ACETONE-BUTANOL FERMENTATION 



143 



In the commercial process the raw fermentation substrate 

 is usually maize meal, and the organism attacks the starch of 

 maize meal by the production of two extracellular enzymes, 

 one of which is an amylase which breaks the starch down to 

 maltose, and the other is a maltase which hydrolyses the 

 maltose to glucose. The fermentation of glucose by CI. 

 acetobutylicum gives rise to the formation of hydrogen, carbon 

 dioxide, acetic and butyric acids, ethyl and butyl alcohols, 

 and acetone; the fermentation of pyruvic acid gives rise 

 mainly to hydrogen, carbon dioxide, and acetic acid, with traces 

 of butyric acid, ethyl alcohol, and acetone. The proportions 

 in the two cases are given in Table XIII, where the results are 

 expressed as molecules of product per mol. glucose or two 

 mols. pyruvic acid (equivalent to 1 mol. glucose) fermented. 



TABLE XIII 

 Products of CI. acetobutylicum Fermentation 



Investigations of this fermentation have been concerned 

 mainly with the production of the commercially valuable 

 substances, acetone and butyl alcohol. If the formation of 

 the various products is followed at intervals during growth in 

 a glucose-containing medium, then we find that the appearance 

 of these substances varies with the time as shown in Fig. 11. 



In the early stages of growth, while the ^H is falling rapidly, 

 acetic and butyric acids are formed together with hydrogen 

 and carbon dioxide, but no acetone or butyl alcohol. Later in 



