You say tomato: Raman reads lycopene

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  • Published: Jun 10, 2016
  • Author: David Bradley
  • Channels: Raman
thumbnail image: You say tomato: Raman reads lycopene

Seeing red

Toward food analytics: fast estimation of lycopene and ß-carotene content in tomatoes based on surface enhanced Raman spectroscopy (SERS) Tomatoes photo by David Bradley

Surface enhanced Raman spectroscopy (SERS) could be a more tenable tool than HPLC in studying carotenoids and other micronutrients present in our food, according to a German study.

While there is ongoing debate about the true benefits of antioxidants on human health, particularly with respect to dietary supplementation it remains current that the presence of highly coloured pigments in the fruit and vegetables we eat do seem to have a positive effect on physiological markers. One such compound, the red pigment lycopene, found in tomatoes, is considered beneficial in general and more specifically in terms of a putative link between eating this popular fruit we often think of as a vegetable and a lower risk of prostate cancer.

Andreea Ioana Radu, Oleg Ryabchykov, Thomas Wilhelm Bocklitz, Uwe Huebner, Karina Weber, Dana Cialla-May, and Jürgen Popp of the Friedrich Schiller University Jena, Institute of Physical Chemistry and Abbe Center of Photonics, and the Leibniz Institute of Photonic Technology Jena, in Germany, writing in The Analyst point to a deficit in our knowledge of lycopene and other carotenoids. They suggest that while much is known about lycopene and beta-carotene, less is known about these compounds in the plant phase. As such, they have turned to surface enhanced Raman spectroscopy (SERS) to help them differentiate between carotenoids in the plant.

Ingestion insights

The team created a suitable simulated matrix was simply by mixing the two carotenoids in defined proportions and then used e-beam lithography (EBL) SERS-active substrate and a 488 nanometre excitation source to probe the sample. They also extracted carotenoids from actual tomato plants and measured those and applied a combination of principal component analysis and partial least squares regression (PCA-PLSR) to the data. They then compared the results with high-performance liquid chromatography (HPLC) measurements of the same extracts. "A good agreement was obtained between the HPLC and the SERS results for most of the tomato samples," the team reports.

The reason that such analytical techniques are important is that despite their being some 600 known carotenoids a mere fifty of those are present in the human diet and just a handful of that fifty is detectable in human blood plasma, namely alpha- and beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin. If these compounds are truly essential to good health, there is something of a discrepancy, one must assume between the abundance of this group of antioxidants in plants in general, among those we eat and within that group the ones that seem to circulate in our blood, presumably for our benefit.

Some of the carotenoids are pro-vitamins forming vitamin A through metabolic activity, but some have oxygen and radical-scavenging properties of their own. This is important given that vitamin A from oily fish, liver and eggs does not always provide enough for our needs. Lycopene itself, of the 5 or 6 carotenoids usually detectable in plasma, is the most efficient in neutralising reactive oxygen species. It is also known to reduce cell division that might occur during the development of cancer. All that said, the detrimental effects of tobacco smoking and alcohol consumption on the body are thought to be exacerbated by excessive carotenoid ingestion.

Please SERS

"It is, accordingly, important from a health point of view to have a balanced dietary regime," the team asserts, emphasising that to achieve such a regime, one must have detailed information regarding the quality and composition of the food one eats. They point out that HPLC is the "golden standard" analytical technique in such endeavours, however it is cumbersome and expensive, whereas SERS offers several advantages provided it can distinguish between the carotenoids at low concentrations in real-world samples. The team obtained "a good agreement" between their HPLC and SERS results for most of their tomato samples at different stages of ripeness, which bodes well for the further development of this technology.

Related Links

Analyst 2016, online: "Toward food analytics: fast estimation of lycopene and ß-carotene content in tomatoes based on surface enhanced Raman spectroscopy (SERS)"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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