Bromocresol Green (BCG) Test
Definition
A colorimetric rapid test for surfactant detergents in milk: BCG at pH 4 partitions into surfactant micelles, shifting from yellow to blue-green within 30 seconds. Sensitive to approximately 0.1% SDS equivalent.
- Target
- Surfactant detergents in milk
- Mechanism
- BCG partitions into surfactant micelles at pH 4
- Colour change
- Yellow to blue-green
- Reaction time
- Within 30 seconds
Common questions
Why does the BCG test target detergent specifically rather than other milk adulterants?+
The colour shift relies on BCG dye partitioning into surfactant micelles, a property specific to detergent-type molecules, so the test does not detect other common adulterants such as melamine or urea, which need separate colorimetric or chromatographic tests.
How sensitive is the BCG test and what does that limit mean in practice?+
It detects surfactant at roughly 0.1% SDS equivalent, so lower-level adulteration below that threshold may go undetected, meaning a negative BCG result is not proof that no detergent contamination is present, only that it is below the test's sensitivity.
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