Radiation decontamination and disinfestation of salted dried tilapia fish (koobi)

Abstract

Salted dried tilapia (Oreochromis niloticus) fish locally called koobi was investigated with the view of establishing the effective radiation dose for controlling microbial and insect activity on the product. Total viable count (TVC) of market samples of koobi ranged between log 10 4.11 - 6.78 cfu/g, whilst mould and yeast count ranged between log 10 1.38-3.38 cfu/g. Staphylococcus aureus counts ranged between log 10 2.85 - 4.15 cfu/g. After 4 weeks' storage under ambient conditions, total viable count increased to log 10 7.5 ± 2.5 cfu/g. Significant reduction in total viable count was observed after treatment with gamma radiation. A least square regression fitted through the data points indicated that 1.3 kGy would be required to reduce the microbial population on the product by one log cycle. Insects and pink colonies of halophilic bacteria were observed on all the nonirradiated samples after 4 weeks' storage. Treatment with 3 kGy gamma radiation eliminated all insect forms, while microbial population was controlled with TVC ranging between log 10 1.9 ± 1.1 and log 10 2.7 ± 1.6 cfu/g throughout the 16 weeks' storage period. The proliferation of halophilic bacteria and subsequent appearance of pink colonies on irradiated koobi was suppressed until the 16th week. Irradiation, therefore, extended the shelf-life of koobi from 4 to 15 weeks.

Ghana Journal of Agricultural Science Vol. 37 2004: 85-90