Ultra-fine grinding increases the antioxidant capacity of wheat bran

In order to study the influence of wheat bran particle size on its antioxidant capacity, the wheat bran was ground under normal and cryogenic conditions with variable intensity to produce ten fractions with different physical structures. The high energy grinding increased 3-fold the specific surface of the bran fractions and also the proportion of particles smaller than 50 μm assimilated to the proportion of disrupted aleurone cells. All the ground bran fractions presented similar total ferulic acid concentration and chemical form (free, conjugated, linked). A positive effect of the grinding on the antioxidant capacity of the bran fractions was noticed. The antioxidant capacity increased from 30 to 45 mmol TEAC/kg when the specific surface increased from 0.09 to 0.26–0.30 m2/g. The antioxidant capacity of the bran fractions was linearly correlated with the specific surface, with the D50 values and with the proportion of particles smaller than 50 μm. In in vitro gastric conditions, the finely ground bran inhibited the accumulation of conjugated dienes more efficiently than coarse bran. In conclusion, the bran structure affects its antioxidant capacity. This effect remained in gastric conditions showing that grinding can be used to produce wheat bran fractions with higher nutritional value.

► The effect of wheat bran structure on its antioxidant capacity is studied.
► The physical destructuration of wheat bran increases its antioxidant capacity.
► The wheat bran specific surface is well correlated with its antioxidant capacity.
► The antioxidant capacity of processed wheat bran remains in gastric digestion.