NMR analysis enables differentiation of tomatoes by geographical origin

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“Despite the annual differences in 1H NMR metabolic profile of Sabaudia cherry tomatoes…the geographical origin differentiation was obtained”

With global trade in foodstuffs now being commonplace, it is especially important to be able to trace the geographical origin of a particular product. This becomes an essential requirement when some products assume elevated value by virtue of the region in which they were produced, e.g., champagne and manuka honey.

Geographical certification is thus a matter of great importance for producers and consumers alike. For producers, it provides a tool enabling them to differentiate their products on the global market and minimizes the risk of being undercut by cheap imitations. Customers with a preference for the characteristic features or taste of produce from a particular region can be assured they are receiving the product they require. Geographical certification consequently provides an indicator of quality assurance. Obviously, to maintain this reputation, it is fundamental that the origin of a product can be proven.

Since the chemical composition of produce is determined by the soil composition and climatic conditions, analysis of the precise chemical content can therefore be used to verify the geographical origin.

A wide range of analytical techniques is available for conducting such measurements, such as isotopic methods, Fourier transform infrared spectroscopy and Raman spectroscopy, and mass spectrometry combined with either gas chromatography or liquid chromatography. Nuclear magnetic resonance spectroscopy (NMR) is particularly favored for the determination of geographical origin due to its ease of execution and the ability to identify all the components present in a single analysis. Indeed, it has proved to be a valuable tool in the verification of the geographic origin of many foodstuffs. It has also successfully discriminated between organic and conventional tomatoes and identified tomatoes from genetically modified plants.

The technique has recently been applied to the differentiation of cherry tomatoes according to geographic origin. Tomato is widely used in Italian cuisine and consequently, Italy is a key producer of tomatoes. A wide diversity of traditional tomato varieties has been developed during Italy’s long history of tomato cultivation. There are now about 92,000 hectares dedicated to tomato production across many different regions in Italy.

Previous research has shown that Sicilian cherry tomatoes of different provenance can be successfully distinguished using a simple separation analysis. However, the final composition of the tomato varies by year according to prevailing climatic conditions. For example, the lycopene content of a tomato is determined by temperature.

The latest study investigated whether NMR could be used to determine the geographical origin of cherry tomatoes despite variations in composition between crops harvested in different years. Shiren cherry tomatoes grown in Pachino (Sicily) and Sabaudia (Latium) were analyzed by 1H NMR using a Bruker AVANCE 400 MHz spectrometer. The spectra obtained were compared using three steps of multivariate statistical analysis. The internal morphological organization of the tomatoes was also visualized by magnetic resonance imaging using a Bruker Avance 300 MHz spectrometer.

The Sabaudia cherry tomatoes from 2004 were found to have higher levels of phospholipids but fewer polyunsaturated acids and lycopene than those of 2005. MRI data also detected differences in the pericarp of tomatoes between tomatoes from different harvesting years.

Despite the chemical variations between crops from different years, it was still possible to differentiate Sabaudia cherry tomatoes from Pachino cherry tomatoes using NMR spectra. The nearest neighbor algorithm classified the Pachino tomatoes with 84% to 87% accuracy and the Sabaudia tomatoes with 77% accuracy. The recognition ability varied from 82% to 84.4% and the prediction ability from 76% to 95%. Better recognition and prediction abilities were achieved using a PCA analysis, whilst maintaining a high level of separation of Pachino and Sabaudia cherry tomatoes. The key components enabling discrimination of the cherry tomatoes by region were phytosterols and differences in aroma components.

Reference

  • Masetti O, et al. Journal of Chemometrics. 2020;34:e3191.

About Bruker BioSpin - NMR, EPR and Imaging

Bruker BioSpin offers the world's most comprehensive range of NMR and EPR spectroscopy and preclinical research tools. Bruker BioSpin develops, manufactures and supplies technology to research establishments, commercial enterprises and multi-national corporations across countless industries and fields of expertise.


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Last updated: Nov 23, 2021 at 10:35 AM

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