ZYMOGENIC BACTERIA 2O; 



There are about one hundred species of bacteria which may 

 cause lactic acid fermentation. They can be grouped as the 

 " lactic acid producers." One of the common species is 

 Bact. acidi lactici, and a very closely related species, B. lactis 

 aerogenes. Msp. comma and the spirilla belonging to the 

 same family, B. prodigiosus and many sarcina found in 

 brewery mashes, possess the power of producing lactic acid. 



Lactose or milk sugar (Ci 2 H 22 Oii) is the ordinary carbohy- 

 drate which is acted upon by the lactic acid organisms. In 

 addition to lactose, glucose and cane sugar may be fermented. 

 Starch, maltose, or cellulose are not acted upon directly by 

 the enzymes of the lactic acid bacteria. They may be 

 changed into the foregoing sugars, however, by enzyme 

 action of other bacteria and then be subsequently attacked- by 

 the lactic acid bacteria and changed into lactic acid. The 

 following is approximately the chemical reaction which takes 

 place on lactose : 



CiaH^Ou + H 2 O = 4 CH 3 CH(OH)COOH (lactic acid). 



Lactic acid fermentation is an aerobic process, and the fer- 

 mentation is immediately inhibited in the absence of oxygen. 

 The maximum acid formation, and, necessarily, the optimum 

 temperature of the lactic acid bacteria, average about 30 C. 

 to 35 C. in the majority of species, and as low as 10 C. and 

 as high as 52 C. in some few varieties. 



Lactic acid fermentation can progress only when the acid 

 produced is neutralized by some alkaline substance in solution, 



