MINERALS IN NUTRITION 31 



Effect of Iodine on Some Milk Enzymes 



Preliminary trials were made with a series of samples which contained 

 added iodine from as low as 50 parts per million of free iodine to as high 

 as 200 parts per million. As the work progressed, the samples were 

 made up to contain not more than 100 parts per million, because more 

 iodine rendered the milk unpalatable. The effects of both organic and 

 inorganic iodine are shown in Table 1. 



Table 1. — Effect of Iodiz.xtion ox Milk Enzymes 



Catalase Pero.xidase Lipase activity 

 activity activity (milliliters 0.1 NaOH) 

 Sample (Milliliters (Milligrams 



o.xygen) pu]i)urogallin) Initial 16 days 



Control, untreated pasteur- 

 ized milk 0.60 87.66 0.5 2.43 



Boiled milk 0.00 trace 0.5 0.50 



Milk with 100 p. p.m. tincture 

 of iodine 1.15 99.25 0.5 2.00 



Milk with 100 p. p.m. organic 

 iodine 1.43 514.28 0.5 2.15 



Catalase. — The presence of this enzyme in normal cows' milk was first shown 

 by Raudnitz (8). The catalase content of milk varies with the breed and 

 with the individual animal. Colostrom and milk from cows in the last 

 stages of lactation contain large amounts of catalase. Several methods 

 have been used for the estimation of catalase; that here employed was 

 the direct oxygen-evolution method, which is simple and accurate. The 

 technique described by Palmer (9) was modified slightly. Twenty milli- 

 liters of a milk sample were measured into a graduated fermentation tube. 

 To this were added 20 milliliters of 3 percent hydrogen peroxide solu- 

 tion. The mouth of the tube was stoppered and the contents allowed to 

 fill the neck. The tube was placed in an incubator at 37.5°' C. and held 

 there until gas was no longer evolved. The catalase activity is shown in 

 the table as milliliters of oxygen liberated from 20 milliliters of milk. 



Peroxidase. — This enzyme is usually considered to be an inherent enzyme of 

 milk. Peroxidase is one of several types of oxidative enzymes which 

 bring about oxidation and reduction of substances, and the formation of 

 organic acids, alcohols, and carbon dioxide. Peroxidase cannot use mole- 

 cular ogygen; it can act only in the presence of hydrogen peroxide or 

 certain organic peroxides. It differs from catalase in that it liberates 

 oxygen in an active state, while the product of catalase is inactive oxygen 

 in the molecular state. 



The method used for the estimation of peroxidase activity was that 

 proposed by Rice and Hanzawa (10). The action is based upon the oxi- 

 dation of pyrogallol to purpurogallin, and the results are recorded in the 

 table on the basis of the peroxidase number (the weight in milligrams 

 of purpurogallin yielded by 10 milliliters of milk). 



Lipase. — Since the term, lipase, is used to designate the enzyme which digests 

 the neutral glycerol fats, its importance in milk should not be overlooked. 



