The bacteriology of fresh and spoiling Lake Victorian Nile perch (Lates niloticus)

Lone Gram*, Christina Wedell-Neergaard, Hans Henrik Huss

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

A total of 177 bacterial cultures isolated from Lake Victorian Nile Perch (Lates niloticus) were investigated. The flora on newly caught Nile perch consisted of organisms belonging to the genera Moraxella, Alcaligenes, Acinetobacter, Pseudomonas, Aeromonas, Micrococcus and other Gram-positive organisms. 39% were identified as Gram-positive species and 61% were negative in the Gram-reaction. Three cultures out of 53 investigated caused weak rotten off-odours in sterile fish broth and one culture, an Aeromonas spp. produced strong rotten, fishy, hydrogen sulphide off-odours. From Nile perch spoiled at ambient temperature, 15 of the 42 strains isolated caused rotten, fishy, hydrogen sulphide off-odours. These specific spoilage bacteria were all identified as Aeromonas and all reduced trimethylamine oxide to trimethylamine and produced hydrogen sulphide. From spoiled iced Nile perch, 74 out of 82 (90%) of the bacteria isolated were identified as Pseudomonas. A small proportion of these (13 out of 74) produced off-odours in sterile fish broth resembling the spoiling fish. These specific spoilers could not be separated from the non-spoilers based on biochemical activities used in classical taxonomy. While the Pseudomonas spp. isolated did not produce trimethylamine or H2S, a few of the remaining isolates (two Shewanella putrefaeiens and five Aeromonas spp.) did produce these compounds. The role of Shewanella putrefaciens in the iced spoilage of Nile perch was, however, insignificant, since they only very late in the storage reached numbers where their spoilage could be detected.
Original languageEnglish
JournalInternational Journal of Food Microbiology
Volume10
Pages (from-to)303-316
Number of pages14
ISSN0168-1605
Publication statusPublished - 1990

Keywords

  • Nile perch
  • Aeromonas
  • Pseudomonas
  • Specific spoilers
  • Fish spoilage

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