Microbially induced off-flavours in aquaculture production
PhD defence by Raju Podduturi
The purpose of this PhD study was to investigate the occurrence of microbially-produced off-flavours in Danish recirculated aquaculture systems (RAS) for pikeperch production and Brazilian cage-farms for Nile tilapia production. Common off-flavours in fish production are geosmin and 2-MIB (2-methylisoborneol), produced by Actinomycetales, especially Streptomyces, myxobacteria and Cyanobacteria. The bacterial metabolites cause muddy and musty taste and odour to the cultured fish, making them unsuitable for human consumption.
Specific objectives were to localize hotspots for off-flavour production, to identify microorganisms potentially involved in off-flavour production, and the conditions influencing this production, as well as to develop depuration practices to remove off-flavours from fish.
In the Danish RAS farm, I found that hotspot for geosmin production were biofilter and denitrification filter. Removal of geosmin from RAS-farmed pikeperch by depuration was examined in clean water and showed that depuration of pikeperch for eight days could significantly reduce the geosmin content. In tilapia from Brazilian open-water fish farms, I found a positive correlation between an instrumental method (GC-MS) and sensory perception of off-flavours in meat of the fish.
For analysis of geosmin-producing organisms, a functional gene-based amplicon sequencing method (targeting the geoA gene involved in geosmin biosynthesis) was developed. My results revealed occurrence of structurally diverse prokaryotic geosmin-producers in different aquatic environments.
Niels O.G. Jørgensen, Associate Professor, PLEN, University of Copenhagen, Denmark
Mikael Agerlin Petersen, Associate Professor, FOOD, University of Copenhagen, DK
Olav Vadstein, Professor, Norwegian University of Science & Technology, Norway
Kasper Urup Kjeldsen, Associate Professor, Aarhus University, Denmark
Mette H. Nicolaisen (chairman), Associate Professor, PLEN, Univ. of Copenhagen, DK