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

Microbiological and chemical changes were evaluated in freshwater prawn sto red under refrigeration at 0 degreesC and 5 degreesC during 10 days, with s pecial 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 micro flora after 10 days storage under refrigeration. Bacteria from Enterobacter iaceae and Vibrionaceae families prevailed among the isolated indole positi ve strains. The use of the Most Probable Number-MPN method, using tryptone broth as culture medium, was the most reliable approach for the quantitativ e evaluation of the indole positive microflora. The stored samples showed i ncreases in pH, L-tryptophan and total volatile bases (TVB), which were mor e intensive at 5 degreesC. The psychrotrophic counts and TVB values of samp les stored at 0 degreesC were lower than the recommended limits (10(7) CFU/ g and 30 mg N/100g, respectively), even after 10 days storage. However, in samples stored at 5 degreesC, these values were reached after 10 and 5 days , respectively. The presence of indole in levels above the limit recommende d by FDA/USA (25 mug/100g) was confirmed in only one sample, suggesting tha t this substance, alone, wouldn't be a good indicator of freshwater prawn q uality stored under refrigeration.