joim OF AGrtrmL re 



Vol. XXII Washington, D. C, October 22, 1921 xM'^j^^ 4 



FLORA OF CORN MEAL '^ >".:-.*. 



By Charles Thom, Mycologist in Charge, and Edwin LeFevre, Scientific Assistant, 

 Microbiological Laboratory, Bureau of Chemistry, United States Department of Agri- 

 culture 



INTRODUCTION 



Corn meal as it comes from the mill carries the mycelia of certain fungi 

 which infect unground grain. In addition, numerous species of molds 

 and bacteria, present in spore form as contaminations upon the surfaces 

 of sound kernels or as saprophytes in partially spoiled grains, are recov- 

 erable by routine cultural examination of the finished meal. Many 

 experiments, extending over several years and including the work of vari- 

 ous members of the Microbiological Laboratory, show that certain groups 

 of organisms are practically always abundant in such cultures. Other 

 species are usually present, but in smaller numbers, and many forms are 

 obtained occasionally as accidental contaminations. In undertaking to 

 study this complex flora, it may be possible to determine by routine cul- 

 ture the species represented and something of their relative abundance in 

 the sample, but the list so obtained gives little information as to the 

 relative importance of the individual species as causes of spoilage in the 

 product. 



The culture media commonly used in such routine examination of food- 

 stuffs present conditions for the growth of microorganisms which differ 

 greatly from those found in corn meal. The nutrients used in preparing 

 such media are selected because they are readily assimilable to most 

 organisms. These nutrients appear in solution or in jelly-like masses 

 which contain high percentages of moisture. Corn meal, on the other 

 hand, presents a range of composition, according to Winton and his 

 associates {8),^ approximately as follows: Moisture, 10 to 18 per cent, 

 but under usual commercial practices ranging from 12 to 15 per cent; 

 protein, 5 to 10 per cent; fat, i to 5 per cent, according to the method of 

 milling; nitrogen-free extract, including starch and sugar, 68 to 78 per 

 cent. Of the nitrogen-free extract, sugars constitute perhaps 3 per 

 cent, and gums and dextrin, some of which are readily fermentable,, 

 perhaps an equal quantity. In dealing with this product as a substratum 

 for organisms, the percentage of water found is an important limiting 



I Reference is made by number (italic) to " lyiterature cited," p. i88. 



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



Washington, D. C. Oct. 22, 1921 



aab Key No. E-16 



(179) 



