Olfactory Threshold Concentration of Two Typical Earthy-Musty Odour Compounds in Black Carps and Bighead Carps

2-methylisoboneol(2-MIB)and geosmin are two typical earthy-musty odour compounds in freshwater.In order to investigate the olfactory thresholds of 2-MIB and geosmin in black carp(Mylopharyngodon piceus)and bighead carp(Hypophthalmichthys nobilis),an improved and optimized pre-treatment method of adsorbing the earthy-musty odours combined with the technology of gas chromatography following microwave distillation-headspace solid-phase microextraction was developed.The fish back muscle samples were placed in vials with the 2-MIB/geosmin solution and reached the adsorption equilibrium.Some samples were evaluated by a panel of ten members using Flavour Profile Analysis(FPA)method,the remaining sample was used for instrumental analysis.In fish muscle blocks,it took 90 and 105 min to establish the absorption equilibrium of 2-MIB and geosmin,respectively.The olfactory thresholds of 2-MIB in the bodies of black carps and bighead carps were 0.35μg/kg and 0.30μg/kg,respectively,while the geosmin thresholds were 0.59μg/kg and 0.51μg/kg,respectively.The concentrations of 2-MIB and geosmin in the bodies of black carps were slightly higher than in bighead carps,which were probably caused by the differences in the body fat content and the volatility of 2-MIB and geosmin.

Accumulation and Elimination Kinetics of 2-Methylisoborneol in Crucian Carp (Carassius carassius)

2-methylisoborneol(2-MIB) is a common, earthysmelling compound that causes taste and odor issues in aquaculture. To quantify the distribution, absorption, and depuration of 2-MIB in crucian carp(Carassius carassius), we detected and measured 2-MIB it via microwave, headspace solid-phase microextraction(HS-SPME), and gas chromatography before and after exposing fish to two different concentrations of 2-MIB(200 ng/L and 500 ng/L). The results showed that during the exposure time, the fish absorbed 2-MIB rapidly within 4 h. After exposure to 2-MIB for 120 h, the 2-MIB in gill and liver were rapidly removed. The processes of accumulation and elimination of 2-MIB in fish were investigated using the one-compartment kinetic model. The modeling results showed that the range of the uptake rate constant(k1) was 0.49-6.91. The range of the elimination rate constant(k2) was 0.05-0.27 and uptake rates were higher than elimination rates. The bioconcentration factor(BCF) was estimated according to the physicochemical properties of 2-MIB, and the bioaccumulation of 2-MIB in fish had a close correlation with the octanol/water partition coefficient(Kow).