Effect of Selected Washing Treatments and Drying Temperatures on bacterial Quality and Safety of Dagaa (Rastrineobola argentea)

Abstract

Microbiological analyses for aerobic bacteria counts and pathogens (coliforms, E. coli, S. aureus, Salmonella spp and V. cholerae) were carried out on small pelagic fish specie commonly found in Lake Victoria, dagaa (Rastrineobola argentea). The samples were obtained from various process steps within the field sun-drying and market conditions in Kisumu, Kenya. Dagaa was also oven-dried at 30oC, 40oC and 50oC after washing with selected solutions i.e. salted (3% sodium chloride), chlorinated solutions (100ppm) and potable tap water, which was used as control. Results obtained indicated that total aerobic bacterial counts in the freshly caught dagaa increased significantly (p<0.05) from 7.41×106 cfu/g to 6.17×107 cfu/g by day 1 of sun-drying. The study also observed presence of total coliforms, E.coli, S. aureus, Salmonella spp and V. cholera at levels above recommended safe limits of 102 cfu/g (total coliforms), 10 cfu/g ( E. coli), 102 cfu/g (S. aureus) and zero tolerance (Salmonella spp and V. cholerae). Oven-drying of dagaa at 50oC and 40oC resulted to significantly (p<0.05) lower counts of total aerobic bacteria when compared to 30oC. The salted and chlorinated-wash treatments showed significantly (p<0.05) lower aerobic bacterial counts when compared to the potable tap water-wash treatments (control) after drying at 30oC, 40oC and 50oC. There was no detection of pathogenic bacteria of public health concerns such as E. coli, S. aureus, Salmonella spp and V. cholerae in the oven-dried dagaa. In conclusion, dagaa dried at 50oC after pre-washing with salt solution was considered the most appropriate with regards to the lowest bacterial counts.

Keywords: dagaa; bacteria; coliforms; E. coli; S. aureus; V. cholerae; Salmonella spp

Journal of Tropical Microbiology and Biochemistry Vol. 4 (1) 2008: pp. 16-23