Microbiological and chemical changes in freshwater prawn (Macrobrachium rosembergii) stored under refrigeration

Abstract

Microbiological and chemical changes were evaluated in freshwater prawn stored under refrigeration at 0°C and 5°C during 10 days, with special emphasis on indole production as a chemical spoilage indicator. The total psychrotrophic and indole positive microflora were mainly mesophilic, with indole positive microorganisms being less than 10% of the total microflora after 10 days storage under refrigeration. Bacteria from Enterobacteriaceae and Vibrionaceae families prevailed among the isolated indole positive strains. The use of the Most Probable Number-MPN method, using tryptone broth as culture medium, was the most reliable approach for the quantitative evaluation of the indole positive microflora. The stored samples showed increases in pH, L-tryptophan and total volatile bases (TVB), which were more intensive at 5°C. The psychrotrophic counts and TVB values of samples stored at 0°C were lower than the recommended limits (107 CFU/g and 30 mg N/100g, respectively), even after 10 days storage. However, in samples stored at 5°C, these values were reached after 10 and 5 days, respectively. The presence of indole in levels above the limit recommended by FDA/USA (25 mug/100g) was confirmed in only one sample, suggesting that this substance, alone, wouldn’t be a good indicator of freshwater prawn quality stored under refrigeration.