Improvement of the AOAC 2009.01 total dietary fibre method for bread and other high starch containing matrices

Abstract

The dietary fibre (DF) content in wheat grain based food products have been established with both the classical AOAC 985.29 dietary fibre and the new AOAC 2009.01 total dietary fibre protocol. There is a good agreement between the high molecular weight dietary fibre (HMWDF) contents measured with the AOAC 2009.01 method and (DF) content measured with the classical AOAC 985.29 method in wheat grain based food products. With the AOAC 2009.01 method also a significant amount of low molar weight dietary fibre (LMWDF), ranging from 1% to 3% w/w, was measured which is not quantified with the AOAC 985.29 method. With semi-preparative GPC the LMWDF (DP⩾3) fractions in the wheat grain based food products were isolated. The monosaccharide composition of the dissolved LMWDF constituents was determined. Glucose was by far the most abundant monosaccharide present with arabinose, galactose, xylose and mannose as minor constituents. It appeared that the LMWDF contains still not fully converted digestible starch/malto-oligosaccharide fragments with DP⩾3, which are erroneously quantified as LMWDF. By introducing an extra AMG hydrolysis step in the AOAC 2009.01 protocol after evaporation of the ethanol and dissolving the residue in deionised water, these malto-oligosaccharides are fully hydrolysed resulting in that way in a correct and lower LMWDF content.