Determination of Geosmin and Methylisoborneol in Catfish Tissue (Ictalurus punctatus) by Microwave-Assisted Distillation−Solid Phase Adsorbent Trapping

Methylisoborneol (MIB) and geosmin (GEO) are algal off-flavor compounds, which when present in catfish tissue create undesirable taste and odors in the prepared products. These undesirable taste and odor problems are not limited to catfish aquaculture. A procedure was developed for the determination of off-flavor compounds in channel catfish tissue that involves microwave radiation distillation with solid phase trapping. This is a modification of a microwave distillation−cold trapping procedure but without the need of a cryogen or a liquid−liquid extraction step. A channel catfish fillet sample is placed in a container located within a microwave oven. This container, which is directly connected to a thermostated condenser containing a solid phase adsorbent, is continually purged with argon gas. The trapped distillate components are eluted with ethyl acetate and then injected into a gas chromatograph−ion trap mass spectrometer for analysis. This technique offers a rapid and sensitive means of off-flavor analysis in fish tissue and improved recovery for MIB from 73 ± 3% (50 ppb) to 85 ± 5% (10 ppm) compared to 62 ± 6% for microwave−cold trap collection. The method detection limits are 1.7 and 1.1 ppb for MIB and GEO, respectively. Keywords: Off-flavors; methylisoborneol; geosmin; catfish; microwave-assisted distillation