destroys the heat-labile proteins of the complement cascade before the serum is added to culture medium. The serum is thawed, brought to 37 degrees C, transferred to a 56 degrees C water bath, held for exactly 30 minutes from the moment the serum itself reaches temperature with gentle swirling every 5-10 minutes, then cooled immediately and aliquoted. For routine culture of established cell lines it is usually unnecessary, because complement activity in fetal serum is low and heating also degrades labile growth factors; it remains standard practice for immunological assays and complement-sensitive cells.
• Recombinant Human Albumin in Cell CultureRecombinant human serum albumin (rHSA) is a 585-amino-acid, 66.5 kDa non-glycosylated protein produced in yeast such as *Pichia pastoris* or in transgenic rice rather than purified from human plasma, and it is used as an animal-origin-free supplement in serum-free and chemically defined culture media. In culture it works as a carrier for fatty acids, lipids, hormones and trace elements, as an antioxidant through its free cysteine-34 thiol, as a scavenger that sequesters toxic metals and excess free fatty acids, and as a shear-protective surface-active protein in stirred and sparged culture. Typical working concentrations are 0.1-10 g/L, most often 0.5-5 g/L, and it is commonly supplied as a 200 mg/mL (20%) solution. Its performance depends heavily on what is bound to it, so fatty-acid-loaded and fatty-acid-free preparations behave quite differently.