Citron and lemon under the lens of HR-MAS NMR spectroscopy

High Resolution Magic Angle Spinning (HR-MAS) is an NMR technique that can be applied to semi-solid samples. Flavedo, albedo, pulp, seeds, and oil gland content of lemon and citron were studied through HR-MAS NMR spectroscopy, that was used directly on intact tissue specimens without any physicochemical manipulation. HR-MAS NMR proves to be very immediate in detecting terpenes, sugars, organic acids, aminoacids and osmolites. It is valuable in observing changes in sugars, principal organic acids (mainly citric and malic) and ethanol contents on pulp specimens and this strongly point to its use to follow fruit ripening, or commercial assessment of fruit maturity. HR-MAS NMR was also used to derive the molar percentage of fatty acid components of lipids in seeds, which can change depending on Citrus species and varieties. Finally, this technique was employed to elucidate the metabolic profile of mold flavedo.