Quercetin

Grades and forms of quercetin powder

Quercetin is a yellow flavonol aglycone that supplement manufacturers buy as a dry powder for capsules, tablets and powder blends. Its EU status is set mainly by national rules and the novel-food check, not by the vitamin and mineral annexes. Its poor water solubility, strong colour and metal binding decide most formulation choices.

Quercetin is traded in two hydration states, anhydrous and dihydrate. The identity data on this page, including the molar mass of 302.23 g/mol, describe the anhydrous molecule. The dihydrate carries water of crystallisation, so one gram of it delivers less quercetin than one gram of anhydrous material.

These points decide the choice of grade:

• Hydration state and assay basis. The specification states the assay on either the anhydrous or the as-is basis. Confirm which before calculating a fill weight.
• Purity profile. Grades differ in quercetin content and in related flavonoids carried over from the plant raw material.
• Physical properties. Particle size and flow vary between grades and matter for encapsulation and direct compression.
• Source and production route. These matter for the novel-food check described below.

SoleChem sends the specification sheet and the certificate of analysis with its quote. State the hydration state and assay basis you need in the quote form.

EU regulatory status

Quercetin is neither a vitamin nor a mineral, so Annexes I and II of Directive 2002/46/EC do not list it. The directive still applies to any food supplement that contains it, including its labelling requirements. See the guide to labelling a food supplement in the EU.

The use of substances other than vitamins and minerals in food supplements is only partly harmonised at EU level. Member states apply national rules: some keep positive lists, some require notification before marketing, and some set maximum amounts. Check each target market with its competent authority.

Under Regulation (EU) 2015/2283, a food not used for human consumption to a significant degree in the EU before 15 May 1997 that falls within one of the categories in Article 3(2)(a) needs authorisation and an entry in the Union list. Status can depend on source, production route and purity, so confirm it for the exact material. Modified or derived forms of quercetin are assessed separately. Where status is unclear, Article 4 of the regulation sets out a consultation procedure. The novel food status guide explains the process.

Article 8 of Regulation (EC) No 1925/2006 lets the Commission prohibit, restrict or place under scrutiny substances other than vitamins and minerals through Annex III. Check Annex III for any entry before finalising a product.

Any claim on the label must comply with Regulation (EC) No 1924/2006. Check the EU Register of nutrition and health claims and the site’s health-claims guide.

Formulation notes

Solubility. Quercetin is very poorly soluble in water. In ready-to-mix powders it disperses rather than dissolves, can settle and colours the drink yellow. In softgels it is used as a suspension in the oil fill.

Colour and taste. The powder is intensely yellow and stains equipment, capsule shells and neighbouring granules. Tablets can show speckling, which a film coating hides. The taste is bitter, which limits use in chewable and gummy formats without masking.

Metal binding. The catechol group on the B-ring chelates metal ions. In multi-mineral blends, especially with iron salts such as ferrous sulfate, discolouration can occur. Run stability trials on the final blend.

Oxidation. The catechol structure oxidises more readily in moist, alkaline conditions and under light. Store and pack away from light and moisture.

Flow and encapsulation. Fine quercetin powders tend to be cohesive. A flow aid such as silicon dioxide improves capsule filling in HPMC or gelatin shells. The capsules guide covers fill design.

Combinations. Quercetin is often formulated with ascorbic acid, bromelain or other polyphenols and flavonoids such as resveratrol. Check each partner for colour and metal-ion interactions.

Label-claim arithmetic. For an as-is assay, the fill weight equals the label claim divided by the assay as a decimal. For an assay on the anhydrous basis, first multiply the assay by (1 minus the water content as a decimal), using both values from the certificate of analysis. Add any overage with the overage calculator.