226 BIOLOGICAL ACTIVITIES OF MOLDS 



details of the processes, the reader is referred to the publications of 

 the Northern Regional Research Laboratory investigators. 



Miscellaneous Minor Fermentations. Gallic Acid. The produc- 

 tion of citric and gluconic acids depends on fermentative changes 

 brought about by molds. However, the production of gallic acid de- 

 pends on a hydrolytic change, the hydrolysis of tannin. Scheele in 

 1787 first discovered gallic acid in an infusion of gallnuts which 

 had been acted upon by a mold, but Van Tieghem *'^ carried out the 

 first real investigation of this hydrolysis. He demonstrated that 

 gallnut extract made and kept sterile would not form gallic acid. 

 However, on growth of the Aspergillis niger and Penicillium glaucum 

 groups of molds, the acid was produced. Later workers showed that 

 molds of A. niger group produced an extracellular enzyme, tannase, 

 which was capable of hydrolyzing tannin to gallic acid. 



Calmette ® has patented a method whereby the clear tannin ex- 

 tract is placed in vats and sterilized, inoculated with "A. gallomyces," 

 and the fermentation allowed to proceed. Agitation and introduction 

 of large volumes of sterile air keep the organism submerged. 



FuMARic Acid. This unsaturated dicarboxylic acid was first re- 

 ported to be produced by molds by Ehrlich ^^ in 1911. Whereas 

 certain species of the genera Mucor, Circinella, Cunninghamella, 

 Penicillium, and Aspergillus produce small amounts of fumaric acid, 

 strains of Rhizopus nigricans form large amounts of this acid. The 

 nutrient solution used is a salt-glucose medium in which the carbo- 

 hydrate-nitrogen ratio is, for highest yields, kept at a range between 

 25 : 1 and 300 : 1. Waksman,*'^ who has patented a commercial process 

 for the production of fumaric acid, found that the addition of zinc 

 may modify these conditions. Thus the zinc and also the iron (which 

 displays an antagonistic effect to zinc) contents must be rigidly con- 

 trolled. The zinc seems to stimulate the mycelial growth of the mold 

 at the expense of fumaric acid production whereas the latter has the 

 reverse effect. He also found that the most favorable sources of 

 nitrogen were salts of ammonia. The optimum temperature for the 

 development of mycelium is 35° C. and the fermentation is best 

 carried out at about 28°. Once the desired level of mycelial growth 

 has been attained, the nutrient solution may be drained off and fresh 

 liquor added in which the fermentation proceeds. This fresh liquor 

 may be a 20 per cent pure sugar solution devoid of salts and other 

 nutrients. 



Kojic Acid. This acid is of academic interest only, at the present 

 time. It was isolated by Saito ^^ in 1907 and studied and its con- 

 stitution established by Yabuta ^* in 1924. Its chemical structure is 



