Exploring 1H NMR relaxometry for wine traceability and authenticity assessment

Mestrado em Engenharia de Viticultura e Enologia (Double degree) / Instituto Superior de Agronomia. Universidade de Lisboa / Faculdade de Ciências. Universidade do Porto

The development of analytical methodologies for wine authenticity assessment is one of the most challenging issues for the scientific community. In this study, the potential analytical applications of 1H NMR relaxometry, in view to wine authenticity investigation, were explored. For that, proton longitudinal relaxation rate dispersions in the range 0.04-300 MHz were investigated in three white and three red varietal wines from Tapada da Ajuda (Lisbon), obtained from Vitis vinifera L. grape varieties, namely Alvarinho, Arinto, Cabernet Sauvignon, Moscatel Graúdo, Touriga Nacional and Trincadeira, from vintages 2008 and 2017 for a total of twelve bottles. To evaluate rain as an environmental source of variability pluviometric data were considered. Dispersions associable to the presence of paramagnetic ions were observed at low frequencies but the results for wine iron content cannot explain the effect. Correlations between the wine characters and the areas drawn by the most representative relaxometry models show an effect of alcoholic strength by volume, glycerol and total dry matter suggesting wine viscosity to modulate relaxivity. To the best of our knowledge, for the first time wine physical-chemical characteristics and glycerol content have been compared to NMR relaxation rate profiles. To investigate the paramagnetic relaxation and evaluate the relaxation associated to wine hydro-alcoholic matrix, water-ethanol mixtures were tested, and linear regressions were obtained. Comparing the results with bibliographic sources, the paramagnetic enhancement on relaxation profiles was associated to the presence of manganese(II), but no parameters have been fitted from the models. The dispersions highlighted possible cross relaxations in the 1.5-6 MHz frequency range. The presence of nitrogen diluted into the wine could explain this behaviour. To inspect how each physical-chemical parameter impacts on wine relaxation profiles the knowledge of manganese content is crucial

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