Assessing Off-Flavor in Fish Tissue

Authors: Grimm, Casey; Lloyd, Steven; Bosworth, Brian; Bett Garber, Karen

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: There are several methods for detecting the off-flavor compounds in water. However, detecting and quantifying these same compounds in fish is problematic as they tend to reside in the fatty parts of the tissue. Furthermore, the compounds may be distributed unevenly throughout a fish fillet. In an attempt to optimize the off-flavor assessment, a single fish fillet was sampled at multiple locations and then the remainder of the filet blended and sampled. The data show that there is an uneven distribution of off-flavor compounds randomly spread throughout the fish. This work would be of interest to quality assessment groups in the aquaculture industry.

Technical Abstract: Geosmin (GSM) and 2-methylisoborenol (2MIB) are two metabolites generated by microorganisms, such as cyanobacteria and actinomycetes. They possess dirt like odors and can be detected at very low concentrations (sub parts per billion) by the human nose. Their presence in water creates a problem for municipal and potable water supplies as well as aquaculture. These compounds are hydrophobic and can be bioaccumlated in aquaculture products, such as catfish, trout, sturgeon and even farm raised shrimp. 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 and costly, and consequently found only at research institutions and not within the industry. This research investigates the location within a fish fillet of the deposits of the off-flavor compounds in order to locate the optimal location for the best sensory or analytical assessment. Previous research has shown variations in concentration when measured longitudinally from head and tail as well as from the top of the fillet to the bottom. In the present research 20 g of fillet tissue was removed form four selected sites: dorsal, belly, tail and along the lateral line. Subsequently the remainder of the fillet was blended and triplicate samples were analyzed for a total of 7 samples per fillet for 30 fillets. 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. The blended fillets served as controls and showed little variation between the three repetitions but significant differences in concentrations for both 2MIB and GSM were observed between individual fillets. Concentrations of 2MIB and GSM were detected in all fish and varied significantly between sites within a single fillet. The site of maximum concentration for GSM and MIB was found to be inconsistent between fillets.