Zeaxanthin

Zeaxanthin is a dihydroxy xanthophyll, (3R,3'R)-β,β-carotene-3,3'-diol, CAS 144-68-3, formula C40H56O2 and molecular weight 568.88, melting at about 215.5 °C. It shares its molecular formula with lutein and is a constitutional isomer of it: zeaxanthin carries two β-rings where lutein carries one β-ring and one ε-ring. Because the two are identical by mass, identity and ratio can only be established by HPLC, and a buyer specifying zeaxanthin should always ask which peak the assay is reporting. Three stereoisomers are commercially relevant and they are not interchangeable. (3R,3'R)-zeaxanthin, CAS 144-68-3, is the form made by plants and algae. meso-Zeaxanthin, the (3R,3'S) isomer, is a separate substance with its own CAS number, 31272-50-1, produced industrially by alkaline isomerisation of marigold lutein under high temperature and high base concentration, which shifts the 4',5' double bond to the 5',6' position and converts the ε-ring into a β-ring. Specify the isomer on the purchase order, because a specification written simply as 'zeaxanthin' will not tell a contract manufacturer which article to expect. Thovek supplies zeaxanthin obtained from Tagetes erecta marigold petals, offered as crystalline powder, standardised powders and cold-water-dispersible beadlets, with meso-zeaxanthin available where a buyer's formulation calls for it. For reference on the synthetic route, zeaxanthin made by the Wittig reaction runs 96 to 98% trans-(3R,3'R)-zeaxanthin with cis-zeaxanthins at a maximum of 2.0%, 12'-apo-zeaxanthinal at a maximum of 0.1% and diatoxanthin at a maximum of 0.2%; that material is a synthetic article and is described here only so that specifications can be compared correctly. Zeaxanthin carries INS 161h(i) and E161h and falls under the JECFA 2018 group ADI of 'not specified' shared with lutein from Tagetes erecta and lutein esters; the earlier 2004 group ADI was 0-2 mg/kg body weight. The conjugated polyene chain oxidises readily, so crystalline and powder grades ship nitrogen-flushed in light-proof packs and should be held at 2-8 °C. Marigold-derived grades are vegan, vegetarian and gluten-free and are free from milk, egg, soy, fish, crustacean and tree nuts. As with lutein, the risk sits in the delivery matrix rather than the active: gelatin-based beadlets are bovine or fish gelatin and break a vegan claim, and tocopherol antioxidants are frequently soy-derived, so both should be specified at order if those declarations matter. Every batch ships with a certificate of analysis covering HPLC assay and isomer identity, UV-Vis confirmation, residual solvents, heavy metals, pesticide residues and microbiology, with Kosher, Halal, non-GMO and vegan documentation available on request.