THE BACTERIAL GROWTH INHIBITOR (LACTENIN) OF MILK : I. THE PREPARATION IN CONCENTRATED FORM

The bacterial growth inhibitory substance found in milk is called lactenin in this paper. It is stable for 1½ hours at pH 4 and at pH 10 and for longer periods in neutral solution. It is not associated with salts and carbohydrates and may be separated from them by dialysis. Lactenin is removed by agents which precipitate the proteins of whey. Part of these proteins may be hydrolyzed by tryptic digestion and the resulting split products, together with the salts and sugar, may then be removed by dialysis without appreciable loss of lactenic activity. This dialysis may be performed in a concentrating dialyzer, under sterile conditions and at low temperature, thus reducing the solution to small volume. The material may then be completely desiccated and kept 3 months with practically no loss of activity. The residue, on treating this dried material with salt solution, is 200 times as active as the original milk, on a dry weight basis. The size of hemolytic zones of the scarlet fever streptococcus grown on a medium containing lactenin is found to furnish a simple and reliable measure of lactenic activity.