The issue is a hot topic in New Zealand and Australia after a wave of negative media coverage followed a hotly-disputed 2015 study which argued only three of 32 products tested met label claims, with the vast majority also displaying excess oxidation markers.
However, scientists at Plant & Food Research and the University of Otago have now used Raman spectroscopy, which involves directing a laser at the target material, in this case the capsule and oil, and measuring the small fraction of light that is scattered.
The scattered light provides a fingerprint of the chemical composition of the oil as well as other useful information around oxidation.
The researchers used 11 brands of polyunsaturated fatty acids (PUFA) oil capsules commonly available on New Zealand shelves.
“Our analysis of Raman spectral variance allowed us to generate models for a range of saturated, monounsaturated and polyunsaturated fatty acids,” said Plant & Food Research marine products scientist Dr Daniel Killeen.
“Although the sample size was relatively small, the preliminary results strongly suggest that the method is a useful tool for rapid quality control of soft gel capsules without compromising the structure of the capsule itself.
“Interestingly, in performing our research, we found the concentration of omega-3 oils across all eleven commercially available samples to be in line with their label claims, which should give consumers reassurance regarding the quality of the oil in the capsules.”
Findings questioned
This latest research further calls into questions conclusions made in 2015 that New Zealand and Australian products contained substantially lower EPA and DHA content than the label stated and were also heavily oxidized.
The claims, made in a study led by the Liggins Institute at the University of Auckland, were subsequently queried earlier this year by industry-backed research, which also found products met their label requirements.
The current study, published in the Journal of Agriculture and Food Chemistry, states that Raman spectroscopy can be used to assess oxidation levels.
“Polyunsaturated oils are vulnerable to oxidation, especially at higher temperatures and when exposed to UV radiation. Some studies have associated oxidised fish oil with negative health outcomes,” said Dr Killeen.
The researchers filled empty capsules with oil that had been deliberately oxidised and compared the results with the unoxidised oil in the purchased capsules.
“We found Raman spectroscopy to have high sensitivity for distinguishing fresh oils from those that had been oxidised. This positions the method as a faster, more direct and more sensitive way to identify oxidation in fish oils than other approaches,” said Dr Killeen.
“The deficiency of polyunsaturated fatty acids, such as omega-3 in the Western diet has created a high global demand for dietary supplements, such as fish oil. This makes rapid and effective quality control methods highly desirable to give consumers assurance and help producers in markets with strict regulations.”
Source: Journal of Agriculture and Food Chemistry
DOI: 10.1021/acs.jafc.7b00099
“Raman Spectroscopy of Fish Oil Capsules: PUFA Quantitation plus Detection of Ethyl Esters and Oxidation”.
Authors: Daniel P. Killeen, et al.