When a microarray result shows two species in a blended product, the natural next question is “in what proportion?” A DNA result can answer part of that question, but not all of it. Knowing where the line falls is what makes a mixture result useful rather than misleading.
What a mixture result tells you
A QAID mixture result reports each species on the panel that was detected in the sample, with assay controls and the relative DNA signal for each one. That answers the questions that matter most for authenticity:
- Is every declared species present?
- Is anything present that shouldn’t be, such as a filler, substitute or undeclared species?
- Which species dominate the DNA signal?
Why DNA signal isn’t ingredient weight
It is tempting to read a 70 / 30 split in signal as 70 / 30 by weight. The biology doesn’t allow it, for three reasons:
- Different materials carry different amounts of DNA. A gram of leaf, root, seed or muscle tissue holds different amounts of extractable DNA, and so do different species.
- Processing affects each ingredient differently. Heat, milling, drying and extraction break DNA down, and not evenly across ingredients. A heavily processed ingredient can give far less signal than its share of the product.
- Extraction efficiency varies with the material. Some materials release their DNA more readily than others.
So relative DNA signal describes the DNA that was recovered and detected, not the mass of each ingredient that went into the product.
A label claim such as “60% species A, 40% species B” is a statement about mass. A DNA signal ratio alone cannot confirm it, and QAID results do not present it as if it could.
Using relative signal well
Relative signal is still informative when it is read in context:
- A species that should be a minor ingredient but dominates the signal is worth investigating.
- A declared ingredient with no detectable DNA is a flag, once the DNA quantity check has confirmed the material type is suitable for DNA testing.
- Across lots of the same product made the same way, a clear shift in the signal pattern can point to a change in supply that deserves a closer look.
The bottom line
Use a mixture result to confirm what is there and to find what shouldn’t be. Where a decision depends on exact proportions by weight, pair the DNA result with a method designed to measure them. Read more about Mixture Analysis, or talk to QAID about the products you need to check.