Off-flavors imparted by the environmental chemical geosmin (GSM) can render aquacultural food products objectionable to consumers. Therefore, sensory evaluation (or “flavor checking”) is often used for quality control. A sensory threshold is a stimulus level (e.g., a flavor intensity) sufficient to produce a change in response, such that: a flavor is just noticeable (detection or difference threshold), the flavor can be identified (recognition threshold), or an off-flavor renders the product unacceptable (rejection threshold).
The present research investigated: 1. The terms consumers use to best describe aroma and flavor of GSM in water, and 2. Sensory thresholds for GSM in Rainbow Trout fillets.
To determine a recognition threshold for GSM, appropriate flavor descriptors must be used. Therefore, a sensory test was conducted with 188 consumers to select the most relevant terms. Across low (20 ppt), medium (200 ppt), and high (1000 ppt) GSM solutions, “earthy” was the most commonly used word to describe GSM flavor and aroma.
GSM was imparted into trout fillets through their diets using a newly proposed model system involving spiking feed to known concentrations. Preliminary detection, recognition, and rejection thresholds were investigated for GSM in air fried trout fillets. However, based on 132 consumer responses, concentrations of 500-600 ppt racemic (+/–)-GSM in fillets did not present significant differences in overall aroma/flavor, liking, nor acceptability, and thresholds were not identified.
Data from these two studies highlight the differences in perception between GSM in water versus a more complex food matrix such as fish muscle. Whereas no sensory thresholds were found in fillets containing up to 588 ppt GSM, GSM taste intensity was considered moderate by 31% and strong by 24% of consumers when present at 200 ppt in water. Therefore, higher concentrations are needed in fillets to find reliable thresholds of interest.