Apr. 24, 1916 



Effect of Pasteurization on Mold Spores 



157 



A study of Table I shows that very few mold spores survive exposure 

 to 140° F. (60° C.) in milk for 30 minutes and that at 145° F. (62.8° C.) 

 still fewer are found. With reference to significant organisms, among 

 the mucors the Mucor racemosus group (3513, 3523.6, 3560) and 

 Rhizopus nigricans, which are found more frequently than all others of 

 this group combined, were destroyed at 130° F. (54.5° C). The common 

 green species of Penicillium are mostly dead at 130° F. (54.5° C); a 

 few stand 135° F. (57.2° C), but two, one of them an undescribed soil 

 organism, survived 140° F. (60° C.) for 30 minutes. Among species of 

 Aspergillus, however, the strains of A. flavus, A. fumigaius, and A. repens 

 all survived 145° F. (62.8° C.) for 30 minutes; A. repens and A. fumigatus 

 both survived 150*^ F. (65.6° C). These three species are always found in 

 forage and feeding stuffs; hence, milk is more or less subject to contamina- 

 tion with them. A. repens grows 

 very poorly in milk, however, and 

 the examination of a great many 

 cultures of milk and its products has 

 shown that the actual development 

 of A . flavus and A . fumigatus is com- 

 paratively rare. Although these 

 organisms grow at blood heat and 

 have demonstrated their pathogen- 

 icity even to human beings at rare 

 intervals as causes of disease in the 

 lungs, there is no report of their 

 growth in the alimentary canal. 



The destruction of mold spores by 

 the holder process of pasteurization 

 is shown more clearly in figure i, 

 where the results have been plotted. 



Pasteurization of milk at 145° F. (62.8° C.) may therefore be regarded 

 as destroying mold spores completely enough to render them a negligible 

 factor in the further changes found in the milk. 



EXPERIMENTS WITH THE FLASH PROCESS OF PASTEURIZATION 



In working with continuous pasteurizers, temperatures of 165° to 175° 

 F. (73-9° to 79.5° C.) are reached by heating within a period of approxi- 

 mately 30 seconds and maintained about 30 seconds. This is followed 

 by quick cooling. Tower temperatures have not been deemed satisfactory. 

 A series of experiments was therefore planned to subject the freshly inocu- 

 lated spores of species of Penicillium, Aspergillus, and of themucors to these 

 temperatures and to determine their relative ability to survive such heat- 

 ing. For this purpose glass tubing about 3 mm. in diameter was drawn 

 into capillary form so that each tube had 3 01 4 inches of the original tub- 



'• ^ 5^'^ ;P^ S^- ISJ^ S^ IS'*^. ?^ 



Pig. I. — Curve of the number of species of molds 

 surviving pasteurization of milk for 30 minutes 

 at a series of temperatures. 



