ACID PRODUCTION BY RHIZOPUS TRITICI IN DECAY¬ 
ING SWEET POTATOES 1 
By H. A. Edson 
Pathologist , Office of Cotton , Truck , and Forage Crop Disease Investigations , Bureau of 
Plant Industry , United States Department of Agriculture 
INTRODUCTION 
Weimer and Harter 2 have recently shown that the carbohydrate 
losses from sweet potatoes undergoing decay by Rhizopus tritici Saito. 
exceed the weight of carbon dioxid evolved, and that the difference is 
considerably greater than the probable amount utilized in the construc¬ 
tion of fungous tissue. They report an increase in the hydrogen-ion 
concentration of the juices of the decayed material, and indicate the 
probability of alcohol formation. They conclude: 
That acids are produced in considerable abundance seems quite evident, and that 
alcohol is formed seems probable. The carbohydrates required for the manufacture 
of acids and alcohol together with that utilized directly in the production of fungous 
material will probably account to a large extent for the decrease in the sugars and 
starch which are not accounted for by the C 0 2 evolved. 
In the hope of securing additional information regarding the carbo¬ 
hydrate changes involved, particularly the identity of the acid or acids 
produced, the present writer, working with material courteously sup¬ 
plied by Weimer and Harter, has carried on certain additional experi¬ 
ments. The results, which are here presented, are confirmatory and 
show that the principal products of the fermentation are ethyl alcohol 
and acetic acid, but that formic acid, a trace of butyric acid, acetone, 
an unidentified aldehyde, and traces of at least two nonvolatile acids, one 
of which is lactic and the other probably succinic, are produced, and 
that a small amount of ammonia appears among the nitrogenous decom¬ 
position products. 
EXPERIMENTAL WORK 
The decayed sweet potatoes employed resulted in most instances from 
artificial inoculation with R. tritici , but in a few cases the decay resulted 
from natural infection. Some tests were made in the early stages of 
decay while it was incomplete but actively progressing. In these cases 
only the softened portions of the tubers were employed. Most of the 
tests were made on material which had undergone complete decay in 
moist chambers in the incubator at 30° C. after which they were held 
for a period which varied from 1 or 2 to 18 or 20 days. 
The results were substantially identical in all cases. For each trial 
about 10 tubers were placed in cotton cloth and subjected to heavy pres- 
1 Accepted for publication Mar. 15, 1923. 
2 Weimer, J. L., and Harter, L. L. respiration and carbohydrate changes produced in sweet 
potatoes by rhizopus tritici. In Jour. Agr. Research, v. 21, p. 627-635. 1921. Literature cited, 
634-635. 
Journal of Agricultural Research, 
Washington, D. C. 
afj 
(9) 
Vol. XXV, No. 1 
July 7, 1923 
Key No. G-317 
