A Comprehensive Study via Proton Nuclear Magnetic Resonance of a Variety of Omega-3 Lipid-Rich Supplements Available in the Spanish Market: Acyl Group Profile, Minor Components, and Oxidative Status

Dietary supplements are a means of increasing the consumption of beneficial ω-3 lipids. Their composition in acyl groups, the structures supporting them, and their minor component profile can influence their oxidative stability and even their health effects. However, information about all these features is not always provided to consumers. The purpose of this study was to characterise via Proton Nuclear Magnetic Resonance (¹H NMR) a variety of ω-3 lipid-rich supplements available in the Spanish market, addressing the previously mentioned aspects, together with their oxidative status. Despite not being indicated on the labelling, ethyl esters were found in most fish oil concentrate-based supplements, sometimes as the main lipid class. Furthermore, considerable levels of partial glycerides were present in some samples. Minor components include tocopherols, sterols, terpenic compounds from added flavourings, and vitamin A, many of them with antioxidant and/or bioactive potential. In addition, other unexpected compounds such as BHT and ethanol were detected. Some discrepancies between real sample composition and label information have been noticed regarding the tocopherol profile. Most supplements contained small quantities of hydroperoxides and considerably fewer aldehydes, with significant differences observed among samples, which were not directly associated with their unsaturation degree. These outcomes reinforce the usefulness of ¹H NMR to provide data about key factors determining the quality of ω-3 lipid-rich supplements in a very simple and fast way.