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From: (J.R. Pelmont)
Newsgroups: de.sci.chemie,sci.chem,sci.chem.analytical
Subject: Re: red cabbage color
Date: Mon, 3 May 1999 16:36:18 +0200

crs <> wrote :

> Hans de Brouwer wrote:
> > Does anyone have information on the structure
> > or formula of the compound that causes the red color
> > in red cabbage?
> Hi Hans,
> Red cabbage contains a pigment called flavin, which is also found in blue
> cornflowers, grapes, red poppies and apple skin. Depending on the pH of
> the fruit or plant the pigment will give a different color. As others have
> noted, this material is an indicator of pH.
> Flavin is usually bound to some other molecule such as a sugar.  When it
> is bound to ribose, the sugar that's part of the structure of DNA, the
> compound is called "riboflavin," otherwise known as vitamin B2.  Since the
> caretakers of sci.chem (who do pro bono work on the FAQs and so on - give
> 'em credit) and the vigilante flamers (who don't) do not want chemical
> structures displayed here (Imagine that.) you will have to go to the
> following web site to see the structure of riboflavin:
> Flavin compounds, in addition to being pH indicators are also partners in
> various two electron REDOX reactions in biochemistry.  ....(SNIP)

The color of red cabbage is likely to be due to a flavonoid, not flavin.
This is a completely different stuff.

Flavins in living systems are aracterized by a three-ring nucleus
corresponding to isoalloxazin. They are redox cofactors indeed, usually
yellow in the oxidized state (flavus in latin means yellow).

I have no data about red cabbage, but the red color is likely to be due
to a flavonoid or alike.

Flavonoid pigments are water-soluble phenolic glycosides having in
common a basic structural unit, i.e. the C15 skeleton of flavone.
Nothing to do with flavins. To flavonoid group belong the anthocyanins.
They are, other than the chlorophylls, the most important group of
coloring matters in higher plants. Other pigments are carotenoids, red
or yellow (the color of tomatoes is due to one carotenoid, I forgot the
name of). The color of ripening fruit is most often due to carotenoids
and xanthophylls. Finally, some pigments are transient products of
chlorophyll degradation.

There is more than one hundred different flavonoid aglycons in plants
(the compounds without attached sugars), with colors from magenta,
orange red, to pink, ivory, .... Some are commonly known : pelargonidin,
peonidin, malvidin, quercetin, luteolin and so on. Some are flavones,
other flavonols. Some flavonols are quite common in leaves : kaempferol,
quercetin and myricetin. There are various hydroxylation patterns in
flavonoids (with possibilities of protonation and proton removal with
pH), and methylations. The color of Rhododendron flowers is due to a
methylated form of quercetin (azaleatin).

The red color of beet roots and the flowers of some cacti is due to a
variant structure, betanin, a betacyanin (with nitrogen atoms in it).
After eating a beet salad, we excrete some of it as a pinkish pigment
through kidneys.

Many of these compounds are easily separated by thin layer
chromatography (here used formely in practical teaching work). It may be
some fun to separate them, but they are sometimes readily oxidized by
air. The color is often sensitive to pH and solvent composition. The
property of being a Ph-indicator does not belong to a particular group
of substances among these pigments.

Please try to confirm if red cabbage gets its color from a flavonoid. I
would be surprised if not so. In my opinion flavins per se should be
ruled out (although they have to be there as in any ordinary cell).

Hoping it will help, best regards

J. Pelmont, Biochimie
Univ. Grenoble I

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