DEPHYTINISATION OF WHEAT BRAN AND THE CONSEQUENCES FOR FIBER-MATRIX NONSTARCH POLYSACCHARIDES

Wheat bran is a rich source of dietary fibre. Modified milling technol ogies can yield fibre-enriched bran fractions but the processing also leads to a concentration of phytate, which has a perceived detrimental effect on mineral metabolism. Endogenous phytase activity in wheat gr ain can be used to reduce phytate levels, and methods to optimise phyt ase activity have been investigated using aleurone-enriched and perica rp-enriched bran fractions. It was found that dephytinisation of wheat bran could be achieved at a relatively low moisture content for each fraction. The extent of dephytinisation could be controlled either thr ough control of moisture content or through time of incubation. By usi ng yeast, the rate of dephytinisation at 35 degrees C was similar to t hat achieved by endogenous phytase alone at 55 degrees C. The endogeno us phytase activity resulted in the destruction of phytate without acc umulation of inositol phosphate intermediates, as monitored using P-31 -NMR spectroscopy. Also, at low moisture levels there was no apparent modification of fibre components through polysaccharidase activities w hich may be present in the bran. Therefore bran fractions can be readi ly dephytinised at low moisture contents and without modification of t he fibre components. Copyright (C) 1996 Elsevier Science Ltd.