Raman Spectroscopy of Fish Oil Capsules: Polyunsaturated Fatty Acid Quantitation Plus Detection of Ethyl Esters and Oxidation

Abstract

Fish oils are the primary dietary source of ω-3 polyunsaturated fatty acids (PUFA), but these compounds are prone to oxidation, and commercial fish oil supplements sometimes contain less PUFA than claimed. These supplements are predominantly sold in softgel capsules. In this work, we show that Fourier transform (FT)-Raman spectra of fish oils (n = 5) and ω-3 PUFA concentrates (n = 6) can be acquired directly through intact softgel (gelatin) capsules. These spectra could be used to rapidly distinguish supplements containing ethyl esters from those containing triacylglyceride oils. Raman spectroscopy calibrated with partial least-squares regression against traditional fatty acid methyl ester analyses by gas chromatography-mass spectrometry could be used to rapidly and nondestructively quantitate PUFA and other fatty acid classes directly though capsules. We also show that FT-Raman spectroscopy can noninvasively detect oxidation with high sensitivity. Oils with peroxide values of as low as 10 mequiv kg, which are on the cusp of falling outside of specification, could be readily distinguished from oils that were within specification (7 mequiv kg).

Response to a Comment by Albert et al. (Nutrients 2017, 9, 137) Entitled “Concerns with the Study on Australian and New Zealand Fish Oil Products” by Nichols et al. (Nutrients 2016, 8, 703)

“…The 10 products selected for analysis by the O3C represented over 80% of the Australian market, which overlaps considerably with the New Zealand market. The larger Bannenberg et al, 2017 study of >40 New Zealand samples [4], which we were aware of at the time and was cited in [2], showed results in full agreement with Nichols et al, 2016 [2], as does one further 2017 New Zealand study of 11 products [5] and a previous study of 15 products by Australia’s Therapeutic Goods Administration (TGA) [2]. …”

“…As has been demonstrated by multiple studies, in marked contrast to Albert et al, 2015 [3], the majority of Australian and New Zealand fish oil products do meet their omega-3 label claims and are not oxidized as reported in four separate studies ([2,4,5] TGA: 2).…”

Encapsulated Fish Oil Products Available in the UK Meet Regulatory Guidelines With Respect to EPA + DHA Contents and Oxidative Status

“…However, the high non‐compliance rate reported by Albert et al has been challenged by others with particular criticism directed towards the analytical methods and types of fish oil products tested . Similarly, follow‐up studies found Australasian fish oil products to have a greater compliance, in terms of EPA + DHA and oxidation status, than previously reported . Many of the samples analyzed by Albert et al for example contained flavorings, often used to mask the “fishy” taste, or whose oils were pigmented.…”

Seafood Phospholipids: Extraction Efficiency and Phosphorous Nuclear Magnetic Resonance Spectroscopy (31P NMR) Profiles

“…Some reports have associated dietary PL with unique health benefits (Schuchardt et al, 2011;Tou, Jaczynski, & Chen, 2007). Commercial fish oils consist of TAG (or in some cases ethyl esters) (Killeen, Marshall, Burgess, Gordon, & Perry, 2017), whereas commercial krill oils are high in PL (Burri, Hoem, Monakhova, & Diehl, 2016;The United States Pharmacopeia Convention, 2014). However, the PL content of krill oil depends heavily on the extraction method used: Supercritical CO 2 extraction yields oils with almost no PLs (Yamaguchi et al, 1986), but the same solvent, mixed with a polar cosolvent (20% ethanol is used commercially) extracts oils that contain 28-52% PL (Burri et al, 2016;Catchpole, Moreno, Montañes, & Tallon, 2017;The United States Pharmacopeia Convention, 2014).…”