Application of Fourier Transform Infrared Spectroscopy for the Characterization of Fish Oil-Based Food Supplements from Czech Retail Market and the Quantification of Eicosapentaenoic and Docosahexaenoic Acid Using Partial Least Square Regression

Abstract The growing demand for fish oil-based omega-3 food supplements underscores the importance of verifying their quality. This study presents the application of practical, rapid, and minimally preparative procedures based on Fourier-transform infrared (FTIR) spectroscopy combined with partial least squares regression (PLS-R) for reliable analysis. The attenuated total reflectance-FT-mid infrared (ATR-FT-MIR) technique was employed to differentiate between natural triacylglycerol (TAG) and concentrated ethyl ester (EE) forms. Additionally, direct electrospray-high resolution mass spectrometry (ESI-HRMS) was used to provide complementary lipid profile information. Data obtained from ATR-FT-MIR and FT-near infrared (FT-NIR), along with reference values from gas chromatography with flame ionization detection (GC-FID), were used to develop PLS-R models for the prediction of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). For verification of the results, FAPAS fish oil material obtained within the proficiency testing procedure was served. The model mixtures containing natural fish oil and selected plant oils (sunflower, soybean, rapeseed) as well as pure plant oils were also included in the PLS-R models aiming at the recognition of possible adulteration. Both FTIR-based models demonstrated strong linear correlations with the GC-FID reference method ( R 2 > 0.97), indicating excellent predictive capability for EPA and DHA quantification. In two of the 33 tested samples, the presence of diacylglycerols (DAG) alongside TAG was confirmed by direct ESI-HRMS. In this study, it was demonstrated that the rapid and simple FTIR spectroscopy methods represent an effective alternative to chromatographic techniques, especially for the routine analysis of fish oil supplements.