Raman spectroscopy for food applications
- How does it work?
- What can it be used for?
- What can it not be used for?
- Related Facilities
- Further Information
|Key words||Raman spectroscopy, scattered light, adulteration, Rayleigh scattering, non-destructive technique|
|Completed by||UTCN, IRTA|
How does it work?
|Primary objective||Non-destructive analysis of food substances, food authentication, traceability and quality control.|
|Working principle|| Raman spectroscopy is a usefull technique for determining structural information of solid samples and aqueous solutions . In fact, a Raman spectrum presents well-resolved bands, carrying information on the vibrational band energies of molecules.
In a Raman spectrometer, a laser beam is fired through a window and reflected by a mirror to the filters that guide the photons to the sample. A set of mirrors are gathering the scattered photons reflected by the sample and pass them through the monochromatore that reduces stray light. Scattered light is light transformed in a spectrum by a photomultiplier tube . The spectrum is confronted with databases of reference spectrums for chemical identification.
Figure 1: Sketch of a Raman spectrometer set-up A small amount of the scattered light is shifted in energy from the laser frequency due to interactions between the incident electromagnetic waves and the vibrational energy levels of the molecules in the sample. Plotting the intensity of this "shifted" light versus frequency results in a Raman spectrum of the sample.
Figure 2- Raman and Rayleigh effects. ext frequency of the incoming (excitation) laser.
Raman spectroscopy can be used for both qualitative and quantitative determinations, since band areas are proportional to concentration. Not all molecules are “Raman active”, since a change in polarisability must be involved. By infrared spectroscopy, on the other hand, only the transitions that cause a change in dipole moment can be observed, leading therefore to different vibrational transitions. This makes the two techniques complementary.
There are different Raman techniques, such as Fourier Transform Raman Spectroscopy (FT-Raman), Surface Enhaced Raman spectroscopy (SERS), Confocal raman Microscopy, Coherent anti-Stokes Raman Scattering (CARS), Resonance Raman Spectroscopy and Raman Sensing. Raman Sensing is related with low-cost fibres optics and miniaturized detectors to be used in remore sensing . For some applications, Raman spectroscopy can be coupled with chemometric analysis (PLS, cluster analysis, etc.) in order to have an appropriate calibration.
|Important process parameters||Acquisition time, intensity of laser, calibration solutions|
|Important product parameters||Polarizability, intrinsic fluorescence properties at excitation frequency|
What can it be used for?
|Products||Most food products with weak intrinsic fluorescence at the excitation frequency.|
|Operations||Raw material authentication, quality assessment|
|Solutions for short comings||
What can it NOT be used for?
|Products||A Raman signal is weak and often hidden by the intrinsic fluorescence of the product. Products with a high fluorescence in the visible and NIR range are not suitable for Raman spectroscopy.|
|Operations||It can not be used in harsh environment.|
|Other limitations||Significantly higher costs compared to IR instruments.|
|Risks or hazards||This technology can be risky for operators; risks are related with the use of laser light (optical hazard).|
|Maturity||Mainly used on lab-scale. Affordable portable Raman spectroscopy systems are also available on the market.|
|Modularity /Implementation||It can be used along the production line (continuous). Since measurement can take place through fibre optic and an apropiated probe, the Raman equipment can be located separately from the production line.|
|Consumer aspects||No literature available.|
|Legal aspects||Please check local legislation.|
|Environmental aspects||No literature available.|
Facilities that might be interesting for you
|Institutes||University of East Anglia, University of the Basque Country, University College Dublin - Agriculture and Food Science, Walloon Agricultural Research Centre, CSIC - Instituto de la grasa, AFRC Institute of Food Research|
|Companies||Thermo Scientific, Renishaw, River Diagnostics, HORIBA Scientific, CRAIC Technologies, Ocean Optics|
Acquisition time, intensity of laser, calibration solutions Polarizability, intrinsic fluorescence properties at excitation frequency Electro-Magnetic equipment 2.1.1 physical other other Literature review, Wiley.com, Web of Knowledge, Amazon.com, Google Books Search terms: Raman spectroscopy, Raman spectroscopy for food applications, Raman and food WikiSysop :Template:Review document :Template:Review status