Introduction
Recirculating Aquaculture Systems (RAS) could help to meet the increasing global demand for seafood given the current environmental challenges (Ahmed & Turchini, 2021). Nonetheless, despite the fact that RAS farms can produce high-quality fish, the occurrence of off-flavors may affect the RAS-farmed fish thus leading to a negative perception in the wake (Moretto et al., 2022). This issue has usually been solely linked to the odor-active compounds geosmin and 2-methylisoborneol, but other compounds may additionally play a role (Jones et al., 2022). Indeed, farmed freshwater fish can contain a range of odorants, commonly described as fishy, grassy, earthy, mushroom-like, moldy, and metallic, all of which are generally considered unacceptable by consumers (Zhou et al., 2024). Consequently, there is a need to comprehensively elucidate odorant compounds in fish reared within commercial RAS facilities. In this project, sensory and analytic instrumental procedures were applied to characterize the aroma profiles and aroma-active compounds in Nile Tilapia and Russian Sturgeon raised in RAS farms.
Methods
The fish samples originated from two recirculating aquaculture farms. All samples were directly stunned, hand-filleted and frozen at -20 °C until use for analysis. The volatile compounds were solvent-extracted (Mahmoud et al., 2017). Briefly, 50 g of the fish fillets were extracted with 100 mL of dichloromethane. Then, the extract was distilled using solvent-assisted flavour evaporation, followed by drying over anhydrous Na2SO4, and concentration to approx. 100 µL. Identification of odorants was achieved using a combination of comparative aroma extract dilution analyses (a gas chromatographic-olfactometric technique), gas chromatography-mass spectrometry and two-dimensional gas chromatography with mass spectrometry and olfactometry. Furthermore, aroma profile analysis was performed according to ISO 13299:2016–09.
Results and Discussion
Overall, the odor attributes soapy, fatty, green, mouldy, earthy, fishy and sea water-like/algae-like were selected by the panellists for the description of the two RAS-farmed fish aromas. Through the combined sensory and instrumental analysis, 108 and 114 aroma-active compounds were detected in Nile Tilapia and Russian Sturgeon, respectively. Of these compounds, 77 and 91 were identified by comparison of the respective retention indices, mass spectra and odor qualities with their corresponding reference compounds. The most important substances classes were aldehydes, organic acids, ketones, alcohols, lactones, terpenes and heterocycles. Some of these substances occurred with high flavor dilution factor (FD) in both Nile Tilapia and Russian Sturgeon.
In sum, sensory-instrumental analysis was successfully applied to identify odorant compounds in Nile Tilapia and Russian Sturgeon reared in RAS. In two independent samples, we thereby demonstrated that in addition to geosmin and 2-methylisoborneol, a range of other odorants was present with high FD factors. This study provides a basis to further develop quality control systems for fish reared in RAS by giving insights into the complexity of seafood aroma.
References
Ahmed, N., & Turchini, G. M. (2021). Recirculating aquaculture systems (RAS): Environmental solution and climate change adaptation. Journal of Cleaner Production, 297. Elsevier Ltd. https://doi.org/10.1016/j.jclepro.2021.126604
Jones, B. C., Rocker, M. M., Keast, R. S. J., Callahan, D. L., Redmond, H. J., Smullen, R. P., & Francis, D. S. (2022). Systematic review of the odorous volatile compounds that contribute to flavour profiles of aquatic animals. Reviews in Aquaculture. https://doi.org/10.1111/raq.12657
Mahmoud, M. A. A., & Buettner, A. (2017). Characterisation of aroma-active and off-odour compounds in German rainbow trout (Oncorhynchus mykiss). Part II: Case of fish meat and skin from earthen-ponds farming. Food Chemistry, 232, 841–849. https://doi.org/10.1016/j.foodchem.2016.09.172
Moretto, J. A., Freitas, P. N. N., Souza, J. P., Oliveira, T. M., Brites, I., & Pinto, E. (2022). Off-Flavors in Aquacultured Fish: Origins and Implications for Consumers. Fishes, 7. https://doi.org/10.3390/fishes7010034
Zhou, Y., Zhang, Y., Liang, J., Hong, H., Luo, Y., Li, B., & Tan, Y. (2024). From formation to solutions: Off-flavors and innovative removal strategies for farmed freshwater fish. Trends in Food Science & Technology, 114. https://doi.org/https://doi.org/10.1016/j.tifs.2023.104318
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 956481