Recirculating aquaculture systems (RAS) provide various production and environmental benefits yet introduce challenges in maintaining high seafood flavour quality. Specifically, the microbial compound geosmin is frequently associated with an ’earthy’ off-flavour in RAS-grown fish. Due to its moderate lipophilicity, geosmin readily accumulates in fish tissue, thereby diminishing palatability and lowering consumer demand for RAS-cultivated fish (Abd El-Hack et al., 2022). There is currently a lack of comprehensive description of the waterborne geosmin biokinetics in fish tissues and only a few models partially describe the absorption and excretion processes (Tucker & Schrader, 2020). Of note is the one-compartment model developed by Howgate (2004), which conceptualises fish as a single compartment consisting of lipids and water, wherein passive uptake and elimination rates are governed by the octanol-water partitioning coefficient between the organism and its surrounding water. Several studies by Schram et al., (2016, 2017, 2018; 2021a; 2021b) advanced the one-compartment model across various aquaculture species. Their findings revealed the non-significant influence of the renewal rate of depuration water on geosmin excretion, contradicting the one-compartment model’s assumption of passive diffusion and implying the involvement of alternative biotransformation mechanisms. Fish liver was proposed as a site for geosmin biotransformation, and faster elimination rates were observed in fed fish compared to starved ones, thereby implicating blood lipid content in improving geosmin excretion. Few recent studies suggest the involvement of cytochrome P450 and UDP-glucuronosyltransferase in geosmin biotransformation in the liver as well as causing oxidative stress in fish (Zhang et al., 2024). The objective of this study was to quantify the absorption kinetics and dynamics of geosmin across three biological tissues: fillet, blood, and liver. Additionally, the study aimed to evaluate the excretion/breakdown of geosmin in the liver and the presence of hormonal stress response. During the trial, rainbow trouts (Oncorhynchus mykiss) were unfed and kept in static water conditioning tanks. Pure geosmin standard was spiked at 400 ng/L and the respiratory uptake and metabolism in juvenile rainbow trout was assessed over time (144h), applying the Before-After-Control-Impact design, hence sampling animals before spiking geosmin and fishing out one entire treatment and one control tanks at five time points. The water, fish blood, fish fillets and livers were collected at each sampling event. A subsample of blood was set aside for biochemical profiling of the blood plasma. Geosmin was traced and quantified with sensory evaluations combined with analytical methods (gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-MS). This research offers valuable insights on the biological mechanism governing geosmin absorption and excretion/breakdown in aquaculture fish and suggests strategies for mitigating off-odours in aquaculture seafood.
References
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