Improved quantification of geosmin and 2-methylisoborneol in farmed fish using stable isotope dilution GC-MS

Authors: Dupre, Rebecca; Smith, Brennan; Lloyd, Steven; TRUSHENSKI, JESSE - Riverence Holdings Llc

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2024
Publication Date: 3/14/2024
Citation: Dupre, R.A., Smith, B., Lloyd, S.W., Trushenski, J. 2024. Improved quantification of geosmin and 2-methylisoborneol in farmed fish using stable isotope dilution GC-MS. Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.3c08130.
DOI: https://doi.org/10.1021/acs.jafc.3c08130

Interpretive Summary: Farmed fish is prone to developing "off-flavors", caused by naturally-occurring microbial metabolites. The off-flavors are typically attributed to geosmin (GSM) or 2-methylisoborneol (MIB). Accumulation of GSM and MIB in farmed fish can be rapid and unpredictable, and removal methods are both time-consuming and costly to farmers. Research of improved preventative and corrective strategies is hindered by the impractical and imprecise methods for measurement of GSM and MIB in fish. In an effort to improve upon existing analytical methods, a multi-sample preparation approach was developed. This revised approach requires less fish and less extraction time per sample compared to previously published methods. Additionally, the accuracy of GSM and MIB measurements in fish is improved by implementing internal standards. These internal standards effectively normalize sample-to-sample deviations that exist in measurements of biological samples. The availability of a practical and accurate method for measurement of GSM and MIB in fish will help researchers understand the dynamics of off-flavors in popular farmed species such as catfish and trout.

Technical Abstract: A requisite to improving the taste and odor attributes of farmed fish is the availability of accurate and practical analytical methods to quantify 2-methylisoborneol (MIB) and geosmin (GSM). Solid phase microextraction (SPME) enables reliable measurement of ng/L quantities of MIB and GSM in water. In contrast, direct headspace (HS)-SPME of biological matrices with variable proximate compositions can increase bias and uncertainty in off-flavor determinations. Analytical recovery plays a crucial role in accurate determination of MIB and GSM in fish, and this study investigates strategies to maximize and account for this recovery factor. MIB and GSM values in off-flavor catfish and trout were measured using direct HS-SPME and distillation as sample preparation techniques. Trout samples prepared by distillation yielded 10-fold higher GSM recoveries than direct HS-SPME (31% versus 3%). A stable isotope dilution method (SIDM) was implemented by routinely spiking samples with known quantities of deuterium-labeled MIB and GSM, allowing for correction of sample-to-sample recovery deviations. SIDM-determined GSM values generated recoveries of 106% and 95% for direct HS-SPME and distilled trout, respectively. Aspects of the strategies and techniques presented can be incorporated into existing analytical methods to improve accuracy and sample throughput. Particularly, routine inclusion of SIDM in the evaluation of MIB and GSM can facilitate identification of reliable practices to control off-flavors in aquaculture.