LIQUID-PHASE COMPOSITION OF INTACT FRUIT TISSUE MEASURED BY HIGH-RESOLUTION PROTON NMR

High-resolution H-1 (proton) NMR spectra were obtained on intact fruit tissues (grape, banana, and apple). Liquid-phase component line widths showed field-dependent broadening due to magnetic susceptibility effects; the effect was larger in more physically heterogeneous tissues (apple > banana > grape). Magic angle spinning (MAS) reduced susceptibility broadening, while water peak suppression increased dynamic range, enabling detection of components at levels at least as low as 0.01 % of fresh weight. Water, glucose, fructose, sucrose, organic acids (malic, citric, tartaric), and total fatty acyl lipids were quantified. Longitudinal relaxation times of nonexchangeable glucose protons were measured in situ in banana and found to be dominated by intra- and intermolecular homonuclear dipolar interactions. This is similar to the situation in vitro. Apparently, rotational motions of the water and sugar molecules within the fruit are relatively unhindered. The combined results have implications for nondestructive analysis of heterogeneous materials and for design of new devices for quality assessment, laboratory analysis, and process monitoring.