Electrostatic properties of wheat bran and its constitutive layers: Influence of particle size, composition, and moisture content

Bran is the by-product of white flour and is composed of distinct adhesive tissues with aleurone and pericarp being the most significant. The present work pointed out the good potential of using electrostatic separation as a bran-fractionation method to produce nutritionally interesting food ingredients. The tribo- and corona-charging behavior of ground bran, an aleurone-rich fraction, and a pericarp-rich fraction were characterized, and the influence exerted by the composition, particle size. and moisture content was determined. The tribo-charging experiments showed that the opening of the aleurone cells after grinding modified the particles surface composition, and thus the samples charging behavior. The cell walls of aleurone and pericarp fractions displayed different tribo-charging characteristics, suggesting that by designing an appropriate tribo-charging device, these two bran layers might be separated. The behavior of the samples after corona-charging was found to be highly influenced by their Moisture content. Dried samples were all found to behave like insulators, whereas when the materials were not dried. the pericarp-rich fraction behaved like a conductor while the fine aleurone-rich fraction behaved like an insulator, probably due to the presence of lipids at the particles surface. These characteristics could also be exploited for the development of another electrostatic separation process. (C) 2009 Elsevier Ltd. All rights reserved.