MRI and HR-MAS NMR spectroscopies to correlate structural characteristics and the metabolome of Fiano and Pallagrello grapes with the action of field spray preparation 500 and the soil spatial microvariability

Abstract

BACKGROUND A number of Italian grape berry varieties, such as Fiano (F) and Pallagrello nero (P), represent National strategic products. Therefore, it is important to identify soil conditions emphasizing their peculiar characteristics as well as find innovative and sustainable treatments improving their compositional and nutraceutical quality. The field spray preparation 500 is a biodynamic product that is presumed to serve as biostimulant on the vine. However, so far, the scientific results probing its effectiveness are still lacking. Moreover, it is necessary to establish a reliable relationship between the grape quality and the spatial microvariability of the vineyard’s soil. On this basis, the main objective of this work consisted in correlating structural and morphological characteristics (via MRI), the primary metabolome (via semi-solid state HRMAS NMR) and important nutraceutical parameters (total phenols and antioxidants via DPPH assay) of F and P grapes with both the action of preparation 500 biostimulant and the vineyard soil microvariability, based on soil apparent electrical conductivity. RESULTS HRMAS enabled the identification of the primary metabolome of F and P. The elaboration of ¹H NMR spectra through chemometrics revealed significant changes in F and P grapes, accounting for both soil microvariability and the application of field spray (the latter also confirmed by PLS-DA and Heat-map clustering). Interestingly, for both F and P it was observed a significantly lower content of carbohydrates after biostimulant treatment while MRI revealed structural characteristics and internal details of intact grapes. The combined use of proton parametric indices, such as relaxation times and diffusion coefficients, indicated alterations induced in grapes by both the spatial microvariability of the soil and the effects of investigated biostimulant. Interestingly, a tight correlation was found between MRI transverse relaxation time and the contents in total phenols and antioxidants. CONCLUSIONS Our results have proven that both soil spatial microvariability and the application of field spray preparation 500 significantly affect the structural, metabolomic and nutraceutical characteristics of grapes. Moreover, the Preparation 500 treatment has increased the nutraceutical value of grapes. Importantly, these data may be potentially used to promote and protect biodynamic grape and predict the quality of the resulting wines.