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

摘要

Gradient Temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur at or near phase transitions. 20 Mb three-dimensional data arrays with 1.0 or 0.2°C increments allow complete assignment of solid, liquid and transition state vibrational modes, including low intensity/frequency vibrations that cannot be readily analyzed with conventional Raman. We compared GTRS and DSC data for commercial fish oil supplements that are excellent sources of docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3). Krill oils and whole fish and shellfish have nearly all their PUFA contained within phospholipids (PL). Development of any fast-throughput optical identification system for seafood products will require improved PL Raman data. We also analyzed molecularly hydrated PL with DHA and other unsaturated lipids. Each fish oil and PL have a unique, distinctive response to the thermal gradient, which graphically and spectroscopically differentiates them. 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 product or source material.