1 68 NUTRITION AND METABOLISM 



By the V same process', the acidityi of sauerkraut, ensilage, pickles is 

 reduced by mycoderma species. Another Mycoderma is known to 

 destroy acetic acid and thus spoil vinegar or fruits and vegetables kept 

 in vinegar; the yeast grows in a thin, dry white scum over the surface, 

 and oxidizes the acetic acid. 



CH3CO2H + 4O = 2CO2 + 2H2O 



The oxidation of alcohols is not always complete. Especially ethyl 

 alcohol is usually oxidized first to acetic acid; this is the common vinegar 

 fermentation. Many diffeyent kinds of vinegar bacteria are known, 

 some forming gelatinous masses of cell membranes called mother-of- 

 vitiegar, while others remain as separate small cells. They all oxidize 

 alcohol first to acetic acid. 



CH3CH2OH + 20 = CH3CO2H + H2O 



But most of them will oxidize later the acetic acid completely to carbon 

 dioxide, after the alcohol is all exhausted, unless the oxygen supply is 

 shut off. This behavior reminds one of the formation and destruction 

 of oxaUc acid by Aspergillus, mentioned previously. It may be re- 

 marked here that the vinegar bacteria cannot attack the sugar directly 

 ^ to any appreciable degree, and the manufacture of vinegar from sugar 

 requires two agents, the alcohol-forming yeast, and the alcohol-oxidizing 

 bacterium. 



Sonie of the acids can also undergo an anaerobic fermentation. 

 This is possible only with hydroxy-acids. The fermentation of the 

 calcium salt of tartaric acid has been the first anaerobic fermentation 

 observed by Pasteur, and the fermentation of lactic acid to butyric 

 acid has a reputation for its chemical peciiUarity. A compound with 

 four carbon atoms is formed from a compound with only three carbons, 

 a very unusual thing in fermentation. 



Fats. — The decomposition of fats is comparatively simple. All fats 

 are glycerides of organic acids, and if they are attacked at all by micro- 

 organisms, they are first split into glycerin and free acid. 



H2C - O - CO - C16H31 HOH H2COH HO2CC1BH31 



I I 



HC - - CO - CuHsi + HOH = HCOH + HO2CC16H31 



I ' I 



H2C - - CO - CibHsi HOH H2COH HO2CC15H31 



Fat Water Glycerin Acid 



