The majority of off-flavor problems in catfish are caused by Geosmin (GSM) and 2-methylisoborenol (2MIB), two metabolites generated by cyanobacteria in the water column. They contribute a muddy, musty aroma to the flesh of the fish at very low concentrations (sub parts per billion). The human nose is very sensitive to these compounds and in some ways superior to modern analytical techniques. Their presence in water creates a problem, not only for the aquacultural industry, but for municipal and potable water supplies as well. These compounds are hydrophobic and can be bioaccumlated in aquaculture products, such as catfish, trout, sturgeon and even farm raised shrimp in lipophylic tissues. Quality assessment of these products is generally accomplished by professional flavor checkers who sniff and/or taste representative samples. Due to the rather unremarkable chemical structure of these compounds, the analytical methods available are time consuming, costly, and consequently found only at research institutions and not within the industry. This research reports on the optimum sampling conditions for flavor checkers to detect these compounds. Cooked and uncooked, location, and storage of catfish samples consisting of 20g of fillet tissue were analyzed following various treatments. Samples were prepared by microwave desorption of the minced tissue and the steam distillate collected in a cold trap. The aqueous solution was analyzed by solid phase microextraction/gas chromatography/mass spectrometry. Concentrations of 2MIB and GSM were detected in all fish and varied significantly between sites within a single fillet. Blended fillets served as controls and showed little variation between repetitions but significant differences in concentrations for both 2MIB and GSM were observed between individual fillets. Cooked fish showed as much as a 60% reduction for 2MIB and 20% for GSM relative to the uncooked samples. Frozen samples resulted in water loss upon thawing, which served to increase the off flavors in the remaining tissue. Maximum concentrations were observed in raw, fresh fillets, in areas of high fat deposits.

Optimizing the analysis for off-flavors in fish tissue

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.