ORGANIC ACIDS AND OTHER PRODUCTS 



13 



maximum of citric acid and will have utilized 40 to 50% of the 

 sugar present. This mineral-nutritional relationship is substanti- 

 ated by Butkewitsch and Timofeeva's results (1935) with cultures 

 deprived of phosphorus, sulphur, and nitrogen. 



Several mechanisms have been suggested to account for the 

 formation of citric acid. Butkewitsch and Fedoroff (1929, 1930) 

 and Chrzaszcz and Tiukow (1930, 1930a) maintain that it forms 

 through acetic acid or from acetates of sodium or potassium. For 

 the formation from acetic acid their scheme is: 



COOH 



COOH 



COOH 



COOH 



CH 

 CH, 



3 _h 2 



CH 2 

 CH, 



-H 2 



CH 

 CH 



+H 2 



CH 2 

 CHOH 



COOH 



Acetic acid 



COOH 



Succinic acid 



CH 3 

 + COOH —?* 



Acetic acid 



COOH 



Fumaric acid 



CH 2 • COOH 

 COH • COOH 

 CH 2 • COOH 



Citric acid 



COOH 



Malic acid 



Bernhauer and Siebenauger (1931) have shown that A. niger 

 can convert ethyl alcohol into citric acid. Bernhauer and Bockl 

 (1932) obtained yields of citric acid from alcohol up to 25% of 

 the theoretical amount. They also showed another possible course 

 of formation, in which aconitic acid appears: acetic acid — > suc- 

 cinic acid — > fumaric acid — > aconitic acid -* citric acid. Their 

 proof rests upon experiments in which they grew A. niger on 

 2.4% potassium aconitate and obtained 23.2 to 25.8% citric acid. 



Even more convincing is Kinoshita's [IwanofT and ZwetkofT 

 (1933)] evidence from the growth of A. itaconicns on a sugar 

 solution containing calcium carbonate. Kinoshita got citric acid, 

 which disappeared, and then itaconic acid thus: 



CH 2 (COOH)COH(COOH)CH 2 (COOH) ^> 



Citric acid 



CH 2 (COOH) • C(COOH) : CH(COOH) 



Aconitic acid 



-C0 2 



> CH 2 (COOH)C(:CH 2 )COOH 



Itaconic acid 



