Microbiological changes in farm reared freshwater prawn (Macrobrachium rosenbergii de Man) in ice

The microbiological changes in farm reared freshwater prawn (Macrobrachium rosenbergii de Man) during ice storage were studied. A total of 156 bacterial cultures from fresh and ice-stored farmed freshwater prawn were isolated and characterized. Total aerobic, mesophilic and psychrotrophic counts and hydrogen sulphide producing bacterial counts were determined. The total aerobic counts at 20 and 37 °C on fresh prawn was in the range of 4–5 log10 cfu g−1. Aerobic counts on M. rosenbergii at 20 °C and 7 °C exceeded 107 cfu g−1 by the end of storage, of which 40–52% were H2S producers. Gram-negative bacteria constituted 73% of the total flora of fresh prawn and Enterobacteriaceae and Aeromonadaceae dominated. After 19 days of iced storage, more than 80% of the bacterial flora of prawn were Gram-negative. Pseudomonas, Aeromonas hydrophila, A. veronii boivar sobria and Shewanella putrefaciens were identified as the dominant spoilage organisms of farm reared M. rosenbergii stored in ice. This study confirms that freshwater prawn carry significant numbers of motile aeromonads capable of growth at low temperature. The results of the study indicated that the shelf-life of freshwater prawn as determined by microbiological data is 12–16 days. Immediate icing of harvested M. rosenbergii is essential to improve the microbiological stability.