EFFECT OF HYDROGEN PEROXIDE TREATMENT OF MILK ON ITS PROTEOLYSIS BY PSEUDOMONAS FLUORESCENS

Since hydrogen peroxide treatment of milk is known to modify milk proteins, investigation was made of the process as a possible means of increasing proteolysis by Pseudomonas fluorescens. Reconstituted nonfat dry milk was treated with the peroxide (to give a 1% concentration) and catalase. After autoclaving, the reconstituted milk was inoculated with P. fluorescens and incubated at 25 C for 14 days. Undigested protein was precipitated at pH 4.6. Hydrogen peroxide treatment did not affect the gross composition of the reconstituted milk. After proteolysis the supernatants from hydrogen peroxide–treated lots had higher ninhydrin values and protein equivalents than controls. Also, the weights of undigested precipitate were less than half those from control lots and the per cent protein equivalent lower. In the peroxide-treated samples the per cent ash and carbohydrate increased in approximate proportion to the decrease in protein equivalent. Removal of cellular material greatly reduced ash and carbohydrate content of the precipitate, but had little effect on the per cent protein equivalent. As shown by weights and composition of undigested precipitates, it is evident that hydrogen peroxide treatment of reconstituted milk increased proteolysis by P. fluorescens. It is speculated that the retarding of heat-induced complexing between κ-casein and β-lactoglobulin by the peroxide treatment facilitated subsequent microbial hydrolysis. © 1969, American Dairy Science Association. All rights reserved.