A spectroscopic approach to determine the formation mechanism of biopolymer particles from wheat bran proteins

Abstract

The mechanism of formation of biopolymer particles, obtained from an aqueous extract of wheat bran, was studied by Fourier transform infrared spectroscopy (FTIR), assisted by energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). Spheroidal biopolymer particles, 204−347 nm diameter, were synthesized by heat-induced aggregation of a 21−43 kDa wheat bran protein fraction. There were reductions of 39.5% and 52.78% in the β-sheet and α-helix conformations, respectively, after exposure of proteins to 68.5°C, whereas β-sheet aggregates increased from 0 to 39.87%. SEM microphotographs showed that the internal structure of biopolymer particles consisted of nanospheres aggregated within a network. The overall analysis, plus evidence found in literature, indicated that temperature made individual proteins to exposure thiol groups, favoring disulfide bridges and β-sheet aggregates, which resulted in the assembly of nanospheres. Nanospheres were then agglomerated in a fractal-like way through non-covalent intermolecular interactions, to build the biopolymer particles. Junctions between biopolymer particles were interpreted as intermolecular β-aggregates, so a cluster-like complex was finally assembled. Shape, size, and surface morphology of biopolymer particles were stable during 18 months at 25°C.