Grain Fractionation to Improve the Nutritional Intensity of Cereal Products
Résumé
Cereal products are generally produced using purified flours extracted from the wheat grain endosperm by the
milling industry. However, whole grains contains appreciable concentrations of micronutrients, phytochemicals
and fibres that are mostly eliminated with the bran. These nutritionally interesting compounds are distributed
within the peripheral layers of the grain (i.e. pericarp, testa and aleurone layer as the major tissues) which
show distinct structure and mechanical properties. New dry fractionation processes were investigated in order
to recover these compounds while keeping a matrix effect (in contrast with wet extraction processes). Starting
material was either whole grain to partially incorporate the peripheral tissues into ”enriched” flours or milled
bran to produce specific ”functional” cereal-based ingredients. A multi-scale approach, from grain batches
to specific molecules, was used to find out the key factors which govern the grain fractionation and their
genetic variability and further develop the new processes. Grains were dissected into their main constitutive
tissues which were individually characterised in terms of composition, structure, mechanical properties and
micro-milling behaviour. This approach allowed to determine the involvement of each of the main peripheral
tissue in the bran rigidity, elasticity and extensibility and gave informations on the way to dissociate them.
Biochemical markers were also identified and could be used to track each of the different tissues in the different
milling fractions produced from complex processes. On the basis of the knowledge acquired from model
studies, combinations of conventional (milling, grinding, sieving) and advanced technologies (pre-treatments,
debranning, abrasion, attrition, jet-milling, air-classification) demonstrated the possibility to produce flours
containing selected peripheral compounds or to prepare different fractions of contrasted composition from
brans.