Colorants iridoids

The solubility of iridoids depends on their state (free, glycosylated, acetylated), but usually they are extracted with polar solvents methanol, ethanol, aqueous alcohols, and rarely acetone. Iridoid glycosides are more or less stable some of them are very sensitive to acids and alkalis. Some iridoid glycosides such as aucubin suffer color modification after chemical or enzymatic hydrolysis they give first a blue to green... 

Francis, F.J., Caramel, brown polyphenols and iridoids, in Colorants, Eagan Press, St. Paul, MN, 83,1999. 

The yellow crocins from gardenia have received some success for the same colorant applications as saffron,37 but the iridoid derivatives have not received the same promotion. The range of colorants available from the same source would seem to make them attractive possibilities. 

FRANCIS, F. J. Caramel, Brown Polyphenols, and Iridoids. Chap. 10 in Colorants, Eagen Press, St. Paul, MN, 1999, pp. 83-8. 

This is the traditional method for alkaloid detection although care should be taken as some nonalkaloids such as iridoids and some flavonoids give a positive reaction Alkaloids give a dark orange-to-red coloration. 

Valepotriatas iridoids from Valeriana and Ken-tranthus spp. Valeriana officinalis contains up to 5 % V., which are responsible for the sedative properties of this drug. Hydroxyl groups on the iridoid structure are esterified with isovaleric acid. Hydrolysis of the esters with HCl causes decomposition of the unstable alcohol moiety with production of a blue color. The most important representative is Valtratum (see). 

Bianco A, Cerichelli G, Guiso M, Lo Baido G, Mazzei RA (1993) Structure of colored compounds formed in a chromatic test of iridoids. Gazz Chim Ital 123 437-440... 

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