Determination of Lactose and Lactose Hydrolysis in Milk Using Cerium(IV)

ABSTRACT Lactose and lactose hydrolysis in milk were determined using a novel method involving a measurement of the time for 0.39M Cerium(IV) [Ce(IV)] in 0.5M nitric acid to be reduced to Cerium(III) [Ce(III)] after an initial precipitation of milk protein and fat. The time for the absotbance at 445 nm to decrease to 0.4 could be directly correlated with standard curves to determine either the amount of lactose or the degree of lactose hydrolysis. This Ce(IV) oxidation method was rapid (15 min) and exhibited good agreement with infrared methods of determining lactose and enzymatic methods of determining percentage lactose hydrolysis. Recoveries of lactose found using the Ce(IV) oxidation method from a number of milk samples containing different amounts of fat were comparable to recoveries using the infrared method of lactose determination.