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.