In article <199605091644.JAA03346 at net.bio.net>, joyperry at UWCMAIL.UWC.EDU wrote:
> I tried this semi-successfully with a botany class. Used onion skins
> (yellowish-brownish dye from carotenoids, I assume), coffee grounds for
> browns, and beets (anthocyanins change from purple to orange depending upon
> pH). In the fall there would be many composites around with good
> chromoplasts; the flower petals are supposed to be good dye sources.
>
These are nice ideas but I would like to make a correction.
Beets produce betalains rather than anthocyanins. Betalains are
nitrogen-containing compounds and are unrelated to anthocyanins, which are
members of the flavonoid group of compounds. They do they serve the same
function, however. The pigment in beets is betanin, which is a glycoside
composed of glucose and betanidin. Betanidin is derived from amino acid
precursors. (I am using an old reference so the details of synthesis have
probably been worked out in more detail.) Betalains are interesting
compounds because, in angiosperms, they are found only in the
Caryophyllales (Centrospermae), with the exception of the Caryophyllaceae
and Molluginaceae, which produce anthocyanins.
