The effect of irradiation on the colour intensity of freeze-dried egg yolk samples (FDEY), from poultry birds given feed containing different concentrations of annatto extract was investigated. Concentrations of 1, 4, 7 and 10 % of annatto extracts were used in the poultry feed formulation and these were compared with feed containing no additive as well as one containing a commercial feed colourant, ‘carophyll yellow’. The FDEY samples coded R1, R2, R3, R4, C and CArespectively were inoculated with Salmonella parathyphi B and irradiated at doses of 0, 3 and 5 kGy with γ radiation from a 60Co source. Microbial counts and colour intensity were determined after irradiation. Results of the microbiological analysis showed that both 3 and 5 kGy doses were adequate in practically eliminatingSalmonella parathyphi B from the samples. However, it was observed from the colour analysis that irradiation at both 3 and 5 kGy doses caused significant (p < 0.0001) deterioration of the colour of the freeze-dried egg yolk samples.
Key words: Irradiation, Salmonella parathyphi B, colour intensity, freeze-dried egg yolk.
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