Oxidation Color Indicators
When a substance is already oxidized, it typically appears pink, brown, or dark in color, depending on the specific compound and degree of oxidation.
Epinephrine Oxidation
The most clinically relevant example comes from epinephrine solutions, which provide clear color indicators of oxidation status 1:
- Pink coloration indicates initial oxidation to adrenochrome 1
- Brown coloration indicates advanced oxidation with melanin formation 1
- Fresh, non-oxidized epinephrine solution should be clear and colorless 1
Epinephrine solutions deteriorate rapidly upon exposure to air or light, progressing from pink (adrenochrome formation) to brown (melanin formation), and such discolored solutions should be discarded 1.
Redox-Sensitive Fluorescent Probes
In laboratory settings, oxidation is detected through specific color changes in fluorescent probes 2:
- Dihydroethidium (HEt) changes from blue fluorescence to red fluorescence when oxidized (forming 2-hydroxyethidium or ethidium) 2
- BODIPY-581/591-C11 undergoes a fluorescence shift from red to green when oxidatively disrupted 2
- Dihydrorhodamine 123 changes to green fluorescence (emission at 536 nm) upon oxidation 2
Enzymatic Browning
In biological systems, particularly plant tissues, oxidation produces characteristic brown pigments 3, 4:
- Polyphenol oxidase (PPO) catalyzes phenolic compound oxidation, leading to dark brown melanin pigments 3, 4
- This enzymatic browning represents the final stage of oxidation in fresh produce 3, 4
Critical Pitfall
Never rely on color alone for clinical decision-making with medications - the absence of discoloration does not guarantee lack of oxidation, as some oxidative changes may not be immediately visible 1. Always check expiration dates and storage conditions in addition to visual inspection.