Comparison of frozen and fresh apple pulp for NMR-based metabolomic analysis

Metabolic profiling and metabolomics studies mainly deal with the multicomponent analysis of cell extracts, biological fluids, and tissues using nuclear magnetic resonance (NMR) spectroscopy, often flanked by mass spectrometry (MS). Technical improvements are needed for a better understanding of the mechanisms that regulate biological systems. In this work, we have utilized two different kinds of starting material for juice production-frozen and fresh apple pulp-monitoring metabolic profiles obtained through NMR analysis. The differences induced by these pre-analytical treatments have been statistically evaluated using unsupervised multivariate method (PCA) and through the analysis of the identified metabolites. Evaluating PCA score plot, it was possible to distinguish between the two juice preparations. Compounds as lactic, citramalic, malic, chlorogenic, and formic acid were identified only in juices obtained from fresh apple pulp. Furthermore, in these kind of juices, other metabolites, such as ethanol, were found at a higher level. Whereas, other compounds, such as threonine, showed higher values in juices deriving from frozen apple pulp. This study highlights the feasibility of H-1-NMR-based metabolomics as a tool for the analysis of apple juices. Our results suggest the use of juices obtained from fresh fruit tissue for the investigation of compositional changes due to physiological disorder, specific growth, or storage conditions. Our analyses emphasize the importance of technical improvement in metabolomics analysis.