ENZYMS IN MILK 233 



slightly alkaline media. Subsequent study by Babcock, Russell, 

 Vivian, and Hastings, however, showed that it could be sharply 

 differentiated from trypsin by its decomposition products. As 

 the authors state: "The digestion products approach more nearly 

 those produced by the liquefying or peptonizing bacteria than 

 they do any of the ferments of animal origin." Ammonia is formed 

 during early stages of digestion when galactase is used, but it is 

 absent in tryptic and pancreatic digestion. Galactase differs 

 further from trypsin in being inhibited by formalin. 



Galactase is different from pepsin, inasmuch as the latter 

 does not act on boiled milk unless free acid is added. The au- 

 thors think that galactase is the main causal agent in the proteo- 

 lytic changes that occur in Cheddar cheese. 



Babcock, Russell, and Vivian have also studied the influence 

 of galactase in the ripening of cottage cheese. Their studies 

 have led to the conclusion that the digestion of casein in cottage 

 cheese is due to the effect of inherent milk enzyms, chiefly galac- 

 tase, but not so much to the action of vital ferments. They 

 showed that when casein is precipitated by acid instead of rennet 

 it undergoes a proteolytic change comparable to that occurring in 

 normal milk. 



Galactase acts best in neutral or slightly alkaline media and 

 is destroyed by heating at 76° C. for ten minutes. Babcock and 

 Russell think that galactase is a true milk enzym and not a bac- 

 terial product, but it is questioned by some whether their milk 

 was really sterile and whether the antiseptics used were in suf- 

 ficient quantity to prevent all bacterial growth. It is further 

 questioned whether galactase is a single enzym or a mixture of 

 several different ones. Furthermore, there is some similarity be- 

 tween galactase and Duclaux's casease, which is clearly a bacterial 

 product. 



Pepsin and trypsin-like ferments have been found in milk by 

 Spolverini, who demonstrated the formation of protein decom- 

 position products which gave the biuret reaction. 



Carbohydrate-splitting Ferment. — An amylase has been dem- 

 onstrated in milk and can be shown to exist by the following 

 method (Koning): Place 10 c.c. of milk in each of a series of 

 test-tubes. Add to the first tube 1 drop of a 1 per cent, solu- 

 tion of starch, to the second tube 2 drops, and so on. Mix and 

 add after thirty minutes 1 c.c. of an iodin solution prepared by 

 dissolving 1 gram iodin and 2 grams potassium iodid in 300 c.c. 

 of water. If all the starch has been digested a yellow color ap- 

 pears after addition of the iodin solution, while if part of the 

 starch only has been digested, the characteristic blue color of the 

 iodin-starch reaction appears. 



