Abstract:
Salted and dried Tilapia, Koobi, obtained from retail outlets and that processed
in the laboratory (under various treatments) were analyzed for their histamine
content. These were done with a view to establishing baseline data on histamine
levels in Koobi as well as investigate the effect of handling, processing and
storage on histamine evolution in Koobi. Sodium chloride levels, moisture contents,
water activity and microbial counts were also determined for the Koobi
samples.
The histamine levels in salted and dried Tilapia, Koobi were generally
found to be low. Koobi samples procured from retail outlets had histamine levels
in the range of 7.06|ig/g to 32.15jag/g. Salting seemed to check histamine
production in Koobi. The high salt content (above 15 percent NaCl) did not
favour microbial growth and may hamper autolysis. Consequently histamine
production through microbial activity as well as autolysis was reduced and microbial
counts were low (2.54 x 103- 1.28 x 106). Salting and drying reduced
the water activity of the Koobi which in turn might have inhibited microbial
decarboxylase activity. Conversion of histidine to histamine appeared inhibited.
Unsalted Tilapia, however, produced elevated levels of histamine
Temperature also did play a role in histamine production. Koobi samples
kept in the freezer did not differ significantly from those kept in the refrigerator
in terms of histamine production. The Koobi samples dried in a solar dryer and
at ambient temperatures also did not show significant differences in their histamine
content; but differed significantly from those kept under cold temperature
(4°C and below). Histamine levels were very low in fresh tilapia indicating that elevated levels of histamine observed in the processed Tilapia (Koobi) could be
attributed to improper handling, processing and storage. Indeed Tilapia iced
immediately after catch showed lower levels of histamine (11,49ug/g) than those
in which icing was delayed for 24 hours(33.17 ug/g). This confirms the importance
of proper handling of Tilapia as a measure to reduce histamine levels in
Koobi.
