Microbiological quality of the dairy product pedha and its improvement using gamma radiation

Eighteen pedha samples procured from A and B grade retail shops were examined for their overall microbiological quality and for the presence of foodborne pathogens viz. Staphylococcus aureus, Salmonella sp., Coliforms, Listeria monocytogenes, Yersinia enterocolitica and Bacillus cereus. The microbiological quality of pedha samples from B grade shops was very poor as compared to pedha from A grade shop as evidenced by the very high total bacterial counts (6 x 10(7) cfu/g), high counts of S. aureus (as high as 7 x 10(6) cfu/g) and presence of coliforms and Listeria and Yersinia sp, in 33% of the samples. All the samples from A grade shops were also positive for S, aureus though negative for coliforms, Yersinia, Salmonella, Listeria and B, cereus. Gamma irradiation of pedha at a dose of 3kGy at 0C reduced overall bacterial load by five log cycles and S. aureus and coliforms could be totally eliminated. However, 5 kGy dose was necessary to eliminate S. aureus if the initial number exceed I x 10(5) cfu/g. Inoculated pack studies confirmed that 3 kGy dose was sufficient for the complete elimination of up to I x 10(5) cfu/g of S. aureus. A dose of 3 kGy had minimal effect on the sensory quality of pedha and even pedha samples irradiated at 5 kGy dose were acceptable. Treatment with 3 kGy dose of gamma radiation totally eliminated S. aureus and coliforms in pedha, thereby ensuring their microbial safety.