Page 112 - Medicinal Plants_PharmD general

Properties of proteins:
All proteins are insoluble in organic solvent and in alcohol, They are

precipitated by salts of heavy metals and by tannic acid. They are generally
precipitated on heating (60-80oC), by marked change of pH and by high
concentration of mineral salts.

Examination of Aleurone Grains:
The material either in sections or in a powdered form is:

1- Defatted by maceration in a mixture of alcohol and ether.
2- Place the defatted sections or little of the defatted powder in a drop of

alcoholic solution of picric acid, leave for a few min. and wash off the
excess stain with alcohol.
3- Add a drop of alcoholic solution of eosin, then wash well with
alcohol: the crystalloids take a yellow stain, the ground substance
becomes red and the globoids remain colourless.

Chemical Tests for proteins:
1- Millon's reagent (A solution of mercuric nitrate and nitrous acid)

The sample is added to the reagent and heated for two minutes at
95°C; the formation of a red precipitate indicates the presence of protein
in the sample.
2- Biuret test:

A chemical test used for detecting the presence of peptide bonds. In
the presence of peptides, a copper II ion forms violet-colored
coordination complexes in an alkaline solution
N.B. Biuret reagent is made of sodium hydroxide and hydrated copper
sulfate, together with potassium sodium tartrate.

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