32 MASS. EXPERIMENT STATION BULLETIN 374 



A rancid milk is obviously an unmarketable product. It is difficult to 

 estimate the activity of lipase in milk because it is present in such small 

 amounts. The method of Rice and Markley (11) vi^as used for the pur- 

 pose because of consistent results reported by several investigators. The 

 digestion of fats by lipase results in an increase in titratable acidity, and 

 the data shown in the table are reported in terms of milliliters of O.IN 

 sodium hydroxide required to neutralize the acidity. 



Comment. — The results recorded in Table 1 show that iodine in concentra- 

 tions as high as 100 parts per million had different effects on the activities 

 of the enzymes studied. Inorganic iodine stimulated catalase activity to 

 a marked extent, and organic iodine v^as even more effective in this 

 respect. Peroxidase activity was over five times as great in samples con- 

 taining organic iodine as in those with inorganic iodine or in the control 

 samples. Lipase activity was inhibited by both forms of iodine, with the 

 inorganic showing the more drastic effect. 



Effect of Iodine on Some Enzymes of the Digestive Systems of 

 Man and Animals 



Renmn. — Commercial calf's rennin was employed, and its clotting time for 

 milk samples was noted. The method used to measure rennin activity 

 was a modification of the Marshall rennin test. Results shown in Table 

 2 are in terms of milliliters of filtrate obtained in three minutes from milk 

 treated with a given proportion of standardized rennin solution. A 

 greater volume of filtrate indicates a greater inhibition of rennin activity. 



Steapsin. — This is a pancreatic enzyme. In determining the effect of iodine 

 on this enzj^me, the Raudnitz method (8) for lipase was employed. The 

 amount of free fatty acid measured was calculated as oleic acid, since the 

 oleic-acid number is frequently employed as an index of lipase activity. 



Comment. — Both organic and inorganic iodine stimulated rennin activity, 

 and the effect was quite marked with organic iodine. In preliminary 

 trials, where more iodine was used (over 100 parts per million), some 

 inhibition of rennin activity was noted, which increased as the quantity 

 of iodine added to the milk was increased. A possible explanation may 

 be that iodine is concerned in some way with making more calcium salts 

 insoluble in the serum, which would retard rennin action. Inorganic 

 iodine had an inhibiting action on the lipolytic activity of steapsin, even 

 after 48 hours. Organic iodine seemed to have no significant effect on 

 the enzyme. 



Table 2. — Effect of Iodization on Rennin and Steapsin 



Rennin activity Steapsin activity 



(milliliters of (oleic acid number) 



Sample filtrate in 



3 minutes) Initial 24 hours 4 8 hours 



Control, untreated pasteur- 

 ized milk 32.3 40.55 98.35 184.67 



Milk with 100 p. p.m. tinc- 

 ture of iodine 20.4 40.55 70.48 138.40 



Milk with 100 p. p.m. organic 

 iodine 9.7 40.55 94.22 179.63 



