244 MILK ! ITS ORIGIN AND COMPOSITION 



separated milk from public creameries must be pasteurized 

 at a temperature not less than 80 C. before being returned 

 to the farms for the feeding of calves and pigs ; these 

 tests assist in determining if the regulation has been 

 carried out. 



Ex. 120. Put some lumps of gum guaiacum in a test-tube 

 containing alcohol and boil for a short time. Filter the yellow 

 solution, and gently add water until near the point at which a 

 permanent milky emulsion is obtained. 



(a) Add a small portion to some fresh milk, and then pour in 

 a few drops of hydrogen peroxide solution. Slightly warm the 

 milk : the production of a blue colour shows the presence of an 

 oxidizing enzyme peroxidase. 



(b} Try the experiment with boiled milk. 



Ex. 121. Make a 2 per cent, solution of paraphenylendia- 

 mine " hydrochlorate." 



(a) Take 10 c.c. of fresh unboiled milk, warm slightly, and add 

 to it 10 or 12 drops of a 3 per cent, solution of hydrogen peroxide. 



From a pipette slowly run into it down the side of the tube 

 i c.c. of the paraphenylendiamine solution. Avoid shaking or 

 mixing the contents, and note within five minutes the production 

 of a blue colour showing the presence of peroxidase in the milk. 



(b) Try the experiment with milk which has been heated for 

 five minutes to 60, 70, 80, 90, and 100 C., and then cooled 

 to about 50 or 55 C. 



Determine the temperature at which the oxidizing enzymes 

 are destroyed. 



Milk contains a reducing enzyme, i.e. an enzyme which 

 possesses the power of " reducing " or taking away 

 oxygen from a compound in which oxygen is only in 

 loose combination. Some reductases are direct reducers ; 

 others, however, such as that found in milk, can only 

 effect reduction when a reducing agent, such as formal- 



