¹H NMR Spectroscopy for Determination of the Geographical Origin of Hazelnuts

Abstract

A total of 262 authentic samples was analyzed by 1H NMR spectroscopy for the geographical discrimination of hazelnuts (Corylus avellana L.) covering samples from five countries (Germany, France, Georgia, Italy, and Turkey) and the harvest years 2013–2016. This article describes method development starting with an extraction protocol suitable for separation of polar and nonpolar metabolites in addition to reduction of macromolecular components. Using the polar fraction for data analysis, principle component analysis was applied and used to monitor sample preparation and measurement. Several machine learning algorithms were tested to build a classification model. The best results were obtained by a linear discrimination analysis applying a random subspace algorithm. The division of the samples in a trainings set and a test set yielded a cross validation accuracy of 91% for the training set and an accuracy of 96% for the test set. The identification of key features was carried out by Kruskal–Wallis test and t test. A feature assigned to betaine exhibits a significant level for the classification of all five countries and is considered a possible candidate for the development of targeted approaches. Further, the results were compared to a previously published study based on LC–MS analysis of nonpolar metabolites. In summary, this study shows the robustness and high accuracy of a discrimination model based on NMR analysis of polar metabolites.

Plant Specialized Metabolites in Hazelnut (Corylus avellana) Kernel and Byproducts: An Update on Chemistry, Biological Activity, and Analytical Aspects

“…When tested for their antioxidant ability by TBARS assays, all compounds isolated from methanol extracts of leaves, flowers, and green leafy covers of Italian Tonda di Giffoni hazelnut exhibited an inhibition of lipid peroxidation at least comparable to curcumin [6,8,9]. The antioxidant activity evaluated by TEAC assay for diarylheptanoids, neolignans, phenylpropanoids, and flavonoids isolated from the hazelnut shells of the same C. avellana (cultivar Tonda di Giffoni) highlighted higher free radical scavenging activity (similar to that shown by quercetin 3-O-glucoside used as reference compound) for kaempferol 3-(4′′-cis-p-coumaroyl)-rhamnoside (41) and kaempferol 3-(4′′trans-p-coumaroyl)-rhamnoside (42), suggesting that the coumaroyl moiety improves the radical-scavenging capacity, while diarylheptanoids giffonin P (85), carpinontriol B (88), and giffonin V (89), possessing similar chemical features, characterized by the presence of 2 phenolic groups, showed a weak radical-scavenging capacity as well as threo-1,2-bis(4-hydroxy-3-methoxyphenyl)-1,3-propandiol (94) [20]. The antioxidant activities by TEAC assay have been evaluated also for both n-butanol extracts of raw and roasted kernels (without skins), obtained from the same plant cultivar, and phenolics compounds occurring in them [27].…”

“…Thus, in their work Cerulli et al evaluated the antimicrobial activity of both methanol extract of leafy covers of C. avellana Tonda di Giffoni and cyclic diarylheptanoids, quinic acid, flavonoid, and citric acid derivatives therefrom isolated against the Gram-positive strains Bacillus cereus and Staphylococcus aureus and the Gram-negative strains Escherichia coli and Pseudomonas aeruginosa [8]. The antimicrobial assays established that the cyclic diarylheptanoids giffonin U (87) and carpinontriol B (88) were the most effective against the tested strains, causing at 40 µg/disk the formation of zones of inhibition completely comparable to those obtained with tetracycline at 7 µg/disk used as positive control.…”

“…The work addressed for the first time the untargeted NMR spectroscopic analysis of a large quantity of hazelnut samples from 5 different Eurasian countries. The data analysis generated a model predicting the origin of samples from a test set with a high accuracy [88]. All the previous described papers concern kernels [89], while Cerulli et al in 2018 explored the metabolome of leaves of C. avellana by 1 H NMR combined with multivariate data analysis (PCA and PLS-discriminant analysis) and to date it remains the only paper describing a nontargeted metabolomics approach on a C. avellana part different from hazelnut [63].…”

Food authentication in real life: How to link nontargeted approaches with routine analytics?

“…Nevertheless, Gallo et al could recently show that on devices with different magnetic field strengths it is possible to obtain comparable data and that especially the operator has a significant influence on the quality of the data [114]. In addition to the above mentioned NMR applications for fruit juice and wine, there are many other examples for the authentication of food such as hazelnuts [115], coffee [116][117][118][119], honey [120][121][122], meat [123,124], or milk [125] and dairy products [126]. The various issue range from the proof of geographical origin [115], the identification of varieties [127], the year of cultivation [128] to technological processes and quality assessments [116].…”

Mit Metabolic Profiling gegen Betrug

“…Haselnüsse sind als hochpreisiges Lebensmittel durch Umdeklaration des Herkunftslands für Lebensmittelbetrug attraktiv. 7 Weitere Anwendungsgebiete solcher Klassifizierungsmodelle können beispielsweise die Unterscheidung von Lebensmitteln aus biologischem und konventionellem Anbau sein oder die Detektion von Zuckerbeimengungen, wie man sie bei Fruchtsäften oder Honig findet. 8,9) Betrug mit Erdnüssen Als Lebensmittelbetrug kommt auch die Beimischung billigerer oder qualitativ minderwertiger Rohstoffe vor, um höhere Gewinne zu erzielen.…”