A Study of the Effects of Handling, Processing and Storage on the Histamine Content in Salted, Fermented Telapia (Oreochromis Nilotica)

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.