Onion Extract (Quercetin)

Onion extract is produced from the bulb and the dry outer scales of Allium cepa L. (Amaryllidaceae, subfamily Allioideae; the genus was formerly placed in Liliaceae and later in Alliaceae). Onion is one of the few widely eaten vegetables whose polyphenol fraction is dominated by a single flavonol family, which is the reason it is bought as a quercetin ingredient at all. In the living bulb most of that quercetin is glycosylated rather than free: the principal forms are quercetin-3,4'-O-diglucoside and quercetin-4'-O-glucoside, the latter also known as spiraeoside (CAS 20229-56-5, C21H20O12, MW 464.4), with quercetin-3-O-glucoside (isoquercitrin) as a minor partner. The papery outer scales are the fraction richest in the free aglycone — quercetin itself, 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one, CAS 117-39-5, C15H10O7, MW 302.24 — because drying and senescence hydrolyse the glucosides. Red cultivars additionally carry cyanidin-based anthocyanins in the scales. Thovek states which plant fraction a lot was made from, since skin-derived and flesh-derived material differ visibly in colour and measurably in flavonol profile. Two decisions have to be settled before an onion extract can sensibly be contracted, and both are routinely left vague in the trade. The first is what the word quercetin means on the certificate: an assay run directly reports the free aglycone only, while an assay run after acid hydrolysis converts the glucosides and reports total quercetin, which is the materially larger number. Thovek states the method and the basis on every certificate of analysis and will run whichever basis the buyer's own release specification uses. The second is strength. Standard grades are 2%, 5% and 10% quercetin by HPLC, with native 4:1 and 10:1 ratio extracts where a buyer wants the whole flavonol and organosulphur profile rather than a marker figure. Offers of "onion extract, quercetin 95%" should be read carefully: at that strength the material is purified quercetin, normally obtained by hydrolysing rutin from Styphnolobium japonicum (the tree still traded as Sophora japonica), and it is a different article with a different tariff position and a different price basis. Thovek quotes that isolate as its own product and does not present it as onion extract. Where onion origin matters contractually, the HPLC fingerprint rather than the total quercetin figure is the control — genuine Allium cepa material shows the glucoside pattern with its accompanying sulphur and anthocyanin markers, whereas an isolate shows the aglycone alone. Manufacture is by aqueous or hydroalcoholic extraction of cleaned, dried and milled material, followed by filtration, vacuum concentration and spray drying, either carrier-free or on maize maltodextrin where a free-flowing powder is wanted; the carrier is named on the specification sheet rather than left implicit. The powder is light to reddish brown with a characteristic onion odour that survives extraction and has to be designed around in flavour work, so deodorised grades are offered for capsule and tablet use. Quercetin is practically insoluble in water, which means a higher-assay grade behaves as a dispersion rather than a solution and beverage applications normally move to a spray-dried or solubilised form. The material is plant-derived, vegan and vegetarian, non-GMO, and free of milk, egg, fish, crustacean, mollusc, soy, peanut, tree nut, sesame, mustard, celery, lupin and gluten; onion is not listed in EU Regulation 1169/2011 Annex II, but it is a recognised fructan (FODMAP) source and some brands label it for that reason. Onion (Allium cepa L.) appears in the 21 CFR 182.20 list of essential oils, oleoresins and natural extractives generally recognised as safe. Every lot ships with HPLC assay and identity, loss on drying, ash, heavy metals by ICP-MS, pesticide residues, residual solvents to ICH Q3C and full microbiology, with halal, kosher and organic certification available.