Although not yet used as commonly as in other scientific fields, Raman spectroscopy is gaining popularity as an analysis technique in food and beverage applications.

Typically, analytical techniques for food and beverage characterization involve determination of the composition via quantitative methods, quality control (including adulteration, bacterial contamination), and identification of impurities or undesired material. Usually, chromatography (GC, GC-MS, HPLC), is employed for such characterization but might be time-consuming, use solvents and require sample preparation. Additionally, contrary to infrared techniques, Raman spectroscopy is not sensitive to high water content, and is thus well adapted to analyze aqueous solutions.

Raman imaging of a thin section of maize cells on a CaF2 substrate.

Raman imaging of a thin section of maize cells on a CaF2 substrate
Acknowledgement : Dr Reg Wilson and Dr Klaus Wellner - Institute of Food Research (IFR), Norwich, United Kingdom

From macro to micro analysis
Raman spectroscopy can be used to examine powders, solids, liquids in different geometries. For example, bulk measurements for assessing the quality of powders or translucent samples can be performed by Transmission Raman to obtain spectra from large volumes. Quantitative analyses based on Raman spectroscopic data of bulk material, representative of the whole sample are then possible. On the other hand, micro Raman brings information on micrometer level, which is required when assessing the distribution of components in grains, particles within powders, or micro-organisms present in foods.

SERS analysis
Usually not sensitive to trace amounts of compounds and limited to the quantification and detection of the major compounds of a mixture, Raman spectroscopy, via the use of SERS (surface enhancement Raman spectroscopy), has proven to be very useful in the detection of trace materials such as pesticides in fruits. SERS involves the enhancement of the Raman signal, using gold or silver nano-substrates, thus allowing the detection of trace organic compounds down to ppm levels.

Typical applications:

Determination of fat / oil composition

Adulteration of oil

Detection and Identification of bacteria and other micro-organisms

SERS detection of pesticides in foods

Analysis of Carotenoïdes

Detection of Melamine in milk

Structural characterization of grains, crops, ...

Quantitative analysis

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