ACTION OF OXIDISING ENZYMES 123 



of colour in the bean from white or violet to brown is 

 only indirectly effected by fermentation, as the brown 

 coloration is due to the work of oxidases or oxidising 

 enzymes. These oxidases are stored up in the proto- 

 plasm of the bean's cells. When the cells are killed 

 without injury to the oxidases, the latter are liberated 

 upon the death of the protoplasm and become active. 



If the oxidases are killed by boiling or the application 

 of strong acids, the characteristic coloration will not 

 take place. Loew describes an experiment which he 

 conducted to prove the action of oxidising enzymes on 

 cocoa beans. A further control experiment was made, 

 in which the pulped cocoa (bean with testa and attached 

 slime layer) was boiled for about twenty minutes with 

 2 per cent, dilute sulphuric acid. The slimy tissue 

 contracted, arid together with the swollen testa was 

 easily separated from the bean. These beans showed 

 a pure red coloration on the outside, while the interior 

 was violet, and no trace of brown colour appeared even 

 after many hours' exposure to the air, since the oxidising 

 enzyme (oxidase) had been killed, together with the 

 living matter (the protoplasm of cells). 



The protoplasm of plant cells dies when they are sub- 

 jected to a temperature of 115 Fahr., but a further rise 

 of from 40 to 55 Fahr. is necessary to destroy the 

 oxidising enzymes. 



Loew further remarks that cocoa beans which have 

 been simply sun-dried are uniformly deep brown. 



This statement is, however, not applicable to all classes 

 of cocoa. The colour of the beans of the Forastero- 

 Amelonado variety generally cultivated by the natives 

 in West Africa is distinctly improved by fermentation. 

 Those beans which the natives dry in the sun without 

 fermentation have a dark blue fracture, whereas properly 

 fermented beans of this variety have a typical chocolate 

 fracture when dried. Beans of this variety which have 

 been insufficiently fermented are also bluish in colour, 

 but this is not so pronounced as in the unfermented 

 beans . 



The dark blue fracture is objected to by buyers, and 

 when it is exhibited in cocoa beans they always realise 

 lower prices than properly fermented beans of the same 

 type. Even when cocoa is fermented properly the char- 



