A Colorimetric Method for the Quantitative Determination of the Degree of Lactose Hydrolysis

Abstract

A colorimetric method for determining glucose was adapted to determine glucose and galactose in the presence of lactose for use in following the enzymatic hydrolysis of lactose. A blue color was produced by heating a mixture of 5 ml. of 0.02[image] KH2PO4, 10 ml. of 7.5% NH4 molybdate, and 10 ml. of unknown sugar soln. Colorimetric measurement at 640 mu. revealed that an equi-molecular mixture of glucose and galactose was approx. 30 times as great as an equivalent amt. of lactose. Application to dairy products required the precipitation of the proteins prior to color development. Analysis of 14 samples containing from 0.1 to 5 g. of added glucose and galactose in equal parts per 100 g. of milk gave an avg. recovery of 98.70%. Addition of ascorbic acid to milk or heating milk for 2 hrs. at 80[degree]C had a slight but insignificant effect on the normal blank value of milk.