ACTION OF HEAT ON MILK 245 



dehyde, is present also. Methylene blue and indigo- 

 carmine, which, lose their colour when reduced, are 

 frequently used in testing solutions for these enzymes. 

 The reductase of milk is called aldehyde catalase. It 

 is probably associated with the fat globules of the milk, 

 reduction taking place more rapidly with stoppings than 

 with the poorer foremilk. 



Ex. 122. Prepare the following solution : 



Schardinger's reagent. 



Saturated alcoholic methylene blue solution . i c.c. 

 Formalin . . . . . 1 c.c. 



Water .... '. '- . . 38 c.c. 



(a) Add three drops to 10 c.c. of fresh milk, and pour in a 

 small amount of melted or liquid paraffin to exclude oxygen. 

 Keep the whole at 45 to 50 C., and note the disappearance of 

 the blue colour in four hours or less. 



(b) Try the experiment with (i) foremilk, (ii) midmilk, and 

 (iii) stoppings. Note the time taken to destroy the colour in 

 each case. 



5. Action of Heat on Milk. When milk is boiled 

 even for a few minutes it acquires a characteristic taste 

 which is disliked, especially by children accustomed to 

 the fresh liquid. , 



Its properties are considerably changed owing to 

 alterations in the physical and chemical nature of several 

 of its constituents. 



The cooked flavour is acquired if a temperature of 

 1 60 F. is maintained for more than about ten minutes, 

 and in much shorter time as the boiling point is 

 approached. The objectionable taste, however, is 

 removed to a large extent both from the cream and the 



