JOiNAL (IF AllfllLTOAL RESEARCH 
Vol. XXVI Washington, D. C., November 24, 1923 No. 8 
COMPOUNDS DEVELOPED IN RANCID FATS, WITH 
OBSERVATIONS ON THE MECHANISM OF THEIR FOR¬ 
MATION 1 
By Wilmer C. Powick 
Biochemist , Biochemic Division , Bureau of Animal Industry, United States Department 
of Agriculture 
INTRODUCTION 
The term “rancidity” is used to denote a certain type of change or 
spoilage in fats and oils that is characterized by a distinctive disagreeable 
odor and taste. While the term is sometimes used to describe the changes 
wrought by bacteria and fungi in such products as butter, it will be lim¬ 
ited in this paper to spoilage that may occur in purified fats under condi¬ 
tions precluding the action of biological agents. It will be distinguished 
further from the condition of acidity, which is llot necessarily associated 
with an objectionable odor and taste and which is developed by a fairly 
well understood mechanism. 
Previous investigators (5; 10; 20; 24 ., p. 52; 32; 36) studying the chem¬ 
istry of rancidity have concluded that this condition results through 
the oxidation of fats by atmospheric oxygen in the presence of light or 
of certain metals as catalysts. While lie mechanism of this action is 
far from being clear, some of the products formed during the develop¬ 
ment of rancidity have been characterized. 
Thus, azelaic acid (27) and most of the saturated acids and aldehydes, 
from acetic up to nonylic (57), have been recovered from certain speci¬ 
mens of rancid fats and adequately identified, and at least one inves¬ 
tigator (57) has held heptylic aldehyde to be responsible for the rancid 
odor. The presence of acrolein (5) and of glyceric aldehyde (40) in rancid 
fats has also been a matter of occasional speculation, but no satisfactory 
evidence on this point has been advanced. While the data available do 
not relate to a sufficient variety of samples, perhaps, to justify the con¬ 
clusion that any one of these compounds is a constituent of every rancid 
fat, it is a matter of common knowledge that qualitative tests indicate 
that the aldehyde group is regularly present, as is also the peroxid group. 
Determinations of acetyl values (5, 13 ), also, have indicated the gradual 
formation of hydroxy compounds during the development of rancidity, 
while other evidence (14) points to the formation of polymerization 
products. If we add to the foregoing the fact that there seems to be 
little room for doubt that in the development of rancidity the point of 
1 Accepted for publication June 35, 1933. This is the second of a series of "Studies on Rancidity." (10).* 
* Reference is made by number (italic) to "Literature cited," p. 360-362. 
Journal of Agricultural Reaearch, 
Washington, D. C. 
ah t 
Vol. XXVI, No. 8 
Nov. 24, 1923 
Key No. A-66 
60379-24-1 
(323) 
