A 2D proton J-resolved NMR method for direct measurements on heterogeneous foods

• An NMR method is developed for direct measurements on heterogeneous food samples.
• Complicated sample pretreatment and special hardware are avoided in the method.
• Resolution-enhanced 2D JRES is provided for analyses of heterogeneous foods.
• The method is convenient and applicable on common liquid-state NMR spectrometers.

NMR spectroscopy is recognized as a powerful tool for food analyses on chemical composition determination, molecular structure elucidation, and functional component identification. Due to inhomogeneous line-broadening effects originating from sample heterogeneities and residual anisotropic interactions, high-resolution NMR available for analyses on heterogeneous food samples generally recurs to sample extraction and magic-angle spinning based measurements. In this study, we proposed an NMR approach for high-resolution 2D proton (1H) J-resolved measurements directly from heterogeneous foods without any sample pretreatment or additional hardware requirement. The noteworthy enhancement in spectral resolution and quality is illustrated in our experiments on two common heterogeneous food samples, a tomato and a fish. The resulting spectra yield a wealth of chemical shifts and J coupling information for analyses on an intact tomato pulp and a whole zebra fish. This method presents a complementary way to the conventional NMR methods for analyses on comparison, discrimination, and classification of heterogeneous foods. Furthermore, this method is applicable on common liquid-state NMR spectrometers since no additional hardware device is required, constituting a convenient and promising manner for practical applications to heterogeneous foods.