Hypoxanthine Ratio Determination in Fish Extract Using Capillary Electrophoresis and Immobilized Enzymes

Fish freshness was assessed using capillary electrophoresis and an immobilized enzyme procedure to monitor degradation of inosine‐5′‐monophosphate (IMP), inosine (HxR) and hypoxanthine (Hx). The enzymatic method used an amperometric probe at + 0.7 V (platinum vs silver/silver chloride) with immobilized xanthine oxidase, catalase, nucleoside phosphorylase, and nucleotidase for converting Hx, HxR or IMP to uric acid. Capillary electrophoresis resolved IMP, inosine and Hx by migration rates resulting from an applied electric field (416 V/cm, 50 μA). Components were detected at 250 nm. The H ratio of Hx/[IMP + HxR + Hx] and simplified K value of [HxR + Hx]/ [IMP + HxR + Hx] were determined in cod, salmon and trout stored on ice (0‐4°C) and at 20°C. The two procedures agreed and for all species H ratio and K values increased with storage time.