No abstract

A novel biosensor for l-ascorbic acid determination in different beverages was elaborated. The ascorbate oxidase enzyme (AAO) from sp., EC 1.10.3.3, was immobilized on a screen-printed carbon electrode with poly(ethylene glycol) (400) diglycidyl ether (PEGDGE) as a crosslinking agent. The standards and samples were measured first with a blank electrode. An inert protein, bovine serum albumin (BSA), was immobilized on the surface of this electrode with PEGDGE. The BSA mass was equivalent to the mass of 10 U of AAO enzyme immobilized on the electrodes (0.021 mg). The linear measuring range for l-ascorbic acid was between 5 and 150 µmol/L. As l-ascorbic acid is a vital vitamin and a common antioxidant used in food industry, fruit juices and vitamin C effervescent tablets were examined. The results were compared to HPLC measurements.

The aim of our work was to develop a selective amperometric biosensor for infected milk detection. The catalase enzyme (EC 1.11.1.6) was immobilized onto the surface of a thin-layer enzyme cell. The measurements were carried out in stopped-flow injection analysis system (0.8 mL min À1 flow rate, + 590 mV polarization potential) in organic phase (6 % sodium acetate buffer 200 mM pH 6.0, ferrocene conductive salt (7.5 mg L À1 ) dissolved in acetonitrile. A certain amount of hydrogen peroxide was degraded by the catalase content of the milk. The degradation of the hydrogen peroxide is proportional to the infection of the milk samples.