Geosmin and Musty-Muddy Flavors in Pond-Raised Channel Catfish

Monthly sensory (taste) analyses of channel catfish Ictalurus punctatus from 11 commercial culture ponds in Alabama during April-October 1983 showed that earthy-musty flavor was the major off-flavor during the summer growing season. Geosmin (1,10-trans-dimethyl-trans-(9)-decalol) was found by gas chromatography in detectable amounts, 3.7 to over 200 μg/kg of fish flesh, in 80% of fish having earthy-musty or detritus (pond mud) flavor. Geosmin was not found in fish without these flavors. The geosmin analysis procedure used in this study recovered 68 to 85% of geosmin added to fish flesh, at concentrations ranging from 8 to 32 μg/kg, with relatively high consistency (SD = 2.5–3.3). Reproducibility in analysis of fish with naturally occurring geosmin (6–15 μg/kg fish) was also favorable (coefficients of variation, 100˙SD/mean, 6.9–16.8%). The compound 2-methylisoborneol, found in muddy-flavored rainbow trout Salmo gairdneri, could not be confirmed as an off-flavor compound in channel catfish. The use of geosmin analysis to partially replace sensory evaluation of channel catfish for off-flavor during summer appears feasible.