Amperometric sensor for fish freshness based on immobilized multi‐enzyme modified electrode

An amperometric biosensor for the determination of fish freshness has been developed by immobilizing 5′‐nucleotidase (NT), nucleoside phosphorylase (NP) and xanthine oxidase (XO) enzymes on a Nafion‐paraquat chemically modified glassy‐carbon working electrode. The sensing principle is based on the oxygen consumption in the enzymatic reaction catalyzed by xanthine oxidase immobilized in the matrix. The quantity of hypoxanthine (Hx), the combined amount of inosine (HxR) and Hx and the total quantity of inosine 5′‐monophosphate (IMP), HxR and Hx can be determined, respectively, by changing the medium conditions. This sensor system can be used to determine the freshness of fish. An indicator of fish freshness, K1, is defined as K1 = {[HxR] + [Hx]}/{[IMP] + [HxR] + [Hx]}. This biosensor prowides a reliable means for determining of Hx, HxR and IMP in fish samples and the freshness of the fish meat.