Recirculating aquaculture systems (RAS) offer many production and environmental advantages, yet present challenges in ensuring high-quality seafood flavour due to the presence of off-odour compounds. Specifically, compounds like geosmin and 2-methylisoborneol (2-MIB) are associated with an “earthy” off-flavour, which can diminish palatability and reduce consumer demand for RAS-grown fish (Abd El-Hack et al., 2022; B. C. Jones et al., 2022). Recent studies examined correlations between off-odour taints in aquaculture fish and the respective feeds, suggesting a potential absorption of such odorous compounds through ingestion (Mahmoud et al., 2018; Podduturi et al., 2017). At the same time, the accumulation of palatable feed-borne odours in seafood may offer a beneficial masking effect on the RAS waterborne “earthy” off-odours as well as enhancing “marine” odours, which are notoriously weaker or absent in aquaculture seafood (B. C. Jones et al., 2022). The red microalga Rhodomona salina, for example, is rich in volatile organic compounds eliciting “marine” odours (Coleman et al., 2022; Van Durme et al., 2013), and algae-based aquaculture feeds have proved to enhance “marine”, “crustacean-like” and “algae-like” flavours in different fish species (Guevara et al., 2011; B. Jones et al., 2016). To explore this opportunity in detail, the present work reports on a dose-response feeding trial that was conducted in a semi-commercial RAS to enhance R. salina-sourced “marine” odours in Atlantic salmon (Salmo salar) and assess the potential mitigation of "earthy" off-odours (B. Jones et al., 2016). Four experimental feeds were formulated and manufactured with increasing inclusion levels of R. salina (Control, 10%, 20% and 30%) and fed to 100 Atlantic salmon reared in two RAS systems for 22 days. Salmon fillets and water were sampled on day 0, 7, 14 and 21. Several algal compounds, were targeted in this study, as were waterborne RAS off-odours, including geosmin, 2-MIB, benzaldehyde, dimethyl sulfide, methional, dimethyl disulfide, dimethyl trisulfide, 3-methyl butanal, a-ionone, furfural, 2,3-octanedione, pentanal, 1-octen-3-ol, (3E,5Z)-octa-3,5-dien-2-one, (3E,5E)-octa-3,5-dien-2-one, (2E,4E)-hepta-2,4-dienal and 6-methyl-5-hepten-2-one. These compounds were traced and quantified with sensory evaluations combined with analytical methods (e.g., solvent assisted flavour evaporation (SAFE), gas chromatography-mass spectrometry/olfactometry (GC-MS/O), aroma extraction dilution analysis (AEDA), and proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-MS). Comparative sensory profiling of salmon fillets was also conducted to verify the absorption of “marine” odours, examine the masking of “earthy” off-odours and identify the optimum concentration and feeding duration of R salina. This research project offers valuable insights and strategies for mitigating off-odours in aquaculture seafood, enhancing the flavour quality, and optimizing cost-efficiency in RAS production.
References
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