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Open AccessArticle

Continuous Gradient Temperature Raman Spectroscopy of Fish Oils Provides Detailed Vibrational Analysis and Rapid, Nondestructive Graphical Product Authentication

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Sensors Development Laboratory, Environmental Microbial and Food Safety Laboratory, United States Department of Agriculture Agricultural Research Service, 10300 Baltimore Avenue, Beltsville, MD 20705, USA
2
Department of Mechanical Engineering, University of Maryland Baltimore County, Baltimore, MD 21250, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Keith C. Gordon
Molecules 2018, 23(12), 3293; https://doi.org/10.3390/molecules23123293
Received: 31 October 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 12 December 2018
(This article belongs to the Special Issue Raman Spectroscopy: A Spectroscopic 'Swiss-Army Knife')
Background: Gradient temperature Raman spectroscopy (GTRS) applies the continuous temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a new means for rapid high throughput material identification and quality control. Methods: Using 20 Mb three-dimensional data arrays with 0.2 °C increments and first/second derivatives allows complete assignment of solid, liquid and transition state vibrational modes. The entire set or any subset of the any of the contour plots, first derivatives or second derivatives can be utilized to create a graphical standard to quickly authenticate a given source. In addition, a temperature range can be specified that maximizes information content. Results: We compared GTRS and DSC data for five commercial fish oils that are excellent sources of docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3). Each product has a unique, distinctive response to the thermal gradient, which graphically and spectroscopically differentiates them. We also present detailed Raman data and full vibrational mode assignments for EPA and DHA. Conclusion: Complex lipids with a variety of fatty acids and isomers have three dimensional structures based mainly on how structurally similar sites pack. Any localized non-uniformity in packing results in discrete “fingerprint” molecular sites due to increased elasticity and decreased torsion. View Full-Text
Keywords: gradient temperature Raman spectroscopy; Raman spectroscopy; long chain polyunsaturated fatty acids; DHA; EPA; fish oil; cod liver oil; eicosapentaenoic acid; docosahexaenoic acid gradient temperature Raman spectroscopy; Raman spectroscopy; long chain polyunsaturated fatty acids; DHA; EPA; fish oil; cod liver oil; eicosapentaenoic acid; docosahexaenoic acid
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Broadhurst, C.L.; Schmidt, W.F.; Qin, J.; Chao, K.; Kim, M.S. Continuous Gradient Temperature Raman Spectroscopy of Fish Oils Provides Detailed Vibrational Analysis and Rapid, Nondestructive Graphical Product Authentication. Molecules 2018, 23, 3293.

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