DEVELOPMENT OF A SYSTEM WITH ENZYME REACTORS FOR THE DETERMINATION OFFISH FRESHNESS

A continuous system for the determination of fish freshness with doubl e enzyme reactors was developed and applied to the determination of th e freshness indicator K K = 100(HxR + Hx)/(IMP + HxR + Hx), where IMP, HxR and Hx are Inosine monophosphate, Inosine and Hypoxanthine, respe ctively. The system was assembled with a three electrode screen-printe d element (graphite as working electrode, silver as counter and silver , silver chloride as reference electrode) placed in a flow cell, a sam ple injection valve and two enzyme reactors. The determination of the total amount of HxR and Hx is realized by flowing the sample through t wo reactors in series: one reactor was packed with nucleoside phosphor ylase (Np) and the other with xanthine oxidase (XO) immobilized on ami nopropyl glass. Similarly, the other term of the equation was evaluate d by flowing through the two reactors the sample treated by Alkaline p hosphatase (ALP) for 5-10 min at 45 degrees C. One assay could be comp leted within 5 min. The system for the determination of fish freshness was reproducible within 2-3% (n = 4). The immobilized enzymes were fa irly stable for at least 3 months at 4 degrees C. More than 200-300 sa mples could be analyzed in about one month by using these enzyme react ors provided the disposable screen-printed electrode should be changed every 30-40 real samples. The results obtained suggest that the propo sed sensor system provides a simple, rapid and economical method for t he determination of fish freshness (K)I. We applied the present system with two reactors for the determination of K values in fish samples a nd compared the results with those obtained by the XO-reactor. Correla tion factor and regression line between the two methods were 0.992 and Y = -3.14 + 1.03X respectively. We concluded that the present flow in jection analysis (FIA) system with XO and Np reactors was suitable as a simple, easy to handle and reliable instrument for quality control i n the fish industry. (C) 1998 Elsevier Science B.V. All rights reserve d.