Product-photo-based composite. Package wording is not a measured A620/A280 ratio or concentration result.

A phycocyanin purity ratio describes a relationship between absorbance measurements, commonly A620/A280. Concentration describes how much phycocyanin is present in a defined volume, while powder content describes an amount relative to the powder’s mass. Buyers need these values separately: a purity ratio is dimensionless and cannot be read as a percentage of phycocyanin in a commercial powder.

For technical purchasing, the useful question is whether two specifications measure the same property under comparable conditions. A larger ratio alone does not establish a stronger ingredient, better color performance, or suitability for the intended food application.

What does A620/A280 measure?

The ratio compares absorbance near phycocyanin’s visible absorption region with absorbance at 280 nm, a wavelength used to assess protein-associated UV absorption. It is a spectral index, not a direct separation and weighing of every component. Use blank-corrected readings from the same prepared sample, with a consistent optical path or documented path-length correction, and within the method’s usable absorbance range. Other absorbing substances and sample preparation can affect the result.

A 2023 experimental study explicitly calculated the purity index as A620/A280 while calculating phycocyanin concentration using a separate equation that included absorbance at 620 and 652 nm. Its methods demonstrate why ratio and concentration are distinct measurements. Gomaa et al., 2023, extraction and concentration methods.

Can two samples have the same ratio but different concentrations?

Yes. Consider the following hypothetical absorbance readings, measured under otherwise comparable conditions and within the method’s working range:

The ratios match even though the absolute absorbance values differ. This simple example explains the distinction; it is not a concentration assay or an AimGrow test result. You would need the specified concentration method and any required additional wavelengths to calculate concentration.

Likewise, diluting an ideal sample can reduce both readings proportionally without changing the ratio. That does not mean every real sample behaves ideally: very low readings, turbidity, nonlinearity, and preparation differences can make the comparison unreliable.

How is solution concentration different from powder content?

A result in mg/mL refers to the tested solution. A result in mg/g or percent by weight refers to a defined material mass. To connect them, the laboratory must account for sample weight, extraction volume, dilution, and the reporting basis.

As a unit-conversion example, suppose a defined procedure extracts 0.100 g of powder into a final volume of 100 mL and reports 0.200 mg/mL after all dilution corrections. The calculated extracted amount is 20 mg, equivalent to 200 mg/g, or 20% of the original sample mass. This assumes the procedure’s extraction and quantification are appropriate; it does not prove complete recovery or establish a universal assay procedure.

Check whether the result is as supplied or on a dry basis. Also ask whether carriers and other ingredients are included in the declared powder composition. Comparing an extract-solution concentration with an undeclared commercial powder percentage can create a false impression of equivalence.

What method details should suppliers disclose?

• Exact ratio definition and wavelengths; do not silently substitute a different visible wavelength.
• Buffer or solvent, pH, extraction steps, clarification procedure, and time before measurement.
• Instrument path length or path-length correction, blank, dilution, and usable measurement range.
• Concentration equation, calibration approach where applicable, correction wavelengths, and units.
• Powder sample mass, final volume, moisture basis, and handling of carrier materials.
• Acceptance limits, batch results, method suitability, and relevant uncertainty or repeatability information.

When laboratories disagree, begin with these conditions and a common sample rather than assuming one result is incorrect. Align the method and reporting basis before setting a purchase acceptance limit.

Does a purity ratio prove food suitability or stability?

No. Treat a claimed “food grade” category as a starting point for clarification, not a substitute for intended-use review, composition disclosure, contaminant specifications, or batch documentation. A spectral ratio by itself does not test all of those properties.

Color stability also needs separate evaluation. An experimental study of food-grade phycocyanin assessed thermal and oxidative behavior under defined conditions and investigated the effects of added sugars and sugar alcohols. Those results describe the tested systems, not an AimGrow product’s shelf life or performance in your formulation. Huo et al., 2022.

When requesting an AimGrow sample, specify your application and ask for the ratio, concentration or powder-content specification, composition, and measurement method as separate fields. Then compare samples under the same preparation and application conditions. That gives purchasing and R&D a more useful decision than ranking suppliers by a single ratio. You can also review AimGrow’s phycocyanin information page before requesting a current specification.