Dietary exposure to geosmin as a means of inducing off-flavor in rainbow trout fillets

Authors: Ardoin, Ryan; Grimm, Casey; DUPRE, REBECCA - Orise Fellow; TRUSHENSKI, JESSE - Riverence Holdings Llc; JACKSON, CHRIS - Riverence Holdings Llc; Smith, Brennan

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/4/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Muddy/earthy flavors in catfish and other farmed fish are considered defects that can result in rejection of these foods by consumers. Geosmin is one chemical known to cause these off-flavors in fish products. This study investigated a novel method to impart geosmin into rainbow trout fillets, by incorporating the chemical into their feed. It was found that dietary geosmin was effectively absorbed into trout fillets during a four week trial. Higher dosing of geosmin resulted in higher concentrations in fillets. Therefore, dietary geosmin can serve as a controlled method to introduce off-flavors into fish fillets and allow researchers to explore methods to get rid of these flavor defects and improve acceptability of farm-raised fish products.

Technical Abstract: Introduction: Geosmin contributes to muddy/earthy off-flavors in farmed fish. Waterborne geosmin is absorbed into fish tissues during ventilation. However, the present study explored dietary exposure as an alternative route of geosmin absorption in Rainbow Trout (Oncorhynchus mykiss). The objectives were to 1) investigate the potential of dietary geosmin to accumulate in trout flesh and 2) to assess whether diet and/or water concentrations and duration of exposure affect geosmin concentrations in raw fillets. Methods: Rainbow Trout were raised in quadruplicate four-compartment raceways supplied with 1st use, flow-through water. Compartments were stocked with fingerling trout, and fish were fed typical trout feeds spiked with geosmin at 0, 0.005, 0.05 or 0.5 mg geosmin kg-1 feed. To limit the potential of diet leaching and confounding effects of aqueous exposure, feeds were assigned to compartments within each raceway from lower to higher concentrations in the direction of water flow. Three fish per compartment were analyzed after one, two, three, or four weeks of feeding (n = 12, N = 4 per diet/time combination). Geosmin in fillets was quantified using microwave distillation-solid-phase microextraction with gas chromatography–mass spectrometry. Weekly water samples were also analyzed. Statistical analyses included ANOVA, polynomial contrasts and regression (a=0.05). Results: Feed spiked with geosmin effectively imparted this off-flavor compound into trout fillets throughout the trial. Level of geosmin in feed had a significant positive quadratic effect on concentrations in fillets. Mean geosmin concentration was highest (414 ppt) in fillets fed the 0.5 mg geosmin kg-1 feed diet after four weeks, and feed geosmin levels were directionally reflected in tissues during each week of the experiment. No significant overall effect of feeding duration nor geosmin content of water was found. These results suggest that geosmin accumulation in fillets was most associated with levels in feed, with higher doses resulting in greater tissue accumulation of geosmin. Significance: Dietary geosmin exposure results in predictable accumulation in the edible tissues of Rainbow Trout. Geosmin-spiked feeds may be used to induce repeatable levels of muddy/earthy off-flavor in Rainbow Trout fillets and serve as a model system for further investigation of corrective strategies to improve sensory quality of farmed trout.