anthocyanins

john markwell markwell at unlinfo.unl.edu
Wed Feb 14 08:41:22 EST 1996


bae at oci.utoronto.ca (Beverly Erlebacher) writes:

>In article <4fdjsn$je0 at ixnews7.ix.netcom.com> clanks at ix.netcom.com (John Clancy ) writes:
>>i'm doing a phase two of a science fair project on anthocyanins, a
>>flavonoid found in roses, red cabbge and african violets.  i read that
>>they can change the plant's color when subjected to acids or bases, but
>>my results last year were inconclusive...this year, i'm doing a better
>>job, but i really don't have enough data on anthocyanins; i guess
>>they're pretty obscure.
>>if anyone can help me i'd really appreciate it.

>Many purple pigments in plants are anthocyanins.  In general, they
>are more red in acid solutions, and blue in basic solutions.  You
>can observe this for yourself by taking some water from cooking 
>red cabbage or beets, and observe the color change when you add
>vinegar or baking soda.

Actually, it is a little more complex than that.  Red cabbage and many
flowers and leaves do contain anthocyanins.  THey generally are red or
blue below pH 4 and will be colorless around pH 5 to 7 and at higher 
pH values (more basic) will turn blue and then fade.  Beets (beet 
root) contains a betalain or betacyanin that does not change color 
with these pH changes.

>To change the color of the plant (or its flowers), you will have to
>change the pH of the solution the anthocyanins are in within the plant
>cell.  This may well kill the plant!

The anthocyanins in plant cells are usually in the vacuole of the 
cell.  THis has a low pH, thus permitting the color.  Cells themselves
(the cytoplasm) must remain neutral, near pH 7.  If you change the pH 
inside a cell, the cell will die.

>It might be an interesting and attractive science fair project to extract
>anthocyanins from several different plants, and use paper chromatography
>to determine how many different bands different plants show, which are the
>same or different between different species, and at what pH different forms
>of anthocyanin show color change.  You could even make up a pH test kit
>using extracts from various plants.

I can provide some ideas for experiments and demos with anthocyanins. 
Why not email me and let me know what grade you are in.

My email address is markwell at unl.edu



>You may want to use alcohol to extract the anthocyanins.  Some good sources
>are beets, red cabbage, red forms of coleus and red-leaved forms of other
>ornamental plants.

You will need to add a small amount of acid to the alcohol.

>The original work that led to the development of chromatography was done
>by a woman in England who was interested in flower pigments.  She separated
>them on long pieces of paper suspended over a stairwell.  The chemists who
>developed chromatography received a Nobel prize for their work in the 1950's.

Actually, chromatography was invented about 1900 by M.S. Tswett to 
separate the chlorophylls from leaves for chemical analyses.  He did 
not receive the Nobel Prize.


>Beverly Erlebacher
>Toronto, Ontario Canada
--
John Markwell			Phone: 402-472-2924
Dept. Biochemistry		FAX:   402-472-7842
University of Nebraska		Internet: markwell at unl.edu
Lincoln, NE  68588-0664



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