Simultaneous determination of glucose and lactose in sour milk using an immobilized glucose oxidase electrode combined with a β-galactosidase-attached measuring cell

Abstract

Glucose and lactose in sour milk are simultaneously determined by the use of a glucose-sensing enzyme electrode combined with a measuring cell which contains a layer of immobilized β-galactosidase. The electrode current changes linearly with time from ca. 1 to a few min after the addition of a glucose/lactose mixture. The lactose content (70 µM~7 mM) is determined from the rate of current change in the linear region, and glucose content (5µM~1.5 mM) is determined by extrapolating the straight current/time line to t=0.40 min, and by measuring the intercept on the vertical (current) axis at t=0.40 min. R.S.D.-values in the 10 successive measurements of 0.3 mM glucose/3.0 mM lactose mixture are 2.4% for glucose and 3.9% for lactose. About 20 samples of sour milk can be analyzed per hour by the present electrode/cell system. © 1990, The Japan Society for Analytical Chemistry. All rights reserved.