Peroxide Increase in Fat of Milk During Foam-Spray-Dried Powder Manufacture

Abstract Fresh milk contains low levels of peroxides which increase in concentration during its conversion to whole milk powder by spray drying. Analysis of peroxide increase during 20 foam-spray-drying runs showed the average peroxide value (meq O 2 /kg fat) of fresh milk taken from bulk tanks to be .019; on concentrating to 50% total solids in a falling film evaporator this value rose to .024; after drying with nitrogen injection, the fat in the finished powders had an average peroxide value of .036. The peroxide content of fat in milk powders produced by conventional spray drying was approximately one-half that in the foam-spray-dried products. Further increases in peroxide of both types of powders could be detected after one to three days of holding in air after manufacture. The low peroxide values were measured using minor modifications of Horgan's method, in which peroxides convert the reduced leuco form of Brilliant Cresyl Blue to its oxidized blue form.