xv, 5 Perkins: Rancidity of Coconut Oil 473 



Od and 6 01 show a combined effect of increased initial acidity 

 and nonfatty material which is noticeable. 



CONCLUSIONS 



Modifying somewhat the conceptions of rancidity outlined at 

 the beginning of this article I submit the following conclusions : 



In the type of rancidity of coconut oil studied the first stage 

 is a hydrolysis, the rapidity of which varies with the initial 

 acidity and the amount of moisture present. Exclusive of any 

 mold action, this hydrolysis may be somewhat accelerated by the 

 action of air, light, and a fat-soluble enzyme. 



The second stage of rancidity is an oxidation of the free 

 fatty acids. Possibly this involves also the oxidation of un- 

 hydrolyzed olein, but the amount of oxidation is dependent on 

 the amount of hydrolysis. 



The oxidation is hastened by light and moisture, but light is 

 not a necessary condition. 



CHEMICAL METHODS FOR THE MEASUREMENT OF RANCIDITY 



The above conclusions are restricted to the type of rancidity 

 studied. Though this appears to be the common type in co- 

 conut oil, the possibility of others is not excluded. Walker :i 

 describes a "peculiar, pungent, 'strong' odor in otherwise pure 

 oils." I have also observed peculiar odors which the remnants 

 of samples 3 Sd and 5 Sd, not used for analysis, developed 

 during storage for several weeks in a very damp refrigerator. 

 Sample 5 Sd, which developed an odor resembling Roquefort 

 cheese, was found to contain a slight growth of mold, identified 

 by Dr. H. S. Yates, of the Bureau of Science, as a species of 

 Torula. No microorganism was found in sample 3 Sd, but it 

 developed a peculiar, acrid odor. When both of these odors 

 had become readily noticeable little or no change could be 

 found in the oxidizability value, fuchsine aldehyde test, or iodine 

 number. The acidity of 3 Sd was 0.87, and that of 5 Sd, 0.95 

 per cent, only 0.08 and 0.07, respectively, higher than the values 

 previously found. 



Such peculiar types of rancidity indicate that a single chem- 

 ical test cannot be expected to enable one to distinguish between 

 edible and nonedible coconut oils. In the ordinary type of ran- 

 cidity, however, occurring under the conditions of our inves- 

 tigation, it appears that the decrease in iodine value, the fuchsine 

 aldehyde test, and the oxidizability number give good indica- 



21 Walker, H. S., Philip. Journ. Sci. 1 (1906) 139. 



