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Evaluating the effect of roasting on coffee lipids using a hybrid targeted-untargeted NMR approach in combination with MRI

Williamson, Kathryn, Hatzakis, Emmanuel
Food chemistry 2019 v.299 pp. 125039
carbon, cluster analysis, coffee beans, discriminant analysis, diterpenoids, endosperm, hydrolysis, magnetic resonance imaging, multivariate analysis, nuclear magnetic resonance spectroscopy, oxidation, principal component analysis, quantitative analysis, roasting, stable isotopes, unsaturated fatty acids
An integrated targeted-untargeted 1H and 13C Nuclear Magnetic Resonance (NMR) analysis was applied to determine the impact of roasting on coffee lipids. For targeted analysis, both an internal standard (IS) method, as well as the ERETIC2 tool based on PULCON (Pulse Length-based Concentration determination), were used for quantitation. PULCON allows for quantitative analysis without sample contamination with an IS and was found to be in very good agreement with the traditional IS approach as indicated by a systematic Bland-Altman comparison study. For the untargeted analysis, NMR was coupled with multivariate statistical analysis (MVSA), namely Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and Orthogonal Projection to Latent Structures Discriminant Analysis (OPLS-DA). 13C NMR spectra were acquired using a z-stored spin-echo sequence to achieve higher spectral quality, which is important for both targeted and untargeted analysis. Results showed that roasting has a clear effect on coffee lipids, with diterpenes, oxidation/hydrolysis products and unsaturated fatty acid chains being the most significant markers. In addition, the application of MRI indicated important morphological alterations in bean structure and lipid migration from the endosperm to the surface of the coffee bean.