June 21,1924 
Quercetin from Apple Peels 
1245 
deep red color which rapidly changed to brown. Quercitrin, a monorhamnoside 
of quercetin, under the same conditions yielded a less bright red color than 
quercetin. It was shown that the brown pigment developed at the expense of 
flavonol or its glucoside in solution. These results with quercetin or its glucoside 
and oxidase suggest that the brown pigment appearing in scalded apple peels may 
be produced by interaction in the tissues of quercetin and oxidase which are nor¬ 
mally present in the skin. The observation that brown discoloration *of scalded 
peels is more prevalent on the greener portions lends support to the possibility of 
quercetin or its glucoside being the parent substance of the brown pigment. The 
bright-red areas are highly resistant to scald and there is reason for believing that 
flavonol occurs in smaller quantities in these localities because of its conversion 
into red or anthocyanic pigment. 
It should be borne in mind, however, that other substances in the apple may 
play a part in the formation under certain conditions of brown or reddish brown 
color. According to Overholser and Cruess 7 the darkening of cut surfaces of 
apple tissue may be due to the oxidation of a tannin-like substance. It is interest¬ 
ing to note in this connection that flavonols and tannins are built up of similar 
nuclei and hence may yield closely related brown products on oxidation. 
SUMMARY AND CONCLUSIONS 
(1) One of the first indications of scald in apples is the appearance on the greener 
portions of the fruit of a typical brown discoloration. A possible relation between 
the suspected occurrence of a flavonol pigment in the skin and scald led to the 
isolation and identification of this pigment. 
(2) The particular flavonol coloring matter, which was found to occur in 
McIntosh apple peels, proved to be quercetin, Ci 5 H 10 O 7 . It was identified by 
means of its penta-acetyl derivative and by combustion of the purified pigment 
itself. 
(3) It is suggested, as a basis for further investigation, that quercetin, or its 
glucoside which has not been isolated, may be the chromogenic substance which 
is responsible for the formation of brown pigment in the peels of scalded apples. 
i Overholser, E. L., and Cruess, W. V. A study of the darkening of apple tissue. Calif. Agr. 
Exp. Sta. Tech. Paper 7: 40 p. 1923. 
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