Sensory properties and analysis of two muddy odour compounds, geosmin and 2-methylisoborneol, in water and fish

Muddy or earthy odours are a problem in water supplies and fisheries. Some species of aquatic actinomycetes and blue-green algae are generally indicated as sources of muddy odour in natural waters. These organisms are capable of producing the muddy-smelling compounds geosmin and 2-methylisoborneol. The sensory properties of geosmin and 2-methylisoborneol in water and in the flesh of four species of fish were studied. Threshold odour concentrations are presented, and they indicate that both compounds have strong odour characteristics. The intensity of the muddy odour as perceived by the judges was proportional to the logarithm of the concentration of muddy odour compounds in the concentration ranges tested (for geosmin, up to 100 μgkg−1, and for 2-methylisoborneol, up to 10 μg kg−1). The results indicate that it may be possible to quantify muddy odour compounds in water and fish by sensory methods.