Amperometric determination of lactose in human and cow's milk using a flow‐injection system with some immobilized enzyme reactors

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Abstract
A bioelectrochemical flow‐injection system is proposed for the determination of lactose in milk from humans and cows. The system includes an amperometric flow‐through platinum electrode to measure hydrogen peroxide, which was enzymatically generated by injecting a 10‐μL sample into the packed‐bed reactors of immobilized β‐galactosidase and glucose oxidase that are incorporated in series in the flow line. Because the presence of glucose interfered with the measurement of lactose, a precolumn packed with coimmobilized glucose oxidase and catalase was positioned just before the two immobilized enzyme reactors to remove the glucose from the milk. The peak current was linearly related to the lactose concentration between 0.01 and 2.0 mM. The determinations of lactose in milk could be performed at a rate of 60 samples/h with satisfactory precision (less than 0.8% RSD) and no pretreatment except for the sample dilution.