Abstract
The presence of bacterial metabolites in aquaculture production facilities and in fish products is a globally occurring issue. Geosmin and 2-MIB (2-methylisoborneol) are among the most common metabolites that cause off-flavours by imparting muddy and musty taste and odour to the cultured fish. Occurrence of off-flavours spoils the fish and the taste makes the fish unsuitable for human consumption. Removal off-flavour from fish is long-term process (requires depuration in clean water for several days) and it increase the production costs. Geosmin and 2-MIB are secondary metabolite produced by Actinomycetales, especially Streptomyces, myxobacteria and Cyanobacteria.
The purpose of this PhD study was to investigate the occurrence of off-flavours in Danish recirculated aquaculture systems (RAS) and in Brazilian Nile tilapia cage-farms. Specific topics were to localize hotspots for off-flavour production in studied aquaculture systems, to identify microorganisms involved in off-flavour production and the conditions influencing this production and furthermore, to develop depuration practices to remove off-flavours from fish.
In this study, I examined the occurrence of geosmin in Danish RAS farms producing pikeperch and Atlantic salmon, and found that biofilter and denitrification filter were hotspots for the geosmin production. I showed that effective management of water treatment system reduces the risk of potential occurrence of geosmin in RAS farms. I also investigated occurrence of off-flavours in Brazilian Nile tilapia farms by an instrumental method (GC-MS) and had the results confirmed by sensory perception of the tilapia meat, and I found a good correlation between the chemical and sensory data.
A functional gene-based (the geoA gene involved in geosmin biosynthesis) amplicon sequencing method was developed to examine the diversity of geosmin-producing organisms in aquatic environments. My study revealed occurrence of structurally diverse prokaryotic geosmin-producers in different aquatic environments. Sorangium-related geosmin-producing bacteria were dominant in Danish RAS system, while an unknown geosmin-producing bacterial group was abundant in the Brazilian fish farms. Application of the developed universal geoA probe to water and sediment in Brisbane River, Australia, showed dominance of geosmin- producing cyanobacteria in both water and sediment.
Removal of geosmin from RAS-farmed pikeperch by depuration in clean water showed that depuration of pikeperch for eight days could significantly reduce the geosmin content.
The purpose of this PhD study was to investigate the occurrence of off-flavours in Danish recirculated aquaculture systems (RAS) and in Brazilian Nile tilapia cage-farms. Specific topics were to localize hotspots for off-flavour production in studied aquaculture systems, to identify microorganisms involved in off-flavour production and the conditions influencing this production and furthermore, to develop depuration practices to remove off-flavours from fish.
In this study, I examined the occurrence of geosmin in Danish RAS farms producing pikeperch and Atlantic salmon, and found that biofilter and denitrification filter were hotspots for the geosmin production. I showed that effective management of water treatment system reduces the risk of potential occurrence of geosmin in RAS farms. I also investigated occurrence of off-flavours in Brazilian Nile tilapia farms by an instrumental method (GC-MS) and had the results confirmed by sensory perception of the tilapia meat, and I found a good correlation between the chemical and sensory data.
A functional gene-based (the geoA gene involved in geosmin biosynthesis) amplicon sequencing method was developed to examine the diversity of geosmin-producing organisms in aquatic environments. My study revealed occurrence of structurally diverse prokaryotic geosmin-producers in different aquatic environments. Sorangium-related geosmin-producing bacteria were dominant in Danish RAS system, while an unknown geosmin-producing bacterial group was abundant in the Brazilian fish farms. Application of the developed universal geoA probe to water and sediment in Brisbane River, Australia, showed dominance of geosmin- producing cyanobacteria in both water and sediment.
Removal of geosmin from RAS-farmed pikeperch by depuration in clean water showed that depuration of pikeperch for eight days could significantly reduce the geosmin content.
| Original language | English |
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| Publisher | Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen |
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| Publication status | Published - Dec 2018 |