216 BIOLOGICAL ACTIVITIES OF MOLDS 



On the other hand, Lewis and Yesair ^- found humidity had little 

 effect on the growth of mold on Frankfurter sausages, probably be- 

 cause the substrate contained sufficient moisture. 



There are probably very few, if any, strictly anaerobic molds, and 

 the great majority are strictly aerobic. However, a few species, 

 notably some of the Mucors and certain strains of the Penicillia may 

 grow to some extent under reduced oxygen tension. The organism 

 used in ripening Roquefort cheese, Penicillium roqueforti, can de- 

 velop with less oxygen than is required by most molds. Williams, 

 Cameron, and Williams " have reported the isolation of two strains 

 of "facultatively anaerobic mold of unusual heat resistance." These 

 organisms were identified as strains of an undescribed species of 

 Penicillium by Thom. They proved to be capable of growing in 

 high vacuum. 



The different species of molds vary markedly in their temperature 

 requirements. See Chapter III. In general it may be stated that 

 the optimum temperature for most species lies somewhere near 30° C. 

 Some growth will take place at temperatures considerably below 

 this, and most forms may grow somewhat at temperatures up to 

 37° C. or even higher. Most species of Penicillium have their opti- 

 mum temperature between 20° and 25° C. and may fail to grow 

 at temperatures above 30° C. On the other hand, w^th many species 

 of Aspergillus the optimum temperature will be around 35° C. One 

 species pathogenic for birds {Aspergillus fumigatus) finds its opti- 

 mum at 40° C. The thermal death points also vary markedly with 

 the species. Some types of spores are of course much more resistant 

 than vegetative mycelium but not nearly so resistant as the spores of 

 bacteria. Thom and Ayres ^* have studied the heat resistance of 

 mold spores with regard to pasteurization of milk. A temperature 

 of 62.8° C. for 30 minutes was sufficient to destroy practically all. 

 Macy, Coulter, and Combs ^^ likewise found molds easily destroyed 

 by pasteurization processes. Flashing for 30 seconds at a tempera- 

 ture of 73.9° to 79.4° C. was necessary to obtain an equal degree of 

 sterilization. Lewis and Yesair found that 60° C. for 5 minutes was 

 sufficient to kill all the molds from meat products which they studied. 

 With dry heat, of course, higher temperatures are required. One of 

 the strains of the facultatively anaerobic penicillia referred to previ- 

 ously, described by Williams and coworkers, produces sclerotia of 

 unusually high resistance to heat. 



