Depuration of geosmin- and 2-methylisoborneol-induced off-flavors in recirculating aquaculture system (RAS) farmed European whitefish Coregonus lavaretus

European whitefish Coregonus lavaretus has increasingly become an important species for aquatic food production, especially in the Nordic countries. Whitefish is produced in traditional cage and pond operations, and in recirculating aquaculture system (RAS) in which, unfortunately, off-flavors and odors, mostly caused by geosmin (GSM) and 2-methylisoborneol (MIB), can accumulate in fish flesh from the circulating water. GSM and MIB have very low human sensory detection limits and, therefore, often disliked by consumers even at low concentrations. In this study, concentrations of GSM and MIB in RAS farmed European whitefish were studied by an analytical method based on headspace solid phase microextraction and gas chromatography–mass spectrometry. Concentrations were determined in different parts of fish: fillet, neck, belly, and tail during a depuration period and in depuration water. The highest initial concentrations were on average 32 ng g−1 (GSM) and 24 ng g−1 (MIB) in European whitefish fillet and 128 ng L−1 (GSM) and 94 ng L−1 (MIB) in water, respectively. After a depuration period of 16 days, concentrations decreased to below the detection limits, indicating the importance of the depuration period.peerReviewe

Off-flavors and lipid components in rainbow trout (Oncorhynchus mykiss) reared in RAS: Differences in families of low and high lipid contents

Recirculating aquaculture systems (RAS)s have become important in land-based fish production. Unfortunately, RAS-farmed fish accumulate off-flavors in their flesh. Off-flavor compounds geosmin (GSM) and 2-methylisoborneol (MIB) are lipophilic compounds and their concentrations need to be controlled in RAS. Therefore, a useful area of study would be the expected impact of total lipid contents and fatty acids in the fish on the accumulation of these off-flavor compounds. The objective of this research was to study the relationships between off-flavor compounds, lipid contents and fatty acids, both at individual and family levels, in rainbow trout (Oncorhynchus mykiss) reared in an experimental RAS. This study showed that 1) the fish and families with high lipid contents accumulated high concentrations of off-flavor compounds, especially when the off-flavor compounds were expressed as contents of total lipids. The overall concentrations of off-flavors ranged from 0.1 to 3.9 ng g−1 ww (GSM) and from 0.1 to 2.4 ng g−1 ww (MIB). 2) The concentrations of polyunsaturated fatty acids (PUFA) and n-3, which are considered health-promoting groups of fatty acids, were lower in fish individuals and families with high lipid content and higher in fish individuals and families with low lipid contents. Therefore, excessive lipid contents may reduce the nutritional value of the fish. 3) Reduced levels of GSM correlated with increased levels of PUFA and n-3 and decreased levels of monounsaturated fatty acids (MUFA, a health-wise neutral effect), and n-6:n-3 ratio. These are highly favorable relationships for aquaculture: high concentrations of health-promoting fatty acids were related to lower off-flavor concentrations. The results imply that changes induced by selective breeding in lipid content may impact both the fatty acid profiles and off-flavor compounds in rainbow reared in a RAS, but large-scale genetic studies are needed to confirm the potential genetic basis of these relationships