Red Beet Fiber NMR

The data provided here include the 1D and 2D NMR spectra of four red beet fiber fractions, the pomace (PF), water-soluble (WSF), water-insoluble (WIF), and microwave-extracted pectin (10/80 min/˚C). The anomeric 1H-1H coupling constants and chemical shift resonances of the observed carbohydrate residues are reported. Additional analyses can be found in the associated paper "Structural characterization of red beet fiber and pectin” (Hotchkiss et al., 2022, https://doi.org/10.1016/j.foodhyd.2022.107549). The dominant anomeric resonances in the 1D-1H NMR spectrum of the WSF (Figure 1), as well as the PF (Figure 2) are at 5.42 ppm, with smaller intensity resonances at 5.23 and 5.09 ppm, followed by increasingly weaker resonances at 5.16, 5.26, 4.56, 5.31 and 5.13 ppm. The resonance at 5.42 ppm is an apparent doublet with a JH1H2 coupling constant of 2.8~3.42 Hz, which is consistent with H2 and H1 being in an axial-equatorial, or conformation. These peaks are assigned as α-Glc(1) and α-Glc(2). Similarly, the weak resonance at 5.26 ppm is a doublet with JH1H=3.15 Hz, which is also conformation, and is assigned as α-Glc(3). The weak doublet centered at 4.56 ppm has a JH1H2 = 7.51 Hz, which indicates an axial-axial orientation, or conformation, and is assigned as β-Glc(2). In the 1D-1H NMR spectrum of red beet WIS (Figure 3), the dominant resonance is at 4.65 ppm (doublet, JH1H2 = 8.1 Hz, conformation) and is assigned as β-Glc(1); this resonance is obscured by the water HOD peak in the water-soluble and pomace fractions. The next most intense peak in the water-insoluble fraction is at 5.24 ppm (doublet, JH1H2 = 3.8 Hz, conformation) which is assigned as α-Glc(3). Weaker peaks are found at 5.10 ppm (broad, JH1H2 = small, conformation), which is assigned as α-Ara, and at 4.52 ppm (doublet, JH1H2 = 7.5 Hz, conformation), which is assigned as β-Glc(2). The weakest anomeric peak observed is at 5.42 ppm (doublet, JH1H2 = 4.4 Hz, conformation), arising from α-Glc(2). All of the fractions contain many non-sugar resonances (0.5-3 ppm) of their 1D-1H spectra (Figures 1-3), that are primarily aliphatic, and comprise about 10% of the proton spectral intensity in WSF and PF, and about 13% of the proton spectral intensity in the WIF. Comparing the sugar resonance regions of the 1D-13C NMR spectra (Figure 4) for WSF, PF and WIF, it is seen that WSF and PF have very similar spectra, both in terms of resonances and intensities. The WIF 1D-13C spectrum, however, the resonances associated with Ara (~110 ppm) and Glc (~99 ppm) are not observed, as well as decreased sucrose resonances (Glc at ~95 ppm and Fru at ~84 ppm). All of these resonances can be weakly detected in the 2D spectra, however, indicating that while their concentration is diminished, they are still present.