60 



RESPIRATION 



If the fermentation is produced bv Saccharomy ces cerevisiae 

 and sodium sulphite is added to the culture solution, the acetalde- 

 hvde is fixed, and its presence can be demonstrated. With the 

 addition of a high percentage of sodium sulphite, glycerine is 

 produced from the acetaldehyde, and the reactions will yield 

 acetic acid and alcohol also. 



By the sulphite process as much as 37% of the sugar fermented 

 by the yeast may be transformed into glycerol. This fact is of 

 enormous interest and at the same time of great importance when 

 it is recalled that in ordinary alcoholic fermentation the yield of 

 glycerol is less than 3%. The sulphite modifies reduction of 

 acetaldehyde by hydrogen, and hydrogen can thus act directly 

 to reduce the intermediate compound, glyceric aldehyde, forming 

 glycerol. 



These chemical changes may be shown briefly as follows: 



C 6 H 12 6 



Glucose 



CH 2 OH 



CHOH 



CHO 



Glyceric 

 aldehyde 



CH 3 



i 



c=o 



CHO 



Methyl- 



glyoxal 



OH 



If sulphite is added, it may unite with the acetaldehyde: 

 CH 3 CH 3 



CHO + Na 2 S0 3 + H 2 + C0 2 -> C— H + NaHC0 3 



l\ 

 HO SOoONa 



In this event the hydrogen is prevented from reducing the 

 :etaldehyde to alcohol; instep 

 hvde directly in this manner: 



acetaldehyde to alcohol; instead it can react with the glyceric alde- 



CH 2 OH CH 2 OH 



CHOH + H 2 -> CHOH 



CHO 



Glyceric 

 aldehyde 



CH 2 OH 



Glycerol 



