THE ISOLATION AND IDENTIFICATION OF QUERCETIN 
FROM APPLE PEELS 1 
By Charles E. Sando 
Chemist , Office of Physiological and Fermentation Investigtions, Bureau of Plant 
Industry , United States Department of Agriculture 2 
Some time ago the writer's interest in possible relations between chemical con¬ 
stituents of the apple and storage scald in this fruit led to an investigation of the 
nonvolatile waxlike substances covering the epidermis. 8 This work has been 
extended to include a study of the yellow flavonol pigment which occurs in apple 
peels. The present paper deals with the isolation of the pigment and with its 
identification as quercetin, a widely distributed member of the flavonol group. 
The isolation of quercetin has previously been reported from apple bark, 4 but 
no mention has hitherto been made of its occurrence in the peel of the fruit. 
PREPARATION OF QUERCETIN 
The material employed in this work consisted of peels of the McIntosh apple. 
It was obtained as a by-product in the investigations of Power and Chesnut 5 on 
the odorous constituents of apples. In their work, the fresh parings were sub¬ 
jected to distillation in a current of steam. The residue from the steam-distilla¬ 
tion was used for the preparation of the flavonol. On account of this treatment 
and the necessity of prolonged extraction with alcohol, in the presence of malic 
acid contained in the parings, the glucoside of the flavonol was not obtained. 
The wet peels after steam distillation were carefully dried and coarsely ground 
for purposes of extraction. The extractions were carried out by using a con¬ 
tinuous extraction apparatus based on the Soxhlet principle. With this appa¬ 
ratus it was possible to extract about 1 kgm. of material at each loading. The 
dried material was first extracted separately with petroleum ether and ether in 
order to remove chlorophyll, carotinoids, and waxlike substances. These ex¬ 
tractions were followed by the use of 95 per cent alcohol, which dissolved the 
coloring matter. The extraction with alcohol was continued for several weeks 
before the last traces of flavonol pigment were removed from the peels. After 
evaporation to eliminate the greater portion of alcohol, hot water was added to 
the syrupy residue. The liquid, upon the addition of neutral lead acetate solu¬ 
tion yielded a precipitate which contained very little of the pigment. The lead 
precipitate was filtered off by means of a Buchner funnel and then basic lead ace¬ 
tate solution added to the filtrate. The basic lead acetate precipitate, which 
contained most of the coloring matter, was separated by filtration and decom¬ 
posed by boiling with 5 per cent sulphuric acid. After removal of lead sulphate 
and cooling, the acid solution was repeatedly shaken with ether in a separatory 
funnel. Evaporation of the ethereal liquid left a residue consisting of crude 
i Received for publication May 21,1924—issued Nov., 1924. 
a In connection with this work thanks are given to Dr. Frederick B. Power for his kindness in supplying 
the material employed. 
1 Sando, C. E. Constituents of the wax-like coating on the surface of the apple. Jour. Biol. 
Chem. 56: 457-468. 1923. 
4 Rochleder, F. Quercitrin and quercetin. Jahresber. Fortschr. Chem. 1867: 731-732. 1869. 
» Power, F. B., and Chesnut, V. K. The odorous constituents of apples. II. Evidence of the 
presence of geraniol. Jour. Amer'. Chem. Soc. 44: 2938-2942. 1922. 
Journal of Agricultural Research, 
Washington, D. C. 
(1243) 
Vol. XXVIII, No. 12 
June 21,1924 
Key No. G-485 
