What causes FBS colour differential?

Fetal bovine serum is this rather quite pretty reddish-amber colour, but most scientists don't think about its color much, except along one of two lines of thought: 1) "yep, checks out, it's a blood product" or 2) "this FBS looks weird, what's going on?"

We run into this when I drop off bottles of FRS Pioneer to research institutes for their regular FBS batch testing ritual. FRS is clear, so unfortunately it's not exactly a blinded head-to-head comparison.

The colour of FBS comes down to hemoglobin and its breakdown products. These heme-derived pigments carry over from blood collection and processing, which can vary from batch to batch. Because it’s commonly used as a processing quality indicator, certificates of analysis often flag FBS hemoglobin content. The same is not true of most sources of variability in FBS.

These variability sources range from the well-known, for example growth factor concentration variability, but extends to protease inhibitors, oxidant capacity, miRNA-containing extracellular vesicles, and dozens of other parameters which modulate cellular biology in completely unaccounted for ways that most scientists never ever think about, let alone record in the methods section of xyz journal.

So you've got some options. Moving to 100% chemically defined media eliminates this variability entirely, but FBS reduction also has a meaningful impact. The research institutes we work with are typically considering reduction of standard FBS concentrations down to 1–2%, and at that level you've already cut a significant fraction of the batch variability.

Plus much as we all love our ritual FBS batch testing processes, wouldn't it be even lovelier if it happened once a decade?

As always, journal articles below if you're keen to dive deeper!

FBS batch variability - https://www.sciencedirect.com/science/article/pii/S3050620425000429

Protease inhibitor deep dive and sources - https://www.linkedin.com/posts/kathleenbashantday_most-scientists-dont-think-about-this-but-activity-7416587209304203264-XT5T?utm_source=social_share_send&utm_medium=member_desktop_web&rcm=ACoAABxyS3cBZRJoB-cKhs2ybXkT-p4uHHtCnJk

miRNA extracellular vesicles deep dive and sources - https://www.linkedin.com/feed/update/urn:li:activity:7431801402559209472/?originTrackingId=MQz2KBX26vsc%2FLqOCAlJsA%3D%3D