ENZYME ELECTRODES FOR THE DETERMINATION OF CARBOHYDRATES IN FOOD

Characteristic features of screen-printed enzyme electrodes for glucose, lactose and sucrose are described. Glucose oxidase was immobilized on a screen-printed Pt electrode either by crosslinking with glutaraldehyde or by adsorption in an enzyme paste which incorporated either platinized graphite or graphite modified with the mediator tetrathiafulvalene. Thus, detection was based on either H2O2 oxidation or mediator oxidation. The highest reproducibility was obtained with sensors based on the enzyme crosslinked with glutaraldehyde. Hence, this immobilization procedure was also used for the preparation of lactose and sucrose sensors. These sensors are based on co-immobilized beta-galactosidase and glucose oxidase and invertase, mutarotase and glucose oxidase, respectively. Adding mutarotase to the enzyme mixture of the sucrose sensor enhanced sensitivity approximately 100 times. The linear range of the sensors could be increased by additional membranes fixed over the electrode surface. The greatest effect was observed using membranes with a reduced number of pores. This also led to a decrease in the sensitivity of the sensor. Additionally, these sensors showed a reduced response to ascorbic acid, the main electrochemically interfering compound in food. Hence, no interference was observed in juices without added ascorbic acid.