ENZYMS IN MILK 



Enzyms or ferments are substances of unknown composition 

 produced by living cells. They accelerate chemical processes and 

 act in relatively small amounts as compared to the substances 

 on which they react; nor are they destroyed by their activity. 

 They are specific; that is to say, each enzym. reacts only with one 

 substance. By their action an equilibrium is established and this 

 reaction is reversible. Usually a distinction is made between 

 intracellular or endo-enz3Tns, or those which react only inside of 

 the hving cells, and extracellular or exo-enzyms, those which are 

 able to penetrate the cell wall and react in the surrounding me- 

 dium. The distinction between organized or living ferments, and 

 unorganized or ferments acting independently from the cell, is 

 not held by most investigators, since Buchner has shown that 

 so-called organized ferments really act by means of imorganized 

 ferments contained in the living cell. By separating ferments 

 from living cells by means of pressure Buchner was able to repro- 

 duce fermentations similar to those brought about by the hving 

 cell. 



Enzyms are sensitive to acids, alkalies, salts, and tempera- 

 ture. Some enzyms act best in slightly acid media, as rennin 

 and pepsin for example; others prefer slightly alkaline media, as 

 trypsin. Excess of acid, alkali, or salt is inhibitory. Some 

 enzyms require the presence of small amounts of certain salts 

 without which they are unable to produce chemical changes. 

 Rennin and the fibrin ferment exert their coagulative influence 

 only when calcium salts are present. Each enzym has an opti- 

 mum, minimum, and maximum temperature, and is destroyed at 

 a certain temperature, which varies with different enzyms. Some 

 enzyms are destroyed at 60° C, or even below, others are destroyed 

 at higher temperature. 



Enzyms are always present in raw milk, and when we read of 

 "life in milk" they are usually referred to. The distinction be- 

 tween inherent milk enzyms and enzyms produced by microbial 

 activity is sometimes made. However, it is difficult to exclude 

 beyond criticism the activity of micro-organisms, since only a 

 small portion of the milk in the udder is really free from bacteria. 

 There is reason to believe that milk is secreted by the mammary 

 gland in sterile condition, but it becomes contaminated with 

 bacteria before it leaves the finest ducts. The so-called strippings 



230 



