Determination of D-fructose in foodstuffs by an improved amperometric biosensor based on a solid binding matrix

An improved amperometric biosensor based on a solid binding matrix (SBM) composite transducer has been used for the determination of D-fructose in foodstuffs samples. The enzyme, D-fructose dehydrogenase (EC 1.1.99.11), was incorporated directly into a solid composite transducer containing both 2-hexadecanone as SBM and chemically modified graphite. Hexacyanoferrate(III) was used as a redox mediator and the current variation caused by the presence of D-fructose was measured amperometrically. The electrochemical properties and the characteristics of the composite fructose biosensors are described. The amperometric signals were fast, reproducible and linearly proportional to D-fructose concentrations in the range 50 x 10(-6)-10 x 10(-3) mol l(-1), with a correlation coefficient of 0.999. A set of measurements at +0.20 V versus SCE for 2 x 10(-3) mol l(-1) D-fructose yielded a relative standard deviation for the steady-state current of 2.11%. The use of a chemically modified graphite by a mild oxidation step was shown to improve the biosensor selectivity against anionic interferents such as L-ascorbate. The biosensor proved to be stable for 6 months and the assay of D-fructose by this electrode was not influenced by the presence of sugars or other interferents commonly found in food samples. The biosensor was used for the determination of n-fructose in some food samples, and the results were consistent with those obtained with the commercially available D-fructose enzyme photometric kit.