1244 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
coloring matter which weighed 2.45 gm. in the air-dried state. This quantity 
of impure pigment was obtained from 68.6 kgm. of fresh skins, which represented 
545.7 kgm. of whole apples. After purification of the crude material only about 
0.5 gm. of pure pigment remained. 
IDENTIFICATION OF QUERCETIN 
Acetylization of the unidentified substance was carried out by boiling the 
impure pigment with anhydrous sodium acetate and acetic anhydride. The 
reaction mixture was poured into water and set aside over night. The product 
thus obtained, after several recrystallizations from 70 per cent alcohol, amounted 
to 1.15 gm. It consisted of a feltlike mass of colorless needles which melted at 
194° to 196° C. When the substance was mixed with pure authentic penta- 
acetylquercetin its melting point was not altered. The substance was thus iden¬ 
tified as penta-acetylquercetin. Combustion of the anhydrous compound dried 
at 160° confirmed this conclusion. 
0.1489 gm. gave 0.3196 gm. CO 2 and 0.0531 gm. H 2 0. 
Found: C = 58.53, H - 3.99. 
Acetylquercetin, Ci 5 H 5 07 (C 2 H 30 ) 5 , requires: C = 58.57, H=3.93. 
From the penta-acetylquercetin the free pigment was regenerated by hydroly¬ 
sis with a few drops of sulphuric acid in glacial acetic acid. After boiling a few 
minutes, the mixture was well diluted with water and set aside in the ice box for 
several days. The insoluble compound was collected in a weighed Gooch crucible 
and dried at 130°. 
0.8436 gm. gave 0.4984 gm. recovered pigment. 
Found: Pigment = 59.08. 
Acetylquercetin, CisHsCMQjHsO^, requires: C 15 H 10 O 7 = 58.98. 
The substance obtained by regeneration from its acetyl derivative responded 
to all the tests of pure quercetin. Crystallized from dilute alcohol, it formed 
a glistening mass of yellow needles which were almost insoluble in water, but 
readily soluble in alcohol. Solution in dilute alkalies intensified the yellow color. 
With alcoholic ferric chloride it gave a dark-green color. When reduced in alco¬ 
holic solution with magnesium ribbon and hydrochloric acid it developed a 
characteristic bright red anthocyanic color. Analysis of the substance, dried at 
130°, showed that it agreed in composition with quercetin. 
0.1559 gm. gave 0.3399 gm. C0 2 and 0.0466 gm. H 2 0 
0.1325 gm. gave 0.2891 gm. C0 2 and 0.0379 gm. H 2 0 
Found: C =59.46, 59.50; H=3.35, 3.21 
Quercetin, Ci 5 H 10 O 7 , requires: C =59.59, H=3.34. 
DISCUSSION 
There is some reason for assuming that quercetin in apple peels may be the 
chromogenic substance which is responsible for the formation of brown pigment 
of scalded apples. The investigations of Nagai 6 have shown that the color of 
aqueous or alcoholic extracts of numerous plant tissues rich in flavones changes to 
brown or reddish-brown when the extracts are treated with freshly prepared plant 
juice containing oxidizing enzyms. This color transformation is attributed to 
the oxidation of certain flavone and flavonol pigments or their glucosides and in 
accordance with this view Nagai has shown that chemically pure preparations of 
the pigments themselves yield brownish colors by the action of enzyms. For 
example, the addition of oxidase to quercetin resulted in the development of a 
e Nagai, I. A genetico-physiological study on the formation of anthocyanin and brown pig¬ 
ments in plants. Jour. Col. Agr. Imp. Univ. Tokyo 8:1-92, illus. 1921. 
