Omega-3 Content of Fish Oil Supplements as Monitored by Benchtop Time-domain NMR

Benchtop time-domain nuclear magnetic resonance (TD-NMR) is well suited for probing the visco-elastic and phase properties of samples of biological and industrial interest. Unlike conventional NMR spectroscopy, TD-NMR relaxometry does not require homogeneous magnetic fields and can be performed using relatively simple low-field instruments. Using TD-NMR, we observed that the T2 values of hydrocarbon chains in non-esterified fatty acids were linearly correlated with fluidity and dependent on cis-double bond content (Robinson, M.D, & Cistola, D.P., 2014, Biochemistry 53, 7515-7522. DOI:10.1021/bi5011859). Here we apply this method to analyze the omega-3 fatty acid content of triglyceride-based fish-oil supplements. The standard chemical methods for assessing the purity and potency of commercial fish oil products are expensive and tedious. Therefore, there is a need for simpler, non-invasive methods for quality control during manufacturing and for consumer safety monitoring. Using TD-NMR, the T2 profiles for pure triglycerides and mixtures reveal four resolved domains, corresponding to different segments of the hydrocarbon chain as well as the glycerol backbone. The T2 value for each resolved domain increases with the number of cis-double bonds. Across a wide series of pure triglycerides, mixtures and commercial fish-oil supplements, the T2 values are linearly correlated with percent ω-3 content, as quantified by gas-liquid chromatography. These results provide a framework for developing a quick, non-invastive benchtop TD-NMR method for analyzing the quality and potency of fish oil products.