EFFECT OF PASTEURIZATION ON MOLD SPORES 



By Charles Thom, Mycologist, Bureau of Cfiemtstry, and S. Henry Ayers, Bacteri- 

 ologist, Bureau of Animal Industry 



INTRODUCTION 



Definite experiments to determine whether spores of the common sapro- 

 phytic molds sur\'ive the temperatures used for the pasteurization of 

 milk have not been reported. These spores are certainly present and are 

 frequently abundant in ordinary market milk. Vague and general state- 

 ments that such organisms do or do not survive are not uncommon, but 

 are not supported by reference to actual work. To obtain such data 

 studies were made with spores from pure cultures of a series of molds in- 

 cluding several species of Penicillium, Aspergillus, and of the mucors, 

 with, in some experiments, the addition of Oidium (Oospora) lactis and 

 one strain of Fusarium. These sets of experiments were made to test, 

 as carefully as laboratory conditions would permit, the temperatures used 

 in pasteurization by the "holder" process, those used in the "flash" 

 process, and the effects of dry heat. 



EXPERIMENTS WITH THE HOLDER PROCESS OF PASTEURIZATION 



Bacteriological studies of milk treated by the holder process have fixed 

 the temperatures between 140° and 145° F. (60° to 62.8° C), main- 

 tained for 30 minutes, as the minimum heating for the destruction of 

 pathogenic organisms which may be found in milk. Although certain 

 bacteria survive this heating it has been found that milk so treated is free 

 from the ordinary disease-producing organisms, safe for consumption, 

 unchanged in taste, and low enough in acid organisms to be handled with- 

 without souring too quickly. 



To study the effect of this process of pasteurization on mold spores, 

 conidia from pure cultures of molds were first transferred to tubes of 

 sterile water to obtain a suspension of spores. Transfers from such a 

 suspension reduce the danger of such spores being blown by air currents 

 into the cotton plugs and upon the walls of the test tubes used, where 

 they might escape the full temperature applied to the milk. In the first 

 series the inoculations were made by transferring i c. c. of this suspension 

 in sterile pipettes into duplicate tubes of sterile milk. In a later series a 

 platinum loop was used, since the tendency of the conidia to float thickly 

 upon the surface of the water made this a quick and effective method of 

 handling them. For most species it was thus possible to transfer spores 

 enough to make a visible film over a part of the surface of the milk. None 



Journal of Agricultural Research, Vol. VI, No. 4 



Dept. of Agriculture, Washington, D. C. Apr. 24, 1916 



dh A — 20 



(153) 



