Determination of Fish Freshness with an Enzyme Reactor Electrode System.

Abstract

A biosensor system for continuous determination of fish freshness using one of the freshness indices [Ki = {(HxR + Hx)/(IMP + HxR + Hx)} .times. 100] of fish, where the IMP, HxR and Hx are inosine monophosphate, inosine and hypoxanthine contents, respectively, was developed. The system consisted of two immobilized enzyme reactor electrodes, an A/D converter, a microcomputer and a peristaltic pump. Nucleoside phosphorylase (NP) and xanthine oxidase (XOD) were simultaneously immobilized onto alkylamine glass beads which were than packed into a column (.vphi. 3 .times. 50 mm), and the enzyme reactor electrode for HxR and Hx was prepared combining this co-immobilized enzymes column and an oxygen probe. Similarly, 5'-Nucleotidase was immobilized together with NP and XOD, and the electrode for IMP, HxR Hx was prepared combining this co-immobilized enzymes column and an oxygen probe. One assay could be completed within 5 min. The relative errors was 4.6% or determination of fish freshness (n = 30). The immobilized enzymes were sufficiently stable for at least one month at 4.degree.C. The results for fish meats (skipjack, horse mackerel, plaice, Japanese red bream, yellowfin tuna) correlated satisfactorily well with those obtained by HPLC method (.gamma. = 0.996).