Pulse EPR Spectroscopy and Molecular Modeling Reveal the Origins of the Local Heterogeneity of Dietary Fibers

Abstract

Optimizing human diet by including dietary fibers would be more efficient when the fibers’ chain interactions with other molecules at the molecular level are understood in depth. Here, we demonstrate the utility of the pulse electron paramagnetic resonance (EPR) spectroscopy, complemented by numerical simulations in probing the atomistic details of the chain conformations for spin-labeled dietary fibers. Barley β-glucan, a native polysaccharide with linear chain, was utilized as a test fiber system to demonstrate the technique’s capabilities. Pulse dipolar EPR data show good agreement with results of the atomistic fiber chain modeling, revealing sinuous chain conformations and providing polymer shape descriptors: the gyration tensor, spin-spin distance distribution function, and information about proton density in the spin probe vicinity. Results from EPR measurements point to the fiber aggregation in aqueous solution already at 20-40 μM dietary fiber concentrations, which agrees with the results of the dynamic light scattering. We propose that the combination of pulse EPR measurements with atomistic modeling can be a perfect experimental tool for in-depth structural investigation of dietary fibers and their interaction under such conditions, and that the presented methodology can be also extended to other weakly ordered or disordered macromolecules and materials.

Keywords: neutral dietary fibers, β-glucan, spin labeling, filtration by relaxation, atomistic modeling, electron-nuclear interactions.