Abstract:

This study was conducted to determine the role of bacteria and
endogenous enzymes in changes in water retention properties and
degradation of adenosine nucleotides in Atlantic cod. In mince, unlike
whole fish, bacteria are distributed throughout the fish and are in contact
with the internal substrates. Therefore, their potential to participate in
deterioration may be better expressed.
NaOCl (150 ppm of OC1) was added to destroy bacteria. The same amount
of deionised and distilled water was added to the normally spoiling
samples. Standard plate counts were used to determine the bacterial kill
achieved by the NaOCl treatment. All samples were packaged in sterile
polythene bags and were stored on ice/ice salt mixtures (1 and 1.6%) in
insulated chests which were held in a cold room. The concentration of
trimethylamine (TMA), and the nucleotide catabolites, hypoxanthine (Hx)
and inosine (HxR), the pH of tissue homogenates, the water uptake ability
(WUA), and the expressible moisture (EM) were determined after 2, 5, 9,
and 14 days.
NaOCl treatment reduced the bacterial load of the mince by about 99%.
The level of TMA in all samples was extremely low (<0.02 TMA-N
mg/100g) until day 9 when the level had increased significantly in the
normally spoiling samples. The TMA levels in the NaOCl treated samples
did not increase significantly throughout the 14 days of storage at -3°C but
had increased significantly (p<0.05) by day 14 in mince at 0 and -2°C. The
level of TMA was significantly (P<0.05) higher in normally spoiling mince
than in NaOCl treated samples at all three storage temperatures. The pH
for both normally spoiling mince and the treated samples increased during
storage regardless of the storage temperature. The increase in pH tended to be higher in spoiling mince stored at 0°C as compared to the NaOCl treated
samples, but there was no significant difference in the pH of normally
spoiling mince and NaOCl treated samples stored at -2 and -3°C. The level
of Hx + HxR increased until day 9. The increase was most rapid at O’C, less
at -2°C and least at -3°C. Normally spoiling mince had significantly higher
levels of Hx + HxR at days 5 and 9. At day 14, however, all samples except
NaOCl treated samples stored at -3°C had lower levels of Hx + HxR than the
levels in the same samples at day 9 and NaOCl treated samples had
significantly higher levels than normally spoiling samples at all three
storage temperatures.
WUA for normally spoiling mince increased with time at all storage
temperatures while no change in WUA was observed in the NaOCl treated
samples. Treated samples also had lower EM. The EM for normally
spoiling samples were higher and increased with time.
A second set of experiments was conducted at 0°C with a lower level of
NaOCl (25 ppm CIO ) applied to all samples. Treatment samples were
inoculated with bacteria recovered from the gills of gutted fish while the
controls were stored without inoculation. The bacterial count for the
controls was about 5% of the count for the inoculated mince. The Hx +
HxR concentration increased during storage and the increase was higher in
inoculated mince. WUA for inoculated samples increased during storage
while that for controls remained approximately constant. EM for
inoculated samples decreased during storage while that for the controls
increased. This study showed that bacteria are capable of causing changes
in chilled fish even within the first week of storage.