NMR-based metabolomics analysis of Calabrian citrus fruit juices and its application to industrial process quality control

The use of NMR spectroscopy combined with chemometric analysis is proposed in this work as an alternative methodology to the traditional techniques of the agro-food industry to investigate the metabolic profile of Calabrian citrus juices and to evaluate changes on the composition and metabolic profile of the juices during the thermal concentration process. First, 23 low molecular weight compounds, present in freshly squeezed orange juice, were identified using 1D 1H and 13C-{1H} NMR experiments and 2D homo and heteronuclear NMR spectra. Later, the 1H NMR spectra of collected samples during the concentration processes were used, coupled with PCA, in order to follow the variations in the metabolic composition of the juices subjected to the thermal process. The study focused on three industrial processes, two concerning the thermal concentration of orange juices while the third concerning the mixed orange and clementine juice concentration. The results indicate that PCA analysis is able to discriminate among the samples coming from the three industrial processes according to the nature of initial fruit batches. Moreover, for each process, the metabolic profile remains unchanged, i.e. there is no degradation or appearance of new compounds, but the PCA data indicate a decrease in the concentration of volatile compounds during the thermal process