What is spectroscopy?

An example of application of vibrational spectroscopy

Previously, I wrote about the fact that spectroscopy can be a valuable tool for food chemists and I provided an example of it in milk authenticity analysis. Moreover, Chiung-Wei, one of the women in STEM I interviewed, is an expert of the field.

Vibrational spectroscopy is called a “non-targeted approach”. I wrote about this kind of analysis here. Spectroscopy methods measure the interaction of samples with the electromagnetic radiation (in this case, with the infrared light).

Samples are irradiated with infrared light and the radiation can be reflected, absorbed or transmitted, depending on the chemical composition of samples. Instruments for spectroscopy detect the intensity of the radiation coming from the sample and produce a spectrum. The spectrum is the fingerprint of the sample.

Now, a practical example: we have hundred of almonds (see the figure above). Producers claim they all have the same geographical origin.

Food scientists analyze the almonds using a spectroscopy technique (step 1) and the spectra are collected (step 2). Statistical analysis involving Principal Component Analysis (PCA) allow researcher to visualize the data in a more “understandable” way (step 3). By looking at the graph (step 4), it is clear that the almonds can be divided in three groups, accordingly to their geographical origin (Spain, USA and Australia).

Food scientists just performed a food authenticity analysis and discover a food fraud.


Ellis et al., 2015, “Point-and-shoot: rapid quantitative detection methods for on-site food fraud analysis – moving out of the laboratory and into the food supply chain”, Analytical Methods, vol. 7, pp. 9401-9414

McGrath et al., 2018, “What are the scientific challenges in moving from target to non-targeted methods for food fraud testing and how can they be addressed? – Spectroscopy case study”, Trends in Food Science & Technology, vol. 76, pp. 38-55

Vlachos et al., 2006, “Applications of Fourier transform-infrared spectroscopy to edible oils”, Analytica Chimica Acta, vol. 573-574, pp. 459-465

Weyer, 2006, “Handbook of Vibrational Spectroscopy”, New York: John Wiley & Sons, Inc.

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