344 BIOLOGICAL ACTIVITIES OF YEASTS 



A few years before World War I, Neuberg and his associates in 

 Germany, in attempts to elucidate the mechanism of ethyl alcohol 

 fermentation by yeast, noted an appreciable increase in the amount 

 of glycerol produced on the addition of sodium sulphite to the fer- 

 menting mash. In effect, an addition compound of acetaldehyde 

 and sodium bisulphite had been formed in accordance with the fol- 

 lowing reactions. 



NazSOs + H2O + CO2 ^ NaHSOa + NaHCOs 

 CH3CHO + NaHSOs -> CHsCHOHSOsNa 



Na2S03 + CH3CHO + H2O + CO2 -^ CHsCHO-HSOgNa + NaHCOs 



This rendered the acetaldehyde unavailable for serving as the hy- 

 drogen acceptor for H2-DPN. 



This was the basis for the Connstein and Ludecke (sulphite) 

 process ^^ developed in Germany. Beet sugar was used as the source 

 of the sugar. Top yeast was found to be more resistant to sodium 

 sulphite and hence more suited for this process. The more sodium 

 sulphite added, the greater was the yield of glycerol and the smaller 

 the yield of alcohol. Alcohol and acetaldehyde were removed by 

 distillation and the excess sulphite precipitated out as the calcium 

 salt. Glycerol was obtained by distillation under partial vacuum. 



The Cocking-Lilly (sulphite-bisulphite) process developed in Eng- 

 land is a modification of the foregoing process. Aqueous solutions 

 of a mixture of sodium sulphite and sodium bisulphite are periodically 

 added to the fermenting mash. Inasmuch as sodium bisulphite dis- 

 plays inhibitory properties,, the proportion of this salt to sodium 

 sulphite is low at the beginning of the fermentation. As the fer- 

 mentation proceeds, the proportion of bisulphite in the mixture is 

 increased. The fermentation time is shorter than in the sulphite 

 process and higher yields of glycerol are obtained. 



In the United States a process was developed by Eoff, Linder, and 

 Beyer ^^ from investigations initiated as a result of reports that 

 glycerol was being produced by fermentation in Germany. The Eoff 

 (sodium carbonate) process depends on the finding that an alkaline 

 reaction increases the yield of glycerol. According to Neuberg, the 

 following overall reaction could be written for the fermentation oc- 

 curring in an alkaline medium. 



H2O + 2C6H12O6 -> 2C3H5(OH)3 + CH3COOH + C2H5OH + 2CO2 



Evidently, the alkaline reaction favors dismutation (the Cannizaro 

 reaction whereby one molecule of aldehyde is oxidized with a con- 



