The spoilage flora of vacuum-packaged, sodium nitrite or potassium nitratetreated, cold-smoked rainbow trout stored at 4 degrees C or 8 degrees C

The spoilage flora of vacuum-packaged, salted, cold-smoked rainbow trout fi llets, with or without the addition of nitrate or nitrite, stored at 4 degr ees C and 8 degrees C, was studied. Of 620 isolates, lactic acid bacteria w ere the major fraction (76%), predominating in all samples of spoiled produ ct. However, the phenotypical tests used were insufficient to identify the lactic acid bacteria to the species level. Gram-positive, catalase-positive cocci, Gram-negative, oxidase-negative rods and Gram-negative, oxidase-pos itive rods were found in 6%, 16% and 2% of the samples, respectively. Of 39 Gram-positive, catalase-positive cocci, 29 were identified as staphylococc i and 10 as micrococci. Eighty-five isolates were found to belong to the fa mily Enterobacteriaceae, with 45 of those being Serratia plymuthica. Eleven isolates from the nitrate treated samples stored at 8 degrees C were ident ified as Pseudomonas aeruginosa. The occurrence of P. aeruginosa and staphy lococci in the nitrate-containing samples, stored at 8 degrees C, may cause problems with respect to the safety of the product. The types of lactic ac id and other bacteria in the spoilage flora were generally reduced by the a ddition of nitrate or nitrite to fillets. (C) 1998 Elsevier Science B.V. Al l rights reserved.