微波蒸馏-顶空固相微萃取-气质联用检测鱼体中土霉味化合物
ANALYSIS OF OFF-FLAVORS IN FISH BY MICROWAVE MEDIATED DISTILLATION WITH HEADSPACE SOLID-PHASE MICROEXTRACTION AND GAS CHROMATOGRAPHY-MASS SPECTRUM
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摘要: 采用微波蒸馏-顶空固相微萃取-气质联用检测鱼体中常见的两种土霉味化合物,即2-甲基异茨醇(2-MIB)和土腥素(Geosmin)。研究并优化了微波蒸馏萃取过程的关键参数(微波蒸馏时间、载气流量),结果表明微波蒸馏6min、载气流70mL/min为土霉味化合物微波蒸馏萃取的最佳条件。在此优化的条件下,土霉味化合物能够充分地从鱼体中蒸馏出来,再采用顶空固相微萃取的方法使馏分中的土霉味化合物吸附于纤维涂层上,将其在250℃高温下解吸,并用GC-MS分析。基于此测定方法,鱼肉中2-甲基异茨醇和土腥素的检测限均达到0.1μg/kg,且其在1-20μg/kg的范围内线性关系良好,相关系数R分别达到0.987、0.995。因此,用该方法分析鱼体中痕量的(ppb级)的土霉味化合物,结果可靠。Abstract: Aquaculture the rearing of fish and other aquatic animals is the best approach for meeting the increasing demand for aquaculture products worldwide. However, the problem of off-flavor has been documented as a serious setback to aqua-culture. Though there are many off-flavors can result in a fish being objectionable, approximately 80% of the rejected fish have the earthy-musty odor, which is primary caused by the presence of either 2-methylisoborneol (2-MIB) or geosmin. Based on the fact that the detection of earthy-musty odorous compounds in fish mainly relied on the sensory method in Chi-na, the present study established the instrumental method to detect 2-MIB and geosmin by microwave mediated distillation with headspace solid-phase microextraction and gas chromatography-mass spectrum (MWDE-SPME-GC-MS). Through in-vestigating the effects of the key parameters, microwave processing time and carrier gas flow rate, in microwave mediated distillation on extracts,it is concluded that 6 min of microwave time and 70 mL/min nitrogen flow were the optimized con-dition on which earthy-musty odorous compounds could be completely distilled from fish flesh. Then the earthy-musty odor-ous compounds were absorbed in the fiber under HS-SPME, and were finally desorbed at 250℃ and determined by GC-MS. The limits of detection for 2-MIB and geosmin in fish were both 0.1 μg/kg. There were significant linear correlation in the range of 1-20 μg/kg for the two earthy-musty odorous compounds, with calibration coefficients at 0.987 and 0.995, respectively. Therefore, trace levels of earthy-musty odorous compounds at ppb in fish could be quantified by this method with credible results.
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