Assembly of biopolymer particles after thermal conditioning of wheat bran proteins contained in a 21–43 kDa size exclusion chromatography fraction

Abstract

Assembly of spherical nanoparticles after Ca2+-induced cold gelation of aqueous extracts of wheat bran was previously reported. Although nanospheres were suggested to be constituted by proteins and stabilized by calcium bridges, their exact origin was not fully demonstrated because of the complexity of wheat bran extracts. To deepen in this respect, by means of a bottom-up approach, the experiment was reproduced with fractions of wheat bran obtained by size exclusion chromatography. After thermal treatment and addition of CaCl2, fractions were characterized by UV–Vis spectroscopy, FTIR spectroscopy, SDS-PAGE electrophoresis, energy dispersive spectroscopy, differential scanning calorimetry, and electron microscopy. Instead of the expected nanospheres, spheroidal particles with diameters 210 – 330 nm were precipitated from a protein fraction of 21 – 43 kDa, even before the addition of CaCl2. Spectroscopic and SDS-PAGE characterization showed that particles were mainly constituted by proteins. Global evidence indicates that calcium did not participate in the assembly of the particles, but rather the driving force for protein aggregation was the denaturation caused by the heat treatment. According to their characteristics, spheroidal particles were classified as biopolymer particles.